EGU General Assembly 2024  

Volatile organic compounds (VOCs) are important mediators of forest-atmosphere interactions, regulating plant performance and atmospheric processes. Amazonian forests comprise the dominant source of VOCs to the global atmosphere. Yet, there is a poor understanding of how VOC emissions vary in response to ecophysiological and environmental controls in Amazonian ecosystems and even less understanding of how ecosystem emissions respond to climate extremes and land use change. I will summarize my work on VOC emissions from different ecosystems and scales in the Amazon and point out that VOCs can be indicators of forest stress and, therefore, a possible metric of forest vulnerability. First, I will present the state-of-the-art of VOC emissions and their interactions with the climate system in the Amazon. Next, I will demonstrate how these interactions can differ when considering different forest types and environmental stresses, including extremes of heat and drought. Finally, I will highlight the recent progress of VOC emissions investigated in the so-called "Amazon arc of deforestation" and indicate the potential of VOCs as a metric of forest vulnerability in climate modeling.

How to cite: Gomes Alves, E.: Volatile Organic Compounds: mediators of forest-atmosphere interactions and indicators of forest vulnerability, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1832, https://doi.org/10.5194/egusphere-egu24-1832, 2024.

My fascination with the biogeosciences started with the investigation of nitrogen (N) and phosphorus (P) enrichment of lakes stimulating the growth of diatoms leading to increased sedimentation and eventual depletion of dissolved silicate from the water column. At that time most research on the global Si cycle was focused on weathering and had not explored the complexity of the terrestrial biogeochemical cycle. Our research demonstrated that diatoms and phytoliths, e.g. biogenic silica that accumulates in the living tissues of growing plants, are transported from lakes and rivers on the continents into the oceans. The emerging understanding is that the flux and isotopic composition of dissolved silicate delivered to the ocean has likely varied over time mediated by a fluctuating continental pool.

An important question we addressed was if reductions of P and N could reduce eutrophication and degradation of freshwater and marine ecosystems. Our analysis explored the rationale for only P or only N reductions and concluded that dual–nutrient reduction strategies were needed for aquatic ecosystems. A focus on only P or only N reduction should not be considered unless there is clear evidence or strong reasoning that reducing the inputs of only one nutrient is justified in that ecosystem and will not harm downstream ecosystems.

The depletion of dissolved oxygen in bottom waters is one of the common responses of aquatic ecosystems to eutrophication. A classic example is the semi-enclosed brackish Baltic Sea. Our research has shown that the Baltic Sea is the largest anthropogenically induced hypoxic area in the world, which has increased 10-fold during the last century due to increased nutrient inputs. Concurrently, the coastal zone has experienced increasing hypoxia during the same period with the Baltic Sea coastal zone containing over 20% of all known sites suffering from hypoxia worldwide. Our research has highlighted the continuously growing problems of hypoxia and anoxia with eutrophication.

Altered global biogeochemical cycles is not only a feature of the Anthropocene but ongoing geological processes. Our recent research has focused on the use of silicon isotope signatures of unaltered sponges and radiolarians to estimate dissolved silicate drawdown as a proxy for the changes in the productivity of diatom communities in the Mesozoic oceans and how the ocean chemistry changed with the evolution of diatoms. Our major results to date suggest that dissolved silicate has been low in the oceans for at least the last 100 million years because of the extreme efficiency of dissolved silicate uptake by diatoms reducing ocean concentrations.

My continued enchantment with biogeochemical processes and collaboration with other creative scientists has lead to uncovering new biogeochemical pathways which stimulates the drive to learn more about how ecosystems operate.

How to cite: Conley, D.: Reflections regarding our biogeochemical studies in lakes and marine environments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12020, https://doi.org/10.5194/egusphere-egu24-12020, 2024.

Paleofire reconstructions are a challenging endeavor primarily due to the numerous factors involved in wildfire frequency, behavior, and regimes. These factors include, but are not limited to fuel composition, moisture, soil types, climate/weather conditions, and topographical features. Therefore, development of robust wildfire proxies requires vigorous experimental testing for multiple variables. Here, we explore the influence of pyrolysis time, moisture, and plant species on a novel proxy for fire intensity—carbon bridgehead fraction of charcoal. Experimentally, we have produced charcoals from three native Texas plants: live oak (Quercus sp.), Ashe juniper (Juniperus ashei), and broomsedge bluestem (Andropogon virginicus) under a range of temperature (300-700°C), moisture (0-100% moisture capacity), and time (0-1 hr) conditions in a tube furnace. Samples were analyzed using solid-state C-13 nuclear magnetic resonance (NMR) spectroscopy with two experiments to calculate carbon bridgehead fraction: cross polarization – magic angle spinning (CP-MAS) to quantify total aromatic carbon and dipolar dephasing (DD) to quantify aromatic bridgehead carbon. Results reveal significant differences between vegetation types, with moisture delaying or slowing the rate of carbon bridgehead formation. Relationship between carbon bridgehead fraction and time are less clear and may be influenced by the formation of pyrolysis byproducts (such as pyroligneous acids and free radicals) and/or signal losses in the cross-polarization spectra. To assess the influence of these factors on carbon bridgehead fraction we plan to conduct additional analyses on our experimental charcoals, including electron paramagnetic resonance (EPR) spectroscopy to quantify the free radicals in samples and C elemental analysis to assess carbon observability by NMR. Future work involves ground truthing the proxy to modern wildfires and subsequently applying it to paleorecords.

How to cite: Sivapalan, V. and Hockaday, W.: The influence of pyrolysis time, moisture, and plant species on carbon bridgehead fraction of charcoal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-763, https://doi.org/10.5194/egusphere-egu24-763, 2024.

Himalayan forests boast an incredible biodiversity, harboring a wide range of flora and fauna and playing a significant role in regulating water resources. Forest fires are one of the disturbances which constitute a major force influencing, even determining, the structure and functions of ecological components-populations, communities, and ecosystems. The ability to withstand disturbance is defined as resistance whereas resilience is the capacity to recover from disturbance. These two terms define the ecohydrological response to forest fire. This study insights on how remote sensing technique can be utilized for the measurement of ecohydrological response of a large extent of region subjected to forest fire based on resistance-resilience framework and how further implementation of these measures would help to know the changes in the interaction been vegetation and water cycle. Normalized burn ratio (NBR) is used to quantify the response.  The outcome of the study reveals that deciduous needled leaf forests are subjected frequently to forest fires compared to other classes of forests during 2002-2022. The regions considered for study showed moderate to high range of resistance but low resilience, signifying the region has gained and lost vegetations in the post-fire. There was a variation in rainfall and run-off occurred during the post-fire year for different burn severities. The present approach has the potential to quantify the response of ecosystems to the forest fire and related effects on hydrology of the region.

How to cite: Ge, N. and Sharma, A.: Assessment of ecohydrological response of Himalayan Forest ecosystems to  forest fires, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1123, https://doi.org/10.5194/egusphere-egu24-1123, 2024.

How to cite: Fan, W., Li, J., Han, Z., and Wu, J.: Impacts of biomass burning in Southeast Asia on aerosols over the low-latitude plateau in China: an analysis of a typical pollution event, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1471, https://doi.org/10.5194/egusphere-egu24-1471, 2024.

Landscape fires are a widespread natural phenomenon that directly influences carbon cycling through the combustion of organic material. Space-based remote sensing, including Active Fire (AF), remains the only way to estimate wildfire activity accurately on the regional-to-global scale. Fire emission inventories generally fall into two categories. “Bottom-up” methodologies rely on observations of AF counts, Fire Radiative Power (FRP), or burned area to estimate the amount of biomass burned, or “Top-down” methodologies, which directly relate observations of FRP to landscape fire emission estimates. Bottom-up methods tend to have a reliance on uncertain parameters, such as pre-fire fuel load and combustion completeness, or a conversion factor between FRP and fuel consumption rate. The Fire Radiative Energy Emission (or FREM) approach is one such top-down methodology that has removed such a reliance, by directly relating FRP to observed rates of emissions, such as CO or aerosols, but has so far been used with geostationary FRP data only. Whilst very effective at lower latitudes, due to the poor spatial resolution and extreme viewing geometry of geostationary data at higher latitudes, the approach is not applicable for fires in this region in its current format. However, by using polar orbiting FRP data and making use of the high latitude orbital convergence, this study looks to adapt the FREM approach to deliver direct estimation of carbon emissions for high latitude (>60°N) landscape fires. We use direct observations of FRP, from Suomi-NPP, NOAA-20 and MODIS, along with observations of Total Column Carbon Monoxide from TROPOMI onboard Sentinel-5P. A series of cloud-free plumes and associated FRP data were identified in Deciduous and Evergreen Needleleaf biomes in North America and Russia in the summers of 2019 – 2023. The resulting emission coefficients and emission totals were compared to pre-existing top-down and bottom-up emission coefficients and totals from the FEER, GFAS, and GFED inventories for high latitude fires between 2018-2023. This adapted FREM approach is shown to provide direct emission estimates without recourse to significant assumptions and can do so in real time – opening up a new avenue for real-time fire emission estimation at high latitudes.

How to cite: Maslanka, W. and Wooster, M.: Direct Estimation of Carbon Emissions from High Latitude Fires: The Adapted FREM Approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1756, https://doi.org/10.5194/egusphere-egu24-1756, 2024.

2023 has witnessed a record-breaking extreme wildfire season in Canada from coast to coast, following closely to the unprecedented wildfire outbreaks in 2019/20 Australia and 2021 Siberia, causing far-reaching threats on terrestrial carbon stock, air quality, and human society. The heightened wildfire activity in specific regions prompts us to rethink the underlying factors driving the global wildfire dynamics. Climate change has been recognized as an important factor in amplifying wildfire risk, mainly through increasing temperature and reducing relative humidity. However, the role of vegetation productivity and phenology on wildfire dynamics remains elusive, even though which can exacerbate or mitigate the climate-induced fire risk. Importantly, changes in vegetation phenology can cause biophysical feedback to the climate system and land surface by modulating the exchanges of water and energy between land and the atmosphere. Considering the climate feedback of vegetation phenology, we hypothesize that peak photosynthesis timing (PPT) can contribute to wildfire activity. To explore it, we provide comprehensive analyses using multiple satellite-based photosynthesis observations from solar-induced chlorophyll fluorescence (SIF), and wildfire activity from national fire perimeters and MODIS global burned area records from 2001 to 2018, as well as diverse methodologies and models. In response to changes in various biological and climatic factors, we find PPT has advanced 1.10 ± 0.57 days per decade at a global scale. This earlier PPT acts to expand the extent of wildfires, with an increase in the global average burned fraction by 0.021% (~2.20 Mha) for every additional day of PPT advancement. Satellite observations and the Earth system modeling consistently reveal that this expansion is attributed to the intensified drought conditions during the potential fire season, induced by the earlier PPT that can modulate the global patterns of temperature, precipitation, and surface soil moisture. Furthermore, current fire-vegetation models participating in the FireMIP project underestimate the sensitivity of burned area to PPT, despite reproducing their negative correlation. Our findings highlight the importance of climate-vegetation-fire feedback loops in future prediction of wildfire dynamics and the strategy of climate change adaptation and mitigation.

How to cite: Lai, G., Li, J., Wang, J., Wu, C., Zhang, Y., Zohner, C. M., and Peñuelas, J.: Exploring the effect of vegetation photosynthesis phenology on wildfire dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2099, https://doi.org/10.5194/egusphere-egu24-2099, 2024.

Wildfires are known to be controlled by fuels and weather. Climate teleconnections may influence wildfires by altering fuel availability and fire weather. In this study, we used the random forest approach to systematically detect relationships between teleconnection climate indices (CIs) and burned area while accounting for different lag times. Results indicate that burned area is especially modulated by climate teleconnections in Africa and Australia. The Tropical Northern Atlantic (TNA) pattern was the most influential CI for the global burned area, followed by the El Niño Southern Oscillation (ENSO), the Indian Ocean Dipole (IOD), and the Pacific–North American (PNA) pattern. To study pathways of how teleconnections affect the burned area, we distinguished two classes of fire drivers: bottom-up fuel availability and top-down weather conditions. Bottom-up fuel drivers showed higher correlation with CIs than top-down weather drivers and served as mediators between teleconnections and wildfires. The mediating effect of top-down weather drivers was only apparent in specific seasons. Our study highlights that in teleconnection-wildfire hotspot regions, knowledge of the relation between CIs and drivers of wildfires could improve long-term wildfire predictability. We recommend that bottom-up fuel drivers should also be integrated into wildfire predictive frameworks as they play an important mediating role in linking teleconnections and wildfires.

How to cite: Qu, Y., Vereecken, H., Veraverbeke, S., and Montzka, C.: The Influence of Climate Teleconnections on Global Burned Area, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4071, https://doi.org/10.5194/egusphere-egu24-4071, 2024.

Biomass burning in Amazon Basin has a significant impact on regional climate and deteriorates regional air quality, which poses a threat to human and ecosystem health. The fire-induced pollution worsens during dry season (Jul to Nov) and shows a strong seasonal variation. Past research has demonstrated that the occurrence of wildfires in Amazon is not only influenced by deforestation, but also interannual climate variability, particularly droughts. Here we estimate the impacts of deforestation and droughts on fire emissions and regional air quality between 2010 to 2015 by using Global Fire Emission Database Version 4 (GFED v4) to drive a global 3-D atmospheric chemical transport model GEOS-Chem High Performance (GCHP) and further examine the effect of PM_2.5 and O₃ on premature mortality across the region. By comparing the “fire-on” and “fire-off” scenarios, we find that biomass burning alone in normal years (2011 and 2013) contributes 5.7 μg m^-3 (47.6% of the total concentration) PM_2.5, 0.08 ppm (46.3%) CO, 0.03 ppb (85.0%) NO_x, and 9.5 ppb (41.2%) O₃; and these numbers during drought years (2010, 2012, 2014 and 2015) increase to 19.6 μg m^-3 (74.7%) for PM_2.5, 0.20 ppm (67.0%) for CO, 0.19 ppb (97.4%) for NO_x, and 15.6 ppb (52.0%) for O₃. We find that these pollutants from wildfires mainly concentrate in the south-eastern Amazon and then transport southward, thus strongly impacting public health in the downwind regions. We estimate that premature mortality due to long-term exposure to particulate matter and ozone by applying the simulated concentration to the concentration-response functions from the European Environment Agency. We find that ~8,500 and ~10,400 deaths per year are attributable to PM_2.5 and O₃ exposure for 2010-2015 respectively. During drought years, we discover there are 2.8% and 3.4% more deaths than normal years for PM_2.5 and O₃ exposure. Our study shows the significance of biomass burning emissions in shaping the air quality in the Amazon region, and highlights the impact of drought events on enhancing biomass emissions, worsening regional air quality and causing public health issues. Therefore, it is important to address the underlying causes of biomass burning in the Amazon, such as deforestation and land use change, and droughts, to protect the region's ecosystems and mitigate the impacts of climate change.

How to cite: Ng, T. H. L., Tai, A. P. K., Sitch, S., Aragao, L., and Zhai, S.: Impacts of land use change and interannual climate variability on biomass burning emissions, air quality and public health in Amazon, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5191, https://doi.org/10.5194/egusphere-egu24-5191, 2024.

Tropical rainforests have exceptionally high biodiversity and store large amounts of carbon in biomass. However, large and frequent fires across tropical rainforests in the last decades threaten the ecosystem integrity of these ecosystems. The general belief is that fires in the Amazon rainforest are all human-ignited and that lightning fires do not occur in rainforests due to the predominant wet conditions. However, recent research indicates the possibility of lightning fires in tropical rainforests. Here, we aim to investigate the occurrence of lightning-ignited fires in the Amazon rainforest, a topic that has been largely overlooked in the current understanding of fire dynamics in this biome. We collected and analyzed data on lightning strikes, fire occurrences, and weather patterns derived from satellite imagery and climate datasets. The objective is to detect, quantify, and characterize lightning fires in the Brazilian Amazon rainforests, thereby providing new insights into the natural fire regime of this crucial ecosystem.

How to cite: Zhang, C., Janssen, T., Jones, M., and Veraverbeke, S.: Are there lightning Fires in the Amazon Rainforest?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5236, https://doi.org/10.5194/egusphere-egu24-5236, 2024.

Monoculture forests are now a dominant forest type in Europe. Created for easier management and increased timber production, they are now witnessing many disturbances due to climate change, such as more frequent windthrows, droughts, fires or insect outbreaks. The functioning of forests impacts other elements of the landscape, including peatlands, which also have been affected by various natural and anthropogenic disturbances (e.g., drainage) that make them more vulnerable to drying and burning. We aim to recognize how peatland functioning has changed along with changing forest management strategies. For this we studied a Sphagnum-dominated peatland located in the Tuchola Pinewoods – one of the largest Scots pine (Pinus sylvestris) monoculture forest in Poland. We used high-resolution multi-proxy palaeoecology including pollen, plant macrofossils and testate amoebae, additionally focusing on a wide range of charcoal analyses: charcoal counts, charcoal morphological types, and Raman spectroscopy. Our results show that the studied peatland experienced several critical transitions in vegetation composition and hydrology over the last 600 years when new forest management techniques were introduced. A reduction in fire activity led to a dominance of Sphagnum and increased peat accumulation rates. Establishment of a monoculture forest further impacted the site and stabilized Sphagnum growth and acidity levels. We believe that these results can be helpful for the improvement of conservation planning for peatlands located in forested areas, especially in monoculture forests.

The study is funded by the National Science Centre, Poland (2020/39/D/ST10/00641).

How to cite: Marcisz, K., Bąk, M., Lamentowicz, M., Kołaczek, P., Theurer, T., Matulewski, P., and Mauquoy, D.: Wetlands in monoculture forests – how fire activity and different forest management strategies impact Sphagnum-dominated peatlands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5348, https://doi.org/10.5194/egusphere-egu24-5348, 2024.

Globally, vegetation fires are a key component of many ecosystems and have substantial impacts on carbon emissions. Yet humans also use and manage fires for a huge range of purposes around the world, dependent on numerous social and biophysical factors. Existing representations of anthropogenic fire in dynamic global vegetation models (DGVMs) have been highly simplified, with readily available global variables (e.g. population density) used to estimate numbers of anthropogenic ignitions. Here, we present results from a novel coupled socio-ecological modelling approach to improve understanding of how human and biophysical factors combine to drive the spatio-temporal distribution of global fire regimes. Specifically, we present the integration of two process-based models. The first is the Wildfire Human Agency Model (WHAM!¹), which draws on agent-based approaches to represent anthropogenic fire use and management. The second model is JULES-INFERNO², a fire-enabled DGVM, which takes a physically-grounded approach to the representation of vegetation-fire dynamics.

The new WHAM-INFERNO model ensemble suggests that as much as half of all global burned area is generated by managed anthropogenic fires - typically small fires that are lit and spread according to specific land use objectives (such as crop residue burning). Furthermore, we demonstrate that including representation of managed anthropogenic fires in a coupled socio-ecological simulation can improve understanding of the biophysical drivers of unmanaged wildfires, by allowing clearer recognition of the role of anthropogenic land management in global fire regimes. Hence, WHAM-INFERNO is applied to understand how landscape fragmentation, wider land use change, and changes in human fire management have together led to observed recent declines in global burned area despite the warming climate. Overall, findings presented here have substantial implications for understanding of present and future fire regimes, indicating that changes to socio-economic systems are at least as important a consideration as climate change.  

1. Perkins, O., Kasoar, M., Voulgarakis, A., Smith, C., Mistry, J., and Millington, J. (2023). A global behavioural model of human fire use and management: WHAM! v1.0. EGUsphere, 1–42. 10.5194/egusphere-2023-2162.

2. Mangeon, S., Voulgarakis, A., Gilham, R., Harper, A., Sitch, S., and Folberth, G. (2016). INFERNO: a fire and emissions scheme for the UK Met Office’s Unified Model. Geosci. Model Dev. 9, 2685–2700. 10.5194/gmd-9-2685-2016.

How to cite: Perkins, O., Kasoar, M., Voulgarakis, A., Edwards, T., and Millington, J.: Half of global burned area is due to managed anthropogenic fire: findings from a coupled socio-ecological modelling approach , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5494, https://doi.org/10.5194/egusphere-egu24-5494, 2024.

Air pollutant emissions from wildfires on Indonesian peatlands lead to poor regional air quality across south-east Asia. Fine particulate matter (PM_2.5) emissions are particularly high for peat fires leading to substantial population exposure to PM_2.5. Despite this, air quality monitoring is limited in regions close to peat fires meaning the impacts of peatland fires on air quality is poorly understood and it is difficult to evaluate predictions from atmospheric chemistry models. To address this, we deployed a network of low-cost (Purple Air) PM_2.5 sensors at 8 locations across Central Kalimantan, where peat fires are frequent. The sensors measured indoor and outdoor PM_2.5 concentrations during August to December 2023. During the haze season (September 1^st to October 31^st), daily mean outdoor concentrations were 120 mg m^-3 but peaked at >400 mg m^-3. Indoor PM_2.5 concentrations were only ~10% lower (mean 110 mg m^-3), indicating that is difficult for the population to reduce their exposure to PM_2.5 from fires. The reduction in mean PM_2.5 concentrations between outdoor and indoor environments was larger in urban locations (-11%) compared with rural locations (-3%), suggesting urban housing may provide better protection from outdoor air pollution. To generate an updated assessment for the population’s exposure to peatland fire PM_2.5 we combine the information from monitoring both indoor and outdoor PM_2.5 concentrations with modelled ambient (outdoor) PM_2.5 concentrations from the WRF-Chem atmospheric chemistry transport model. Our updated exposure assessment accounts for the population’s personal exposure to peatland fire PM_2.5 for the first time.

How to cite: Graham, A. M., McQuaid, J. B., Smith, T. E. L., Nurrahmawati, H., Ayona, D., Mulawarman, H., Adam, C., Spracklen, D. V., Rigby, R., and Choiruzzad, S. A. B.: Updated Exposure Estimate for Indonesian Peatland Fire Smoke using Network of Low-cost Purple Air PM2.5 sensors, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6077, https://doi.org/10.5194/egusphere-egu24-6077, 2024.

Wildfire is an integral part of temperate ecosystems, but human activities have significantly altered fire regimes, including frequency, size, intensity and seasonality. Romania, located in central-eastern Europe, recently exhibited the highest biomass burning in Europe. However, little is known of the trends and determinants of fire recurrence, apart from the common use of fire to clear crop residues on arable land. This study utilizes satellite-based fire data (FIRMS) from 2001 to 2022 and land cover maps (CORINE) to investigate temporal trends in fire occurrence across ecoregions and land cover types in Romania and identify those most susceptible to fire.

Over 2001-2022, Romania witnessed a total of 0.44 fires/ km² averaging 0.02 fires/km²/yr. Our analysis revealed a declining trend in fire occurrence along an elevation gradient, from plains to hills, plateaus and mountains, aligning with the prevalence of the dominant land cover classes and climatic gradients. Agricultural land cover types demonstrated the highest fire incidence, with arable land exhibiting the highest rate (0.04 fires/km²/yr) and forests the lowest (below 0.01 fires/km²/yr). Following the accession of Romania to the EU in 2007 and the prohibition of agricultural fires, a reduction in burning on arable land (crop residues) can be observed, while the use of fire in other agricultural classes persisted or even increased, indicating a more complex effect of socio-economic developments on fire pattern. Specifically, areas more marginal for agriculture, such as complex agricultural fields interspaced with housing and natural vegetation continued to employ fire as a management tool.

Natural land cover classes, such as wetlands principally occupying the Danube Delta (0.06 fires/km²/yr) and natural grasslands (0.01 fires/km²/yr), also experienced substantial fire occurrences and an intensification in more recent periods. Given the rarity of naturally ignited fires (lightning) in Romania, the intentional use of fire to clear dry reed biomass for land regeneration appears to be prevalent also in moist areas. Remarkably, broadleaved and mixed forests burned more frequently than coniferous forests despite the latter having traits to convey high flammability and burn with high frequency. This feature suggests that fires in broadleaved forests, predominant at low and mid elevations, likely expanded from neighbouring agricultural lands.

Crucially, our analysis highlights that years with elevated fire occurrence coincide with extreme droughts and heatwaves (e.g., 2012, 2015), emphasizing the influence of extreme climate conditions in accelerating fire episodes and the spread of fires initiated in agricultural areas into natural and semi-natural habitats. Given the substantial occurrence of fires in agricultural land but also in natural habitats, such as wetlands and grasslands in Romania, research investigating the risks and vulnerability of these habitats to fire should be prioritized.

How to cite: Mattes, T., Marzolff, I., and Feurdean, A.: Excessive fire occurrence in Romania from 2001 to 2022: Trends and drivers across ecoregions and land cover classes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6624, https://doi.org/10.5194/egusphere-egu24-6624, 2024.

Wildfires have become more prevalent in recent years because of climate change. Meanwhile wildfires, as a major type of biomass burning, could emit a large amount of black carbon (BC) and brown carbon (BrC) to the atmosphere. Since BC and BrC play important roles in climate change, air pollution and human health issues, it is necessary to research their physicochemical properties to evaluate their impacts on urban areas. Here we present BC mass concentration and absorption coefficients measured by aethalometer (AE43), combing with the chemical constitutions acquired by GC-MS, during the record-breaking 2023 wildfire season in Canada. The back-trajectory analysis indicated that the smoke mainly came from north Quebec where the wildfires took place. We demonstrated how BC and BrC emitted by wildfires could affect urban regions after long-range transport.

How to cite: Li, H. and Ariya, P.: Measurement of Physicochemical Properties of Black Carbon and Brown Carbon and the Impacts of Canada Record-Breaking Wildfires in Summer 2023 , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6761, https://doi.org/10.5194/egusphere-egu24-6761, 2024.

Nitrogen deposition can exert a significant impact on global ecosystems. The increased occurrence of natural factors such as wildfires are becoming more important in atmospheric deposition especially with the continued decreases of the anthropogenic emissions in developed countries. In this study, we investigate the mechanisms by which the increasingly frequent wildfires affect nitrogen deposition in the United States using comprehensive datasets and multiple linear regression (MLR) methods. We found a downward trend in nitrogen deposition in the U.S. (-0.09 kgN ha yr^-1), mainly due to the decreases in oxidative nitrogen deposition (-0.1 kgN ha yr^-1). In contrast, reduced nitrogen deposition showed a slight increase (0.02 kgN ha yr^-1). Our preliminary results show that wildfires contributed ~10% to the U.S. domestic deposition overall, but the magnitudes and signs of impact vary geographically, depending on the frequency and intensity of wildfires and the dominant deposition types. On average across the U.S., wildfires predominantly negatively contribute to wet deposition, while their contributions to dry deposition is smaller or slightly positive. Specifically, wildfires enhance dry deposition in the western U.S. while inhibiting wet deposition in the southeastern U.S. Wildfires exert a suppressive effect on both oxidized and reduced forms of nitrogen deposition in the southeastern U.S. Our study highlights the significant influence of wildfires on nitrogen deposition, underscoring the need to consider wildfire events in environmental management and policy-making.

How to cite: Mu, J., Zhang, Y., Tao, C., Liu, Z., Zhao, Y., Zhang, L., Zhang, Y., and Xue, L.: The Impact of Wildfires on Atmospheric Nitrogen Deposition in the United States: A Multiple Linear Regression-based Analysis, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7467, https://doi.org/10.5194/egusphere-egu24-7467, 2024.

In 2020, the Northeastern Siberian lowland tundra faced an extreme drought and unprecedented wildfires. The burning of carbon-rich soils in this region can release large amounts of carbon, worsening climate change and Arctic warming.  However, we know little about of how droughts impact vegetation and how this vegetation might become fuel for large fires in the typically wet landscapes of the Northeastern Siberian lowland tundra. We studied the impact of the extreme summer drought in 2020 on the tundra vegetation and the resulting burn patterns in the Indigirka lowlands using a combination of in-situ, thermal, and multispectral remote sensing data from drone and high-resolution satellite imagery. The fine-scale vegetation types revealed increased landscape-wide drought susceptibility indicated by an overall loss of land surface cooling. This suggests a shift towards an energy budget dominated by sensible heat flux, which may feed back and intensify the heatwave.  Further, we found that mostly dry vegetation types were affected by fire in the NE Siberian coastal tundra, while wetter vegetation types did not burn, leading to a fine-scale heterogeneous burn pattern. Our results indicate that the enhanced drought susceptibility of vegetation types may have led to higher fire fuel connectivity of the tundra landscape. Consequently, this may have resulted in the large burn extents observed in 2019 and 2020. Our analysis is an effort toward the prediction of fire fuel connectivity and fire management in remote Arctic areas.

How to cite: Rietze, N., Assmann, J., and Schapeman-Strub, G.: Vegetation types influence fine-scale drought impact on land surface cooling and burn patterns in the Siberian coastal tundra, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7895, https://doi.org/10.5194/egusphere-egu24-7895, 2024.

Mediterranean forests are recurrently affected by wildfires. Fire activity is expected to accelerate in the future due to landscape homogenization, fuel accumulation, and climate warming. A key aspect to prevent and mitigate the negative impacts of wildfires on ecosystems is to understand the factors that govern the recovery of forest communities. This study analyzes the post-fire recovery potential of four representative Mediterranean tree-communities (Pinus halepensis, Pinus nigra, Pinus pinaster, and Quercus ilex) affected by large wildfires (> 500 ha) during the summer of 1994 in Spain. For this purpose, information collected in the field 25 years after the fires in 203 forest plots (131 burned and 72 unburned control plots) was coupled with remote sensing, geospatial, and forest inventory data, to build an empirical model capable of assessing recovery. Remote sensing data provided a proxy for burn severity, through the Composite Burn Index, and allowed modelling the local topography (slope and aspect) of the terrain. The geospatial data included climatic information on temperature and precipitation trends. These data were entered into the model, calibrated using Random Forest, to provide information on the degree of recovery, inferred from the similarity (in terms of vegetation height, aboveground biomass, species diversity) between the burned and unburned control plots. Results showed that only the 25% of the burned plots can be considered as recovered. The burn severity had a significant effect on the recovery albeit strongly modulated by local topography. Overall, the key features of the recovered plots were a low-to-moderate burn severity and a favorable topographical setting, especially the shading effect of steep northwestern slopes. Furthermore, a warmer and more humid climate improved the capacity of recovery. These results constitute a valuable tool for improving forest management and preserving ecosystem services.

How to cite: Hoffren, R., de la Riva, J., Domingo, D., Lamelas, M. T., Ibarra, P., García-Martín, A., and Rodrigues, M.: Combining stand-level and remote sensing data to model post-fire recovery of Mediterranean tree-forest communities – A case study in Spain., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8017, https://doi.org/10.5194/egusphere-egu24-8017, 2024.

Wildfires pose an increasing threat to boreal forest and tundra ecosystems in boreal North America (Alaska and northwestern Canada), as their frequencies rise under global warming. These fires exhibit strong interannual variability that is influenced by regional atmospheric circulation. However, potential impacts of remote boundary forcings on regional fires and the underlying mechanisms remain unclear. This study provides a comprehensive analysis on the impacts of spring sea surface temperature (SST) and sea ice on interannual variability of burned area in this region during fire season (summer) from 1997 to 2020 using GFED5 burned area, SST and sea ice concentration data from the Met Office Hadley Centre, and ERA5 reanalysis data. Results show that in spring a warmer SST in the East Pacific and reduction of sea ice in the northern Chukchi Sea lead independently to an increase in burned area in boreal North America. The correlation coefficients between the SST and sea ice factors with the burned area in boreal North America are 0.43 and –0.44 respectively. The SST-fire relationships can be explained as follows: A warm SST anomaly in the East Pacific triggers a northeastward-propagated Rossby wave, inducing a high-pressure anomaly over boreal North America in spring. Consequently, this circulation anomaly causes a higher surface temperature and thus vegetation growth or drying. As temperatures rise and lightning activity intensifies in summer, burned area increases. On the other hand, the process of sea ice affecting burned area is different. A reduction in sea ice coverage in the northern Chukchi Sea leads to a decrease in surface albedo, resulting in an increase in heat flux. The heat release persists from spring to summer and causes a high-pressure circulation anomaly in boreal North America in summer, which suppresses regional water vapor convergence and precipitation, reducing soil moisture and surface air humidity and increasing vapor pressure deficit (VPD) thereby promoting fuel flammability.

How to cite: Zhao, Z., Lin, Z., and Li, F.: Impacts of Spring East Pacific SST and Arctic Sea Ice on Interannual Variability of Summer Burned Area in boreal North America, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8303, https://doi.org/10.5194/egusphere-egu24-8303, 2024.

In recent years, the EU Commission has enacted various firefighting policies to combat and diminish the adverse effects of wildfires. The Mediterranean area has experienced an observable extension of its wildfire season, coupled with rapid shifts in fire-weather dynamics, resulting in exceptionally severe wildfire occurrences. As of 2022, the EU has recorded an approximate total burned area of 792,902 hectares, with forests accounting for 66% of this figure (Rodrigues et al., 2023).

The main objective of this study is to anticipate extreme wildfire conditions by providing a synthetic product depicting the chances of a fire event starting and escaping containment. To do so, we combined empirical models of ignition likelihood and effectiveness of the initial attack stage. We employed machine learning techniques to calibrate binary regression models using historical wildfire ignition data and geospatial layer depicting the main drivers of ignition and containment, namely: accessibility, human pressure on wildlands, fuel moisture and availability. We illustrate our approach along the Mediterranean coastal region of Spain. Our approach enables us to predict wildfire contention capacity under diverse population growth and climate warming scenarios. This strategy aims to improve disaster risk reduction by pointing wildfire management zones and prioritizing intervention in high-risk areas.

Results indicate a high predictive ability to model human-caused wildfire ignition (AUC>0.80) but a modest capability to capture the containment capability (AUC≈0.70). Accessibility by road largely controls the spatial pattern of ignition and containment, with dead fuel moisture content modulating the temporal pattern of probability. We further illustrate the approach by providing insights into future SSP (Shared Socieconomic Pathways) scenarios by synthesizing both products into comprehensive management zones (Rodrigues et al., 2022).

References

Rodrigues, M., Camprubí, À.C., Balaguer-Romano, R., Megía, C.J.C., Castañares, F., Ruffault, J., Fernandes, P.M., Dios, V.R. de, 2023. Drivers and implications of the extreme 2022 wildfire season in Southwest Europe. Science of The Total Environment 859, 160320. https://doi.org/10.1016/j.scitotenv.2022.160320

Rodrigues, M., Zúñiga-Antón, M., Alcasena, F., Gelabert, P., Vega-Garcia, C., 2022. Integrating geospatial wildfire models to delineate landscape management zones and inform decision-making in Mediterranean areas. Safety Science 147, 105616. https://doi.org/10.1016/j.ssci.2021.105616

How to cite: Gelabert Vadillo, P. J., Jiménez Ruano, A., Catelo, F., and Rodrigues Mimbrero, M.: Anticipating future extreme wildfire events by coupling ignition and success of initial attack models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8506, https://doi.org/10.5194/egusphere-egu24-8506, 2024.

Biomass burning (BB) plays a key role in the biosphere–atmosphere interaction. It is a major source of trace gases and aerosols that alters the atmosphere and the water cycle. Additionally, these emissions are often related to other detrimental impacts including biodiversity loss in fire-sensitive biomes, increase of respiratory diseases, and massive economic losses. BB emissions are used as inputs in models that estimate air quality and the effect of fires on Earth’s climate. Hence, an accurate estimation of BB emissions is paramount. While BB emissions spread over most of the global vegetated areas, the integration of orbital remote sensing and modelling is the most effective approach to estimate them from regional to global scales. BB emission estimation follows the relationship between burned biomass and the emission factor (EF - mass emitted of a given species, for example carbon dioxide, per mass of dry matter burned). The burned biomass can be estimated using two approaches: (i) based on the relationship among burned area, above-ground biomass, and combustion completeness; or (ii) based on fire radiative power (FRP), a quantitative measurement that is directly related to the rate of burned biomass and is estimated to each active fire detected by several orbital sensors such as the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor. EF values, which are Land Use and Land Cover (LULC) based, are required to estimate BB emissions independently on the approach adopted to estimate the burned biomass. Although novel approaches to improve the accuracy of BB emissions have been developed, the impact of EF values on the final estimated emissions remains uncertain. We have evaluated the impact of the EFs on the final estimate of fine particulate matter (PM_2.5) emitted from BB in the Brazilian Amazon during a nineteen years’ time series (2002-2020) by running the PREP-CHEM-SRC emissions preprocessor tool under four EF scenarios: the tool original EF values based on the work of Andreae and Merlet (2001), the average EF values recently updated by Andreae (2019), and the minimum and maximum EF values also proposed by this author. The minimum (maximum) EF values were defined as the average EF value for each LULC class minus (plus) one standard deviation. The PM_2.5 emissions were estimated at the spatial resolution of 0.1º using the FRP approach implemented on PREP-CHEM-SRC (3BEM_FRP model) having MODIS active fires as input, since this approach requires fewer inputs and the impact of the EFs over the emissions would be more evident. Our results showed that the annual average PM_2.5 emission in the Amazon varied by 163% between the four EF scenarios (from1,426 Gg and 3,747 Gg), while the scenario based on the average values was the closest to the one based on PREP-CHEM-SRC original EF values (2,582 Gg and 2,213 Gg, respectively – an increase of 17%). These results contribute to the better understanding of how this single parameter impacts on the estimation of BB emissions.

How to cite: Mataveli, G., W. Jones, M., Pereira, G., R. Freitas, S., Oliveira, V., Brambleby, E., and E.O. C. Aragão, L.: Unravelling Variability: Discrepancies in Amazonian Biomass Burning Emissions Under Different Emission Factor Scenarios , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8507, https://doi.org/10.5194/egusphere-egu24-8507, 2024.

Global warming and climate change-induced rise in Earth’s temperature have increased the frequency of forest/wildfires over the past decade. Therefore, understanding the effect of fire emissions on aerosol-cloud interactions is crucial for improving Earth system models.

         We present observations from in-situ measurements of aerosol properties at the Puijo SMEAR IV station in eastern Finland and the Zeppelin Observatory in Ny-Ålesund, High Arctic. Both stations are frequently inside low-level clouds due to their topographic prominence. During the autumn of 2020, fire emissions from the same active fire region in south-eastern (SE) Europe reached both stations after ~2 - 8 days of atmospheric aging. This enabled us to investigate the changes in aerosol and cloud properties for clouds formed under the influence of aged fire emissions (referred to as the ‘fire’ period) and under cleaner conditions with no fire emission influence at these stations (‘non-fire’ period). The aerosol hygroscopicity parameter (κ_chem) was derived from the chemical composition data obtained from online aerosol mass spectrometers and was used to derive the number concentration of cloud condensation nuclei (N_CCN) from the measured particle size distributions.

         At both stations, the aerosol number concentration in the accumulation mode and the cloud condensation nuclei concentration (N_CCN) were higher during the fire period than during non-fire times. However, the aerosol hygroscopicity increased at Puijo but decreased a Zeppelin from the non-fire to fire period. At Puijo, in-situ measured cloud droplet number concentration (CDNC) was by a factor of ~7 higher when comparing fire to non-fire periods. This was in good agreement with the satellite observations (MODIS, Terra). At Puijo, the higher CCN concentrations during the fire period cause a depletion of the water vapor available for cloud droplet activation leading to larger observed activation diameters during cloud events despite the higher hygroscopicity of the aerosol particles.

         These observations show the importance of SE European fires for enhancing the CCN activity in Finland and the high Arctic. Results from this study emphasize the complex interplay between particle size and chemical composition, and how fires even from sources far away can have strong impacts in these remote regions.

How to cite: Kommula, S. M., Buchholz, A., Gramlich, Y., Mielonen, T., Hao, L., Pullinen, I., Vettikkat, L., Joutsensaari, J., schobesberger, S., Tiitta, P., Leskinen, A., Rees, D. H., Haslett, S., Siegel, K., Lunder, C., Zieger, P., Krejci, R., Romakkaniemi, S., Mohr, C., and Virtanen, A.: Effect of long-range transported fire emissions on aerosol and cloud properties at high latitudes: In situ measurements and satellite observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8668, https://doi.org/10.5194/egusphere-egu24-8668, 2024.

The Arctic-boreal region is warming rapidly, with consequences for northern ecosystems and global climate. Fires across the Arctic-boreal region are a major natural disturbance mechanism that initiate climate warming (positive) and cooling (negative) feedbacks. Understanding the net forcing effect from boreal fire on climate is crucial in managing and mitigating climate change impacts of boreal fires. Here we report radiative forcing estimates from boreal forest fires across Alaska and Western Canada (Arctic Boreal Vulnerability Experiment-domain). Our results integrate the effect of greenhouse gas emissions (warming) and aerosols emission (net cooling) have through direct combustion, post-fire vegetation recovery sequestering carbon (cooling), fire-induced permafrost degradation emitting CO₂ and CH₄ (warming), and changes in surface albedo (cooling). Alaskan fires are on average climate warming (1.34±2.95 W/m² per burned area) – uncertainty given as spatial standard deviation, while Canadian fires show on average a climate cooling (‑2.26±2.48 W/m² per burned area) effect. The emissions from the combustion of organic soils and post-fire permafrost thaw dominate the positive feedback for Alaskan fires, whereas the cooling effect of post-fire changes in surface albedo because of prolonged spring snow cover dominate for the western Canadian fires. Our work demonstrates large-scale spatial variability in the climate feedbacks from North American boreal forest fires. Such fine-scale spatial information on the warming and cooling influences of forest fires could be useful in designing forest management and fire suppression activities informed by climate impacts.

How to cite: van Gerrevink, M., Veraverbeke, S., Cooperdock, S., Potter, S., Zhong, Q., Moubarak, M., Goetz, S. J., Mack, M. C., Randerson, J. T., Turetsky, M. R., van der Werf, G., and Rogers, B. M.: Warming and cooling influences of North American boreal fires, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9225, https://doi.org/10.5194/egusphere-egu24-9225, 2024.

In recent years, boreal forests have experienced unprecedented fire activity. These fires have contributed substantially to carbon emissions and posed hazards to human health. In the remote northeast Siberian taiga, the vast majority of fires are ignited by lightning strikes and not by human activity. Furthermore, active fire suppression is largely absent in these remote areas, resulting in uncontrolled fire growth. Here, we present a detailed look at the places and times where these lightning fires do finally stop spreading and aim to identify the causes. We employ various remote sensing and geo-spatial datasets including fire weather as well as landscape variables such as the presence of surface water, road networks, woody fuel load, fire history, elevation and landcover, to pinpoint the limitations to fire growth along fire perimeters recorded between 2012 and 2022 at a 300-meter spatial resolution. We were able to attribute 87% of all fire perimeter locations to a statistically significant (p < 0.01) change in one or more of these fire limitations over either time (fire weather) or space (landscape). The analysis reveals that fire growth is mainly limited by a change in the vegetation (fuel type and fuel load) as well as a change to less favourable weather for fire spread, although there are clear regional differences in the importance of specific limitations. Overall, fire weather seems to be the most important limitation to fire growth in the north of the Siberian taiga where continuous permafrost is present. With a rising frequency of lightning strikes, droughts, and heatwaves in boreal regions, uncontrolled lightning fires have the potential to expand even further in the future, leading to significant implications for vulnerable permafrost landscapes and, consequently, the global carbon cycle.

How to cite: Janssen, T. and Veraverbeke, S.: What limits the growth of lightning fires in the remote northeast Siberian taiga?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9270, https://doi.org/10.5194/egusphere-egu24-9270, 2024.

Large burned areas (BA) in southeastern Australia were regularly registered during hot and dry years, such as the Black Saturday (2009) and the Black Summer (2019-2020) extreme bushfires. These types of extreme climate conditions are expected to become more frequent, leading to an increased risk of large BA in this region.

In this work, the influence of drought conditions and hot events on the BA in southeastern Australia was assessed, using correlation and copula functions. Bivariate copula functions were fitted, and conditional probabilities of large BA given climate extremes were computed. Three classes of drought intensity were studied, namely moderate, severe, and extreme, as well as three thresholds for temperature extremes, namely the 80^th, 90^th, and 95^th percentiles. Monthly BA were computed as the sum of the burned pixels in the fire season (from October to March), using data from the MODIS Burned Area product. The analysis was performed on forests, grasslands, and savannas separately. Drought conditions were assessed with SPEI at several time scales, computed with data from the CRU TS4.07 dataset. Maximum and minimum daily temperature were retrieved from the ERA5 dataset.

Results showed that the correlation between BA and SPEI was high in the current and previous 1 month for all land covers, being highest in savannas and lowest in grasslands. Short time scales of SPEI had the highest correlation on grasslands, and the opposite was observed in forests and savannas. The correlation with maximum temperature increased until 10-15 days before the fire event and surpassed 0.6 over forests. Minimum temperature presented much lower correlations and there was not a pronounced increase in the previous days, as observed with the maximum temperature.

The conditional probability of large BA increased with the intensity of the drought on all land covers, and it reached almost 100% probability of exceeding the 50^th percentile of BA under extreme droughts on forests and savannas. For the case of the 80^th percentile of BA, the probability was lower, but the difference given drought and non-drought conditions was larger than for the 50^th percentile. On savannas and forests, the conditional probability was still high when considering SPEI in the previous 2 and 3 months.

Maximum temperature yielded a higher probability of BA for the two highest percentiles. Savannas presented the lowest probability of BA given hot events, and forests the highest. The probability increased up to 10 days before the fire. Overall, the probabilities obtained given drought conditions are higher than given hot events, particularly for larger fires. Moreover, high probabilities obtained with large time scales and longer lead times are indicative of the importance of drought conditions before the fire season and may help predict the occurrence of large BA.

Acknowledgments: This study was partially supported by FCT (Fundação para a Ciência e Tecnologia, Portugal) through national funds (PIDDAC) – UIDB/50019/2020, by project Floresta Limpa (PCIF/MOG/0161/2019), and by project 2021 FirEUrisk, funded by European Union’s Horizon 2020 research and innovation programme under the Grant Agreement no. 101003890). A.R. was supported by FCT through https://doi.org/10.54499/2022.01167.CEECIND/CP1722/CT0006. 

How to cite: Páscoa, P., Russo, A., Ribeiro, A., and Gouveia, C.: Burned area and climate extremes in different land covers in southeastern Australia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10145, https://doi.org/10.5194/egusphere-egu24-10145, 2024.

The Brazilian Cerrado is a heterogeneous biome formed by a mosaic of savannas, grasslands, and smaller patches of denser woody forms. In this biome, fire is a natural disturbance agent that contributes to maintaining its open ecosystems and rich biodiversity. However, modern human activities and climate change are altering its fire regimes. In tropical savannas, land-use expansion is usually associated to a decrease in burned area primarily through land fragmentation, but also through active fire suppression. Meanwhile, climate change is fostering fire weather conditions, exacerbating fire activity. Hence, the two main drivers of fire could be pushing burned area in opposite directions, both with important ecological consequences for the Cerrado. However, it remains unclear how these two drivers interact, which is essential to devise effective fire management policies and conservation plans.

In this study, we use a causal inference framework to quantify the interaction between anthropic area percentage – as a proxy of human presence and fragmentation – and various climatic variables on their effects on Cerrado’s burned area. As well, we explore the spatial structure of temporal trends in burned area, anthropic expansion and climate change, and quantify the causal effect of the last two on the former.

We use geospatial data from different sources on a 0.2^o grid over the Cerrado for the period 1985 to 2020. We use burned area and land use data from the MapBiomas project, and climate re-analysis data from ERA5 Land, CHIRPS and TerraClimate. We design our models using Directed Acyclic Graphs, a graphic representation of the causal relations between the predictors and burned area that informs variable selection for causal inference. Hence, based on these DAGs, we build multilevel Bayesian regression models to quantify the effects of the predictors and their interactions.

We find that a larger presence of land-use activities keeps burned area low and, importantly, hinders the effects of the climate. That is, while in landscapes composed mostly of native vegetation hotter and drier conditions increase burned area as expected; in anthropic landscapes, humans completely limit burned area responsiveness to climate. We also find spatially heterogeneous increasing and decreasing trends in burned area over the period, but concentrated in those areas of the Cerrado that were mostly natural in 1985. In these areas, a large anthropic expansion brought about a decrease in burned area, while we observe an increase in burned area in relation to climate change only in the areas that remained intact throughout the study period.

In conclusion, burned area in the Cerrado is shaped primarily by the extent of human presence in the landscape, even limiting the effects of the climate, while climatic effects become relevant in areas with larger tracts of native vegetation, suggesting that these areas may be more vulnerable to climate change.

How to cite: Segura-Garcia, C., Bauman, D., S. Arruda, V. L., Alencar, A., and Oliveras Menor, I.: Human land occupation regulates the effect of the climate on the burned area of the Cerrado biome, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10377, https://doi.org/10.5194/egusphere-egu24-10377, 2024.

Lightning ignitions are the dominant causes of wildfires in many regions, responsible for 80% of burned areas at high latitudes and about 70% of fires in the Amazon rainforest. With global wildfire activities and extreme fire events (e.g., intensity, duration, and size) increasing under the changing climate conditions, understanding the interactions between lighting, landscape characteristics, and wildfires is crucial for predicting and mitigating the impacts of climate change. Cloud-to-ground lightning activities are driven by a combination of large- and local-scale factors, e.g., local atmospheric circulations and convection and topography. Furthermore, the number of lightning strikes is predicted to increase by 10 – 30 % per degree warming. Decadal satellite observations have revealed Earth’s lightning hotspots at very high resolution, however, there is a paucity of fine-scale lightning strikes and lightning-ignited wildfires (LIW) in the Earth system and climate models. Currently, many climate and ESM  models do not include fires at all or simulate them with meteorological inputs and grid-average lightning at the scale of atmospheric models (25 to 100 km), introducing large uncertainties of LIW due to the lack of information at the scales relevant to fire dynamics.  Lack of information about lightning trends and variability hinders the prediction and projection of fires and their contribution to carbon and other atmospheric tracers and global warming. For example, in the US National Oceanic and Atmospheric Administration (NOAA) Geophysical Fluid Dynamics Laboratory (GFDL) ESM4.1 model, the fire model uses a climatology of lightning strikes from preindustrial to 2100.

In this presentation, we will demonstrate the implications of capturing subgrid lightning distributions in the GFDL land model LM4.2 for the global simulations of wildfire dynamics over the available records (1998-2013) and provide insights into future projections. LM4.2 captures sub-grid heterogeneity of land cover and use, soil geomorphology, and topography, facilitating the understanding of LIW distribution across global to regional and sub-grid scales. In this study, we leverage 0.1° × 0.1° lightning observations from the Lightning Imaging Sensor (LIS) and Optical Transient Detector (OTD) in the GFDL LM4-HB to characterize fine-scale lightning strike distribution and associated LIW.

How to cite: Wang, R., Zorzetto, E., Malyshev, S., and Shevliakova, E.: Characterizing lightning-ignited wildfire occurrences at sub-grid scales in orography-aware NOAA/GFDL land model LM4.2, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10606, https://doi.org/10.5194/egusphere-egu24-10606, 2024.

Since 2006 the Canadian Forest Fire Weather Index System (FWI) has been employed operationally at Met Éireann to predict the risk of forest fires in Ireland. Around 11% or 770,000 ha of the total land area of Ireland is afforested, but there are also large areas of open mountain and peatlands covered in grasses, dwarf-shrub and larger woody shrub type vegetation which can provide fuel for spring wildfires under suitable conditions. After winter, vegetation can be dead or have a very low live moisture content, and the flammability of this vegetation can be readily influenced by prevailing weather, especially following prolonged dry periods.

Different decision support tools are available to different sectors, namely:

• The General Public: who have access to fire weather index meteograms on Met Éireann’s public website.
• Local Authorities, who have access to the ANYWHERE multi-hazard warning system, which provides multiple sources of information about fire danger and propagation.
• The Department of Agriculture, Food and Marine (DAFM), who are provided with information and additional support from National and European partners and networks.

DAFM is the Forest Protection authority in Ireland responsible for issuing Forest Fire Danger Notices which improve preparedness for fire responses and are based on a range of factors including information provided by Met Éireann who calculate the FWI and FWI components using observation data at synoptic stations, and the predicted FWI for the next five days ahead based on numerical weather prediction data. This allows fire responders to build resilience and prepare for impending fires.

The FWI is determined based on the types of forest fuel and how quickly they dry out/get rewetted, and components of fire behaviour. The FWI represents the fire intensity as the rate of energy per unit length of fire front (kW/m). The components which provide the most accurate indication of risk under Irish conditions are the Fine Fuel Moisture Code and Initial Spread Index, based on the fuels involved and ignition patterns observed to date. Since 2022 Met Eireann provide the FWI as well as the individual components Fine Fuel Moisture Content and Initial Spread Index via the public website for synoptic stations. These indices are based on observations and a seven-day forecast into the future using ECMWF predictions. This allows all county councils responsible for wildfire preparedness to access this information swiftly and directly.

Met Éireann also use the ANYWHERE multi-hazard warning tool which allows for visualisation of multiple fire-related risk factors and warning indices to be viewed simultaneously. The ANYWHERE system, in combination with our station-based forecast and antecedent conditions, provide fire managers and response teams with excellent information with which to make decisions.

How to cite: Flattery, P., Finkele, K., Downes, P., Hally, A., and Nugent, C.: A Decision Support System for Forest Fire Danger Notices in Ireland , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10793, https://doi.org/10.5194/egusphere-egu24-10793, 2024.

The temporal coverage (∼2000 to present) of global burned area satellite observations limits many aspects of fire research e.g., long-term trend analysis, disentangling the effect of various drivers on fire behaviour and detection and attribution of changes to climate change. As a result, global fire models are more frequently being called upon to answer questions about past and future fire behaviour. Unfortunately, the limited temporal coverage of the observations also hinders the development and evaluation of these fire models. The current generation of global fire models from ISIMIP are able to simulate well some characteristics of regional fire behaviour such as mean state and seasonality. However, the performance of these models differs greatly from region to region, and aspects such as extreme fire behaviour are not well represented yet. Here, we explore the possibility of using machine learning algorithms to model burned area from the same input parameters that are passed to global climate models. Once trained, this data-driven model can be evaluated against regional proxies for past fire behaviour e.g., tree rings and charcoal records. Hopefully, this data-driven reconstruction can provide valuable insights on the 20^th century burned area, and can help improve and evaluate fire models.

How to cite: Lampe, S., Gudmundsson, L., Humphrey, V., Vanderkelen, I., Le Saux, B., and Thiery, W.: Reconstructing 20th century burned area by combining global fire model input, satellite observations and machine learning, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10920, https://doi.org/10.5194/egusphere-egu24-10920, 2024.

Quantifying burned area and associated fire emissions is paramount to understand how changing fire patterns affect radiative forcing and air quality. It is now well established that many fires are too small to be detected by coarse resolution satellite burned area products on which the Global Fire Emissions Database (GFED) relied. In the fifth version of GFED (GFED5) we therefore combine burned area derived from mapped coarse-resolution burned area from the MODIS sensor -which excels in detecting larger fires- with small-fire burned area. The latter is derived from MODIS active fire detections scaled to burned area using ratios constrained by higher-resolution burned area datasets from Landsat and Sentinel-2 for selected regions. Burned area in cropland regions was based on the Global Cropland Area Burned (GloCAB) dataset. Total global burned area is 61% higher than in GFED4s. We converted burned area to emissions using a simplified version of the CASA model used in previous GFED versions, but which now runs at a 500 m spatial resolution. This allows for better constrained modeled fuel loads based on field measurements. Although GFED5 emissions are aggregated to a 0.25 degree grid due to the statistical nature of deriving our burned area, we can now account for heterogeneity in fire processes within these large pixels. Emissions (3 Pg carbon per year) are roughly 50% higher than in GFED4 and we show how diverging trends in grassland versus forest ecosystems impact trends in total emissions. Finally, we show how converting fire carbon losses to trace gas and aerosol emissions is now better constrained due to the addition of several new emission factor measurement campaigns. In the savanna biome we now account for spatial and temporal variability in emission factors.

How to cite: van der Werf, G., Randerson, J., van Wees, D., Chen, Y., Vernooij, R., Giglio, L., Hall, J., Morton, D., Barsanti, K., and Yokelson, B.: Burned area and fire emissions according to the fifth version of the Global Fire Emissions Database (GFED), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10947, https://doi.org/10.5194/egusphere-egu24-10947, 2024.

Lightning is recognised as a crucial wildfire ignition source worldwide, especially in remote regions including boreal and temperate forests where large carbon stocks are held. The societal consequences of these wildfires, as well as their contribution to climate change, can be immense. The occurrence of lightning is projected to increase in these areas under climate change, however robust assessments of lightning contribution to wildfire risk have been restricted to selected regions due to the narrow spatial extent of cloud-to-ground lightning records. Consequently, evaluations of lightning-fire relationships using existing global lightning observational datasets have been limited to considering the total amount of lightning. Only cloud-to-ground lightning can ignite a wildfire, therefore when considering impacts on wildfire risk it is essential to distinguish between lightning types.

Using Vaisala’s unique Global Lightning Dataset (GLD360), which discriminates between cloud lightning and cloud-to-ground lightning strikes, we present our preliminary analyses of the spatial patterns and seasonality of cloud-to-ground lightning. Here, we show the regional variation in the lightning frequency and the cloud-to-ground fraction, as well as the strength (current) and polarity of cloud-to-ground lightning strikes.

By considering cloud-to-ground lightning strikes only, we characterise the spatial and seasonal variation in lightning events with the potential to ignite wildfires. Combining global observations of lightning strikes with observations of individual fires and coincident meteorology will advance our mechanistic understanding of wildfire ignition potential in a range of weather conditions, improve the process representation of the ignition process in global models, and refine projections of changing wildfire risks under climate change.

How to cite: Brambleby, E., Veraverbeke, S., Mataveli, G., Joshi, M., and Jones, M.: Global cloud-to-ground lightning data to inform wildfire ignition patterns, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11206, https://doi.org/10.5194/egusphere-egu24-11206, 2024.

This research delves into the dynamics of forest fires across various Indian regions, particularly during the unique COVID-19 lockdown period. The study's core focus is on the interaction between forest fires, climatic factors, and vegetation indices in a scenario of reduced human activity. It employs a multidimensional methodology, integrating satellite imagery and climatic data from periods before, during, and post-lockdown. The lockdown provides a critical opportunity to assess the impact of decreased human interference on forest fire patterns. Advanced statistical techniques are used to analyze the relationship between vegetation indices, fire occurrences, and meteorological conditions. This approach aims to uncover the underlying mechanisms driving these relationships, moving beyond simple trend identification. The research offers a nuanced perspective by differentiating natural factors from human influences. This distinction is vital in understanding the environmental dynamics during the lockdown. The findings have significant implications, offering insights for policymakers and environmentalists in enhancing forest fire management strategies. Emphasizing the need for a comprehensive understanding of environmental interactions, this study contributes to forming more informed and sustainable approaches to natural disaster management in the face of global challenges like climate change and pandemics.

How to cite: Kate, R. and Bhattacharya, J.: Forest Fires during COVID-19: Assessing Environmental Interactions and Fire Dynamics Amidst Reduced Human Intervention in India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11291, https://doi.org/10.5194/egusphere-egu24-11291, 2024.

Climate warming is occurring most rapidly at high latitudes, heightening the vulnerability of carbon-rich peatlands to fire. Northern peatlands comprise the largest terrestrial carbon store, and exert a net cooling effect on the climate. Warmer and drier conditions due to the anticipated climate change are expected to contribute substantially to increased fire severity and frequency in the northern high latitudes, potentially shifting peatlands from being carbon sinks to being greenhouse gas emission sources. Therefore, peat fires, which are considered the largest and most persistent fires on Earth, can significantly impact the global carbon cycle, atmospheric composition, climate, air quality, and human health. Representing peatland fire feedbacks to climate in Earth system models is essential for accurately predicting the future of the climate system. Here, we present the first steps of an effort to distill lab results on peat burning and emissions into global fire modelling. Since peat moisture content and the depth of burn have been experimentally proved to be critical for the representation of peat fires, we aim to incorporate those mechanisms into a global model functionality. More specifically, we aim to represent the mechanistic understanding of the ignition and spread of peat fires in INFERNO-peat, the peat module of the JULES-INFERNO global fire model. To assess the added value of our updated model, we compare the simulated burnt area and carbon emissions with observation-based products. As boreal regions remain a big mystery for the future of our planet, our improved model representation of peat fires in northern high latitudes contributes to a better understanding of future atmospheric composition, radiative forcing and climate. 

How to cite: Tarasi, D., Boleti, E., Blackford, K., Kasoar, M., Grillakis, E., Rein, G., Mulyasih, H., and Voulgarakis, A.: Northern high latitude peat fires: from lab to modelling , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11432, https://doi.org/10.5194/egusphere-egu24-11432, 2024.

Amazon forest conservation is critical for reaching net-zero carbon emissions and protecting regional biodiversity but these efforts are at risk from deforestation, fire and drought. In particular, accurate quantification of carbon losses from forest and deforestation fires are required to understand long-term impacts of fire on the carbon cycle and inform management strategies. Recent developments in the detection of burned area, near-real time tracking of fire patch metrics, and higher-resolution fire emissions models allow for improved estimates of carbon losses from fire. Nevertheless, independent validation of these novel approaches often remains elusive, leading to large disagreement between different emissions inventories.

Here, we compare carbon emissions estimates from several state-of-the-art fire emissions models, including a 500-m resolution GFED version, GFAS, and the Sense4Fire project, in a case-study for the Amazon region. Where necessary, we have updated the models to extend to 2022 and to include the most recent version of model input data from MODIS (Collection 6.1). We analysed the added years of data to elucidate recent trends in fire-related carbon emissions across the Amazon and adjacent biomes. For validation, we ingested the CO emissions from the considered fire emissions models into an atmospheric transfer simulation (IFS-COMPO) and compared those to column CO observations from Sentinel-5P TROPOMI. Finally, we propose an optimization methodology for matching modelled CO concentrations to observations with the objective of constraining regional carbon losses from fire. Results provide novel insights into carbon losses from fire across different fire types and land use practices, and can be extended to global scale for improved estimates of global fire emissions.

How to cite: van Wees, D., Huijnen, V., Forkel, M., de Laat, J., Andela, N., and Wessollek, C.: Comparison and validation of state-of-the-art fire emissions models for the Amazon, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11599, https://doi.org/10.5194/egusphere-egu24-11599, 2024.

Forests play a substantial role in generating externalities and supporting services essential for maintaining key ecosystem functions and processes. Fire has long been a natural element of forest dynamics, contributing to model the structure, composition, and diversity of vegetation. However, changes in fire regimes in recent decades in Europe (e.g., more frequent and severe fires) have led to negative ecological, social, and economic impacts, particularly marked by a decline in the provision of ecosystem services. Mediterranean Europe, being a region highly prone to wildfires and currently experiencing a change in fire regimes, exemplifies this situation.

In this study, we aim to understand the effects of postfire oak afforestation on the provision of ecosystem services (ES). We analysed 15 afforestation projects with the deciduous Pyrenean oak (Quercus pyrenaica) carried out in 1994-2006 in similar soil type (Cambisols) in the North and Center of Portugal, including seven pure and eight mixed oak stands. For each project area, we identified an adjacent control area affected by the same fire event but without oak afforestation or evident management. In 2021-2022, for each project and control areas, we collected field data on: site conditions, stand characteristics, forest biometry, understory vegetation (height and cover), floristic richness and diversity, oak natural regeneration and litter. At the moment of data collection, the majority of projects (10) were 12 to 17 years old, with the remaining projects (5) having been implemented 21 to 25 years ago. Collected data was used to quantify provisioning ecosystem services (wood volume) and regulation and maintenance services (forest and litter carbon, fire protection, maintenance of nursery populations, habitats, and seed dispersal).

Afforested areas supplied more provisioning services (higher wood volume), as a consequence of a higher tree density when compared to non-afforested areas. Total carbon content and litter carbon were not significantly different between afforested and control areas. Nevertheless, afforested and control areas exhibited distinct patterns concerning carbon in the different forest layers: carbon in the tree layer was significantly higher in afforested areas, while carbon in the understory layer was significantly higher in control areas. Afforested areas also showed a significantly higher fire protection service, as a consequence of lower fuel load from regular understory shrub management. Lastly, we found no significant differences in services related to maintenance of nursery populations and habitats (estimated with floristic species and diversity), and seed dispersal (estimated with oak natural regeneration), although afforested areas presented a higher number of oak seedlings.

Our study shows that postfire afforestation in oak forests may have a positive, null or negative impact on ES, depending on the service under analysis, highlighting the existence of trade-offs among multiple ES. We emphasize the importance of a comprehensive understanding of the impacts of postfire afforestation on ES to guide postfire management, aiming to enhance forest resilience in the face of predicted climate change.

How to cite: Lopes, L. F., Santos, E. S., Nunes, L., Fernandes, P. M., and Acácio, V.: Analysing the effects of postfire oak afforestation on the provision of ecosystem services, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11809, https://doi.org/10.5194/egusphere-egu24-11809, 2024.

New fire vulnerable communities are emerging in traditionally non-fire prone regions of the world. But these communities are often largely unaware of the developing threat and do not hold the core wildfire knowledge to galvanise collective community-based action to mitigate the risk. Furthermore, we urgently require knowledge of fuel moisture dynamics and flammability of fuels in such regions to provide accurate assessments of fire danger at the national scale. Here we characterise the moisture content and flammability of heather through engaged environmental science, demonstrating the potential of the approach to develop a public consciousness and knowledge of wildfire within communities. Fuel sampling kits were sent to 150 samplers who collected ~1000 vegetation samples across the UK (from Land’s End to John O’Groats) over a period of two days during a single period of high fire danger. The validity of the volunteer approach for collecting high quality fuel moisture data was also assessed from the analysis of a separate ~1500 samples collected by 17 samplers in a single test plot. The approach provides a simple nationally available entry point for residents traditionally unaware of both the wildfire risk and the management of their community for wildfire mitigation. Empowering samplers offers potential future opportunity to create meaningful local datasets, to build communities, and in doing so give a strong voice to residents in regional and national policy discussions.

How to cite: Kettridge, N., Ivison, K., Crawford, A., Clay, G., Belcher, C., Graham, L., and Little, K.: The Great Fuel Moisture Survey: developing fundamental wildfire science and sustainable community owned agency in traditionally non-fire prone societies, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11962, https://doi.org/10.5194/egusphere-egu24-11962, 2024.

Peatland soil is a valuable component of natural capital by constituting the largest terrestrial carbon sink (~30% of the global soil carbon) and an essential freshwater source. Despite covering only ~3% of the Earth’s surface, peatlands provide crucial ecosystem services i.e. water-quality improvement and climate regulation by storing carbon in peat. However, peat degradation due to anthropogenic activities (e.g. drainage) as well as global climate change exposes this ecosystem to fire risk.
This study assessed the medium-term (~5 years) impacts of the 10 August 2018 wildfire within The Roaches Nature Reserve. This area spans the southeastern sector of the Peak District National Park and Special Area of Conservation (SAC-UK0030280). According to the Staffordshire Wildlife Trust (responsible authority for Reserve management), the human-caused fire broke out in a wooded area and aided by wind, spread to the peatland. Here, we integrated soil analyses and vegetation surveys of a burnt and unburnt area i) to assess possible correlations between soil biogeochemical properties and vegetation cover with ii) remote sensing to collect data on fire severity exploring temporal and spatial wildfire impacts.
Processing of satellite imagery highlighted a high-severity fire impact within the perimeter of the burned area, which predicts alteration of soil characteristics. Preliminary outcomes on the soil indicated deacidification and reduced water content in the burned peat remains 5 years post-fire.
Given that global peatland conservation is an important tool for addressing climate-change, this research appears necessary to develop effective management strategies, including rewetting of peatlands postfire.

How to cite: Marfella, L., Ashby, M. A., Hennessy, G., Marzaioli, R., Rutigliano, F. A., and Glanville, H. C.: Effects of 2018 wildfire on soil properties in a peatland within the Peak District National Park (central England), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11965, https://doi.org/10.5194/egusphere-egu24-11965, 2024.

The ignition, spread, and severity of wildfires are driven largely by weather conditions (Jain et al. 2020: https://doi.org/10.1139/er-2020-0019; Liu et al. 2013: https://doi.org/10.1371/journal.pone.0055618).  The main tool for weather prediction across the globe is a set of physical, coupled atmosphere/ocean models, called numerical weather prediction (NWP).  Despite rapid improvements in the last few decades, NWP alone is not sufficient for wildfire prediction, because it does not resolve every process related to wildfire.  One solution is to post-process NWP with statistical models, which correct the NWP model towards better resolving processes related to the phenomenon of interest (here, wildfire).  This post-processing is called model-output statistics (MOS) and typically involves linear regression.  However, recent work has advanced MOS by incorporating more powerful statistical models from deep learning (DL).  We use DL to predict extreme fire weather and behaviour at multi-day lead times throughout the United States.

For fire weather, we have trained U-nets -- a type of deep neural network -- to predict at lead times of 3-240 hours over the United States.  The output (target) variables are seven indices from the Canadian Fire Weather Index System (CFWIS), computed from the ECMWF Reanalysis version 5 (ERA5).  These seven indices include the fine-fuel moisture code (FFMC), initial-spread index (ISI), overall fire-weather index (FWI), etc.  Meanwhile, the input (predictor) variables come from five sources.  The first is a forecast time series of atmospheric state variables (height, temperature, humidity, and wind) from the Global Forecast System (GFS) NWP model.  The second is a forecast time series of surface and subsurface moisture (soil moisture, accumulated precipitation, and snow depth) from the GFS.  The third is a set of constant fields (terrain height/slope/aspect, land-sea mask, etc.) describing the underlying terrain.  The fourth is a lagged time series of CFWIS over the past several days, i.e., past target values.  The fifth is a forecast time series of CFWIS indices, computed by applying the CFWIS functions directly to GFS-forecast weather variables.  These are the uncorrected (GFS-only) CFWIS forecasts, to be corrected by the U-net.

For fire behaviour, we have trained random forests -- ensembles of decision trees -- to predict fire radiative power (FRP) at lead times of 1-48 hours over the United States.  The labels (correct answers) for FRP are obtained from the Regional ABI and VIIRS Emissions (RAVE) merged satellite product.  Predictors for the random forest include the first three sources listed for the U-net above, plus a lagged time series of FRP over the past 24 hours, i.e., past target values.

Both models -- the U-net for fire weather and the random forest for fire behaviour -- are trained with built-in uncertainty quantification.  Thus, at every lead time and grid point, both models provide an expected value and an estimate of their own uncertainty.  We will present objective evaluation results (for both the mean forecast and uncertainty) and explainable artificial intelligence (XAI) to understand what the models have learned, e.g., which spatiotemporal weather patterns in a given area are most conducive to extreme fire weather/behaviour.

How to cite: Lagerquist, R. and Kumler, C.: Using deep learning to improve multi-day forecasts of extreme fire weather and behaviour throughout the United States, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12223, https://doi.org/10.5194/egusphere-egu24-12223, 2024.

Forest fires pose a growing global threat, exacerbated by climate change-induced heat waves. The intricate interplay between changing climate, biophysical, and anthropogenic factors emphasizes the urgent need for sophisticated predictive models. Existing models, whether process-based for interpretability or machine learning-based for automatic feature identification, have distinct strengths and weaknesses. This study addresses these gaps by integrating human domain knowledge, crucial for interpreting forest fire dynamics, into a machine learning framework. We introduce FLAM-Net, a neural network derived from IIASA's wildfire Climate impacts and Adaptation Model (FLAM), melding process-based insights of FLAM with machine learning capabilities. In optimizing FLAM-Net for South Korea, new algorithms interpret national-specific forest fire patterns, and multi-scale applications, facilitated by U-Net-based deep neural networks (DN-FLAM), yield downscaled predictions. Successfully tailored to South Korea's context, FLAM-Net and DN-FLAM reveal spatial concentration near metropolitan areas and the east coastal region, with temporal concentration in spring. Performance evaluation yields Pearson's r values of 0.943, 0.840, and 0.641 for temporal, spatial, and spatio-temporal dimensions. Projections based on Shared Socioeconomic Pathways (SSP) indicate an increasing trend in forest fires until 2050, followed by a decrease due to increased precipitation. During the optimization process of FLAM-Net for Italy, optimal parameters for sub-areas are identified. This involves considering biophysical and anthropogenic factors at each grid, contributing to improved localized projection optimization by utilizing various sets of optimal parameters. There by, this process illuminates the intricate connections between environmental factors and their interpretation in the dynamics of forest fires. This study demonstrates the advantages of hybrid models like FLAM-Net and DN-FLAM, seamlessly combining process-based insights and artificial intelligence for interpretability, accuracy, and efficient optimization. The findings contribute scientific evidence for developing context-specific climate resilience strategies, with global applicability to enhance climate resilience.

How to cite: Jo, H.-W., Corning, S., Kiparisov, P., San Pedro, J., Krasovskiy, A., Kraxner, F., and Lee, W.-K.: Integrating Human Domain Knowledge into Artificial Intelligence for Hybrid Forest Fire Prediction: Case Studies from South Korea and Italy, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12320, https://doi.org/10.5194/egusphere-egu24-12320, 2024.

Prescribed (Rx) and controlled fires are an important land management tool used globally for a variety of reasons, including the reduction of hazardous fuel loads, ecological conservation, agriculture, and natural resource management. Its use has important implications for wildfire risk, biodiversity, and carbon storage. However, the use of Rx and controlled fires is highly dependent upon weather conditions, requiring a weather window during which a careful balance of temperature, moisture, and wind ensure that the burns achieve their objectives while minimizing ecological damage or risk to human lives or assets. The planning and execution of Rx burns must also consider how these weather conditions interact with the local vegetation and ecology. As fire weather is projected to grow more extreme under the impacts of climate change, there is a growing need to monitor this effect on the ability to carry out Rx burning.

Here, we introduce a new dataset, GlobalRx, which includes around 140,000 records of Rx and other controlled fires from 16 countries, encompassing 207 ecoregions and 13 biomes around the world. For each record, we have geolocated values of various metrics of fire weather and fire danger (e.g. fire weather indices, vapour pressure deficit) from the ERA5 meteorological reanalysis, as well as the biome, ecoregion, fuelbed type, and protected area status from global thematic layers. We demonstrate the usefulness of this dataset for analyzing viable meteorological windows under which Rx fires may be conducted across diverse environmental settings in the present climate, as well as how these Rx burning windows may shift under the threats of climate change. This dataset has potential to shed light on how Rx burning windows may shift under future climate change, as well as opportunities to understand other drivers and effects of Rx burning.

This project has been supported by valuable contributions from non-public data from a consortium of data providers: Parks Canada, South Africa National Parks, Brazilian Institute of the Environment and Renewable Natural Resources, East-Pyrenees Prescribed Burning Team, Institute for Nature Conservation and Forests (Portugal), Regional Forest Fire Service (Italy), Russian Federal Forestry Agency, H2020 LifeTaiga Project, Government of the Principality of Asturias, Council of Andalucía, Council of Galicia, Forestry England, National Forestry Commission of Mexico, ZEBRIS Geo-IT GmbH, Hokkaido University, Pau Costa Foundation, Asian Forest Cooperation Organization.

How to cite: Hsu, A., Thurgood, J., Smith, A., Anderson, L., Clarke, H., Doerr, S., Fernandes, P., Kolden, C., Santín, C., Strydom, T., and Jones, M. and the GlobalRx Consortium: GlobalRx: A global assemblage of regional prescribed fire records for use in assessments of climate change impacts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12529, https://doi.org/10.5194/egusphere-egu24-12529, 2024.

The intensity of a wildfire can be assessed based on its released energy, obtained through remote measurements of the fire's radiative power. Since the Fire Radiative Power (FRP) is proportional to the amount of burned biomass and therefore to smoke production. Higher FRP values are associated with more severe fires, suggesting higher levels of smoke production and, consequently, higher emissions of particulate matter and other pollutants. The specific composition of smoke emissions can vary depending on factors such as the type of vegetation burned, the temperature of the fire, and the combustion conditions. In general, fire smoke is composed of a variety of air pollutants, including gases (NOx, CO, VOCs, O₃, PAHs, etc) and particulate matter (PM). The objective of this work is to evaluate the ability of FRP, to be used as an indicator of fire smoke pollution. Particulate matter (PMx) and carbon monoxide (CO) concentrations emitted during recent wildfires in Portugal are analyzed to assess the link between pollution concentration levels and fire intensity over the affected areas, taking into account the spatial and temporal characteristics of each event. For this purpose, two particularly severe fires with significant impacts on air quality in central and southern Portugal were analyzed namely the ones taking place in October 2017 and August 2018. Concentrations of PMx and CO were evaluated through CAMS data, and the radiative power through the FRP product of the SEVIRI/MSG disseminated by LSA-SAFThe results show that the emitted pollutant concentrations significantly exceeded the established daily target limit values (air quality and public health guidelines). The fire intensity, based on the emitted Radiative Energy (FRE) derived from FRP, aligns with the known severity of these events, consistent with the observed concentrations of air pollutants, being demonstrated that the FRP can be associated with smoke production, especially PMx emissions during a fire. Thus, the proposed methodology using FRP can be a valuable tool for assessing the impact of wildfires on air quality and understanding the potential for smoke dispersion over fire-affected regions. The role of FRP as an indicator of air pollution highlights the potential use of FRP in assisting in management activities, operational planning, and emergency intervention during ongoing fires. 

Acknowledgments: This study is partially supported by the European Union’s Horizon 2020 research project FirEUrisk (Grant Agreement no. 101003890); and by the Portuguese Fundação para a Ciência e a Tecnologia (FCT) I.P./MCTES on behalf of DHEFEUS -2022.09185.PTDC and the project FAIR- 2022.01660.PTDC).

How to cite: Durao, R., Alonso, C., Russo, A., and Gouveia, C.: The role of fire radiative power to estimate fire-related smoke pollution., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13237, https://doi.org/10.5194/egusphere-egu24-13237, 2024.

Fire is an important, widespread Earth-system process, influencing local ecosystems and climate around the globe. Over half of global burned area occurs in Africa, with over 10% of the continent affected by fire every year. Fire temporarily alters the surface properties, including surface albedo, causing long-lasting changes to the surface radiation budget.

We present the analysis of 20 years of fire and albedo data in Africa, using the MODIS product suite. We show that fire causes an average immediate albedo decrease, recovering exponentially with a time constant of several weeks. While the magnitude of albedo changes shows large spatial and temporal variations and a strong land cover type (LCT) dependency, exponential recovery is observed in the majority of LCTs. We show that fires cause long-term brightening, observing on average a small positive albedo change 10 months after a fire, but we find this is driven almost exclusively by slow vegetation recovery in the Kalahari region.

Using downward surface shortwave flux estimates we calculate the fire-induced surface radiative forcing (RF), peaking at 5±2 Wm⁻² in the burn areas, albeit with a significantly smaller effect when averaged temporally and spatially. We find that the average long-term RF is negative because of the brightening observed.

Our temporal analysis does not indicate a decrease in overall fire-induced RF, despite a well-documented reduction in burning in Africa in the recent decades, suggesting that the RF of individual fires is increasing because of higher levels of downward surface shortwave flux. We hypothesise this may be due to lower levels of smoke aerosols in the atmosphere.

How to cite: Flegrova, M. and Brindley, H.: Two decades of fire-induced albedo change and associated radiative effect over sub-Saharan Africa, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13416, https://doi.org/10.5194/egusphere-egu24-13416, 2024.

       Fire is the primary form of terrestrial ecosystem disturbance globally and a critical Earth system process. So far, most Earth system models (ESMs) have incorporated fire modeling, with 19 out of them submitted fire simulations to the CMIP6. Transitioning from CMIP5 to CMIP6, much more models submitted fire simulations and the dominant fire scheme has evolved from GlobFIRM to the Li scheme. However, it remains unknown how well CMIP6 ESMs perform in fire simulations. This study provides the first comprehensive evaluation of CMIP6 fire simulations, through comparisons with multiple satellite-based datasets and the Reading Paleofire Database of global charcoal records (RPD).

        Our results show that most CMIP6 models simulate the global amounts of present-day burned area and fire carbon emissions within the range of satellite-based products, and reproduce observed major features of spatial pattern and seasonal cycle as well as the relationships of fires with precipitation and population density, except for models employing the GlobFIRM fire scheme. Additionally, most CMIP6 models can reproduce the response of interannual variability of tropical fires to ENSO, except for some models incorporating the SPITFIRE fire scheme. From 1850 to 2015, CMIP6 models generally agree with RPD, with some discrepancies in southern South America before 1920 and in temperate and eastern boreal North America, Europe, and boreal Asia after 1990. Compared with CMIP5, CMIP6 has solved the serious issues of CMIP5 which simulates the global burned area less than half of observations, fails to capture the high burned area fraction in Africa, and underestimates seasonal variability. CMIP6 fire carbon emissions simulations are also closer to RPD. However, CMIP6 models still fail to capture the present-day significant decline in observed global burned area and fire carbon emissions partly due to underestimation in anthropogenic fire suppression, and fail to reproduce the spring peak in NH mid-latitudes mainly due to an underestimation of crop fires. Based on our findings, we identify potential biases in fire and carbon projection based on CMIP6 models. We also provide suggestions for the fire scheme development, and bias correction methods when generating multi-source merged fire products.

How to cite: Li, F., Song, X., Harrison, S., and Lin, Z.: Evaluation of global fire simulations in CMIP6 Earth system models, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14202, https://doi.org/10.5194/egusphere-egu24-14202, 2024.

In 2023, 6,551 wildfires across Canada burned 184,961 km² of the landscape—about 5% of Canadian forests—emitting nearly 480 megatonnes of carbon, with emissions leading to air quality warnings as far away as Washington DC, USA. In early June, the air quality index in New York City was over 400, and by mid-June, smoke plumes passed above Europe. As wildland fires of increasing severity occur with increasing frequency, driven by global climate change and decades of fire suppression, societies near and far from high-risk ecosystems face increased exposure to wildfire emissions that may have both acute and long-term health impacts. Prescribed fire interventions show promise for reducing the risk of large wildfires in fire-prone ecosystems, but implementing prescribed fire can be difficult, in part due to concerns about the potential health impacts of prescribed fire smoke on nearby communities. To provide decision support for land managers aiming to reduce wildfire risk with prescribed fire treatments, we will produce a geospatial database of daily pollutant emissions and fire intensity from simulations of prescribed and wildland fires over a 20-year period for: 1) a baseline scenario of no management actions, 2) one or more scenarios of prescribed fire locations and timing based on interaction with tribes and Okanogan-Wenatchee National Forest (OWNF) managers, and 3) scenarios of prescribed fire locations and timing based on fire paths, locations of highly valued resources, areas available and suitable for treatment, determined by the research team. We can accomplish this by iterating between FSim, the Large Fire Simulator, which stochastically simulates large wildfire ignition and spread across a LANDFIRE fuels landscape, and FFE-FVS, the Forest Vegetation Simulator with the Fire and Fuels Extension, which simulates post-fire regeneration, forest growth, management actions including prescribed fire, fuel dynamics, and fuel consumption and pollutant emissions from prescribed fires and wildfires. Because FSim takes a Monte Carlo approach, simulating fires over 10,000 or more hypothetical fire seasons comprised of daily weather sequences, we will be able to estimate the probability of each landscape pixel burning in a wildfire and the conditional probability of that pixel burning at different flame lengths, allowing us to provide emissions estimates within a risk-assessment framework for managers. The framework will allow land managers to quantify the likelihood that smoke impacts from near-term prescribed fire treatments will be offset by reductions in severe smoke events from future wildfires. Additionally, the smoke event geospatial datasets may provide input into atmospheric transport models which could be used to simulate regional to national scale smoke impacts. We will pilot the project in Okanogan-Wenatchee National Forest, Washington, USA, working with the forest’s managers to design fuel treatment scenarios that will yield realistic fire occurrence trajectories and emission estimates to inform near-term prescribed fire operations. As a U.S. Federal Bipartisan Infrastructure Law Research & Development “proof of concept” project, the Wildland Fire Smoke and Emissions Tradeoff Decision Support project will inform U.S. Forest Service management policy and strategy around the use of prescribed fire in other National Forests in the U.S.

How to cite: Sindewald, L., Urbanski, S., Riley, K., Eckerson, C., Dye, A., and Houtmann, R.: Wildland Fire Smoke and Emissions Tradeoff Decision Support, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14446, https://doi.org/10.5194/egusphere-egu24-14446, 2024.

Tropical dry forests are recognized globally as the first frontier of human land-use change, due to multiple factors that make them amenable to human occupation, especially with the use of fire. However, in southern India, biodiversity ‘hotspots’ with human habitation are not uncommon with a long-term co-existence of humans in pristine environments. This points to the need for more accurate evidence-based (using charcoal, pollen, phytoliths) understanding of if, when and how land use and land cover changes impact regional vegetation-fire relationships. We reconstruct the environmental history for Mudumalai National Park, a fire-prone dry forest with >30% of the park subject to annual fires and a west-to-east rainfall-vegetation gradient. We examined a 150 cm sediment profile from an excavation in a seasonal wetland in the wettest part. The record spans 1200 years in time (bracketing radiocarbon dates) with very low macrocharcoal counts (mean - 4), with highest numbers in the surface and near-surface layers. Molecular fire proxies Polycyclic Aromatic Hydrocarbons (PAHs) were also found present - Phenanthrene (Phe), Anthracene (Ant), Fluoranthene (Fl), Pyrene (Py), Benzo[ghi]fluoranthene (Bghi), Benz[a]anthracene (BaA), Chrysene (Chr), Benzo(b)fluoranthene (BbF), Benzo(k)fluoranthene (BkF), Benzo[e]pyrene (BeP), Benzo[a]pyrene (BaP), and Perylene (Pry). Notably, Fl, Py, Bghi, BbF, BaA,and BeP constituted 90% of the total concentrations. Diagnostic ratios of PAHs for source determination pointed at a pyrogenic source consistently across all samples. Paleovegetation proxies n-alkanes (C14-C33) were analyzed and the average chain length (ACL) showed a transition towards higher chain lengths towards the surface indicating a change towards grass sources (C31, C33) in addition to woody biomass-derived compounds (C27, C29). Further analysis to characterize the human-fire-vegetation relationships is underway and to our knowledge, as the first report from a protected forest in India, our study offers critical insights for forest fire management in forested landscapes.

How to cite: Ramya Bala, P., Kumar, N., Behera, D., Ambili, A., and Sukumar, R.: Reconstructing human-fire-vegetation inter-relationships in a protected dry tropical forest, Mudumalai National Park, southern India, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14748, https://doi.org/10.5194/egusphere-egu24-14748, 2024.

Climate change has influenced fire activities, altering the fire risk associated with air pollution and human health. However, the specific contribution of climate change to fire risks on air pollution and health burden has not yet been discovered. In this study, three fire-vegetation models were employed to simulate fire aerosol emissions under two simulations over the past six decades: an observation climate scenario and a counterfactual scenario where the long-term climate change trend is removed. Combining fire aerosol emissions with a chemical transport model and an avoidable mortality risk model, we calculated global fire PM_2.5 and its associated mortality. By comparing the results under the two simulations, we demonstrated the climate change has increased the fire PM_2.5 and its mortality. The findings indicated an increase in fire mortality over the six decades: 46,401 in the 1960s and 98,748 in the 2010s, with 3-8% attributed to climate change. Clear relationships were observed between the contribution of climate change to fire mortality and relative humidity or air temperature in some regions. This suggests that fire risks in these regions are sensitive to climate change and necessitate the development of adaptation strategies to mitigate risks in the future.  

How to cite: Park, C., Takahashi, K., Fujimori, S., Jansakoo, T., Burton, C., Huang, H., Kou-Giesbrecht, S., Reyer, C., Mengel, M., and Burke, E.: Climate change has increased fire PM2.5 and its associated health burden, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14762, https://doi.org/10.5194/egusphere-egu24-14762, 2024.

In this work we showcase the in-progress results from the FirePATHS project (PID2020-116556RA-I00). The project aims to assess the evolution of fire danger under different emission and forest management scenarios through the explicit interaction of the climate-vegetation-fire system. For this purpose, a methodological framework combining different simulation models of the elements of this system is proposed. The core of the process lies in the modeling of vegetation dynamics at stand scale according to different trajectories of climatic evolution to characterize the state and typology of fuels and the subsequent simulation of potential fire behavior during the 21^st century.

We analyzed a set of 114 Pinus halepensis plots, surveyed in the field during 2017;  68 plots burned during the summer of 1994 and 46 unburned control stands. We used the medfate model to simulate forest functioning and dynamics, which provides the necessary fuel model parameters to be entered into fire behavior models (Fuel Characteristics Classification System, implemented in medfate as well). The combination of these two approaches provides time-varying estimates of fire behavior metrics (e.g., flame length or rate of spread). The simulation was conducted under SSP climate scenarios (SSP 126, 245, 370 and 585) depicting different levels of climate warming, vegetation dynamics and, hence, fire danger. Likewise, we devised a set of forest management prescriptions aimed at reducing climate vulnerability of tree communities and reducing extreme wildfire potentials. A baseline scenario with no management was also assessed.

We observed very contrasting trajectories between burned and control stands, with the first leading to increasing fuel loads, except in SSP 585. Fire potentials depicted a significant increase in surface fire behavior, with adaptive and mitigation management being able to mitigate it to some extent.

How to cite: Rodrigues, M., Gelabert, P., Lamelas, T., Hoffrén, R., de la Riva, J., Domingo, D., Vega-García, C., Ibarra, P., Ameztegui, A., and Coll, L.: Fire hazard trajectories under climate change and management scenarios, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14891, https://doi.org/10.5194/egusphere-egu24-14891, 2024.

Spatiotemporal patterns and trends of atmospheric aerosols in high latitude region have been analyzed. Aerosol observation data from 2000-2022 acquired from the earth observing satellites including the Moderate Resolution Imaging Spectroradiometer (MODIS), the Ozone Monitoring Instrument (OMI), or geostationary satellites such as the Geostationary Korea Multi-Purpose Satellite-2A (GK-2A) . Results showed that Aerosol Optical Thickness (AOT) over the high latitude region has gradually decreased before 2016. However, AOT has increased significantly over the past 8 years. This increase was clearly shown in North America and North Asia, and was associated with an increase with fire activities. Smoke plumes originated from fire active fires transported eastward with meteorology, but occasionally moved toward the Arctic region. The occurrence of fires and the production and transport of aerosols will be a consequence or factor of the recent rapid climate change.

Acknowledgement: This research was supported by Basic Science Research Program through the National Research Foundation of Korea (NRF) funded by the Ministry of Education (NRF-2019R1I1A3A01062804).

How to cite: Lee, K.-H., Kim, K., and Lee, D.: Effects of recent increase in anomalous fires and smokes at high latitude regions on regional atmosphere, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15398, https://doi.org/10.5194/egusphere-egu24-15398, 2024.

Wildfires in South America are a significant concern, causing high emissions and deforestation rates. They affect air quality, radiation balance, and sensitive ecosystems like the Amazon rainforest. Wildfires are expected to intensify with future land use and climate changes, making it crucial to enhance decision-making tools. Models of atmospheric composition, combined with wildfire emissions inventories, support decision-making by simulating events and their impacts on air quality. There are currently a range of wildfire/biomass burning emission inventories, which all use different approaches. This can lead to substantial differences in estimated emissions and thus impacts on atmospheric composition estimation.  This study aims to assess four inventories (2004-2022) in South America: Global Fire Emissions Database (GFED), Fire INventory from NCAR (FINN), Global Fire Assimilation System (GFAS) and Brazilian Biomass Burning Emission Model (3BEM-FRP), focussing on carbon monoxide (CO) given its relatively large emission and complementary satellite missions retrieving atmospheric CO. Our results analyse the temporal consistency in the emission seasonal cycles from the inventories and quantify the spatial agreement/differences between them. We also exploit the Measurements Of Pollution In The Troposphere (MOPITT) retrieved CO to assess the links between emission inventory tendencies with that of the atmospheric temporal evolution. Finally, we use an offline version of the INteractive Fire and Emission algoRithm for Natural envirOnments (INFERNO) model, within the Joint UK Land Environment Simulator (JULES) framework to investigate simulated skill of emissions of CO against the observational constraints above as INFERNO is the fire model of choice in the UK Earth System Model (UKESM).

How to cite: Velasquez Garcia, M. P., Pope, R., Turnock, S., and Chipperfield, M.: Investigation of spatiotemporal variability in South American wildfire emissions and its impacts on CO concentrations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15436, https://doi.org/10.5194/egusphere-egu24-15436, 2024.

The Mediterranean region, already a climate change hotspot, is experiencing milder winters, hotter and drier summers, and increased extreme weather events, leading to longer fire seasons and increasing fire impacts. The socio-economic consequences of wildfires are significant, including the loss of human lives, infrastructure, and economic activity. Additionally, wildfires contribute significantly to climate change, accounting for up to 20% of global greenhouse gas emissions annually. Climate change is expected to worsen these conditions in the near future.

Given these circumstances, it is necessary to accelerate the transition towards the implementation of integrated and holistic fire management approaches aligned with future hazards. In the framework of The HUT project (The Human-Tech Nexus - Building a Safe Haven to cope with Climate Extremes), financed by the Horizon Europe program, the "Ogliastra-DEM8" case study (located in Sardinia, Italy) is aimed at responding to this necessity.

In particular, the main objective of The HUT is to mitigate the effects of climate-related events, by integrating and leveraging best practices and successful multi-disciplinary experiences and focusing on the prevention and preparedness phases of the disaster risk management cycle. In this context, the specific aim of the "Ogliastra-DEM8" case study is to provide the scientific/knowledge base needed to help policymakers and decision-makers defining adaptation and mitigation strategies that are effective in reducing fire impacts and associated costs in the short to medium-term under a changing climate. Towards this end, innovative tools (e.g., fire simulators, catastrophe insurance products, nature-based solutions) and stakeholder engagement, including participatory methods, will be developed.

This work presents the first phase of the work aimed at evaluating enablers and barriers to multi-hazard/systemic risk reduction by (i) reviewing the literature from other projects based in Sardinia, (ii) mapping and engaging stakeholders during an initial round of workshops, and (iii) debating fire-smart land management and adaptation options. Preliminary results indicate key barriers such as stakeholder conflicts, administrative silos, lack of political will, and funding complexities. All these elements contributed to varying degrees to the lack of a comprehensive approach towards integrated and sustainable management of the entire territory. On the other hand, enablers include stakeholder engagement, evidence of performance and co-benefits, and community awareness.

Further work will integrate stakeholder opinions into fire exposure and risk mapping under climate change conditions, with the goal of selecting and co-designing with them which fire-smart land management and adaptation options can be applied and where to protect the most important and vulnerable communities and ecosystems.

How to cite: Bacciu, V., Costa Saura, J., Pellizzaro, G., Arca, B., Duce, P., Spano, D., and Sirca, C.: Integrating stakeholders’ opinion in land management to build climate resilience in the context of fire risk, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15518, https://doi.org/10.5194/egusphere-egu24-15518, 2024.

Soil and ash are key sources of sediment, carbon, nitrogen, and associated pollutant movement following a wildfire. Their transport into freshwater systems can pose severe environmental and socio-economic implications including impacts to water quality and aquatic ecosystems, disruptions to drinking water supply and high remediation costs, as well as the depletion of carbon and nutrients from areas affected by erosion. We assessed the risk of soil erosion, ash and contaminant transport, and water contamination in three burned European catchments in Central Europe (Germany and the Czech Republic), Portugal and Spain using the European Water Erosion Prediction Project cloud interface with the Wildfire Ash Transport and Risk (WEPPcloud-EU WATAR) watershed model. The watersheds varied in size from 100 to 22,000 ha and represent distinct climatic conditions. To our knowledge, this is the first application of this model in European post-fire scenarios. We calibrated and validated the model using catchment runoff data (where available) and nearby streamflow data from both pre- and post-fire periods when runoff data was unavailable. Additionally, we used sediment transport data (where available) along with ash contaminant content data to calibrate and validate erosion and ash transport rates. Model performance was assessed using statistics like Nash-Sutcliffe Efficiency (NSE), coefficient of determination (R²) and percent bias (PBias (%)). Once the model was calibrated and validated, we estimated the post-fire risk of soil erosion, ash transport, and ash pollutant concentrations in the affected areas. The simulations provided the probabilities of occurrence and return periods for severe erosion events, as well as for ash and contaminant transport events. Based on these simulations, we identified hillslopes that were the main sources of runoff, erosion, ash and contaminant transport. This information is important to managers who can prioritize the application of mitigation treatments and prevention plans. Given the projected increase in fire weather in many regions in Europe, our findings suggest that the WEPPcloud-EU WATAR model is an increasingly useful tool in predicting and mitigating soil erosion and water contamination impacts of European burnt catchments.

How to cite: Neris, J., Sánchez-García, C., Basso, M., Lew, R., Srivastava, A., Dobre, M., Robichaud, P., Brooks, E., Santin, C., and Doerr, S.: Assessing post-fire soil erosion and water contamination risk in European fire-affected catchmentswith WEPPcloud-EU WATAR watershed model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16087, https://doi.org/10.5194/egusphere-egu24-16087, 2024.

The Republic of Sakha (Yakutia), the coldest permanently inhabited region on Earth, is characterized by unique ecological relationships between larch forest, permafrost, and wildfires. Together, they can stabilize each other, preserving the larch-dominated biome. Abundant lakes have important cultural and subsistence-related functions and are dynamically connected to warming permafrost processes. Recently intensified wildfire seasons, however, raised questions regarding the causes and impacts of long-term (centennial to millennial) fire regime changes. Despite recent progress, eastern Siberia is still sparsely covered by reconstructions of long-term fire history. This also limits any evaluation of fire regime impacts on permafrost lake development and catchment erosion. Past studies have shown the benefit of combining paleoecological fire reconstructions with geochemical data to shed light on fire regime changes and their impacts on lake catchments, as well as traces of potential human land use.

We present nine new records of Late Holocene wildfire activity, based on macroscopic charcoal in lake sediments (including information on charcoal particle sizes, morphologies, and length to width ratios), accompanied by sediment geochemistry data from high-resolution XRF core scanning. The studied lakes are located in the Lena-Amga interfluve of the Central Yakutian Lowlands, the Verkhoyansk Mountains, and the Oymyakon Highlands. The new data cover both thermokarst and glacial lakes, and a range from remote to rural settings and low to high elevations. Charcoal concentration in the lowland lakes is on average three times as high as in the highland lakes. Contrary to our hypothesis, charcoal concentration in most lakes is negatively correlated to many XRF-derived lithogenic elements indicating detrital input from catchment erosion (e.g., Ti, K). Reminiscent of earlier findings [1], multiple lowland sites share a signal of sharply decreasing biomass burning around 1300 CE. This coincides with the initial settlement of the Sakha people and increased catchment erosion. The new fire reconstructions allow for the evaluation of potential human impacts on past fire regime changes in Yakutia, while improving the region’s representation in global synthesis studies.

[1]  Glückler R. et al. (2021): Wildfire history of the boreal forest of south-western Yakutia (Siberia) over the last two millennia documented by a lake-sediment charcoal record. Biogeosciences 18 (13): 4185–4209. https://doi.org/10.5194/bg-18-4185-2021.

How to cite: Glückler, R., Dietze, E., Kruse, S., Andreev, A., Biskaborn, B. K., Zakharov, E. S., Baisheva, I., Stieg, A., Tsuyuzaki, S., Stoof-Leichsenring, K., Pestryakova, L. A., and Herzschuh, U.: Fire, permafrost, and people: Late Holocene fire regimes and their impacts on lake systems in Yakutia, Siberia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16263, https://doi.org/10.5194/egusphere-egu24-16263, 2024.

Wildfires are a central but relatively unexplored component of the Earth system. Severe wildfire events can lead to intense destruction of both nature and property, as was the case during the anomalously intense 2023 Canadian wildfire event. Last year, approximately 5% of the total forest area of Canada burned [1] [2], which is the highest wildfire damage Canada has ever sustained [1].

Conditions pertaining to climate change and modifications in atmospheric conditions are considered to be responsible for this record series of wildfires [3]. Increasing mean temperatures and decreasing humidity in the region has exacerbated wildfire risk. Carbon emissions from the 2023 Canadian wildfires have been the highest on record [4], including large amounts of carbonaceous aerosol which can exert substantial atmospheric radiative forcing. Also, Canadian fire emissions contributed around 20% of global emissions from vegetation fires. Thus, beyond the well-known health risks of wildfire emission compounds, it is important to also study the consequences of these emissions on large-scale atmospheric composition and meteorological behavior.

In this work, the global and regional atmospheric impact of the previously mentioned series of wildfires is investigated using the EC-Earth3 and UKESM1 earth system models. Simulated atmospheric conditions with and without the wildfire emissions, as provided by the Copernicus Atmosphere Monitoring Service (CAMS) Global Fire Assimilation System (GFAS), are compared through atmospheric modelling in the context of the Canadian 2023 fire season. The investigation reveals the connections between the emissions produced by this series of wildfires and atmospheric phenomena of importance, such as large-scale circulation, temperature patterns, and precipitation.

[1] "Fire Statistics". Canadian Interagency Forest Fire Centre. Retrieved January 4, 2024.

[2] The State of Canada’s Forests: Annual Report 2022. Canadian Minister of Natural Resources.

[3] Barnes, Clair, et al. "Climate change more than doubled the likelihood of extreme fire weather conditions in eastern Canada." (2023).

[4] “Copernicus: Emissions from Canadian wildfires the highest on record – smoke plume reaches Europe”. Atmosphere Monitoring Service, Copernicus. Retrieved January 4, 2024.

How to cite: Rosu, I.-A., Kasoar, M., Boletti, E., Parrington, M., and Voulgarakis, A.: Global atmospheric impacts of aerosols emitted from the 2023 Canadian wildfires, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16293, https://doi.org/10.5194/egusphere-egu24-16293, 2024.

Wildfires release approximately 2.1 Pg C to the atmosphere each year. The impact of wildfires on the carbon cycle, however, extends well beyond direct emissions, involving complex interactions among various source and sink processes. One such process, the enhanced post-fire soil organic carbon (SOC) erosion, remains unquantified as a potential C sink mechanism. Post-fire SOC erosion functions as a C sink when the subsequent burial and stabilization of eroded C offsite, coupled with the recovery of net primary production and SOC content onsite, outweigh the C losses to the atmosphere during post-fire transport of SOC. In this work, we synthesize published data on post-fire SOC erosion and evaluate its overall potential to act as C sink. In addition, we estimate its magnitude at continental scale following the 2017 wildfire season in Europe, showing that SOC erosion can indeed play a quantitatively significant role in the overall C balance of wildfires. 

How to cite: Girona-García, A., Vieira, D., Doerr, S., and Santín, C.: Exploring the role of post-fire erosion as a carbon sink mechanism, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16592, https://doi.org/10.5194/egusphere-egu24-16592, 2024.

Biomass burnings are one of the major sources of greenhouse gases in the atmosphere, impacting air quality, public health, climate, ecosystem dynamics, and land-atmosphere exchanges. In the tropics, South America represents about 10 % of the tropical emissions and present a large diversity of biomes and fire conditions. Over the last two decades, satellite observations have provided crucial information, notably via active fires detection, Fire Radiative Power (FRP) estimates and burned area (BA) measurements from imagers such as Moderate Resolution Imaging Spectroradiometer (MODIS) and Visible Infrared Imaging Radiometer Suite (VIIRS). Global inventories (e.g., GFED, GFAS, FEER, QFED, etc.) heavily rely on these satellite-derived indicators to estimate emissions from biomass burnings. However, emissions derived from these various models can significantly differ among them and large uncertainties persist regarding fire emissions, their variability, and their links with several drivers (e.g., type of combustion, vegetation, transport, etc.).

In this context, we propose a novel approach to estimate emissions from biomass burnings by directly using greenhouse gas concentrations in the atmosphere derived from spaceborne observations. Leveraging a decade of observations from the Infrared Atmospheric Sounding Radiometer (IASI) on-board the three Metop satellites, we have access to an unprecedented spatial coverage of global mid-tropospheric CO₂ and CH₄ concentrations twice a day (9:30 AM/PM LT). From this dataset, we developed the Daily Tropospheric Excess (DTE) method, which is based on the use of the diurnal cycle of biomass burnings and the vertical transport of their emissions to link the observed diurnal variations of the mid-tropospheric CO₂ and CH₄ concentrations to burnings activities.

We will demonstrate the relevance of the DTE for analyzing CO₂ and CH₄ emissions from various type of burnings, biomes, and human activities across South America. This will be achieved by comparing DTE with existing indices of fire characteristics such as FRP and BA from MODIS/SUOMI satellite observations, alongside global emissions databases like GFED and GFAS. Globally, we will show that their spatial distribution, seasonal intensity, and interannual variability are consistent with each other, even if some differences have been found and will be discussed. Additionally, geostationary data from GOES-R, MSG, and Himawari-8 satellites will be used to analyze the impact of observation times on the differences observed between the various datasets and the DTE.

How to cite: Bon, V., Crevoisier, C., and Capelle, V.: Study of greenhouse gases emitted by biomass burnings with a decade of infrared observation of CO2 and CH4 by IASI, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16676, https://doi.org/10.5194/egusphere-egu24-16676, 2024.

Fire is an integral part of savanna and grassland biomes and globally approximately half of landscape fire emissions originate from savannas and grasslands. Emissions of trace gases and aerosol particles from landscape fires are characterised by emission factors (EFs), which denote the amount of emitted substance per mass of combusted biomass. EFs vary depending on both the biomass that is consumed in the fire and the combustion characteristics of the fire, i.e. the ratio of flaming to smouldering combustion. However, emission inventories tend to use only one average EF for each biome.

Here, we use a set of 27 laboratory experiments to characterise the effect of combustion characteristics on submicron aerosol EFs from savanna and grassland biomass acquired from South Africa as well as boreal forest floor samples from Finland. Combustion experiments were carried out at the ILMARI facility in Kuopio, Finland from May to June 2022 under an open stack mimicking natural burning and dilution. Sample was injected into a 29 m³ environmental chamber for ageing studies. Chemical and physical properties of both fresh and aged smoke were observed with a host of instruments including e.g. AMS, FIGAERO-CIMS, VOCUS, SP2 and SMPS. The ratio of flaming to smouldering combustion was characterised by modified combustion efficiency (MCE), i.e. CO₂/(CO₂+CO).

The increase of organic aerosol EF with increasing smouldering fraction (i.e. decreasing MCE) was very similar for both the grassland and savanna combustion experiments. Surprisingly, also the boreal forest floor EFs closely follow the same trend, where smouldering-dominated combustion EFs are more than 10 times higher than EFs for flaming combustion. We observed also that the submicron aerosol particle size distribution shifts towards larger sized particles with increasing smouldering fraction. Furthermore, both the number and the mass of the size distribution cannot be fully characterised with a single log-normal size distribution, which needs to be considered when converting mass emissions into number size distribution in simulations.

How to cite: Vakkari, V., Buchholz, A., Hao, L., Ihalainen, M., Jaars, K., Köster, K., Le, V., Miettinen, P., Mukherjee, A., Peltokorpi, S., Pullinen, I., Siebert, S. J., Sippula, O., Somero, M., Vettikkat, L., Virtanen, A., Yli-Pirilä, P., Ylisirniö, A., and van Zyl, P. G.: Effect of combustion conditions on aerosol particle emissions from savanna and grassland fires, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17593, https://doi.org/10.5194/egusphere-egu24-17593, 2024.

Fire substantially influences and modulates the global carbon cycle through numerous processes, interactions, and feedbacks. Fires are also strongly intertwined with human activities; people act both as drivers of change through ignitions, suppression, land-cover change, prescribed burning, and climate change, and are affected in return by changes in fire regimes. 

Despite fire’s many complex interactions throughout the Earth System, it is often viewed only as a destructive process, and one that solely acts as a source of atmospheric carbon. In terms of fire’s carbon budget, the release of carbon only represents the very initial stages of the process, missing the drivers and complex ways in which fire shapes plant species evolution and ecosystem trajectories, nutrient cycling and redistribution, carbon allocation, deposition and sequestration over different spatiotemporal scales. Therefore, there is a clear need to fully understand the role of fire in the Earth System holistically. However, different aspects of fire’s role in the carbon cycle are often studied by different communities and disciplines, hindering this much-needed integrated understanding. 

Through the Fire Learning AcRoss the Earth Systems (FLARE) workshop (September 2023) we brought together fire scientists across multiple disciplines to facilitate transdisciplinary discussion. We propose that the visualization of fire processes as carbon colours across the Earth System can be a thematic tool for unifying disciplines. It explores all aspects of fire and smoke implications for living systems and opens questions about fire’s role in carbon budgets, afforestation, and climate change and related mitigation strategies. We also identified several scientific challenges for the community where, by working together, we can address some fundamental questions for fire’s role in the carbon cycle, such as: What is the contribution of fire and of individual fire events to the global carbon cycle? How do changes in fire regimes influence ecosystem stability across different timescales? How do future changes in fire regimes influence global climate, allowable emissions and carbon budgets, and temperature mitigation ambitions? In this presentation, we explore how we can bring a more interdisciplinary approach to fire science to address these fundamental questions.

How to cite: Burton, C., Plummer, S., Liguori-Bills, N., Perron, M., Kelley, D., Morrill, M., Vannière, B., Hall, J., Hantson, S., Forkel, M., Völker, C., Dintwe, K., Santin, C., Thoreson, J., Poulter, B., Jones, M., and Hamilton, D.: The FLARE Workshop perspective on Fire’s Role in the Carbon Cycle, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17935, https://doi.org/10.5194/egusphere-egu24-17935, 2024.

Wildfires are an important disturbance in global ecosystems and are a critical driver of trends in the land carbon budget. Fire is an extreme phenomenon, with the largest burned area often occurring during extreme fire seasons generating large fires. Days with fire conditions conducive to fire ignition and spread are increasing in a warming climate in many regions of the world, contributing to increases in fire occurrence and annual burned area. However, the climate, fuel, and weather conditions that lead to extremely large fires in different biomes are poorly understood.

Here, we explore the temporal evolution of extremely large fires in temperate and boreal regions using new satellite-derived fire event tracking datasets optimized to match higher resolution time series of fire progression from aircraft and other sources. We aimed to understand the specific environmental conditions required for the development of a large fire. Our analysis revealed a disproportionate impact of multiple fire ignitions in creating large fires through merging. Our findings suggest that the largest fires in both biomes may be commonly created through multiple fires growing together. We hypothesize that a combination of physical and anthropogenic factors may accelerate merging, making these fires extremely difficult to contain and more robust to environmental controls regulating extinction. In our analysis, we use the Fire Events Database, the Arctic-boreal Fire Atlas, and GOFER, which enable attribution of ignition sources. Our analysis may contribute to an improved understanding of the influence of large-scale lightning storms in creating extremely large and destructive fire events.

How to cite: Scholten, R., Banerjee, T., Chen, Y., Desai, A., Liu, T., Morton, D., Veraverbeke, S., and Randerson, J.: What makes a fire grow extremely large?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18169, https://doi.org/10.5194/egusphere-egu24-18169, 2024.

Fire risk analyses, usually focused on fire hazard (i.e. the probability of fire occurrence), often neglect an important issue such as the sensitivity/vulnerability (i.e., the degree of potential damage, sensus IPCC) of different locations within the area of interest.  Such lack of consideration comes from past data processing constrains that limited fire severity studies to analyse only single or few fire events. Nowadays, online data repositories and processing platforms (e.g. Google Earth Engine) allow to easily integrate and process a vast amount of data from multiple sources that might prove useful for developing tailored tools for decision making. Here, we present an example for predicting potential fire severity based on the analysis of more than 1 000 fire events from southern France and western Italy which integrates climate, topographical and remote sensing variables. Furthermore, we assessed if the model “used” the explanatory variables under a meaningful biophysical sense.   Using the random forest algorithm and the relativized difference of the Normalized Burn Ratio (rdNBR) as proxy of fire severity, we reach to explain up to 75% of the variability in the data with most of the variables showing a clear and interpretable effect. Our results suggests that this type of approach might prove useful for better address fire risk assessments.

How to cite: Costa Saura, J. M., Bacciu, V., Spano, D., and Sirca, C.: Taking advantage of satellite data, large datasets of fire records and cloud computing for modelling potential fire severity useful for better assess fire risk, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18811, https://doi.org/10.5194/egusphere-egu24-18811, 2024.

Agricultural residue burning is a common practice in various regions of the world, which may have several environmental impacts, including on air quality, and the potential for triggering wildfires. In Portugal, this practice is particularly prevalent during the wet season, spanning from October to April. It involves open field burning of pruning residues and extensive burning to clear shrubbery, creating pastures for livestock. This research, conducted within the framework of the PRUNING project - Mapping open burning of agricultural residues from Earth Observations and modelling of air quality impacts- aims to explore the potential for detecting such events through satellite remote sensing.

The primary focus of this study is to assess the limitations of satellite remote sensing detection, with the overarching aim of integrating these findings into a systematic monitoring framework for open burning of agricultural residues. Additionally, the study aims to predict pollutant emissions and assess their impacts on air quality, providing valuable insights for environmental management and sustainable agricultural practices.

To achieve this goal, an in-depth analysis of known burning events was conducted using infrared thermal sensors. Multiple products, including Fire Radiative Power and fire masks from various sensors (e.g., MODIS, VIIRS, and Sentinel 3), were employed to characterize these known open field burning events. The results of this work allow verifying the tradeoffs effects associated with spatial, spectral, and temporal resolutions for each sensor, elucidating their impacts on the precision and accuracy of event detections. In parallel, this study evaluated the accuracy of the MINDED-FBA method in characterizing these known events. This automatic detection method, allows incorporating data from higher spatial resolution sensors (e.g., Sentinel-1, Sentinel-2, Landsat), for determining the extent of burned areas through multiple multispectral indices. In this context, the MINDED-FBA method may also be used to validate thermal anomalies detection products. Finally, the results of this work have also been compared to a national level register database of open burning, provided by the ICNF (Institute for Nature Conservation and Forests).

How to cite: Oliveira, E., Gata, J., Lopes, D., Disperati, L., Gama, C., and Silva, B.: Mapping open burning of agricultural residues from Earth Observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18894, https://doi.org/10.5194/egusphere-egu24-18894, 2024.

Exceptional wildfire activity occurred in the Arctic during the last years due to pronounced heat episodes. The Arctic has an abundance of peat and soils with organic content. When peat is burnt, the carbon flux into the atmosphere is virtually irreversible and this process may become of global significance for Arctic fires. Furthermore, smoke from smoldering fires (below-ground, peat) has a different chemical composition than smoke from flaming fires. It is therefore important to distinguish peat fires and above-ground, potentially flaming fires in fire emission estimation.

The operational Copernicus Atmosphere Monitoring Service (CAMS) is tracking global fire activity and emissions with its Global Fire Assimilation System (GFAS) as a near-real time service. GFAS uses satellite-based observations of fire radiative power (FRP), which links observed thermal radiation directly to the biomass combustion rate, i.e. amount of biomass burnt and corresponding emission of carbon into the atmosphere, based on satellite retrievals from MODIS and VIIRS. 

Here, we present a partitioning of the Arctic fire activity represented in GFAS into smoldering below-ground and potentially flaming above-ground fires using two approaches: (1) masking the fire activity maps with published peat maps and (2) analysing the observed diurnal cycles of the fire activity at all locations. We subsequently apply adapted emission factors and compare the resulting emission estimates to the standard values produced by CAMS for carbon, carbon monoxide, nitrogen dioxide and aerosols.

Furthermore, we may confront the fire emission estimates with independent atmospheric smoke observations by feeding them into IFS-COMPO, which is used to generate hindcasts of atmospheric composition, including tropospheric columns of CO and NO2. This allows an evaluation of the estimated trace gas emissions, by comparing the model simulations to satellite retrievals of carbon monoxide and nitrogen dioxide. It thus provides an independent assessment of the estimated fire emissions, and, in turn, carbon flux.

How to cite: Kaiser, J., Stebel, K., Schneider, P., and Huijnen, V.: Arctic peat fire emissions estimated from satellite observations of fire radiative power, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18941, https://doi.org/10.5194/egusphere-egu24-18941, 2024.

Landscape fires are increasingly represented in dynamic global vegetation models to understand impacts on carbon emissions and climate. Deliberate human fire use and management influence landscape fire characteristics, varying in space and time depending on social, economic, and ecological factors. For example, fire is used variously in rural livelihoods involving e.g., agriculture, hunting, gathering, and for other cultural practices, often depending on the time of year. Yet existing global fire models typically represent human fire use as a constant function of gridded datasets such as population density or gross domestic product.

Recently, initiatives have begun to draw together available data on global fire use from across multiple disciplines and disparate sources into coherent databases. We draw on information from one of these databases, the Livelihood Fire Database (LIFE), which includes case studies in 587 locations worldwide, to assess the availability of data on seasonality of anthropogenic fires associated with small-scale rural livelihoods. By defining seasonal cycles relative to the local variation of precipitation and evapotranspiration at each case study location, we look for patterns in the spatiotemporal nature of anthropogenic fires associated with different fire-use purposes - such as clearing vegetation for agriculture, maintaining pasture for livestock, or driving game when hunting - and consider the potential for this analysis to inform fire models.

For many fire types, especially those related to hunting, gathering, human wellbeing, and social signalling, there are limited quantitative data available, but it is possible to draw qualitative insights from case studies. Where quantitative data are available, we find some correspondence between fire seasonality and the intended fire-use purpose, suggesting that distinguishing between distinct fire-use purposes could improve the representation of human fire use in fire models, and consequently the seasonal cycle of fire emissions. Case studies demonstrate that environmental and social conditions drive variation in fire use for the same purpose, reiterating that a wide range of factors influence human behaviour and that assumptions of uniform drivers of anthropogenic fire may be misleading. Many of the fires now being revealed in global burned area data by new fine-scale remote sensing products are likely human-set; continued collection, collation, and analyses of data on human fire use globally is important to ensure appropriate anthropogenic representation in fire models.

How to cite: Kasoar, M., Smith, C., Perkins, O., Millington, J., and Mistry, J.: Global seasonality of small-scale livelihood fire, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18977, https://doi.org/10.5194/egusphere-egu24-18977, 2024.

How to cite: Leskow-Czyżewska, D., Bojinski, S., Chimot, J., Meraner, A., Parrington, M., and Fierli, F.: Monitoring wildfires from satellite, integration in Copernicus services and characterizing atmospheric impacts from the regional to the global scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19223, https://doi.org/10.5194/egusphere-egu24-19223, 2024.

Current global burned area products are available at coarse spatial resolutions (300-500 m), what leads to large amounts of errors, hindering an accurate understanding of fire-related processes. This study proposes a global calibration method for a sensor-independent burned area algorithm, previously used with 300 m Sentinel-3 Synergy data, and here implemented with 20 m Sentinel-2 MSI imagery. A binomial model that combines reflectance-based burned area predictions constrained by spatio-temporal densities derived from VIIRS active fires is calibrated using a reference dataset generated from Landsat imagery at a sample of 34 units across the globe. Preliminary leave-one-out cross-validation analyses show promisingly high accuracies (Dice of coefficient of 84.8%, commission error ratio of 13.2%, omission error ratio of 17.1% and relative bias of -4.5%), especially taking into account the mismatch of acquisition dates between reference and algorithm input data, what introduces apparent errors on the validation results.

How to cite: Padilla, M., Ramo, R., Sierra, S., Mota, B., Lacaze, R., and Tansey, K.: Burned Area Mapping with Sentinel-2 based on reflectance modelling and deep learning – preliminary global calibration and validation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19330, https://doi.org/10.5194/egusphere-egu24-19330, 2024.

Fire is a natural disturbance capable of altering plant distributions and community assemblages, influencing species evolution through the selection of traits and strategies, and affecting biogeochemical cycles. This powerful tool of landscape transformation can negatively impact even a fire-dependent ecosystem when natural fire regimes are altered. In recent times, interactions between human activities in the Cerrado (e.g., deforestation and intentional fires used to clear land), and a hotter and drier climate (due to climate change), have altered natural fire regimes causing more frequent and intense fire events, negatively impacting biodiversity, human health, and the regional climate. These fire-disturbed areas are widespread and highly vulnerable to future degradation from compounding disturbances, but they still harbour valuable biodiversity and carbon stocks that deserve protection and restoration. Monitoring the impacts of fire disturbance on vegetation structure and the potential pathways of recovery is critical to understand and protect resilient ecosystems under a rapidly changing climate. Robust monitoring requires the integration of modelled and field-based data tools and techniques. Field inventories alone are insufficient to capture the spatiotemporal variability of impacts of fire on native vegetation and should be coupled with remotely sensed data, among which, LiDAR (light detection and ranging) is unparalleled in characterising 3-D vegetation structure. Thus, the combination of LiDAR and forest inventory data is ideally suited for scaling the impacts of fire on forest vegetation and associated carbon stocks. In this study, we are assessing key metrics of vegetation structure derived from a combination of LiDAR and field data collected at the Experimental Station Serra das Araras, Mato Grosso state, Brazil. This field site comprises Cerrado vegetation that has been subject to three experimental fire treatments: every year, every two years, and every three years beginning in 2017, as well as fire suppression for over three decades. We are investigating whether key vegetation structural metrics can capture different fire treatments and identify spatial patterns of disturbance. We are also assessing if these patterns are different when comparing LiDAR data collected with a handheld scanner versus an airborne drone. This study aims to refine our methods and improve our understanding of vegetation structure responses across a gradient of fire disturbance regimes and potential post-fire recovery trajectories, which are key not only for ecological studies but also for emerging carbon markets – one of several mechanisms aimed at achieving climate change mitigation, conservation, and sustainable development outcomes. We hope to improve the process of carbon stock mapping in disturbed ecosystems and use the outputs to drive scenarios modelling at larger scales, providing a more comprehensive assessment of what future Cerrado carbon dynamics might look like under a range of possible disturbance/recovery dynamics.

How to cite: Machado, M., da Cruz, W., Carniello, M. A., Sturdivant, E., Navarro-Rosales, F., Macedo, M., Walker, W., and Oliveras Menor, I.: "Fire impacts in the Cerrado: Integrating LiDAR and field data to monitor vegetation structure and post-fire recovery.", EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19716, https://doi.org/10.5194/egusphere-egu24-19716, 2024.

There is growing concern over future trajectories of burning on Earth. One the one hand, some regions have seen the emergence of large and novel wildfires, whilst satellite observations continue to show declining burnt area globally, most notably in the tropics. Quantifying the response of global wildfire regimes to future changes in especially challenging given that wildfires are driven by climate, vegetation, and human activities, and that these different factors may have contrasting and opposing effects.

Using global empirical models of burnt area, fire size and fire intensity we explore the trajectory of future fire regimes under high and low climate change mitigation efforts. The models are driven by lightning ignitions, climate, vegetation properties, topography, and human factors. Making use of a set of sensitivity analysis, we show a global shift in wildfire patterns by the end of the 21^st century even with warming kept below 1.5°. Burning will generally be reduced in tropical regions but larger and more intense wildfires will occur in extra-tropical regions. Under low mitigation, increases in burnt area worldwide overwhelm the human-driven decline, with up to a 60% increase in burnt area by the end of the century. However, fire size and intensity will be increasingly limited by dryness and vegetation fragmentation.

These results suggest that even under high climate change mitigation, fire management strategies must urgently be revised as current fire-suppression policies will no longer be effective in much of the world. Regional-level fire management, led by local stakeholders, should be encouraged. Wildfire risk and management must also be incorporated into mitigation scenarios that rely on extending forest area if these mitigation scenarios want to remain realistic.

How to cite: Haas, O., Prentice, C., and Harrison, S. P.: Future global wildfire regimes under high and low climate mitigation efforts , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20564, https://doi.org/10.5194/egusphere-egu24-20564, 2024.

Recently, global mean methane concentrations have increased strongly. Methane is one of the most important greenhouse gases and plays a key role in atmospheric chemistry. Especially, due to its long lifetime of approx. 10 years and its significant effect on Earth’s climate change, a detailed knowledge of its source regions and their temporal evolution is crucial.

In this study, we present a unique data set of methane measured in situ over the Amazon rainforest region during the wet season in the CAFE Brazil (Chemistry of the Atmosphere Field Experiment) aircraft campaign from December 2022 to January 2023 in Manaus, Brazil. Methane was measured with an infrared quantum cascade laser absorption spectrometer on board the High Altitude and LOng-range aircraft (HALO). These observations show enhanced concentrations of methane in and above the boundary layer of the Amazon rainforest. Locally, dry air mixing ratios of up to approx. 2100 ppbv could be measured up to 4 km of altitude. Detailed analysis shows only a small contribution from anthropogenic sources. Especially over permanent wetlands and deforested areas, the methane concentrations were enhanced. Furthermore, the data has been compared to satellite measurements from the National Oceanic and Atmospheric Administration (NOAA), indicating good agreement in the free troposphere. Nevertheless, the mean levels directly above the Amazon rainforest are approx. 100 ppbv higher than the global background. Moreover, a global distribution based on airborne data from several campaigns (PHILEAS 2023, CAFE Brazil 2022/23, SouthTrac 2019, CAFE Africa 2018, WISE 2017, ATom 2016/17, OMO 2015, ESMVal 2012) shows that the methane surface concentrations over the Amazon rainforest has a local maximum. This calls for more detailed investigations of methane near the surface in the Amazon and raises an important question: Have we underestimated the Amazon rainforest as a significant source of the global methane budget?

How to cite: Ort, L., Röder, L. L., Hoor, P., Lelieveld, J., and Fischer, H.: Enhanced methane concentrations measured over the Amazon rainforest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2140, https://doi.org/10.5194/egusphere-egu24-2140, 2024.

Land and freshwater ecosystems play a significant role in affecting the global methane budget. With future warming, the increase of methane emissions could create large positive feedbacks to the global climate system.  We have used observation data of methane fluxes from diverse land and freshwater ecosystems to calibrate and evaluate extant land and freshwater biogeochemistry models of the Terrestrial Ecosystem Model (TEM) and the Arctic Lake Biogeochemistry Model (ALBM) to quantify the global methane emissions for the past few decades and the 21^st century in a temporally and spatially explicit manner. Land ecosystems could emit methane from wetlands while uplands could uptake atmospheric methane. TEM simulates that global wetlands emissions are 212 ± 62 and 212 ± 32 Tg CH₄ yr⁻¹ due to uncertain parameters and wetland type distribution, respectively, during 2000–2012. After combining the global upland methane consumption of −34 to −46 Tg CH₄ yr⁻¹, we estimate that the global net land methane emissions are 149–176 Tg CH₄ yr⁻¹ due to uncertain wetland distribution and meteorological input. During 1950–2016, both wetland emissions and upland consumption increased during El Niño events and decreased during La Niña events. For freshwater ecosystems, we find that current emissions are 24.0 ± 8.4 Tg CH₄ yr⁻¹ from lakes larger than 0.1 km². Future projections under the RCP8.5 scenario suggest a 58–86% growth in emissions from lakes.  Warming enhanced methane oxidation in lake water can be an effective sink to reduce the net release from global lakes. Additionally, these studies identify the key biogeochemical and physical processes of controlling methane production, consumption, and transport in various hotspot emission regions.  We also highlight the need for more in situ methane flux data, more accurate wetland and lake type and their area distribution dynamics information to better constrain the quantification uncertainty of global biogenic methane emissions across the landscape.

How to cite: Zhuang, Q.: Quantifying global biogenic methane emissions from land and freshwater ecosystems across the landscape , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2178, https://doi.org/10.5194/egusphere-egu24-2178, 2024.

In light of the challenges posed by climate change, global governments, including the United Kingdom (UK), have committed to addressing and mitigating the impacts of climate change, emphasizing the pursuit of Net Zero objectives. The terrestrial ecosystems on a global scale, functioning as pivotal carbon reservoirs, assume a critical role in climate change mitigation, especially within the context of an imminent scenario marked by accelerated warming and drying conditions. Recognizing that the carbon sequestration capacity of ecosystems is intricately linked to their energy and water cycling dynamics, this study presents the Uniform FLUXes (UFLUX)-ensemble dataset (https://sites.google.com/view/uflux) that accurately quantifies carbon, water, and energy fluxes across ecosystems in a consistent and mutually comparable manner. The UFLUX ensemble, relying on the upscaling of in-situ eddy covariance (EC) tower measurements using satellite vegetation proxies and meteorology reanalysis, constitutes the methodological foundation of this research.

The UFLUX originated from our prior investigations into filling gaps in EC fluxes. This is due to the analogous nature of the procedures involved in flux gap-filling and upscaling, wherein both entail the interpolation/extrapolation of fluxes, albeit in the temporal and spatial domains, respectively. The fluxes in UFLUX are upscaled through the application of a uniform set of algorithms and environmental determinants, aiming to mitigate the sources of uncertainty. The UFLUX methodology has demonstrated effectiveness in capturing the global CO₂ fertilization effect. Furthermore, it has exhibited resilience to agricultural management interventions and has adeptly captured flux variability at a high spatial resolution of 20 meters in southwest England. These accomplishments lay the groundwork for generating the UFLUX-ensemble dataset.

The resulting UFLUX-ensemble dataset incorporates 60 members considering specific advantages of multiple satellite and meteorology reanalysis products. Aligned with the Net Zero vision articulated by nations, and recognizing the imperative of addressing data storage requirements, the dataset is made available on three scales: 1) daily 100-m resolution for the UK, 2) half-yearly 100-m resolution for Europe, and 3) monthly 0.25°×0.25°resolution for the entire globe. This diverse data provision is designed to assist climate actions, particularly in countries grappling with specific socio-economic challenges. A rigorous technical validation underscores the merits of the UFLUX ensemble, demonstrating its ability to capture 0.8 % of the flux variability with errors amounting to 0.76 g C m^-2 d^-1 and 11.67 W m^-2. The UFLUX-ensemble dataset serves as a valuable resource, offering insights to inform land management practices, including nature-based solutions, with the overarching objective of augmenting carbon sequestration in terrestrial ecosystems and contributing to the realization of a carbon-neutral future.

How to cite: Zhu, S. and Xu, J.: The UFLUX ensemble of multiple-scale carbon, water, and energy fluxes., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2479, https://doi.org/10.5194/egusphere-egu24-2479, 2024.

We have used the NASA Goddard Institute for Space Studies (GISS) Earth system model GISS-E2.1 to study the future budgets and trends of global and regional CH4 under different emission scenarios. GISS-E2.1 is one of the few ESMs that can be driven by anthropogenic CH4 emissions, as well as interactive natural sources such as wetlands, and can simulate the tropospheric CH4 chemistry. In frame of the recent short-lived climate forcers (SLCFs) assessment by the Arctic Monitoring and Assessment Programme (AMAP), we used the GISS-E2.1 model with prescribed long-lived greenhouse gas (GHG) concentrations. In the present study, we have supplemented these simulations using the interactive CH4 sources and sinks in order to quantify the model performance and the sensitivity to CH4 sources and sinks. We have used the Current Legislation (CLE) and the Maximum Feasible Reduction (MFR) emission scenarios from the Eclipse V6b emission database to simulate the future chemical composition and climate impacts from 2015 to 2050. We have also simulated 1995-2014 in order to evaluate the model performance following the AMAP-SLCF protocol.

The prescribed GHG version underestimates the Global Atmospheric Watch (GAW) surface CH4 observations during the period between 1995 and 2023 by 1% [-8.4%-2.0%], with a correlation (r) of 0.71 [-0.41 0.99]. The largest underestimations are over the continental emission regions such as North America, Europe, and Asia, while biases are smallest over oceans. On the other hand, the simulation with interactive sources and sinks underestimates the GAW observations more than the prescribed simulation, by 18.5% [-25% -10.4%], with a lower r of 0.36 [-0.82 0.93]. Opposite to the prescribed simulation, the biases are largest over oceans and smaller over the continents, however they are still larger over land than the prescribed simulation. The interactive simulation, with large sources virtually over land and strong sink over oceans, has a land/ocean ratio larger than 1 while the prescribed simulation has this ratio equal to 1 as it distributes the global prescribed CH4 concentration equally in longitude over a given latitude. This clearly shows that the interactive sources and sinks should be represented in models in order to realistically simulate the chemical composition and the oxidative capacity of the atmosphere.

As expected, the MFR scenario simulates lower global surface CH4 concentrations and burdens compared to the CLE scenario, however in both cases, global surface CH4 and burden continue to increase through 2050 compared to present day.  In the CLE scenario, increases are largest over the equatorial belt, in particular over India and East China, while the MFR scenario shows increases over the whole Southern Hemisphere, however much smaller compared to CLE. Finally, the interactive simulation shows that the chemical CH4 sink increases in the CLE scenario, while it slightly decreases in the MFR, leading to a larger CH4 lifetime in the MFR scenario compared to in the CLE scenario.

How to cite: Im, U., Tsigaridis, K., Bauer, S., Eckhardt, S., Shindell, D., Sørensen, L. L., and Wilson, S.: Future CH4 budgets as modelled by a fully coupled Earth system model using prescribed GHG concentrations vs. interactive CH4 sources and sinks, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2492, https://doi.org/10.5194/egusphere-egu24-2492, 2024.

Radiocarbon can be used as an independent and objective tracer to evaluate fossil fuel CO₂ (CO_2ff) emissions, because of its complete depletion in fossil fuel sources. Here, we present a study on the CO_2ff emissions reduction during the COVID-19 lockdowns in 2020 based on atmospheric Δ¹⁴CO₂ observation at Chinese background sites. We observed obvious enhancements (several per mill to dozens of per mill) of atmospheric Δ¹⁴CO₂ during the COVID-19 lockdowns compared with that in the same period. A preliminary analysis showed that these enhancements indicate several percepts to dozens of percents CO_2ff emissions reduction from Eurasia (exclude China) and different parts in China during the COVID-19 lockdowns.

How to cite: Niu, Z.: Decrease in fossil fuel CO2 emissions during COVID-19 lockdowns based on  Δ14CO2 observation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3721, https://doi.org/10.5194/egusphere-egu24-3721, 2024.

Climate change poses a significant environmental challenge for humanity, and accurately predicting its intensity as well as its impact on terrestrial ecosystems is crucial. To achieve this, monitoring, modelling, and mapping greenhouse gas (GHG) exchanges between the biosphere and the atmosphere is essential. Monitoring is also important to achieve the European Union’s goal to achieve a balance between GHG emissions and removals by 2050 and maintain negative emissions thereafter. While in situ measurement techniques, such as the eddy covariance flux tower (ECFT), have been used for decades to measure ecosystem-level exchanges of carbon, such as Net Ecosystem Exchange (NEE) of CO₂, their footprint is limited to only 1 km². To overcome this limitation, satellite remote sensing data has been used to upscale these measurements to regional and global scales, but previous work has relied on low-resolution remote sensing data, such as the Moderate Resolution Imaging Spectroradiometer (MODIS) sensor (at 250m or 500m spatial resolution).

This study aims to use a combination of high-resolution remote sensing data and measurements from in situ ECFT data to model the NEE of CO₂ across ~92% of Ireland's terrestrial area, covering major land covers such as wetlands (coastal and peatlands), grassland, and forestry. The model will integrate datasets from both ESA (Copernicus Sentinel-1 and 2) and NASA (MODIS PAR) with the light response curve parameters derived from the ECFT data in Ireland, to model NEE CO₂ at a national scale. The results will be useful for monitoring, reporting, and verifying NEE across a range of ecosystems in Ireland. They can also be used to enhance National Inventory Reporting and national ambitions on climate, influence targeted policymaking, and verify land management decisions.

How to cite: Habib, W. and Connolly, J.: Satellite-driven model to upscale Irish CO2 Net Ecosystem Exchange (ICONEEx), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4150, https://doi.org/10.5194/egusphere-egu24-4150, 2024.

Since the preindustrial era, the ocean has removed roughly 40% of fossil CO₂ from the atmosphere, and it will eventually absorb at least 80% of human CO₂ emissions. While there is no doubt that the ocean is a critical player in the global carbon cycle, many uncertainties remain and the drivers and magnitude of interannual-to-decadal timescale variability remain poorly constrained. A key question is the extent to which external forcing, specifically the variability of the atmospheric pCO₂ growth rate, or internal ocean variability is the dominant mechanism of variability. We use a suite of experiments from the ECCO-Darwin data-assimilative ocean biogeochemistry model to isolate and explore the impact of these two drivers. We demonstrate that at the global scale, external and internal variability equally drive ocean sink variability. However, as the spatial scale becomes more regional, internal variability becomes increasingly dominant. To diagnose the future evolution of the global-scale ocean carbon sink in response to a changing atmospheric growth rate, both skillful observation-based products and data-assimilative models will be required.   

How to cite: McKinley, G., Fay, A., Carroll, D., and Menemenlis, D.: Drivers of ocean carbon sink variability across spatial scales, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4196, https://doi.org/10.5194/egusphere-egu24-4196, 2024.

 A key goal of the Paris Agreement (PA) is to reach net-zero greenhouse gas (GHG) emissions by 2050 globally, which requires mitigation efforts from all countries. Africa’s rapidly growing population and gross domestic product (GDP) make this continent important for GHG emission trends. In this project we study the emissions of carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) in Africa over 3 decades. We compare bottom-up (BU) approaches, including United Nations Convention Framework on Climate Change (UNFCCC) national inventories, FAO, PRIMAP-hist, process-based ecosystem models for CO₂ fluxes in the land use, land use change and forestry (LULUCF) sector and global atmospheric inversions. For inversions, we applied different methods to separate anthropogenic CH₄ emissions. The BU inventories show that, over the decade 2010–2018, fewer than 10 countries represented more than 75 % of African fossil CO₂ emissions. With a mean of 1373 Mt CO₂ yr⁻¹, total African fossil CO₂ emissions over 2010–2018 represent only 4 % of global fossil emissions. However, these emissions grew by +34% from 1990–1999 to 2000–2009 and by +31% from 2000–2009 to 2010–2018, which represents more than a doubling in 30 years. This growth rate is more than 2 times faster than the global growth rate of fossil CO₂ emissions. The anthropogenic emissions of CH₄ grew by 5 % from 1990–1999 to 2000–2009 and by 14.8 % from 2000–2009 to 2010–2018. The N₂O emissions grew by 19.5 % from 1990–1999 to 2000–2009 and by 20.8 % from 2000–2009 to 2010–2018. When using the mean of the estimates from UNFCCC reports (including the land use sector) with corrections from outliers, Africa was a mean source of greenhouse gases of 2622 (min: 2186, max: 3239) Mt CO₂ eq. yr⁻¹ from all BU estimates (the min–max  indicate range uncertainties) and of +2637 (min: 1761, max: 5873) Mt CO₂ eq. yr−1 from top-down (TD) methods during their overlap period from 2001 to 2017. Although the mean values are consistent, the range of TD estimates is larger than the one of the BU estimates, indicating that sparse atmospheric observations and transport model errors do not allow us to use inversions to reduce the uncertainty in BU estimates. The main source of uncertainty comes from CO₂ fluxes in the LULUCF sector, for which the spread across inversions is larger than 50 %, especially in central Africa. Moreover, estimates from national UNFCCC communications differ widely depending on whether the large sinks in a few countries are corrected to more plausible values using more recent national sources following the methodology of Grassi et al. (2022). The medians of CH₄ emissions from inversions based on satellite retrievals and surface station networks are consistent with each other within 2 % at the continental scale. The inversion ensemble also provides consistent estimates of anthropogenic CH₄ emissions with BU inventories such as PRIMAP-hist. For N₂O, inversions systematically show higher emissions than inventories, either because natural N₂O sources cannot be separated accurately from anthropogenic ones in inversions or because BU estimates ignore indirect emissions and underestimate emission factors. 

How to cite: Mostefaoui, M., Ciais, P., McGrath, M. J., Peylin, P., Patra, P. K., and Ernst, Y.: Greenhouse gas emissions and their trends over the last three decades across Africa, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4472, https://doi.org/10.5194/egusphere-egu24-4472, 2024.

Peatlands are the world’s largest storage of soil organic carbon. While natural peatlands act as sinks of atmospheric carbon, drainage and disturbance (e.g., due to land use and climate change) turn peatlands into net carbon sources. Greenhouse gas (GHG) emissions from drained peatlands are therefore part of national GHG-emission reports, guided by the IPCC wetlands supplement. Herein, default emission factors (EF) are defined both for drained and rewetted peatlands, the former split into tropical and boreal/temperate wetlands, the latter further sub-categorized into nutrient poor and rich peatlands. These default emission factors are to date largely based on a limited number of static chamber-based studies, many measured over relatively short periods of time (1-3 years). As carbon flux measurements on peatlands have gained more attention, recent publications have added several new datasets to the EF calculations, significantly reducing the EF and narrowing confidence intervals. However, the final values are still almost entirely derived from chamber-based measurements with inherent limitations and uncertainties.

The Eddy-Covariance (EC) method is an alternative, established method to quantify carbon fluxes from ecosystems, spatially and temporally integrated (typically every 30 min throughout the year, representing a “flux-footprint” covering a whole ecosystem). As EC-based measurements are increasingly applied and such data are now available from several disturbed peatlands over several years, it is plausible to revise the default EFs. In this study we compile global EC time series for CO₂ fluxes from disturbed peatlands of different land use categories with a focus on drained and rewetted peatlands affected by no or by  minor extensive management practices.  We investigate the diurnal, seasonal and annual variability of the fluxes. The net carbon emissions are compared to the EFs currently in use. With available ancillary data such as climate, water table depths, nutrients, ecosystem type and (succession-) state of the ecosystem we asses controlling factors for carbon fluxes. This investigation yields important context to evaluate the uncertainty and reliability of default emission factors for disturbed peatlands. Additionally, we apply a process-based model (CoupModel) to an own study-site to generate a higher-tier emission factor, including seasonality and climate variations.

How to cite: Behrens, N., Knorr, K.-H., and Gharun, M.: Peatland IPCC emission factors in the light of new EC carbon flux time series, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5271, https://doi.org/10.5194/egusphere-egu24-5271, 2024.

As one of the world’s economic engine and the largest greenhouse gases (GHGs) emitter of fossil fuel in the past two decades, China has expressed the recent ambition to reduce GHG emissions by mid-century. The status of GHG balance over terrestrial ecosystems in China, however, remains elusive. Here, we present a synthesis of the three most important long-lived greenhouse gases (CO₂, CH₄ and N₂O) budgets over China during the 2000s and 2010s, following a dual constraint bottom-up and top-down approach. We estimate that China’s terrestrial ecosystems act as a small GHG sink (-29.0 ± 207.5 Tg CO₂-eq yr^-1 with the bottom-up estimate and -75.3 ± 496.8 Tg CO₂-eq yr^-1 with the top-down estimate). This net GHG sink includes an appreciable land CO₂ sink, which is being largely offset by CH₄ and N₂O emissions, predominantly coming from the agricultural sector. Emerging data sources and modelling capacities have helped achieve agreement between the top-down and bottom-up approaches to within 25% for all three GHGs, but sizeable uncertainties remain. 

How to cite: Gao, Y., Wang, X., Wang, K., Sang, Y., Wang, Y., Zhang, Y., Hong, S., Zhang, Y., Yuan, W., and Piao, S.: The greenhouse gas budget of terrestrial ecosystems in China since 2000, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5576, https://doi.org/10.5194/egusphere-egu24-5576, 2024.

Both the tropical Pacific and Atlantic upwelling systems are modulated by their respective Ninos (ENSO and Atlantic Nino), which significantly affect the regional and global climate variability. Coincidentally, two of largest ocean carbon outgassing systems are also located in these domains. As a result, the interannual variability of ocean CO₂ fluxes in these regions have predominant imprint on the globally integrated variations (Landschutzer et al., 2016). In contrast to the effect of anomalously cold surface temperature, the upwelling of deep-water rich in dissolved inorganic carbon is understood to be the main driver for the mean CO₂ outgassing. In the tropical Pacific, El Nino (La Nina) leads to a suppressed (stronger) upwelling condition and an anomalously weaker (stronger) carbon outgassing. On the other hand, the Atlantic Nino and Nina exert considerable variability in the surface freshwater and temperature, which leads to spatially heterogeneous responses in the contemporary CO₂ fluxes. In both systems, we discover a critical role of subsurface alkalinity in regulating the observed variability, primarily through altering the surface buffering capacity (Koseki et al., 2023). We show that bias in CMIP6 Earth system models in simulating the mean contemporary alkalinity state in the tropical Pacific leads to contrasting future impacts (Vaittinada Ayar et al., 2022) and could have ramifications on the climate carbon cycle feedback. 

References

Koseki, S., J. Tjiputra, F. Fransner, L. R. Crespo, and N. S. Keenlyside (2023), Disentangling the impact of Atlantic Nino on sea-air CO₂ fluxes, Nature Communications, 14, 3649, https://doi.org/10.1038/s41467-023-38718-9.

Landschützer, P., N. Gruber, and D. C. E. Bakker (2016), Decadal variations and trends of the global ocean carbon sink, Global Bio- geochem. Cycles, 30, 1396–1417, http://doi.org/10.1002/2015GB005359.

Vaittinada Ayar, P., L. Bopp, J. R. Christian, T. Ilyina, J. P. Krasting, R. Séférian, H. Tsujino, M. Watanabe, A. Yool, and J. Tjiputra (2022), Contrasting projections of the ENSO-driven CO₂ flux variability in the equatorial Pacific under high-warming scenario, Earth Syst. Dynam., 13, 1097–1118, https://doi.org/10.5194/esd-13-1097-2022.

How to cite: Tjiputra, J., Koseki, S., and Vaittinada Ayar, P.: Non-intuitive differences in Ninos-driven CO2 flux variability and long-term changes in the tropical Pacific and Atlantic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6021, https://doi.org/10.5194/egusphere-egu24-6021, 2024.

The global atmospheric CO₂ growth rate is a product of the combined effects of emissions and uptake from both anthropogenic and natural carbon sources. Therefore, an evaluation of the global CO₂ growth rate should be preceded to understand the global carbon-climate process. In this study, we analyzed the long-term changes in the global CO₂ growth rate from 1991 to 2020, using data from 42 global sites and model simulations to assess recent changes in the global carbon-climate feedback process. Our results indicate that the annual CO₂ growth rate has increased by 0.032 ppm yr^-2 since the 2000s. A comprehensive assessment of carbon cycle components contributing to atmospheric CO₂ growth rate changes reveals that the strengthening of this rate is linked to a decline in terrestrial carbon absorption over the last decade. This decline is primarily associated with a slowdown in the increasing trend of Net Primary Productivity. Consequently, the reduced terrestrial carbon uptake in recent decades contributed to an approximately 3 ppm increase in global CO₂ concentration by 2020. Our findings highlight that the vegetation's carbon uptake capacity can no longer offset anthropogenic CO₂ emissions, underscoring the importance of achieving global carbon neutrality in climate change mitigation.

This work was supported by Korea Environment Industry & Technology Institute(KEITI) through Project for developing an observation-based GHG emissions geospatial information map, funded by Korea Ministry of Environment(MOE) (RS-2023-00232066)

How to cite: Park, C. and Jeong, S.: Recent increasing trend of global CO2 growth rate due to a slowdown in terrestrial carbon uptake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7267, https://doi.org/10.5194/egusphere-egu24-7267, 2024.

Globally permafrost soils store huge quantities of carbon (C) in dead organic matter (DOM). Currently, the permafrost region is estimated to be a small net C sink. However, as the climate warms permafrost soils have begun to thaw, making a massive quantity of DOM available for potential decomposition and likely shifting the region to a net source of C. Process-models of terrestrial ecosystems are a vital tool in evaluating our understanding of ecosystem function, but also in generating forecasts of C emissions under varied climate change scenarios in support of decision support. But different models contain competing hypothesise of ecosystem functioning, leading to divergent forecasts despite convergent estimates of contemporary net C emissions. These process-models also result in contrasting estimates of the internal C-cycling. We currently lack a consistent, rigorous observational constraint on ecosystem C-stocks and dynamics (particularly below ground) due to varied challenges across both in-situ and satellite-based Earth Observation (EO). Here, we present a Bayesian model-data fusion approach (CARDAMOM) which combines diverse observations of terrestrial ecosystems (e.g. leaf area, soil C, biomass, net C exchange) to calibrate an intermediate complexity model (DALEC). CARDAMOM generates a probabilistic estimates of DALEC parameters at pixel scale based on local information. Using these local calibrations, DALEC offers a probabilistic, data-constrained estimate of current ecosystem C-cycling including its internal dynamics, which can be used to evaluate large scale process-models. We evaluate process-model estimates of key ecosystem properties, e.g. DOM residence time, and their climate sensitivity. Through this process we can identify and exclude process-models which are inconsistent with data from forecast analyses.

How to cite: Smallman, L. and Burke, E.: Quantifying permafrost C-cycling by fusing process-models and observations , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7366, https://doi.org/10.5194/egusphere-egu24-7366, 2024.

Atmospheric methane levels (the second largest contributor to climate change) have more than doubled over the last 200 years, though with highly variable trends over time. The relative contribution of different sources and sinks to the global CH₄ budget remains uncertain despite ongoing efforts to improve the estimates based on various approaches, and particularly the causes for an accelerated increase in recent years remain unclear. Therefore, understanding and quantifying methane sources at global to regional scales is essential to reduce uncertainties in the global methane budget and its feedback with the climate system.

Within the Arctic region, wetlands and lakes constitute a major natural source of methane. With temperatures rising at rates at least twice the global average over the last decades, Arctic permafrost is increasingly thawing. Associated disturbance processes hold the potential to increase methane emissions, and as a consequence result in a positive feedback to climate change. However, until now neither observations nor model estimates could provide clear evidence of such a trend in emissions. As a consequence, current and possible future contributions of Arctic ecosystems to the accelerated increase in the global atmospheric methane levels remain highly uncertain.

To help reduce methane emission uncertainties in the high northern latitudes, we estimated global CH₄ fluxes to the atmosphere using the Jena CarboScope Global Inversion System, with a strong focus of our analysis on the Arctic region. We used wetland flux from JSBACH model as prior and assimilated atmospheric observations from regional networks available over the last years for the region above 60°N latitude (a total of 23 towers) to quantify the methane emissions over this region between 2010 to 2020. We found a clear seasonal pattern with emission peaks during July and August. As a sensitivity test to evaluate the improvement to constrain the Arctic methane fluxes with the assimilation of the regional data, we also conducted an inversion using just the global background surface stations (a total of 30 global stations). We found higher mean annual methane flux to the atmosphere when assimilating the regional data, with the largest difference between May to August. These estimates were finally evaluated against an ensemble of inverse model estimates from Global Methane Project available for the period between 2010 to 2017.

How to cite: Basso, L., Rödenbeck, C., Brovkin, V., Georgievski, G., and Göckede, M.: Estimating methane emissions at high northern latitudes using regional data and global inverse modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8175, https://doi.org/10.5194/egusphere-egu24-8175, 2024.

Indonesia is currently known as one of the three largest contributors of carbon emissions from land and land cover change (LULCC) globally, together with Brazil & the Democratic Republic of Congo. However, there is a limited reliable data on LULCC across Indonesia, leading to a lack of agreement on drivers and trends in carbon emissions. This can also be seen in the annual global carbon budget (GCB). Here, we assess the new satellite-based land cover dataset from Mapbiomas over Indonesia to illustrate how changes in forest and agriculture (mainly palm oil) areas across Indonesia determine trends in carbon emissions from land use change (ELUC). ELUC is simulated with a process-based Dynamic Global Vegetation Model, JULES-ES using annually varying LULCC maps from Mapbiomas as input. Our results show that the forest loss and agriculture expansion have a strong correlation and trend in the last two decades. Furthermore, palm oil plantation is the major contribution to the forest-agriculture dynamics, mainly appearing in Kalimantan & Sumatera island. This dynamic has a major impact on Indonesia ELUC with a positive trend in ELUC of 0.06 PgC/yr² since 2000 . The use of the satellite-based dataset, Mapbiomas, is shown to improve our understanding of the LULCC dynamics over Indonesia, hopefully contributing to a reduction of the ELUC uncertainty for Indonesia and the SE Asia region.

How to cite: Brasika, I. B. M., Friedlingstein, P., Sitch, S., and O'Sullivan, M.: Drivers and trends in Land-use change and associated carbon emissions over Indonesia, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8349, https://doi.org/10.5194/egusphere-egu24-8349, 2024.

In recent years, methane (CH4) has attracted increasing scientific attention as the second most abundant anthropogenic greenhouse gas (GHG) in the atmosphere. Due to the high reduction potential and the relatively short atmospheric lifetime of around 9 years, mitigation measures can become effective within a relatively short period of time. However, the current estimates of CH4 fluxes from emission inventories are still subject to uncertainties at both global and regional scale.

An effort to reduce uncertainties from those bottom-up flux estimates is given by inverse modelling, which provides a robust tool to verify GHG emissions by combining GHG observations as well as atmospheric transport modelling and statistical optimization.

In this study, we use an inverse modelling approach to estimate CH4 fluxes at European scale for the year 2022. Additionally, we use the European in-situ observation network to explore the feasibility of reducing uncertainties in CH4 fluxes in Austria, a European country with a limited availability of stationary observations. This work is part of the Austrian ASAP18 flagship project “GHG-KIT: Keep it traceable”.

Hereby, the inverse modelling tool FLEXINVERT is used, which is based on the backward simulations of the Lagrangian particle dispersion model FLEXPART (FLEXible PARTicle). In particular, we investigate to what extent prolonged backward trajectories of 50 to 100 days contribute to better constrain the CH4 fluxes. In an attempt to estimate background concentrations as accurately as possible, we use global CH4 concentration fields obtained with the chemical transport model FLEXPART (CTM).

How to cite: Wittig, S., Raju, A., Nabavi, S. O., Vojta, M., Redl, P., Hoheisel, A., Hirtl, M., Groot Zwaaftink, C., and Stohl, A.: Estimation of methane emissions at European scale with a special focus on Austria, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8601, https://doi.org/10.5194/egusphere-egu24-8601, 2024.

Methane and carbon dioxide mole fractions are measured continuously at the atmospheric station at Plateau Rosa since 2018, with a Picarro cavity ring down spectrometer G2301. The station, at 3480 meter MSL, represents an ideal location for, on one hand, measurements of background air and, on the other hand, intercepting air with recent boundary layer contact. Since 2021 the site contributes as an atmospheric station to the ICOS network.

In this study we present the methodology used to filter background data, and we provide an analysis of the continuous record of CH₄ since 2018. We used Hysplit back trajectories and the FLEXPART atmospheric transport model coupled with EDGAR inventories to identify source areas in Europe. We focused our analysis on April 2022, when the CH₄ increment above the baseline was consistently high.

We demonstrate how the CH₄ mole fraction data measured at the station at Plateau Rosa provide information on the global CH₄ trend, and that, with our continuous record, we can detect high emissions events over Europe.

How to cite: Zazzeri, G., Apadula, F., Lanza, A., and Henne, S.: The methane record at the ICOS background station at Plateau Rosa: identification of source areas in Europe, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9459, https://doi.org/10.5194/egusphere-egu24-9459, 2024.

Understanding terrestrial carbon fluxes is a prerequisite for accurately predicting the global biospheric uptake and release of CO₂ under climate change and other environmental stressors. Terrestrial carbon fluxes in the southern hemisphere still exhibit quite large uncertainties due to limited measurements and a lack of comprehensive process understanding. This study focuses on the South American Temperate (SAT) region, employing various Dynamic Global Vegetation Model (DGVM) models (TRENDY v9) to investigate carbon flux dynamics. We find significant discrepancies between these DGVM models in terms of both phasing and magnitude. To address this, atmospheric XCO₂ measurements from the Greenhouse Gases Observing Satellite (GOSAT) during the period 2009-2018 are incorporated into an atmospheric inversion using the model TM5-4DVar to obtain net CO₂ fluxes. We identify DGVM models that match the inversion results, particularly showing the same phasing and similar magnitude of net ecosystem exchange (NEE) as the inversion results. The matching DGVMs show that the increase in NEE during the mid of the year is driven by an early increase in heterotrophic respiration whereas the autotrophic respiration remains in phase with the gross primary production (GPP) and is delayed with respect to heterotrophic respiration. The observed flux behavior is linked to the onset of rainfall in the semi-arid regions of SAT, resembling findings in Australia by Metz et al. (2023). We hypothesize that soil rewetting processes in semi-arid areas play an important role in constraining the global carbon budget and should be represented more accurately in global carbon cycle models to improve the estimation of the global carbon budget.  

Metz, E.-M., Vardag, S.N., Basu, S., Jung, M., Ahrens, B., El-Madany, T., Sitch, S., Arora, V.  K., Briggs, P. R., Friedlingstein, P., Goll, D.S., Jain, A.K.,  Kato, E., Lombardozzi, D., Nabel,J .E. M. S., Poulter, B., Séférian, R., Tian, H., Wiltshire, A., Yuan, W., Yue, X., Zaehle, S.,  Deutscher, N.M.,  Griffith, D.W.T., Butz, A. Soil respiration–driven CO2 pulses dominate Australia’s flux variability. Science, 379, 1332-1335, https://doi.org/10.1126/science.add7833, 2023. 

How to cite: Vardag, S. N., Artelt, L., Metz, E.-M., Basu, S., Jung, M., and Butz, A.: Terrestrial Carbon Flux Dynamics in the Southern American Temperate Region: Insights from Dynamic Global Vegetation Models and GOSAT XCO2 Measurements  , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9609, https://doi.org/10.5194/egusphere-egu24-9609, 2024.

The Arctic-boreal zone and its permafrost regions have historically been sparsely measured for carbon dioxide and methane fluxes. This data sparsity has created significant uncertainties in Arctic-boreal carbon budget estimates. However, over the past decade, the availability of Arctic-boreal carbon flux data has increased substantially. Yet, it remains scattered across different repositories, papers, and unpublished sources, making it hard to estimate more accurate Arctic-boreal carbon budgets. To address this research gap, we have compiled a database of Arctic-boreal carbon fluxes (ABCFlux v2) from flux repositories, literature, and site principal investigators, which will be openly distributed. The database includes carbon dioxide fluxes of gross primary production, ecosystem respiration, and net ecosystem exchange, and plant-mediated, diffusive, ebullitive, and storage methane fluxes measured with eddy covariance and chamber techniques with supporting methodological and environmental metadata from terrestrial (including wetland) and freshwater ecosystems. It has in total over 12,000 site-months and 30,000 unique monthly flux values, therefore almost doubling earlier synthesis efforts in the region. Here, we present preliminary results on carbon flux magnitudes across key land cover types and multidecadal trends based on the in-situ data and machine-learning based upscaling. These indicate, for example, that the Arctic-boreal region has been an increasing annual terrestrial net ecosystem CO₂ sink with the boreal biome primarily driving this trend. This collaborative initiative, involving contributions from over 100 researchers, serves as an important step in reducing uncertainties in Arctic-boreal carbon budgets and enhancing our understanding of climate feedbacks.

How to cite: Virkkala, A., Wargowsky, I., Vogt, J., Kuhn, M., Natali, S., Rogers, B., Goeckede, M., Arndt, K., Watts, J., Windholz, T., and Madaan, S.: A new synthesis of Arctic-boreal carbon fluxes for improved carbon budget estimates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10840, https://doi.org/10.5194/egusphere-egu24-10840, 2024.

New constraints on carbon exchanges between atmospheric, terrestrial and aquatic systems are needed to reduce uncertainty in future predictions of the global carbon cycle and climate change. Radiocarbon is a powerful tool for studying the carbon cycle due to its to its ~5700-year half-life that sheds light on processes occuring on centennial to millenial timescales, as well as the ¹⁴C “bomb spike” resulting from above-ground nuclear weapons testing in the mid-20^th Century that serves as a tracer of carbon flow among more rapidly cycling pools. The “Radiocarbon Inventories of Switzerland” (“RICH”) project is a collaborative initiative that involves undertaking a first-of-its-kind, national-scale ¹⁴C survey spanning all major carbon pools and encompassing the five different Swiss ecoregions. The project is acquiring a comprehensive “snapshot” of ¹⁴C measurements for carbon species in the atmosphere, soils and the hydrophere (e.g. ¹⁴C in atmospheric and soil-derived gas samples, ¹⁴C in bulk samples and different sub-fractions of soil, water and sediment samples), and developing historical context through ¹⁴C analysis of natural archives and of archived samples spanning the pre-bomb era to the present. The measurements are being used to study various carbon cycle processes, including turnover rates of different soil carbon fractions, budgets of riverine carbon, and anthropogenic emissions of CO₂ and CH₄. New, integrated atmospheric-terrestrial-aquatic carbon cycle models are being developed and calibrated, and existing models are being evaluated. This presentation will outline the goals and scope of the RICH project, and provide illustrations of the information that is now flowing from this collaborative undertaking. The project structure is envisioned to serve as template that can be  adapted in carbon cycle studies on regional to global scales, and the scientific outcomes will be relevant not only to Switzerland but also to the broader understanding of carbon cycle processes.

How to cite: Eglinton, T., Graven, H., Hagedorn, F., Szidat, S., Brunmayr, A., Duborgel, M., Geissbuehler, D., Laemmel, T., Minich, L., Mittelbach, B., Rhyner, T., and White, M.: Constraining atmosphere-terrestrial-aquatic carbon cycle processes at national and ecoregional scales with radiocarbon data: Introducing the Radiocarbon Inventories of Switzerland (RICH) project, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11622, https://doi.org/10.5194/egusphere-egu24-11622, 2024.

Atmospheric carbon dioxide (CO₂) is a significant greenhouse gas, and its concentration has increased by 51% compared to the pre-industrial value. Concerning its impact on the earth’s climate system, there is an urge to reduce CO₂ emissions, hence mitigating global warming and climate change. This requires adequate knowledge of its source-sink distribution and quantification of the CO₂ budget. Inverse modeling has emerged as an effective tool to constrain greenhouse gas (GHG) fluxes using the spatiotemporal pattern of atmospheric concentration measurements. In this regard, this study focuses on estimating CO₂ fluxes over Europe using the Bayesian inverse modelling framework FLEXINVERT during the year 2021. In-situ CO₂ concentrations were taken from various locations across Europe (World Data Centre for Greenhouse Gases, WDCGG) and data were averaged every 3 hours. The Lagrangian Particle Dispersion Model FLEXPART (FLEXible PARTicle) is employed to calculate the source-receptor relationship (SRR). The FLEXPART model has been run backward in time to trace back the particles (released from the locations of observation sites) for 10 days. Background CO₂ concentrations are calculated using the sensitivity of concentration at the termination points from FLEXPART and the global 3D concentration from the FLEXible PARTicle-chemical transport model (FLEXPART-CTM). The uncertainty reduction, calculated from posterior and prior flux uncertainties, indicates how well the prior fluxes are optimized. In addition, longer backward simulations can be carried out to assess the impact of transport on background CO₂ concentrations and the uncertainty reduction.

How to cite: Raju, A., Wittig, S., Vojta, M., Nabavi, O., Redl, P., Hoheisel, A., Hirtl, M., Zwaaftink, C. G., and Stohl, A.: Constraining CO2 fluxes over Europe using FLEXINVERT and in-situ measurements, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12156, https://doi.org/10.5194/egusphere-egu24-12156, 2024.

Methane (CH4) is the second most important greenhouse gas, contributing to approximately 30% of the additional greenhouse effect since 1750. Its varied sources and relatively short lifetime in the atmosphere (~9 years) offer interesting mitigation opportunities. To develop practical strategies for mitigating climate change, precise quantification of methane fluxes and a better understanding of its spatial distribution and biogeochemical cycling are imperative. The observations currently used to infer methane sources and sinks face limitations affecting calculation accuracy. Surface stations measuring CH4 are sparse and notably absent in major emitting regions. In contrast, satellite-derived data, while providing broader coverage, present systematic errors and estimate atmospheric composition with an accuracy range of 1-10%. Additionally, passive satellite shortwave infrared (SWIR) measurements exhibit higher sensitivity near surface emission sources but are less effective in high latitude regions. Conversely, passive satellite thermal infrared (TIR) measurements have a higher sensitivity between the free troposphere and the stratosphere.Current worksare currently being developed to integrate TIR and SWIR to obtain consolidated CH4 information on the vertical atmospheric profile. This studyaims on improving methane flux estimates using the top-down approach, which integrates observations, flux priors, and an atmospheric chemical transport model utilizing Bayesian methodology. This will be perfomed on the inversion system developed at the LSCE (Community Inversion Framework – CIF) using the global transport model LMDz. We analyze the information provided by different observing systems (TIR, SWIR and surface network) at the global scale and for a period between June 2018 and June 2020. In a first step, the sensitivity of the fluxes to the observations is estimated. In a second step, Observing System Simulation Experiments are performed to evaluate the performance of the different observations system to retrieve the target fluxes. Considering both steps, observing systems are chosen to provide the best information in terms of sensitivity and spatial representation (vertical and horizontal).

How to cite: Montenegro, N., Saunois, M., Berchet, A., Martinez, A., Bousquet, P., and Pison, I.: Estimating methane sources and sinks by assimilating satellite data in a global atmospheric inverse system., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12441, https://doi.org/10.5194/egusphere-egu24-12441, 2024.

Disparities in estimates of the ocean carbon sink, whether derived from global ocean biogeochemical models or from data products based on observations of surface ocean pCO₂, question our ability to accurately assess ocean carbon uptake and its trend over recent decades. A potential factor contributing to the inconsistency between data products and model-based estimates is the pre-industrial air-sea carbon flux that is required to isolate the anthropogenic component from the total air-sea carbon flux estimated from observations. This pre-industrial air-sea carbon flux is thought to stem at the global scale from an imbalance between riverine carbon discharge to the ocean and sediment carbon burial.  Using a mass-balanced approach and comprehensive estimates of carbon inputs to the ocean by rivers and groundwater as well as carbon burial in marine sediments, Regnier et al. (2022) estimated that the pre-industrial ocean was outgassing 0.65 ± 0.30 petagrams of carbon per year. This updated estimation was used in the latest Global Carbon Budget (Friedlingstein et al., 2023) to derive an estimate of the ocean carbon sink over recent decades. In this study, we use a series of ocean biogeochemical pre-industrial simulations with varying assumptions related to carbon riverine input and burial to develop a theoretical framework to determine the ocean carbon outgassing and its spatial distribution. Building upon previous efforts, we integrate a carbon mass-balance approach with consideration of the ocean alkalinity budget. While conventionally assumed that the global alkalinity inventory was in equilibrium during the pre-industrial era — with riverine alkalinity discharge offset by CaCO₃ burial — we demonstrate that an imbalance in the pre-industrial ocean alkalinity budget could significantly affect the carbon outgassing flux. This novel conceptual framework allows us to reestimate the pre-industrial carbon flux while considering the ocean alkalinity budget. Furthermore, it provides a simple method to reevaluate this flux in light of new assessments of carbon or alkalinity sources and sinks, while also covering their uncertainty ranges.

How to cite: Planchat, A., Bopp, L., and Kwiatkowski, L.: Reassessing the pre-industrial air-sea carbon flux considering the ocean alkalinity budget, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12480, https://doi.org/10.5194/egusphere-egu24-12480, 2024.

From 2020, the atmospheric methane burden has grown at the fastest rate in the detailed observational record. This rise has been accompanied by an unprecedented plunge in d¹³C(CH₄). The causes of recent accelerated growth are as yet uncertain but the geographic spread of growth and the rapid isotopic plunge suggest strong rises in isotopically light emissions from both Tropical and Boreal wetlands. These emissions may be due to rising precipitation and temperatures in parts of the tropics, and by rising temperatures in northern Canada, Siberia, and Europe. Over the longer period since 2007, methane’s actual growth is comparable to methane’s growth in the ‘worst case’ very high baseline emission scenario RCP8.5 (8.5 W/m² forcing increase relative to pre-industrial). If the recent trend were to continue for more than another decade it could make the 2°C target as hard to achieve as the 1.5°C target is now. Natural feedbacks to climate warming in wetlands need to be included in future modelling and should be incorporated in climate modelling projects such as CMIP7. Methane’s recent accelerated growth also has wide implications for climate negotiations as it reduces the permissible total anthropogenic greenhouse gas emissions if the Paris Agreement is to be achieved. Strong growth in non-anthropogenic methane emissions, driven by feedback impacts on natural and quasi-natural sources, was not expected in modelling at the time of the Paris Agreement and shows the urgency of improving our understanding of the feedback impacts of climate change. The simplest way to limit methane’s growth is for all nations,  including non-signatory countries, to cut anthropogenic emissions urgently and sharply, meeting or exceeding the targets of the Global Methane Pledge.

How to cite: Manning, M. R., Nisbet, E. G., Michel, S. E., Lan, X., Dlugokencky, E., Lowry, D., Fisher, R. E., and France, J. L.: Methane’s record rise 2020-2023: likely causes, impacts and consequences, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12481, https://doi.org/10.5194/egusphere-egu24-12481, 2024.

Despite major advances in the estimation of all fluxes in the global cycles of carbon and oxygen, mathematical imbalances continue to arise when these fluxes are combined. Between 1997 and 2022, the global budget imbalances (BIM) for CO₂ and O₂ budgets – a quantification of the missing sources and/or sinks of CO₂ and O₂ – are -18 Tmol/yr and 41 Tmol/yr, respectively. The CO₂ BIM has tended to become increasingly negative over the last decade, while the O₂ BIM has tended to become increasingly positive. To identify the origins of the BIMs, we carried out a systematic analysis of the combination and permutation of all available individual flux estimates provided by a sub-set of contributors to the Global Carbon Budget 2023 update. We first examine the possibility that inaccuracies in the ocean air-sea fluxes contributes to the CO₂ and O₂ BIM. We show that the interannual variability of the air-sea O₂ flux required for a reduction of the O₂ BIM tends to be close to that simulated by several ocean models. An in-depth analysis of the Southern Ocean has confirmed their ability to simulate reasonable interannual variability in the air-sea fluxes of O₂ and CO₂. We conclude that in order to simultaneously reduce the negative trend in CO₂ BIM and the positive trend in O₂ BIM in the recent decade, a reduction in the increasing trend in the terrestrial CO₂ sink over the last decade is most likely required.

How to cite: Mayot, N., Le Quéré, C., and Manning, A.: Identifying the origins of the global carbon budget imbalance using oxygen, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12756, https://doi.org/10.5194/egusphere-egu24-12756, 2024.

Accurate estimation of critical greenhouse gas fluxes, particularly carbon dioxide (CO₂) and methane (CH₄), is vital for shaping effective climate change policies. Leveraging the state-of-the-art Community Inversion Framework (CIF), we estimate high-resolution emissions across Europe (-12°E to 37°E, 35°N to 73°N). Using the Lagrangian Particle Dispersion Model (FLEXPART) with ECMWF meteorological data, we calculate surface flux footprints at 0.2° × 0.2° resolution, enhancing comparisons with national inventories. Assimilating data from 40+ in-situ observations, including ICOS and non-ICOS stations, our 4-dimensional variational optimization refines prior high-resolution flux estimates. Diverse sources contribute to the total flux, including fossil fuel emissions, biomass burning, land emissions, air-sea exchange. Flux corrections enhance accuracy, yielding posterior estimates with reduced bias and heightened correlation. Major CH₄ emitters (France, Germany, Italy, Spain, Poland, and the UK) collectively contribute 72% of total emissions. The EU27 + UK average is 16.47 ± 1.33 Tg CH₄/yr. Posterior anthropogenic emissions reveal a regional mean reduction of > 5 gC/m²/month in summer compared to prior estimates, highlighting seasonal emission dynamics.

How to cite: Mengistu, A. G., Tsuruta, A., Tenkanen, M., Markkanen, T., Raivonen, M., Leppänen, A., Berchet, A., Thompson, R., Lindqvist, H., and Aalto, T.: High-Resolution Inversion Modeling of Carbon Dioxide and Methane Emissions in Europe: Assessing Accuracy and  Dynamics, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13094, https://doi.org/10.5194/egusphere-egu24-13094, 2024.

Record breaking atmospheric methane growth rates were observed in 2020 and 2021 (15.2±0.4 and 17.6±0.5 ppb yr^-1), reaching their highest level since the commencement of ground-based observations in the early 1980s. Here we use an ensemble of atmospheric inversions informed by surface or satellite methane concentration observations to infer emission changes during these two years relative to 2019. We found a global increase of methane emissions of 20.3±9.9 Tg CH₄ in 2020 and 24.8±3.1 Tg CH₄ in 2021. The emission rise was dominated by tropical and boreal regions with inundated areas, as a result of elevated groundwater table. Strong, synchronous, and persistent emission increases occurred in regions such as the Niger River basin, the Congo basin, the Sudd swamp, the Ganges floodplains and Southeast Asian deltas and the Hudson Bay lowlands. These regions alone contributed about 70% and 60% of the net global increases in 2020 and 2021, respectively. Comparing our top-down estimates with simulation of wetland emissions by biogeochemical models, we find that the bottom-up models significantly underestimate the intra- and inter-annual variability of methane sources from tropical inundated areas. This discrepancy likely arises from the models’ limitations in accurately representing the dynamics of tropical wetland extents and the response of methane emissions to environmental changes. Our findings demonstrate the critical role of tropical inundated areas in the recent surge of methane emissions and highlight the value of integrating multiple data streams and modeling tools to better constrain tropical wetland emissions.

How to cite: Lin, X., Peng, S., Ciais, P., Hauglustaine, D., Lan, X., Liu, G., Ramonet, M., Xi, Y., Yin, Y., and Zhang, Z. and the Coauthors: Recent methane surges reveal heightened emissions from tropical inundated areas, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13246, https://doi.org/10.5194/egusphere-egu24-13246, 2024.

While the Southern Ocean (SO) provides the largest oceanic sink of carbon, some observational studies have suggested that the SO total CO₂ (tCO₂) uptake exhibited large (~0.3 GtC/yr) decadal-scale variability over the last 30 years, with a similar SO tCO₂ uptake in 2016 as in the early 1990s. Here, using an eddy-rich ocean, sea-ice, carbon cycle model, with a nominal resolution of 0.1°, we explore the changes in total, natural and anthropogenic SO CO₂ fluxes over the period 1980-2021 and the processes leading to the CO₂ flux variability.

The simulated tCO₂ flux exhibits decadal-scale variability with an amplitude of ~0.1 GtC/yr globally in phase with observations. Notably, two stagnation in tCO₂ uptake are simulated between 1982 and 2000 as well as since 2012, while a re-invigoration is simulated between 2000 and 2012. This decadal-scale variability is primarily due to changes in natural CO₂  (nCO₂) fluxes south of the polar front associated with variability in the Southern Annular Mode (SAM). Positive phases of the SAM lead to enhanced SO nCO₂ outgassing due to higher surface natural dissolved inorganic carbon (DIC) brought about by a combination of Ekman-driven vertical advection and DIC diffusion at the base of the mixed layer. The pattern of the CO₂ flux anomalies indicate a dominant control of the interaction between the mean flow south of the polar front and the main topographic features. While positive phases of the SAM also lead to enhanced anthropogenic CO₂ (aCO₂) uptake south of the polar front, the amplitude of the changes in aCO₂ fluxes is only 25% of the changes in nCO₂ fluxes. Due to the larger nCO₂ outgassing compared to aCO₂ uptake as the SH westerlies strengthen and shift poleward, the SO tCO₂ uptake capability thus reduced since 1980 in response to the shift towards positive phases of the SAM.

How to cite: Menviel, L., Spence, P., Kiss, A., Chamberlain, M., Hayashida, H., England, M., and Waugh, D.: Reduced Southern Ocean CO2 uptake due to the positive SAM trend, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13846, https://doi.org/10.5194/egusphere-egu24-13846, 2024.

We examined the sub-seasonal to interannual variability and multi-year trend of sea surface CO₂ partial pressure (pCO₂) and air-sea CO₂ flux at a coastal site of the East China Sea (31⁰N, 122.8⁰E) based on high-frequency time-series data collected by a buoy since 2013. Seasonal average sea surface pCO₂ was highest in autumn, but the lowest value can appear in winter or spring, depending on the biological productivity in spring. The seasonal amplitude of pCO₂ was up to 123 μatm. Based on property-property relationships and a simple mass budget model, we found that temperature change, biological activity, water mixing and air-sea CO₂ exchange all made significant contributions to the seasonal variation of pCO₂. From winter to summer, seasonal warming and atmospheric CO₂ uptake elevated the pCO₂, while net biological production, weakened vertical mixing and the retreat of the Yellow Sea Coastal Water (YSCW) lowered the pCO₂. Conversely, from summer to winter, seasonal cooling and CO₂ emission lowered the pCO₂, while respiration, enhanced vertical mixing and the YSCW intrusion raised them up. Over short-term timescale, biological production and respiration frequently drew down or elevated the pCO₂ by 150-400 μatm within 5-10 days during warm months. When biological activity was suppressed during cold months, such short-term variations were dominated by water mixing with a smaller pCO₂ amplitude of 5-60 μatm within 2-6 days. This site was a sink of atmospheric CO₂ in winter and spring, but a CO₂ source in summer and autumn. Annually, it was a moderate CO₂ source in 2014 (air-sea CO₂ flux was 2.88 ± 11.02 mmol m⁻² d⁻¹), a weak CO₂ sink in 2016 (-0.21 ± 12.23 mmol m⁻² d⁻¹), and a weak CO₂ source in the combined year of the first half of 2017 and the second half of 2018 (0.40 ± 9.11 mmol m⁻² d⁻¹). The relatively high CO₂ source in 2014 was likely due to the weaker biological production in spring and more typhoon passage in autumn. From 2013 to 2019, the wintertime sea surface pCO₂ didn’t follow the increasing trend of the atmospheric pCO₂, leading to an enhancing carbon sink in winter.

How to cite: Luo, Y., Zhang, Z., Chen, J., Xu, Y., Cao, F., Huang, T., Guo, X., and Dai, M.: Sea surface pCO2 variability on different time scales in the East China Sea based on high-frequency time-series observations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14038, https://doi.org/10.5194/egusphere-egu24-14038, 2024.

Peatland ecosystem degradation and changes made in hydrology by artificial drainage may affect the biogeochemistry of peatlands and, together with projected global warming, may lead to significant changes in greenhouse gas (GHG) fluxes. Drainage of peatlands increases organic matter's aerobic decomposition, changes native vegetation, and may decrease the storage of C. The vegetative characteristics of forest ecosystem types may change a net GHG sink peatland to a source in drained organic soils.

However, soil CH₄ and N₂O fluxes in peatlands are spatially and temporally (interannual, seasonal) variable, and detailed data from drained nutrient-rich organic soils in the hemiboreal zone is lacking. We conducted a study spanned over two years comprising drained (n=18) and undrained (n=7) peatland forests with dominant tree species of Scots pine (Pinus sylvestris), Norway spruce (Picea abies), birch (Betula sp.), and black alder (Alnus glutinosa) spread across Estonia, Latvia, and Lithuania. Instantaneous fluxes of CH₄ and N₂O were measured monthly for the whole year using the manual static chamber method. Environmental parameters in soil, such as soil water level (WTL), moisture, and temperatures at depths (0-40 cm), were monitored continuously, and detailed soil chemical analyses were conducted. To constrain the factors regulating temporal fluxes of various environmental conditions and differentiate annual emissions between land use in the Baltic region.

The results show that all drained forest soils were annual CH₄ sinks (−37.0 ± 4.5 μg C m^−‍2 h^−‍1), while undrained forests were emitters on average 388.5 ± 142. Mean annual CH₄ uptake is significantly higher in deep-drained soils −45.5 ± 3.6 μg C m^−‍2 h^−‍1 (WTL > −50cm) than in poorly drained soils (p<0.05), regardless of dominant tree species. The in situ and annual CH₄ fluxes statistically correlated with soil water level and temperature. Most of the drained sites emitted N₂O (49.4 ± 17.8 μg N m^−‍2 h^−‍1); drained wet forest sites were higher emitters (84.7 ± 32.4) than drier sites (23.67 ± 15.6) in comparison to tree species. The instantaneous N₂O fluxes were directly controlled by soil surface temperature and oxygen concentration of soil water, whereas variability in annual N₂O emissions was associated with soil water content. Moreover, soil nutrient status regulated by specific ground vegetation functional groups has significantly impacted the emissions of nutrient-rich organic soils.

This research was supported by the LIFE programme project "Demonstration of climate change mitigation potential of nutrients-rich organic soils in the Baltic States and Finland" (2019-2023, LIFE OrgBalt, LIFE18 274CCM/LV/001158).

How to cite: Sardar Ali, M. K., Schindler, T., Vahter, H., Kull, A., Mander, Ü., Lazdiņš, A., Līcīte, I., Bārdule, A., Butlers, A., Čiuldienė, D., Vigricas, E., Jauhiainen, J., Laiho, R., and Soosaar, K.: Soil CH4 and N2O fluxes from drained and undrained peatland forests in the Baltic region., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14545, https://doi.org/10.5194/egusphere-egu24-14545, 2024.

Fires in the Amazon are of great concern because they threaten the integrity of the tropical forest biome, the carbon cycle, and air quality. Fire emissions depend on the burning behaviour of vegetation biomass, woody debris, and litter. However, the effects of fuels on the combustion process and on the composition of fire emissions are simplified in current fire emission inventories and models. Several new fire emission approaches have recently been developed to better quantify fire emissions by either making use the improved spatial resolution of modern satellite observations or by developing new modelling approaches. 

Here we compare several current and novel approaches to quantify fuel consumption and fire emissions for the Amazon and Cerrado for the fire season in 2020. The approaches include the widely used GFAS, a top-down approach based on Sentinel-5p observations (KNMI.S5p), a bottom-up approach based on active fire observations from VIIRS (GFA.S4F), two bottom-up approaches based on MODIS burned area data (500-m version of GFED, REFIT.AC), a data-model fusion approach with dynamic emission factors that integrates several Earth observation products (TUD.S4F), and three dynamic global vegetation models in diagnostic mode with prescribed burned area. The different approaches to estimate fire emission show that forest and deforestation fires dominate the regional total fire emissions. However, large differences exist in the very high emissions of individual fires that mainly contribute to the regional total fire emissions. We found a higher agreement in estimated CO and NOx emissions between approaches for savannah fires (normalised RMSE < 20%) than for forest and deforestation fires (nRMSE 30%). We estimate that only 10% of all fire events contribute between 85% and 97% of the regional total fire emissions. By using the TUD.S4F data-model fusion approach with dynamic emission factors, we show that most fire CO emissions originate from the burning of woody debris, which burns with low combustion efficiency and hence has higher emission factors for CO. Comparisons with regional field-based investigations show, however, large differences in estimates of surface fuel loads and fuel consumption. Our results demonstrate the advantage of exploring several complementary fire emission approaches to better understand the underlying processes and to account for regional to global fire emissions and their uncertainties.

How to cite: Forkel, M., Wessollek, C., Andela, N., de Laat, J., Huijnen, V., Kinalczyk, D., Marrs, C., van Wees, D., Bastos, A., Ciais, P., Fawcett, D., Kaiser, J. W., Kutchartt, E., Klauberg, C., Leite, R. V., Li, W., Silva, C., Sitch, S., Goncalves De Souza, J., and Plummer, S.: Multiple approaches for quantifying fuels, combustion dynamics, and regional fire emissions in the Amazon and Cerrado, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14672, https://doi.org/10.5194/egusphere-egu24-14672, 2024.

The development of high-quality controlled databases of sea surface partial pressure of CO₂ (pCO₂) combined with robust machine learning-based mapping methods that fill pCO₂ gaps in time and space, enable us to quantify the oceanic air-sea CO₂ exchange and its spatiotemporal variability only based on in-situ observations (pCO₂-products). However, most existing pCO₂-products do not explicitly include the coastal ocean or have a spatial resolution that is too coarse (e.g., 1°) to capture the highly heterogeneous spatiotemporal dynamics of pCO₂ in these regions thus limiting our ability to resolve long-term trends and the interannual variability of the coastal air-sea CO₂ exchange (FCO₂).

To address this limitation, we updated the global coastal pCO₂-product of Laruelle et al. (2017) using a 2-step machine learning interpolation technique (relying on Self Organizing Maps and a Feed Forward neural Network) combined with the most extensive monthly time series for coastal waters from the Surface Ocean CO₂ Atlas (SOCAT), spanning from 1982 to 2020 to reconstruct monthly high spatial resolution (0.25°) continuous coastal pCO₂ maps. This updated coastal pCO₂-product is then used to reconstruct the temporal evolution of the global coastal FCO₂ based on observations.

Our results show that since 1982, the extended coastal ocean, covering an area of 77 million km² in this study, has been acting as an atmospheric CO₂ sink, removing -0.4 Pg C yr^-1 (-0.2 Pg C yr^-1 with a narrower coastal domain roughly equivalent to continental shelves) from the atmosphere. Moreover, the intensity of this CO₂ sink has been increasing over time at a rate of 0.1 Pg C yr^-1 per decade (0.03 Pg C yr^-1 decade^-1 in the narrower domain). The long-term change in the air-sea CO₂ flux is largely driven by the air-sea pCO₂ gradient, dominated by the sea surface pCO₂, however wind speed and sea-ice coverage play significant roles, regionally. This new coastal pCO₂-product provides a valuable constraint for understanding the strengthening of the global coastal ocean CO₂ sink, fill the coastal gap in synthesis studies such as the Global Carbon Budget and serves as a benchmark for evaluating emerging results of ocean biogeochemical models.

How to cite: Roobaert, A., Regnier, P., Landschützer, P., and Laruelle, G. G.: Global coastal ocean CO2 trends over the 1982–2020 period, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14775, https://doi.org/10.5194/egusphere-egu24-14775, 2024.

As the remaining carbon budget to limit global warming in line with the Paris Agreement is rapidly shrinking, accurate estimates of the emissions from land-use and land cover change (ELUC) and the terrestrial natural CO2 sinks (SLAND) are crucial. In current carbon budgeting approaches, the ELUC and SLAND estimates are conceptually not consistent, since they stem from two different model families that differ in how CO₂ fluxes are attributed to environmental or land-use changes. Consequently, anthropogenic and natural budget terms are not fully distinguished. ELUC is estimated by bookkeeping models, which typically use time-invariant carbon densities representing contemporary environmental conditions. They thus assume a steady environmental state and neglect changes in environmental conditions preceding or succeeding a land-use change event, e.g., denser growing forests in response to rising atmospheric CO2 concentrations, which emit more when cleared for agricultural land. SLAND is estimated by dynamic global vegetation models, which account for environmental changes but assume that the land cover distribution remained at its pre-industrial state. They thus include carbon sinks in forests that in reality were cleared decades ago. Here we suggest an approach for consistent budgeting of ELUC and SLAND by integrating the response of vegetation and soil carbon to environmental changes, derived from dynamic global vegetation models, into a spatially explicit bookkeeping model (BLUE). A set of dedicated simulations allows us to disentangle and re-attribute environmental and land-use components of the land-atmosphere CO2 exchange. Our results show that land is a cumulative net source of CO₂ since 1850, which contrasts current global carbon budgets indicating a net sink. The underlying reason is both a higher estimate of ELUC than previously suggested as well as a smaller land sink: The implementation of environmental changes increases global ELUC over time (14% compared to current estimates for 2012-2021) mainly due to increased emissions from deforestation and wood harvest, which are only partly offset by increased sinks through reforestation/afforestation and other regrowing vegetation. Our SLAND estimate calculated under actual land cover amounts to 3.0 GtC yr^-1 for 2012-2021, which is substantially lower both globally and regionally compared to estimates assuming pre-industrial land cover: we find a SLAND is smaller by 0.7 GtC yr^-1 in 2012-2021, i.e., 19% lower as compared to the conventional approach using pre-industrial land cover. The overestimate of SLAND under pre-industrial land cover is particularly pronounced in regions with strong ecosystem degradation, such as Southeast Asia, Brazil, and Equatorial Africa. The consistent estimation of terrestrial carbon fluxes is thus essential not only to provide a tangible estimate to monitor the progress of net-zero emission commitments and the remaining carbon budget, but also to highlight the need to protect remaining natural ecosystems for climate regulation. Our approach provides greater consistency with atmospheric inversions and provides a finer split of anthropogenic and natural fluxes useful for a direct comparison of global carbon cycle models to national greenhouse gas inventories.

How to cite: Pongratz, J., Dorgeist, L., Schwingshackl, C., and Bultan, S.: A consistent budgeting of terrestrial carbon fluxes , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15244, https://doi.org/10.5194/egusphere-egu24-15244, 2024.

The Southern Ocean has long been known to be an important region for ocean CO₂ uptake, and one which is especially sensitive to changes in the overlying climate. Here we assess the Southern Ocean CO₂ uptake (1985–2018) using data sets gathered in the REgional Carbon Cycle Assessment and Processes Project Phase 2 (RECCAP2). These include global ocean biogeochemical models (GOBMs), surface ocean pCO₂-products, data-assimilated models, and interior ocean biogeochemical observations. Over this period the Southern Ocean acted as a sink for CO₂, with magnitudes which are roughly half of those reported by RECCAP1 for the same region and timeframe. Close agreement is found between GOBMs and pCO₂-products, partly due to some compensation of seasonal and regional differences. Seasonal analyses revealed agreement in driving processes in winter (with uncertainty in the magnitude of outgassing), whereas discrepancies are more fundamental in summer, when GOBMs exhibit difficulties in simulating the balance of non-thermal processes of biology and mixing/circulation. The data sets emphasize strong latitudinal variations in the mean and seasonality of the CO₂ flux and asymmetries in the mean and amplitude of the CO₂ flux between Atlantic, Pacific and Indian sectors. The present-day net uptake is to first order a response to rising atmospheric CO₂. This drives large amounts of anthropogenic CO₂ (C_ant) into the ocean, thereby overcompensating the loss of natural CO₂ to the atmosphere driven by the changing climate. The GOBMs show, however, a 20% spread and an overall underestimate of C_ant storage in the ocean interior. An apparent knowledge gap is the increase of the sink since 2000, with pCO₂-products suggesting a growth that is more than twice as strong and uncertain as that of GOBMs. This is despite nearly identical pCO₂ trends in GOBMs and pCO₂-products when both products are compared only at the locations where pCO₂ was measured.

How to cite: Patara, L., Hauck, J., Gregor, L., Nissen, C., Hague, M., Mongwe, P., Bushinsky, S., Doney, S. C., Gruber, N., Le Quéré, C., Manizza, M., Mazloff, M., and Monteiro, P. M. S.: Mean, Seasonal Cycle, Trends, and Storage of the Southern Ocean carbon cycle in the RECCAP2 assessment (1985-2018), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16495, https://doi.org/10.5194/egusphere-egu24-16495, 2024.

Drained peatlands need to be rewetted to reduce carbon dioxide (CO₂) emissions caused by microbial peat oxidation and to limit soil subsidence. Raising groundwater levels will subsequently increase the chance of methane (CH₄) emissions, a much more potent greenhouse gas (GHG) gas than CO₂. While intact peatlands are long-term carbon sinks and have a net cooling effect, despite the CH₄ emissions, how disturbed peatlands will respond to rewetting is less certain. There are several rewetting strategies outside of returning the land to unproductive uses, such as paludiculture (agriculture on inundated soils) and installing water infiltration systems (WIS) in pastures.

In the Netherlands, more than 85% of the peatlands are used for agriculture and have been extensively drained. Rewetting these peatlands is necessary to reduce CO₂ emissions, however the effect this will have on CH₄ emissions needs to be understood such that optimal rewetting strategies can be chosen to minimise GHG emissions. In this presentation, we report our efforts into monitoring CH₄ emissions across Dutch peatlands with a network of eddy covariance (EC) systems since 2020 for the Netherlands Research Programme on Greenhouse Gas Dynamics in Peatlands and Organic Soils (NOBV) project. Fluxes of CO₂ and CH₄ have been observed across 20 field sites that cover the current Dutch peatland extent using a combination of permanent and mobile (alternating between two paired sites) EC towers that measured the land uses of paludiculture, semi-natural, pastures with WIS, pastures with high and low groundwater levels, and a lake. We focus on the main drivers of CH₄ emissions in Dutch peatlands, evaluate the impact of land use on annual CH₄ emissions, and emission upscaling.

How to cite: Buzacott, A., Kruijt, B., Bataille, L., Berghuis, H., Biermann, J., van Giersbergen, Q., Fritz, C., Nouta, R., van den Berg, M., van der Velde, Y., and van Huissteden, J.: Methane emissions from Dutch peatlands measured by a national eddy covariance network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16630, https://doi.org/10.5194/egusphere-egu24-16630, 2024.

CO₂ fluxes from land use and land-use change (F_LUC) are a major source of carbon to the atmosphere. They are composed of gross emissions, mainly from deforestation, peat burning, and peat drainage, and gross removals, mainly from re- and afforestation. The importance of F_LUC for climate change mitigation strategies is increasing due to the potential of storing large carbon amounts via re- and afforestation, harvested wood products, and other vegetation-based carbon dioxide removal methods, such as bioenergy with carbon capture and storage. Yet, F_LUC estimates remain largely uncertain and show substantial discrepancies between different quantification methods, which makes it challenging to provide reliable projections of their potential future evolution.

Here, we review the main characteristics, uncertainties, and discrepancies of individual methods used to estimate F_LUC, and we highlight promising steps to reduce F_LUC uncertainties and to harmonize the various F_LUC estimates. Differences between the approaches are mainly due to differing definitions and assumptions, such as the definition of anthropogenic fluxes and managed land (leading to a gap in F_LUC of ~1.8 GtC/yr in 2000-2020 between F_LUC estimates by bookkeeping models used in the Global Carbon Project and inventory-based estimates reported by countries to the United Nations Framework Convention on Climate Change) and the inclusion of environmental effects on carbon stocks (leading to a gap of ~0.4 GtC/yr in 2000-2020 between F_LUC estimates from dynamic global vegetation models and bookkeeping models). Furthermore, the individual estimation methods have large uncertainties, mainly arising from the usage of differing land-use forcing data, missing observational constraints, differences in how models implement individual processes, and the degree of implementation of land use practices in models.

To improve the confidence in the individual F_LUC estimates, we argue for a systematic model evaluation and an improved parametrization of models, in particular regarding land-use forcing data, carbon densities of vegetation and soils, and the represented processes. Alongside, remaining framework inconsistencies, such as a precise and consistent definition of F_LUC and the consideration of transient C densities need to be resolved. This undertaking requires developments in several directions. Earth observations may provide data on carbon densities in vegetation and soil at high spatial resolution, improved estimates of forest regrowth rates as well as impacts of forest management. Models need to be further improved to consider all relevant land-use processes and provide more fine-granular output to guarantee that the different estimates are comparable and/or translatable into each other.

Providing harmonized and more accurate F_LUC estimates is essential to improve the stocktake of countries' land use-related CO₂ emissions, to provide an accurate budget of the global carbon cycle, and to effectively plan and monitor land-based carbon dioxide removal methods.

How to cite: Obermeier, W., Schwingshackl, C., Ganzenmüller, R., Bastos, A., Ciais, P., Grassi, G., Luijkx, I., Sitch, S., and Pongratz, J.: Reviewing differences and uncertainties in land-use CO2 flux estimates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18116, https://doi.org/10.5194/egusphere-egu24-18116, 2024.

Given the role of the ocean in mitigating climate change through CO₂ absorption, it is important to improve our abil ity to quantify the historical ocean CO₂ uptake, including its natural variability, for carbon budgeting purposes. In this study we present an exhaustive intercomparison between two ocean modelling practices that can be used to reconstruct the historical ocean CO₂ uptake. By comparing the simulations to a wide array of ocean physical and biogeochemical observational datasets, we show how constraining the ocean physics towards observed temperature and salinity results in a better representation of global biogeochemistry. We identify the main driver of this improvement to be a more realistic representation of large scale meridional overturning circulation together with improvements in mixed layer depth and sea surface temperature. Nevertheless, surface chlorophyll was rather insensitive to these changes, and, in some regions, its representation worsened. We identified the causes of this response to be a combination of a lack of robust parameter optimization and limited changes in environmental conditions for phytoplankton. We conclude that although the direct validation of CO₂ fluxes is challenging, the pervasive improvement observed in most aspects of biogeochemistry when applying data assimilation of observed temperature and salinity is encouraging; therefore, data assimilation should be included in multi-method international efforts aimed at reconstructing the ocean CO₂ uptake.

How to cite: Bernardello, R., Sicardi, V., Lapin, V., Ortega, P., Ruprich-Robert, Y., Tourigny, E., and Ferrer, E.: Ocean biogeochemical reconstructions to estimate historical ocean CO2 uptake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19922, https://doi.org/10.5194/egusphere-egu24-19922, 2024.

The ocean is a strong sink for anthropogenic CO₂, absorbing around a quarter of emissions since the industrial era. Quantifying the ocean carbon sink is necessary for constraining the global carbon budget; however, discrepancies remain between estimates of the ocean carbon sink over the last 30 years from observation-based data products and those from numerical models. Moreover, larger regional uncertainties highlight the need for a better understanding of the drivers of ocean carbon sink variability, to help improve models and to better constrain future climate projections. A comprehensive understanding of the sink must include knowledge of (1) the air-sea flux of CO₂, (2) the accumulation of carbon in the ocean interior, and (3) how it is redistributed within the ocean by changes in the physical circulation. This characterisation is typically achieved using numerical models, which are constrained by resolution and the need to parameterise processes including physical mixing at the sub-grid scale.

We present a novel method for characterising the ocean carbon sink from a combination of oceanographic datasets, and for reconciling our knowledge of the ocean’s uptake of CO₂ with that of interior carbon storage rates. Our Optimal Transformation Method (OTM) uses a water mass framework to diagnose the transport and mixing of tracers such as heat, salt, and carbon consistent with observed interior changes and estimates of boundary forcings. The water mass framework has the advantage that the transport and mixing of conservative tracers are diagnosed exactly, with no need for parameterisation. We validate OTM using outputs from a data-assimilating biogeochemical ocean model and demonstrate its ability to recover the model’s ‘true’ air-sea CO₂ fluxes when initialised with biased priors. OTM reduces root-mean-squared errors between diagnosed air-sea CO₂ fluxes and the model truth from prior to solution by up to 71%, while simultaneously estimating inter-basin transports of heat, freshwater, and carbon consistent with the model. Following successful validation, we apply OTM to a combination of observational data products to diagnose estimates of the ocean’s uptake and redistribution of carbon since 1990, utilising reanalyses of air-sea heat and freshwater fluxes, interior temperature and salinity, air-sea CO₂ fluxes, and machine-learning reconstructions of interior ocean carbon.

How to cite: Mackay, N., Zika, J., Sohail, T., Ehmen, T., and Watson, A.: A water mass transformation method applied to diagnosing ocean carbon uptake, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20295, https://doi.org/10.5194/egusphere-egu24-20295, 2024.

Quantifying greenhouse gas (GHG) emissions is a critical task for climate monitoring and mitigation actions.  Under the Paris Agreement, for example, accounting and reporting of GHG emissions are mandatory for Parties.  Reported emissions are often calculated using activity data approaches.  The robustness of the activity data collection is a key for obtaining accurate emission estimates; however, in a period of open conflict or war, the systems for data collection can be desperately damaged and destroyed and thus the ability of achieving robust GHG estimates and transparent reporting can be significantly hampered.  Also, military emissions, which are thought to be often poorly quantified, should increase significantly than peace times. 

We attempted to quantify GHG emissions during the first 18 months of the 2022/2023 full-scale war in Ukraine.  We first identified major, war-related, emission drivers and processes from the territory of Ukraine.  We analyzed publicly available data and used expert judgment to estimate emissions from (1) the use of bombs, missiles, barrel artillery, and mines; (2) the consumption of oil products for military operations; (3) fires at petroleum storage depots and refineries; (4) fires in buildings and infrastructure facilities; (5) fires on forest and agricultural lands; and (6) the decomposition of war-related garbage/waste.  Those sources are often not covered by current GHG inventory guidelines, and thus are not likely to be included in national inventory reports. 

Our estimate of the war-related emissions of carbon dioxide (CO2), methane, (CH4) and nitrous oxide (N2O) for the first 18 months of the war in Ukraine is 77 MtCO2-eq. with a relative uncertainty of ±22 % (95 % confidence interval).  It is important to note that these emissions are considered to be emissions from Ukraine in reporting because the emissions occurred within the territory of Ukraine.  The current emission accounting system (e.g. UNFCCC) is not designed to account war/conflict time emissions adequately.  The uncertainties due to the unaccounted emissions are also aliasing to our global and regional carbon budget calculations.

How to cite: Bun, R., Marland, G., Oda, T., See, L., Puliafito, E., Nahorski, Z., Jonas, M., Kovalyshyn, V., Ialongo, I., Yashchun, O., and Romanchuk, Z.: Quantifying unaccounted greenhouse gas emissions due to the war in Ukraine – driver analysis, emission estimation, and implications to emission reporting, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20413, https://doi.org/10.5194/egusphere-egu24-20413, 2024.

Miombo woodlands are the world’s largest savanna, covering 2-3 M km², and are the dominant land cover in the dry tropics of southern Africa. Here we quantify the dynamics of the miombo region carbon cycle, diagnosing stocks and fluxes and their interactions with climate and disturbance, and evaluate their representation in Trendy land surface models (LSMs). We produce a constrained multi-year analysis (2006-2017) using earth observation time series of total wood C (C_wood) and leaf area index to calibrate an intermediate complexity ecosystem model forced with observed climate, deforestation and burned area. Statistical analyses determine the relationships between carbon cycling, environmental and disturbance variables, and evaluate LSMs. The analysis suggests that the regional net biome production is neutral, 0.0 Mg C ha^-1 yr^-1 (95% Confidence Interval -1.7 - 1.6), with fire emissions contributing ~1.0 Mg C ha^-1 yr^-1 (95% CI 0.4-2.5). Spatial variation in biogenic fluxes and C pools is strongly correlated with mean annual precipitation. Burned area is also positively correlated with these pools and fluxes. Areas that are more frequently burned tend to have greater precipitation, and shorter residence time of C_wood. Fire-related mortality from C_wood to dead organic matter likely exceeds fire-related emissions from C_wood to atmosphere, and likely exceeds natural rates of C_wood mortality. LSMs match the biogenic fluxes of the analysis, but diverge on C stocks, timings of heterotrophic respiration and magnitude of fire emissions. The analysis suggests that climate, through precipitation, drives spatial variability in C_wood and GPP across the region. Fire disturbance is the major driver of losses from C_wood. Larger annual precipitation is correlated with both greater GPP and greater fire disturbance. These factors have opposing but unbalanced impacts on Cwood, but the precipitation-GPP effect dominates. Patterns of C cycling across the region are a complex outcome of climate controls on production, and vegetation-fire interactions.

How to cite: Williams, M., Milodowski, D., Luke, S., McNicol, I., Dexter, K., Ryan, C., O'Sullivan, M., Valade, A., Hegerl, G., and Sitch, S.: Fire-precipitation interactions control biomass carbon and net biome production across the world’s largest savanna, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20466, https://doi.org/10.5194/egusphere-egu24-20466, 2024.

It has been advocated that nitrogen (N) availability plays an essential role in mediating plant and microbial growth in cold environment, and could thus regulate the direction and magnitude of permafrost carbon (C)-climate feedback. However, compared to widely concerned N, little is known about soil phosphorous (P) availability and its biological acquisition strategies in permafrost environment. Here we explored soil microbial P acquisition strategies using shotgun metagenomics across the Tibetan permafrost area, encompassing a large scale survey spanning 1,000 km. In contrast to the traditional opinion that microorganisms in cold area usually obtain P mainly through mineralization process, our results revealed that the P cycling genes responsible for solubilization, mineralization and transportation were widespread, illustrating multiple microbial strategies for acquiring P in permafrost regions. Moreover, the higher gene abundance related to solubilization and mineralization as well as an increased ration of MAGs carrying these genes were detected in the active layer, while the greater abundance of low affinity transporter gene (pit) and proportions of MAGs harbouring pit gene were observed in permafrost deposits, reflecting a stronger potential for P activation in active layer but an enhanced P transportation potential in permafrost deposits. Taken together, these results highlight that besides microbial P mineralization, multiple P-related acquisition strategies and their differences among various soil layers should be considered simultaneously to improve model prediction for the responses of biogeochemical cycles in permafrost ecosystems to climate change.

How to cite: Wang, L. and Yang, Y.: Divergent microbial phosphorous acquisition strategies between active layer and permafrost deposits, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2973, https://doi.org/10.5194/egusphere-egu24-2973, 2024.

Seagrasses are marine-flowing plants that form an important coastal ecosystem. Although occupying less than 0.2% of the ocean’s surface, seagrasses store over 15% of the accumulated global carbon storage in the ocean’s sediments. Thus, Seagrass meadows play a pivotal role in mitigating climate change by carbon sequestration. Seagrasses are widely distributed in oligotrophic tropical waters despite the low nutrient levels in the water column due to their ability to absorb nutrients from the sediment porewater. Moreover, seagrasses can actively mobilize unavailable nutrients e.g., iron and phosphorus in the rhizosphere via multiple biogeochemical interactions. This provides them with an important advantage over pelagic photoautotrophs, which are limited by the availability of nutrients in the water column. Despite their ability to transport nutrients from sinks e.g., sediments to the water column where they can be recycled trough grazing or decomposition, the potential role of seagrass as a revers sedimentary phosphate pump remains unclear. The aim of this study is to examine the effect of seagrass disappearance on phosphate flux in marine coastal environments. In a series of incubation experiments, the change in the phosphate release was examined in different tissues of seagrass Halophila stipulacea. The results showed that the while the highest decomposition rate of the rhizomes was the fastest, the highest phosphate release rate was measured in the leaves, despite having similar phosphate content. Since the leaves mostly decompose in the water column, the released phosphate is made available to planktonic photoautotrophs and further enhances more carbon fixation. Overall, we suggest that in oligotrophic environments seagrasses act as a reverse phosphate pump by accessing phosphate in the sediment and later translocating it to the aboveground parts and releasing in the water column, thus fertilizing planktonic photoautotrophs and enhancing further carbon sequestration.

How to cite: Soto, N., Antler, G., and Gross, A.: Seagrasses' role as a reverse sedimentary phosphate pump, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3208, https://doi.org/10.5194/egusphere-egu24-3208, 2024.

Enhanced productivity of forest ecosystems in response to rising levels of anthropogenically generated atmospheric carbon dioxide (CO₂) has the potential to mitigate against climate change by sequestering carbon in woody biomass and soils. However, the physiological response of trees to elevated atmospheric CO₂ may be constrained by the availability of soil nutrients, predominantly nitrogen and phosphorus (P). Here, we assess the impact of elevated atmospheric CO₂ on P cycling in a temperate 180-year-old oak (Quercus robur L.) forest exposed to free-air CO₂ enrichment (ambient + 150 ppm) for six years. Soil cores were collected to a depth of 1 m in July 2023 and separated into three horizons and three layers (O, A, B, 30-50, 50-70, 70-100 cm) before analysis using the Hedley¹ sequential P fractionation and the DeLuca²biological based P extraction techniques. Plant available P in soil pore water and total organic P from the O horizon increased by 84 and 128%, respectively, whilst organic P extracted with phosphatase increased by 62% under elevated CO₂. Total organic P in soil horizons beyond the B horizon (> 15 cm) decreased under elevated CO₂ in comparison with ambient CO₂. As soil organic P is derived from the turnover of both vegetation and microbial biomass, increased soil organic P in the O horizon may be due to the faster turnover of organic matter or an increase in the net primary productivity of the forest. Soil P cycling in this forest ecosystem appears to be predominantly influenced by biological rather than chemical processes, since elevated CO₂ only affected the organic P and not inorganic P fractions. Forest productivity may be constrained by P limitation in future elevated CO₂ environments, if there is faster organic matter turnover which is probably the case in our study.

¹Hedley, M. J., Stewart, J. W. B., & Chauhan, B. (1982). Changes in inorganic and organic soil phosphorus fractions induced by cultivation practices and by laboratory incubations. Soil Science Society of America Journal, 46(5), 970-976.

²DeLuca, T. H., Glanville, H. C., Harris, M., Emmett, B. A., Pingree, M. R., de Sosa, L. L., Cerdá-Moreno, C. & Jones, D. L. (2015). A novel biologically-based approach to evaluating soil phosphorus availability across complex landscapes. Soil Biology and Biochemistry, 88, 110-119.

How to cite: Soltangheisi, A., Pinder, A., Blazey, K., Grzesik, R. T., Marshall, M., Kourmouli, A., Mayoral, C., Hart, K. M., Ullah, S., Hartley, I. P., MacKenzie, A. R., and Smith, A. R.: Elevated atmospheric CO2 increased soil plant available and soil organic phosphorus in a mature temperate oak (Quercus robur L.) forest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3472, https://doi.org/10.5194/egusphere-egu24-3472, 2024.

[Background] Phosphorus (P) availability in soils and sediments is a critical parameter influencing primary production in terrestrial and aquatic ecosystems, controlled by both P chemical fractions in solid phase and solution composition. A recent study using Arctic soils reported that the addition of Si to the soil released P bound to Fe(II) compounds, but reports on other soils and sediments are limited. In our previous study, we detected higher P concentrations in stream water and iron-bound P content in river sediments in the marine sedimentary rock catchments of the Akita coastal area compared to catchments in the adjacent igneous rock area. Furthermore, high-P stream waters were NaCl water type with relatively lower Ca²⁺ and higher SiO₂ concentrations. In this study, we evaluated the effects of different solution compositions and amorphous Si addition on P solubilization in sediments using river sediments from marine sedimentary and igneous rock regions. [Method] We tested each five river sediments (<2 mm) in the headwaters of western Akita Prefecture, Japan, where the surface geology is composed of marine sedimentary rocks and igneous rocks. Available Si (easily water-soluble Si) was measured by a long-term flooded incubation in distilled water at 30°C for 30 days. In the P dissolution incubation, four types of treatment solutions (distilled water, 1 mM NaCl and NaHCO₃ solutions, and 0.5 mM CaCl₂ solution) were added to 0.5 g sediment and in the Si addition treatment, amorphous Si (hydrophilic fumed silica, AEROSIL300) was also added. SRP, DOC and pH in the solution were measured after shaking for 48 hours. A statistical analysis was performed using a linear mixed model (LMM) with SRP, DOC and pH in the liquid phase as objective variables. The surface geology, four types of solutions, and the Si addition as explanatory variables. Additionally, each five sediment was treated as a random effect. [Results and discussion] Easily water-soluble Si content in sediments was significantly higher in marine sedimentary rock areas (p < 0.001), indicating that the easily soluble Si causes higher SiO₂ concentration in stream water. The incubation results showed Si addition significantly increased P concentration in the liquid phase (p < 0.001), and combined Si addition with NaHCO₃ treatment further increased P concentration. Conversely, CaCl₂ treatment significantly decreased the liquid-phase P concentration. The influence of surface geology on extracted P concentration was not significant. Si addition did not affect pH (p = 0.58) and DOC (p = 0.90), while the effects of solution composition on pH and DOC were also significant; NaHCO₃ solution increased pH and DOC while CaCl₂ solution decreased pH and DOC. In conclusion, in marine sedimentary rock areas in coastal Akita with NaCl water type where Ca²⁺ concentration is relatively low and sediments have higher easily soluble Si, P release from sediments easily occurs and a high P concentration keeps in the liquid phase.

How to cite: Hayakawa, A., Kuroe, Y., Kawata, A., Nishina, K., Ishikawa, Y., and Takahashi, T.: Silicone availability and NaCl water type enhances the phosphorus release from sediments in coastal forest catchments in Akita, Japan, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4491, https://doi.org/10.5194/egusphere-egu24-4491, 2024.

Baltic Sea is a geologically young semi-enclosed brakish-water body which water exchange with the ocean has been gradually declining. Approximately 85 million people live in the Baltic Sea's catchment area, resulting in significant human impact on the basin's ecosystem. Eutrophication due to anthropogenic discharge of nutrients is considered to be the most serious environmental problem which leads to a greater growth of phytoplankton and algae, deterioration of water quality, and lack of oxygen in near-bottom water masses. As a result of recent large-scale input of nutrients, phosphorus has accumulated in the seabed sediments from where it can be remobilized and released into the water column under favorable conditions (hypoxic or anoxic). Marine sediments contain phosphorus in various components i.e. fractions, but not all of them are affected by remobilization. Therefore, knowing how phosphorus fractions are distributed in seabed sediments is important.

One part of the Baltic Sea that has received little attention, but will significantly affect the entire Baltic Sea in the future, is the Gulf of Riga. The Gulf of Riga accounts for less than 5% of the total area of the Baltic Sea and less than 2% of the total water volume. Due to its shallowness and limited connection with the open Baltic Sea, the Gulf of Riga is strongly influenced by riverine input. Intense agriculture, rapid development of industry, and urbanization have resulted in high loads of nutrients into the Gulf of Riga already since the 1960s.

Phosphorus fractions and their vertical distribution were studied from the sea-bottom sediments from the Gulf of Riga and other coastal areas of western Estonia. The amount of potentially mobile phosphorus stored in the surface sediments of the Gulf of Riga is several times higher than in other accumulation areas of the Baltic Sea, with concentrations as high as 980 mg/kg(dw). A strong correlation between Mn and mobile phosphorus concentration suggests that Fe-Mn concretions control the amount of phosphorus in the sediments of the Gulf of Riga. Although the bottom waters of the Gulf of Riga are currently predominantly oxic, a decreasing trend of deep-layer oxygen concentrations and more frequent hypoxia in the Gulf of Riga during previous decades have been documented. Considering the large amount of potentially mobile phosphorus in the sediments of the Gulf of Riga, surpassing the annual total phosphorus input to the Baltic Sea, a substantial release of phosphorus could be inevitable, possibly impacting the entire Baltic Sea ecosystem.

How to cite: Ausmeel, M., Liira, M., Paiste, P., Lepland, A., and Suuroja, S.: Phosphorous in the seabed sediments of the Gulf of Riga, Baltic Sea: Fe-Mn concretions as main carriers of mobile phosphorous , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6352, https://doi.org/10.5194/egusphere-egu24-6352, 2024.

In modern low sulfate and anoxic (euxinic) waters, the precipitation of mineral vivianite (an easily oxidized hydrated ferrous-iron phosphate) has played a crucial role in restraining the limiting nutrient element phosphorus (P) recycling back to the water column and consequently decreasing primary productivity. Although such low sulfate and anoxic conditions were widespread in ancient coastal oceans, vivianite has not been directly discovered in the paleo-sediments, which hampers the understanding of P cycling in ancient anoxic environments. Here, we combined techniques of scanning electron microscopy-energy dispersive X-ray spectroscopy, focused ion beam-transmission electron microscopy and P K-edge X-ray absorption near edge structure spectroscopy to analyze samples of P-bearing siliceous rocks and shales from the early Cambrian Yurtus Formation in the Tarim Craton, northwest China. Our results have demonstrated that micron- to nano-scale vivianite crystals are well preserved in the rocks and the vivianite dominates the P phase in some samples. The cherty matrix of the rocks most likely increased the chances of preservation of the oxidation-sensitive vivianite. In light of recent advances, we suggest that vivianite was a crucial P phase in ancient continental margin sediments, spanning most time from the Neoarchean to the early Cambrian. During this interval, the precipitation of vivianite was likely aided by the prevalent dynamic ocean euxinic conditions linked with the seawater sulfate reservoir and the flux of organic matter settling. We propose a negative feedback mechanism in which vivianite precipitation from ancient euxinic waters restricted P availability for biota, reduced marine primary productivity, and possibly abated the rate of Earth's oxygenation and associated evolution of life. This work was financially supported by NSFC projects (grants 42072264, 41730213) and Hong Kong RGC GRF (17307918).

How to cite: Cao, X., Ju, P., Han, Y., Lu, L., and Shao, D.: Vivianite verified in early Cambrian strata in northwestern China: Implications for phosphorus recycling in ancient anoxic oceans, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7212, https://doi.org/10.5194/egusphere-egu24-7212, 2024.

Phosphorus (P), as an indispensable nutrient element in Earth’s biological system, exerts a pivotal role on the burial of organic carbon over million-year time scales. By producing oxygen and consuming carbon dioxide, organic carbon burial may have paved the path for multicellular organisms by reforming the anoxic atmosphere to an oxic one. Organic carbon burial, on long time scales, is ultimately limited by continental P influx released by chemical weathering of P-bearing minerals. As crystalline rocks characterized by prominent discrepancy in P-bearing mineral composition undergoing various dominant weathering forces on surficial environment, P availability for organic carbon burial could be controlled by lithology. To decipher the conundrum of P releasement, a catchment scale case study was conducted, encompassing a series of lithologies following the crystalline rock order. Preliminary data suggests that the P release efficiency is lithology-constrained, indicating an enhanced P releasement in felsic catchment. The result gives us a hint that felsic crust would export more P to the ocean and promote the organic carbon burial, the lithology-constrained P releasement also enlightens us a new perspective to understand the coevolution among crust, atmosphere and life.

How to cite: Ouyang, S.: Lithology-constrained phosphorus (P) releasement, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9578, https://doi.org/10.5194/egusphere-egu24-9578, 2024.

Improved management of phosphorus (P) is essential for achieving a range of Sustainable Development Goals (SDGs), including maintaining food security, preserving water quality, and mitigating climate change. This requires an integration of comprehensive mechanistic understanding with accurate spatial data. In this interdisciplinary review, we combine insights from empirical P research, digital soil mapping, biogeochemical modeling, and environmental law to critically examine the current state, pinpoint challenges and propose novel pathways for desperately needed P maps. We first elucidate the relevance of spatial data on P for different SDGs. Subsequently, we summarize the current efforts in mapping P pools at regional to global scales, and discuss the challenges of mapping “available P” due to substantial local scale variability and poor correlation with predictors relative to other soil properties. The practical applicability of these recently published maps is tested by evaluating them with independent measurement data. Finally, we outline ways forward to enhance the accuracy and reliability of P maps, as a basis for science-informed management of P resources.

How to cite: Helfenstein, J., Ringeval, B., Tamburini, F., Goll, D. S., He, X., Mulder, V., Wang, Y., Alblas, E., and Frossard, E.: Linking phosphorus research to impact: advances and challenges in mapping soil phosphorus pools, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9674, https://doi.org/10.5194/egusphere-egu24-9674, 2024.

Long-term application of organic products (manure, biosolids, other wastes) and inorganic phosphatic fertilizers have created hot spots of phosphorus (P) saturated soils in intensive animal production regions worldwide. In such regions, P losses from P-saturated (i.e., legacy P) soils continue to plague efforts to improve water quality. Understanding the P cycling and fluxes from these P-saturated soils is critical to advancing our knowledge and developing strategies to manage P in soils and curb P losses. This presentation will discuss P cycling and transport in agricultural catchments (with Maize-Soybean rotation) from the lenses of P chemistry in soils and hydrologic responses from soils to further advancements in managing the P cycle in the soil-plant-water continuum for agricultural sustainability and environmental protection.

How to cite: Toor, G., Radolinski, J., Lucas, E., Burgis, C., Kennedy, B., Sun, F., and Steinhilber, P.: Phosphorus Cycling and Transport in Phosphorus Saturated Soils of the Chesapeake Bay Watershed, USA, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14368, https://doi.org/10.5194/egusphere-egu24-14368, 2024.

Phosphorus (P) is an essential nutrient for plant growth and is applied to agricultural soils in the form of organic manure or inorganic fertilizer. To guide farmers in achieving optimal crop yields, P fertilizer recommendations are in place with the rationale to bring soils to a “target soil P status” following the classic build-up and maintenance approach. The target soil P status where crop yield is not limited by P deficiencies is generally operationalized as the soil P status at which 90-99% of the potential crop yield is found in long-term fertilization field experiments. Though these fertilizer recommendations allow for an economic optimization of crop yield versus P inputs, environmental objectives are barely considered. In our research, we revised the classic build-up and maintenance approach to balance crop production, water quality and the use of finite P reserves. This revision requires insights into the P sorption capacity of soils (PSC) and its saturation with P. We identify the oxalate extraction method as a key component of this approach since it quantifies the PSC from the combined measurement of amorphous iron- and aluminium-(hydr)oxides and the total pool of reversibly bound P. For the Netherlands, we show the implications of the approach for P fertilizer use. We quantified soil amorphous iron- and aluminium(hydr)oxides contents at a 25m resolution across the soil depth profile using a Digital Soil Mapping approach and used these predictions to translate agronomic soil P data to new insights to optimize P fertilizer use. We finally argue that agronomic P target levels should be lowered in soils with a low PSC to decrease the risk of P leaching and in soils with a high PSC to ensure judicious use of finite P reserves.

How to cite: van Doorn, M., van Rotterdam-Los, D., Ros, G. H., and de Vries, W.: Balancing crop production, water quality and the use of finite P reserves by using the soil P sorption capacity in revised fertilizer recommendations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14436, https://doi.org/10.5194/egusphere-egu24-14436, 2024.

Organic phosphorus (P) plays a crucial role in maintaining the health and productivity of soils. Understanding the composition of organic phosphorus in soils is thus relevant to a range of disciplines, spanning from agricultural sciences to ecology. Over the past few decades, efforts have been directed towards characterizing and quantifying various soil organic P compounds and determining their turnover rates. Despite these efforts, the precise nature of soil organic P remains unclear, particularly that of orthophosphate monoesters, which dominate ³¹P NMR spectra of NaOH-EDTA extracts globally.

Typically, the monoester region of 1D ³¹P NMR spectra appears as a series of sharp signals "sitting" on a broad background where the broad background can account for a substantial part of the monoester region. This is prompting questions about how to integrate and identify these signals and to what extent this fraction may be ecologically important. To investigate this monoester background, we employed 1D ³¹P NMR and 2D ¹H-³¹P NMR¹, along with ³¹P transverse relaxation (T₂)² measurements to calculate intrinsic linewidths. We related this linewidth to molecular weight to unveil the nature of the observed background. Analysing seven soils from different ecosystems, we observed linewidths ranging from 0.5 to 3 Hz for both resolved monoester signals and the background. This suggests that the background comprises numerous, possibly exceeding 100, sharp signals associated with small (<1.5 kDa) organic P molecules.

Organic P in the form of nucleic acids, phospholipids, P-containing metabolites, and phosphorylated proteins dominate the P content of live leaves, leaf litter and microbial tissues. Furthermore, P-containing metabolites are exuded by roots and are present in a vast array of organisms. Evidence that the background potentially can contain a large number of small metabolites is thus not surprising and may account for an important part of the organic P pool given that the background accounts for about 55% of the monoester region. Our findings warrant further research specifically addressing to what extent this pool may play for plant and microbial P nutrition.

We provide recommendations for treating ³¹P NMR spectra to accurately quantify phosphomonoester species, representing a crucial step in linking observed P speciation to its bioavailability. Our findings align with previous ³¹P NMR studies detecting background signals in soil-free samples and new evidence suggesting that alkali-soluble soil organic matter consists of self-assemblies of small organic compounds mimicking large molecules.

¹Vestergren, J.; Vincent, A. G.; Jansson, M.; Persson, P.; Ilstedt, U.; Gröbner, G.; Giesler, R.; Schleucher, J. High-Resolution Characterization of Organic Phosphorus in Soil Extracts Using 2D ¹H–³¹P NMR Correlation Spectroscopy. Environmental Science & Technology 2012, 46 (7), 3950–3956. https://doi.org/10.1021/es204016h.

²Vincent, A. G.; Schleucher, J.; Gröbner, G.; Vestergren, J.; Persson, P.; Jansson, M.; Giesler, R. Changes in Organic Phosphorus Composition in Boreal Forest Humus Soils: The Role of Iron and Aluminium. Biogeochemistry 2012, 108 (1), 485–499. https://doi.org/10.1007/s10533-011-9612-0.

How to cite: Haddad, L., Vincent, A., Giesler, R., and Schleucher, J.: 31P NMR Reveals Predominance of Small Molecules in Organic Phosphorus within NaOH-EDTA Soil Extracts, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16417, https://doi.org/10.5194/egusphere-egu24-16417, 2024.

Application of phosphorus (P) fertiliser to soybean accounts for a large proportion of the global consumption of P as an agricultural fertiliser. Despite this key a knowledge gap exists surrounding the mechanisms of P fertiliser uptake and how it interacts with nitrogen fixation processes and yield improvements.

This paper aims to improve the understanding of P cycling in global cropping systems and will present a global meta-analysis of published data quantifying the effect of P fertiliser application on soybean above- and below-ground plant response variables. 790 paired observations (P fertiliser treatment and control treatment) were synthesised from 81 peer-reviewed articles that reported soybean response, including seed yield and nodulation, to P addition under a range of different environmental conditions.

We tested the hypothesise that:

• soybean productivity will increase following P addition, with this response being driven by below-ground processes;
• environmental conditions, particularly soil chemical properties would explain the variance in the observed response.

Analysis of these observations showed an overarching increase in soybean plant response following P addition. We found that several environmental and experimental conditions, particularly soil phosphorus status and phosphorus fertiliser rate influence the response of soybean to phosphorus addition, highlighting the complexities of sustaining P use across such a globally cultivated crop.

We recommend further experimental work needs to be conducted, which controls for such factors and allows for the improved mechanistic understanding of below-ground processes, to inform better use of finite P resources.

How to cite: Walling, H., Rufino, M., Rotundo, J., Borras, L., Rothwell, S., Quinton, J., and Haygarth, P.: A meta-analysis of global soybean plant growth and yield improvement in response to phosphorus addition, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16549, https://doi.org/10.5194/egusphere-egu24-16549, 2024.

Phosphorus (P) is a key nutrient controlling primary production in aquatic systems. In coastal systems, the P cycle involves dynamic interactions between terrestrial, aquatic and sedimentary compartments. Over the last century, human activities such as deforestation, intensive agricultural practices and the disposal of municipal and industrial wastes have increased P inputs to coastal ecosystems. As a result, this increase in P inputs has led to an increase in the occurrence of algal blooms and higher oxygen demand in estuaries. In the Loire estuary, dissolved oxygen deficits have been a recurrent and worrying issue for several decades despite the improvement of water quality over the last 30 years due to reduced wastewater discharge and better effluent treatment. In this context, the burial of bioavailable P may influence the recovery of waters from eutrophication. The major P burial phases are apatite, organic P and iron-bound P. The results of sequential chemical extraction and pore water analysis carried out over a 5m-long sediment core from the intertidal Brillantes mudflat in the Loire estuary indicated a greater abundance of the iron-bound P compared to other phases. Iron-bound P occurs in two different forms: phosphorus bound to iron oxides and in the iron phosphate mineral known as vivianite. Vivianite is a ferrous iron phosphate mineral formed under reducing and low sulphate conditions in sediments where organic matter serve as electron donor for ferric iron reduction. Results of sequential chemical extraction of freeze-dried sediment samples combined with pore water data and scanning electron microscope–energy dispersive x-ray spectroscopy (SEM-EDXS) on resin-embedded sediment samples indicated that vivianite-type minerals may act as an important sink for P at the studied site. Authigenic vivianite crystals were found below the shallow sulphate/methane transition zone (SMTZ) at 94 cm depth and contain significant amounts of manganese, as observed in freshwater sediments. We therefore hypothesise that anthropogenic over-fertilization of coastal regions in the last century may have increased the importance of vivianite authigenesis in surface sediments. Consequently, vivianite is likely to be an important sink for P in estuarine systems worldwide.

This study is part of a PhD financed by the European Project Life REVERS’EAU.

How to cite: Barhdadi, M., Mouret, A., Barras, C., Morin, G., Maillet, G., Durand, M., Mojtahid, M., Bénéteau, E., Dubosq, N., and Metzger, E.: Vivianite as a phosphorus sink in estuarine systems: The case study of the Brillantes mudflat, Loire, France, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17700, https://doi.org/10.5194/egusphere-egu24-17700, 2024.

The Galápagos archipelago, a volcanic island chain, is comprised of a series of progressively older islands with increasingly weathered soils away from the volcanic hotspot. Volcanic soils are known for their high phosphate sorption capacity. In this study, we explore differences in soil microbial abundance and activity across a soil age gradient (1.5 to 1070 ka) to understand how soil microorganisms are affected by soil development, shifting soil characteristics and P sorption over extensive periods.

Basal respiration, substrate-induced respiration and microbial biomass P decreased with soil development, suggesting increasing nutrient limitation for soil microbes. Also, soil enzymatic stoichiometry revealed a limitation driven mainly by P and not by N or C. C- and N-acquiring exoenzyme activities peaked at 26 ka with lower activities in younger and older soils. Phosphatase activity increased with soil age, indicating microbial P limitation in the older soils. This is only partly in line with  P sorption-desorption characteristics along the studied weathering sequence. Phosphate sorption capacity was high in the 4.3 ka soils likely due to amorphous soil constituents. A change towards 2:1-type crystalline clays after 26 ka of soil weathering led to weaker P sorption and stronger desorption, and acidification and increased P occlusion in Al and Fe (hydr)oxides became an important factor for microbial P limitation in the older soils.

Our results reveal striking differences in soil properties on the Galápagos Islands, suggesting relatively little nutrient constraints for soil microbes, despite strong P sorption, in the younger volcanic soils but growing P limitation in the older, highly weathered soils. These observations have important bearings on nutrient cycling and may therefore also affect the evolution of plant and animal species on this unique archipelago.

How to cite: Keiblinger, K. M., Socianu, S., Rechberger, M., Gerzabek, M., and Zehetner, F.: Microbial phosphorus limitiation with soil age along a chronosequence on the Galapagos Islands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19011, https://doi.org/10.5194/egusphere-egu24-19011, 2024.

Many eutrophic lakes suffer from long term accumulation of legacy phosphorus (P) in sediments. Repeated cycling of P between sediments and water column leads to delayed recovery from eutrophication even after abatement of external loading. Moreover, in complex multi-basin lake systems, legacy P can be internally redistributed over time, leading to spatial heterogeneity in regeneration and burial of P and consequent impacts on water quality. Few studies have attempted to map such internal variability in individual lakes in the context of understanding long term recovery from eutrophication. Here we use a combination of sediment trap deployments through one full stratification cycle (May-October 2021), sediment core biogeochemical analyses, and mass balance calculations, to quantify P cycling in Lake Hiidenvesi, a dimictic lake with 5 sub-basins in southern Finland. We show that exchange of P between sediments and water column is more intense in shallow (approximately 0-10 m depth) non-stratified sub-basins, due to both sediment resuspension and diffusive fluxes across the sediment-water interface. In contrast, deeper stratified sub-basins serve as P sinks by promoting sedimentation in relatively quiescent conditions. Due to lateral exchange of water and suspended materials between sub-basins, P is shuttled towards long term burial in deeper, downstream sub-basins. Budget calculations show that net sediment P burial exceeds external loading on the whole-lake scale, indicating a long-term trend towards recovery from eutrophication. However, temporary retention and repeated recycling of legacy P in the shallower upstream sub-basins continues to impact negatively on water quality, despite external loading reductions. The results have implications for understanding the timescales of recovery and for targeting restoration actions aimed at modifying internal P cycling to improve water quality.

How to cite: Jilbert, T., Zhao, S., Vesterinen, J., and Niemistö, J.: A spatial perspective on internal phosphorus cycling in morphologically complex eutrophic lakes: the importance of stratification, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20517, https://doi.org/10.5194/egusphere-egu24-20517, 2024.

          Utilisation of dissolved organic phosphorus (DOP) by marine microbes as an alternative phosphorus (P) source when phosphate is scarce can help sustain non-Redfieldian carbon:nitrogen:phosphorus ratios and efficient ocean carbon export. Alkaline phosphatase (AP) is an important enzyme group that facilitates the remineralisation of DOP to phosphate and thus its activity is a promising proxy for DOP-utilisation, particularly in P-stressed regions. In order tounderstand the global spatial patterns and rates of microbial DOP utilization and their environmental controls, we compiled a Global Alkaline Phosphatase Activity Dataset (GAPAD) with 4083 measurements collected from 79 published manuscripts and one database， and further investigated the possible mechanisms controlling global ocean APA. We find that DOP concentration, salinity, excess phosphate (P*), and chlorophyll a concentrations are critical factors in predicting global patterns of APA, which together explain as much as 39% of the variance in the observed APA dataset. Among all environmental factors, DOP concentration explains the most variance in the observed APA data and is negatively correlated with APA. P* is negatively correlated with APA，while chlorophyll a concentration is positively correlated.  Moreover, wind speed, dust iron deposition rate, and zinc concentration are also possible important environmental factors controlling APA. Using structural equation modeling, DOP and P* concentrations have a total negative effect on APA of -0.36. and -0.2 respectively, while chlorophyll a concentration and salinity have a total positive effect of 0.16 and 0.24. Via a set of numerical competition experiments between an AP-producing phytoplankton and a non AP-producing competitor, AP-producing phytoplankton are found to have an advantage in regions with low P*, but only alongside sufficiently high DOP and DIN concentrations. This trend arises due to the trade-off between P acquisition and N allocation to AP synthesis and is not affected by varying the model assumptions regarding nutrient supplies, N-demand, and key physiological traits.  Extending our results to the global ocean using DIN, DIP, and DOP datasets enables us to pinpoint key regions where optimal conditions for DOP-utilisation are prevalent. These findings align closely with the patterns illuminated by our APA dataset. Our results show that on a global scale, when phosphate limitation is severe, plankton utilize DOP through producing AP, and this will help understand the biogeographical shift of different microbial groups in response to future climate change. Further work is needed to include the parallel role of the trace metal co-factors iron and zinc in driving AP synthesis and its spatial distribution in our modelling experiments.

How to cite: Su, B., Song, X., Duhamel, S., Mahaffey, C., Davis, C., Ivančić, I., Zhou, S., and Liu, J.: Controls on global patterns of dissolved organic phosphorus utilisation in the surface ocean, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20917, https://doi.org/10.5194/egusphere-egu24-20917, 2024.

Phosphorus (P) is essential for cellular metabolism. Many metabolic pathways and processes depend on it, including energy production through ATP, DNA and RNA synthesis, and protein phosphorylation during post-translational signaling adaptation.

In marine sediments and oceanic water, the stoichiometric ratio between carbon and phosphorus has been found to vary with latitude, but in algae and phytoplankton, which are responsible for primary production and CO₂ uptake from the atmosphere, this ratio is relatively constant. This constant ratio is known as the Redfield ratio and  it is often used as a constraint in modeling.

In soils, where microorganisms control nutrient cycling and consequent carbon sequestration, the C:P is more variable both in soil and microbial biomass. First, microorganisms exhibit a wide range of metabolic adaptations to environmental pressure, and the physical and mineralogical properties of the soil play a significant role in nutrient control, e.g. through sorption/desorption reactions. Due to these complexities, using nutrient ratios for modeling soil organic carbon dynamics and predicting the impact of anthropogenic influences on global changes is challenging. Is it possible to find a connection between carbon and phosphate that encompasses the "Redfield" ratio and reflects their tight link in cellular metabolism?

By examining the oxygen isotope composition in inorganic phosphate (δ¹⁸O-Pi), we can determine the extent of oxygen exchange between water and phosphate, which is controlled by biological processes. Intracellularly, this exchange occurs through phosphoryl transfer, a fundamental process in cellular phosphate cycling. 

During the last 10 years, we conducted a series of incubation experiments where we measured CO₂ respiration and δ¹⁸O in resin and microbial cytosolic phosphate in soils from different environments. These incubations were performed with waters of varying ¹⁸O isotopic composition. By analyzing δ¹⁸O in microbial cytosolic phosphate at the beginning and end of the incubation, we could measure the level of oxygen exchange between water and phosphate.

Comparing the results from these incubations, we observed a significant correlation between the percentage of oxygen exchange and the cumulative CO₂ respired during the incubation. This correlation was consistent  through different soil ages, mineralogy, phosphate levels, and incubation length. When normalizing the percentage of oxygen exchange to moles of oxygen exchanged per moles of carbon respired, it appears that for every mole of oxygen exchanged due to phosphoryl transfer, there is a nearly fixed amount of carbon respired. This suggests that the moles of oxygen exchanged through phosphoryl transfer recorded in soil microbial phosphate can provide information about metabolic carbon expenditure.

This finding would provide new insights on the link between P and C in soil microbial biomass. The controlled nature of the incubation experiments may not fully reflect the biological activity in soil environments, so it would be necessary to perform field-based incubation experiments to confirm the link between carbon respiration and phosphorus microbial cycle. This information could potentially improve our understanding of carbon dynamics and be used for further modeling purposes.

How to cite: Tamburini, F., Siegenthaler, M., and Pistocchi, C.: Beyond “Redfield ratio”: Oxygen exchange between water and phosphate can provide insights into carbon dynamics in soils, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21673, https://doi.org/10.5194/egusphere-egu24-21673, 2024.

For a comprehensive understanding of the phosphorus (P) storage and cycling in temperate soils, it is necessary to explore further the bonding pathways of organic P (Po) and inorganic P (Pi) to mineral surfaces and soil organic matter (SOM), and their interconnections with organic carbon (OC) at a micro-scale other than conventional bulk analysis. In the past decade, nanoscale secondary ion mass spectrometry (NanoSIMS) has been increasingly recognized as a promising imaging technique to understand soil biogeochemical processes, particularly in exploring organo-mineral associations in soils at the microscale (Mueller et al., 2023). However, its application in studying P, and the identification and distinction of Po and Pi remains challenging, hindering a comprehensive understanding of the P cycling in soils.

In our study, four temperate soil types, including Cambisol, Luvisol, Phaeozem and Fluvisol, were taken from Bavarian Forest in South-East Germany. The pH of these soils ranges from 5.4 to 6.3, with poor to medium P stocks but distinct Po stocks in fine fractions (<20 μm). Previous bulk studies have hinted at different pathways in P bonding to mineral surfaces and SOM. NanoSIMS was employed to further explore and visualize these bonding pathways. Recent advancements in NanoSIMS technology, particularly improved O^- sources for cation detection and the capability for ³¹P^- and ³¹P¹⁶O^2- detection enable us to identify and distinguish Po and Pi at a microscale by ³¹P¹⁶O^2-/³¹P^- ratio, in which a lower ratio in specific areas corresponds to a more dominant presence of Po, and vice versa.

From NanoSIMS images, preliminary results reveal that a proportion of Po associates with either clay minerals or Fe (hydr)oxdies without assimilating into SOM. This Po fraction is suspected to originate from highly decomposed SOM, where N has either been assimilated by microorganisms or leached away, and Po is stabilized to mineral surfaces due to strong bonding strength. In contrast, the Po assimilated into SOM is associated with various cations, including Ca, Al and Fe, which may suggest the origin from particulate organic matter. Interestingly, the fine plant residue is depleted in Po in the fine fraction.

In conclusion, our study provides valuable insights into distinguishing different bonding pathways of these P forms within clay minerals, Fe (hydro)oxides, and SOM by using advanced NanoSIMS data, and emphasizes the interconnection with OC and Po and Pi in the fine fraction.

Reference: Mueller, C. W., Hoeschen, C., Koegel-Knabner, I., 2023. Understanding of soil processes at the microscale—Use of NanoSIMS in soil science. Encyclopedia of Soils in the Environment (Second Edition). Elsevier. 10.1016/B978-0-12-822974-3.00045-8

How to cite: Lei, K., Bucka, F. B., Höschen, C., Hu, Y., and Kögel-Knabner, I.: Exploring spatial distribution and characterization of inorganic and organic phosphorus in temperate soils using NanoSIMS , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21972, https://doi.org/10.5194/egusphere-egu24-21972, 2024.

The critical role of Dissolved Organic Phosphorus (DOP) in supporting primary production has spurred efforts to characterize DOP composition so that insight may be gained into its bioavailability and cycling in aquatic systems. The degree to which DOP is bioavailable to primary producers will determine, in part, the extent of carbon uptake and sequestration.  Ascertaining DOP composition has proven to be an analytically challenging endeavor.  As a consequence, the DOP pool remains poorly characterized, and our predictive power relative to DOP-bioavailability, and coupled carbon cycling, remains limited. Analytical impediments to characterizing DOP composition in natural waters include its low concentration, requiring pre-concentration before compositional features can be probed via spectroscopy, and the fact that organic phosphorus compounds are not easily amenable to standard organic geochemical approaches, such as chromatographic or mass spectrophotometric methods, particularly in salt water. While 31-Phosphorus Nuclear Magnetic Resonance (³¹P-NMR) spectroscopy has provided intriguing information on the distribution of the 2 major DOP compound types (phosphoesters, phosphonates), the crucial question of DOP bioavailability cannot be addressed by this method. We present novel DOP molecular weight distribution and bioavailability data, generated using a coupled sequential ultrafiltration-bioavailability approach from a marine water column depth profile and locations across a gradient in phosphate concentration in the Atlantic and Pacific Oceans.  There is substantial compositional variability in the marine DOP pool, both in the pattern of DOP molecular weight distribution at different sites, as well as the distribution of bioavailable mono- and diesters of phosphate across molecular weight fractions.  In some cases, a substantial fraction of DOP in different molecular weight size classes is non-reactive to the two enzymes used to assay potential bioavailability, raising the interesting possibility of non-bioavailable DOP. The significance of recognizing that the oceanic DOP pool is compositionally heterogeneous, and variably bioavailable, lies in that fact that such information is a prerequisite to building ecosystem models that capture the influence of P biogeochemistry on primary production and carbon cycling in aquatic systems.

How to cite: Dyhrman, S., Ruttenberg, K., Hull, D., and Leon Soon, S.: Heterogeneous Dissolved Organic Phosphorus Composition and Bioavailability in Marine Systems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-22214, https://doi.org/10.5194/egusphere-egu24-22214, 2024.

Biogenic volatile organic compounds (BVOCs) are carbon compounds released by plants through secondary metabolism. In the global background of nitrogen (N) deposition, plants respond to environmental changes by altering BVOCs and photosynthetic strategies. However, there is very little research on the release and photosynthetic characteristics of BVOCs in bamboo in response to N deposition. Therefore, we took Pleioblast amarus as a research object and conducted pot experiments to set up four different nitrogen deposition levels (referred to as "N deposition") (0 kg N hm-2-a-1(N0), 30 kg N hm-2 a-1(N1), 60 kg N hm-2 a-1(N2), and 90 kg N hm-2 a-1(N3)) to explore the effects of different N deposition levels on the release and photosynthetic characteristics of BVOCs in leaves, and analyzed the correlation between the indicators. The results showed that: (1) the percentage of isoprene emission from Pleioblast amarus bamboo leaves increased with the increase of N deposition level (significantly positively correlated), but the N deposition level did not significantly affect the total number of BVOCs; (2) the increase of N deposition level significantly increased the net photosynthetic rate and isoprene (ISO) emission rate of leaves, with the highest ISO emission rate under N3 treatment, which was 80. 39%, 75.07%, and 50.84% higher than N0, N1, and N2, respectively; (3) ISO emission rate and total BVOCs emission of Sanming bitter bamboo were significantly positively correlated with net photosynthetic rate and photosynthetic effective radiation of leaves, but ISO emission rate and total BVOCs emission were significantly negatively correlated with chlorophyll b and total chlorophyll content (P≤0.05). In conclusion, the increase in nitrogen deposition led to a remarkable increase in isoprene emissions from Sanming bitter bamboo leaves. 

How to cite: Li, L. and Liu, X.: Effects of nitrogen deposition on volatile organic compounds composition, isoprene emissions and photosynthetic characteristics of Pleioblast amarus, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2236, https://doi.org/10.5194/egusphere-egu24-2236, 2024.

Rice uses 34-43% of the global irrigation water and is responsible for the usage of 24-30% of the world's total freshwater. More than 75% of rice produced in India is cultivated using the traditional continuous flooding (CF) irrigation method, which is a labour-intensive, time, water and energy-consuming process and a key source of global methane emissions. Alternate Wetting and Drying (AWD) is a popular water-saving approach trailed in Asia including India to reduce water use and methane emissions, whilst sustaining rice production. AWD is a method of periodic soil saturation followed by drying compared to CF. The objective of this research was to evaluate greenhouse gas (GHG) fluxes and internal and external nitrogen cycling processes as influenced by AWD and CF management regimes. A mesocosm experiment was set up in the laboratory using imported Indian paddy soil where Jasmine rice (var KDML 105) was grown. Our results depicted that plant biomass (52.57%), root biomass (28.57%), height (24.77%), effective tiller number (45.15%), stem sheath diameter (53.38%) and stomatal conductance (66.49%) were significantly (p<0.05) higher in CF compared to AWD treatment. A similar trend was observed in rice leaf chlorophyll (Chl a, b and total chl) contents. Interestingly, the chlorophyll a and b ratio observed was higher (1.63) in AWD compared to CF (1.03) conditions. This was likely during the process of chlorophyll b degradation and conversion to Chl a, thus resulting in the increase of a to b ratio to cope with the stress by maintaining the leaf photosynthetic efficacy. Soil enzyme activity revealed that β-glucosidase (BG), β-N-acetyl-glucosaminidase (NAG), and acid phosphatase (AP) were higher in AWD, whereas leucine aminopeptidase (LAP) activity was significantly higher in CF. Higher LAP activity might be a response to limited nutrient availability, as LAP helps to release amino acids that serves as a source for N mineralization and N supply. The ¹⁵N isotope tracing study revealed that denitrified N₂O flux was significantly (p<0.05) higher in CF compared to AWD where source partitioning (% N₂O denitrified) was 99.32% in CF and 27.01% in AWD. Higher gross mineralization was observed under AWD (3.92 ± 0.31µg^-1 g^-1 d^-1) due to the promotion of aerobic microbial activity compared to CF (1.31 ± 0.31µg^-1 g^-1 d^-1). A similar trend was observed for the consumption and immobilization of NH₄⁺ and gross nitrification rates. GHG emissions rate viz., CH₄-C, CO₂-C, and N₂O-N emissions were significantly higher under CF by 61, 3 and 72.%, respectively. Moreover, the global warming potential projected was higher under CF averaging at 10.92 mg kg^-1 soil compared to 2.19 mg CO₂ kg^-1 soil under AWD. Reduced GHG emissions under AWD provides for a significant negative feedback to global warming potential and future initiatives should keep emphasizing the optimization of this practice for its significant contribution to both climate change mitigation and sustainable agriculture.

How to cite: Ullah, S., Kaviraj, M., Guo, Y., Micucci, G., and Sgouridis, F.: Rice cultivation under continuous flooding vs alternate wetting and drying: implications for biomass, nitrogen cycling and greenhouse gas flux, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2534, https://doi.org/10.5194/egusphere-egu24-2534, 2024.

Organic nitrogen (ON) is an important participant in the Earth’s N cycle. Previous studies have shown that penguin feces add an abundance of nutrients including N to the soil, significantly changing the eco-environment in ice-free areas in Antarctica. To explore the molecular transformation of ON in penguin guano-affected soil, we collected guano-free weathered soil, modern guano-affected soil from penguin colonies, ancient guano-affected soil from abandoned penguin colonies, and penguin feces from the Ross Sea region, Antarctica, and Fourier transform ion cyclotron mass spectrometry (FT-ICR MS) was used to investigate the chemical composition of water-extractable ON. By comparing the molecular compositions of ON among different samples, we found that the number of ON compounds (>4,000) in weathered soil is minimal, while carboxylic-rich alicyclic-like molecules (CRAM-like) are dominant. Penguin feces adds ON into the soil with > 10,000 CHON, CHONS and CHN compounds, including CRAM-like, lipid-like, aliphatic/ peptide-like molecules and amines in the guano-affected soil. After the input of penguin feces, macromolecules continue to degrade, and other ON compounds tend to be oxidized into relatively stable CRAM-like molecules, this is an important transformation process of ON in guano-affected soils. We conclude the roles of various forms of ON in the N cycle are complex and diverse. Combined with previous studies, ON eventually turns into inorganic N and is lost from the soil. The lost N ultimately returns to the ocean and the food web, thus completing the N cycle. Our study preliminarily reveals the molecular transformation of ON in penguin guano-affected soil and is important for understanding the N cycle in Antarctica.

How to cite: Wu, L., Sheng, M., Liu, X., and Fu, P.: Molecular transformation of organic nitrogen in Antarctic penguin guano-affected soil, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2749, https://doi.org/10.5194/egusphere-egu24-2749, 2024.

The long-lived greenhouse gas nitrous oxide (N₂O) and short-lived reactive nitrogen (Nr) gases such as ammonia (NH₃), nitrous acid (HONO), and nitrogen oxides (NO_x) are produced and emitted from fertilized soils and play a critical role for climate warming and air quality. However, only few studies have quantified the production and emission potentials for long- and short-lived gaseous nitrogen (N) species simultaneously in agricultural soils. To link the gaseous N species to intermediate N compounds [ammonium (NH₄⁺), hydroxylamine (NH₂OH), and nitrite (NO₂^‒)] and estimate their temperature change potential, ex-situ dry-out experiments were conducted with three Chinese agricultural soils. We found that HONO and NO_x (NO + NO₂) emissions mainly depend on NO₂^‒, while NH₃ and N₂O emissions are stimulated by NH₄⁺ and NH₂OH, respectively. Addition of 3,4-dimethylpyrazole phosphate (DMPP) and acetylene significantly reduced HONO and NO_x emissions, while NH₃ emissions were significantly enhanced in an alkaline Fluvo-aquic soil. These results suggest that ammonia-oxidizing bacteria (AOB) and complete ammonia-oxidizing bacteria (comammox Nitrospira) dominate HONO and NO_x emissions in the alkaline Fluvo-aquic soil, while ammonia-oxidizing archaea (AOA) are the main source in the acidic Mollisol. DMPP effectively mitigated the warming effect in the Fluvo-aquic soil and the Ultisol. In conclusion, our findings highlight the important role of NO₂^‒ in stimulating HONO and NO_x emissions from dryland agricultural soils. In addition, subtle differences of soil NH₃, N₂O, HONO, and NO_x emissions indicated different N turnover processes, and should be considered in biogeochemical and atmospheric chemistry models.

How to cite: Wu, D., Song, Y., Yu, Y., and Dörsch, P.: Nitrite stimulates HONO and NOx but not N2O emissions in Chinese agricultural soils during nitrification, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3699, https://doi.org/10.5194/egusphere-egu24-3699, 2024.

In this study, we aimed to constrain and characterize the dynamics of denitrification in three different fields: one conventional arable and two types of pasture (“leys”). During a one-year field campaign, denitrification was measured using our newly developed method combining the application of ¹⁵N tracer and artificial atmosphere for the incubation of soil cores under field conditions (Micucci, 2022), while total N₂O emissions were measured using static flux chambers during parallel incubations. Our objectives were to determine the best way to upscale soil core denitrification measurements and trace the fate of applied synthetic nitrogen fertilizer via denitrification in conventional agriculture in comparison to pastures under regenerative agriculture practices.

We determined that the best way to derive field-scale fluxes of denitrification was to use the core method to calculate the source partitioning coefficient (SPC) and product ratio (PR) and use these metrics in combination with static chamber data. The SPC is defined as the proportion of total N₂O emissions that originates from denitrification while the product ratio measures the proportion of denitrification product emitted as N₂O rather than N₂.

During the field campaign, we estimated that 22 kgN ha^-1 were lost via denitrification in the arable field, amongst which 15.17 were attributed to fertilizer application, representing around 8% of the 200 kgN ha^-1 applied. Furthermore, 9 % of the denitrified fertilizer was emitted as N₂O rather than N₂. On the other hand, the unfertilized ley emitted only 2.6 kgN ha^-1 via denitrification annually. Overall, the total N₂O emissions in the fertilizer arable field were responsible for around 2 t eqCO2 ha^-1 year^-1 compared to 0.15 in the unfertilized ley, highlighting the importance of land management in strategies of greenhouse gas emission reduction.

How to cite: Micucci, G., Sgouridis, F., Krause, S., Lynch, I., McNamara, N. P., Roos, F., Jonathan, L., and Ullah, S.: Constraining the denitrification process in conventional and regenerative agriculture, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4369, https://doi.org/10.5194/egusphere-egu24-4369, 2024.

Current soil biogeochemical models have difficulties matching the observed composition of soil organic matter (i.e., the relative proportions of deadwood, raw litter, organic horizon, particulate organic carbon, and mineral-associated organic carbon). In reality, nitrogen (N) controls microbial decomposition and physiological processes, whereas in most models it is merely considered a plant nutrient. In addition, many N fertilization studies have shown that N exerts different effects on different C pools via changing exoenzyme activities, microbial growth, and necromass production via microbial turnover. These divergent effects control SOM composition and have C-cycle consequences.

We expanded the CENTURY model by incorporating multiple hypothesized microbial responses to nitrogen availability, including 1) decomposition reduction of recalcitrant substrates when N is in excess; 2) decomposition stimulation of high C:N substrates when N limitation is alleviated; 3) microbial adaptation of turnover rate; 4) microbial adaptation of CUE; and 5) secondary feedback to decomposition via changes in microbial biomass in response to N. We systematically tested multiple model variants using two sets of simulations, one along a natural N gradient in Swiss forests, and another one with artificially increased N input (i.e., simulating an N-fertilization experiment). We evaluated the simulated outputs using data on soil organic matter fraction stocks, their relative proportions, and temporal responses under N addition.

From the simulation results, we identified the necessary processes to explain the temporal response pattern of different C pools to N addition, in accordance with findings from meta-analyses. In addition, we identified patterns of SOM composition over a natural gradient of N supply (no artificial N addition), which can again be explained by the N-driven processes we implemented. We conclude that considering the direct effects of nitrogen as a key additional constraint on microbial processes is essential to improve the realism and accuracy of soil biogeochemistry models.

How to cite: Yeung, C. C., Bugmann, H., Hagedorn, F., and Díaz-Yáñez, O.: How does nitrogen control soil organic matter composition? – A theory and model, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4706, https://doi.org/10.5194/egusphere-egu24-4706, 2024.

Atmospheric deposition of natural and anthropogenic sourced reactive nitrogen (Nr, mainly including NH₃, NH₄⁺, NO_x, NO₃^- and etc.) has substantial influence on terrestrial and aquatic ecosystems, driving global nutrient imbalances and increasing risks to human health. Although it has been demonstrated that atmospheric Nr deposition has a substantial impact on nitrogen pools in remote and/or sensitive lakes, there is a scarcity of systematic evaluations regarding atmospheric Nr deposition's impact on the nitrogen burden in eutrophic lakes with riverine input as the primary source. Utilizing a regional chemical transport model, combined with observations of riverine nitrogen input, we investigate the contribution of atmospheric Nr deposition to a eutrophic Lake Chaohu in eastern China. The results indicate that riverine total nitrogen (TN) input to the lake was 11553.3 t N yr^-1 and atmospheric TN deposition was 2326.0 t N yr^-1 in the year of 2022. For Nr species which are directly available for the biosphere supporting algae and plant growth, riverine NH₄⁺ input was 1856.1 t N yr^-1 and atmospheric NH_x (NH₃ and NH₄⁺) deposition was 824.5 t N yr^-1. The latter accounts for ~ 1/3 of total NH_x input to the lake. For NO_y (HNO₃ and NO₃^-) species, atmospheric deposition was estimated to also contributes a similar amount to the NH_x species. The results suggest that even in regions with dense human activities with primary riverine N input, atmospheric deposition of Nr could also contribute significantly to the bio-available nitrogen in lake systems, and addressing eutrophication in Lake Chaohu and other eutrophic lakes will also need to consider the reduction of NH₃ and NO_x (i.e., NO + NO₂, the precursor of NO_y) emissions, in addition to the mitigation of riverine N input.

How to cite: Li, W., Wang, X., Zhang, Z., Liu, X., and Geng, L.: On the Contribution of Atmospheric Nitrogen Deposition to Nitrogen Burden in an Eutrophic Lake in Eastern China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5161, https://doi.org/10.5194/egusphere-egu24-5161, 2024.

Saltmarshes have the potential to sequester large amounts of carbon, however, the value of stored carbon may be partially offset by emissions of the potent greenhouse gas nitrous oxide (N₂O). Increased nutrients [NO₃^- and NH₄⁺] have been shown to increase N₂O emissions from saltmarshes, however, a global-scale analysis of this relationship has not been performed. Here, we present a global meta-analysis to investigate the relationship between N₂O fluxes and porewater nitrogen and determine the relative importance of porewater NO₃^- and NH₄⁺ as key drivers of enhanced saltmarsh N₂O fluxes. Both porewater NO₃^- and NH₄⁺ were significantly, positively correlated with N₂O fluxes (p < 0.01), explaining 25 and 18% of the variation in fluxes, respectively. We estimate a global saltmarsh N₂O flux of 0.012 Tg N₂O yr^-1, which is six times higher than the current estimate (0.0021 Tg N₂O yr^-1), representing an offset of 19% of the estimated global saltmarsh carbon burial. Using predicted future increases in riverine DIN export, our meta-analysis suggests that 17-31% of the estimated global saltmarsh carbon burial could be offset by a surge in N₂O emissions under chronic mineral N pollution. This meta-analysis indicates the importance of reducing nutrient inputs into saltmarshes to reduce N₂O fluxes and maximise their negative radiative forcing.

How to cite: Collier-Woods, D., Ullah, S., and Comer-Warner, S.: Surges in global N2O fluxes from saltmarshes are driven by increasing porewater nitrate and ammonium concentrations, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5244, https://doi.org/10.5194/egusphere-egu24-5244, 2024.

For the agri-environmental monitoring of Switzerland, nitrogen balances on farm level for all Swiss farms were calculated and aggregated in order to obtain regionalized nitrogen balances. This monitoring attempts to incorporate as much existing data as possible to minimize multiple data collections from farmers. Data from the agricultural policy information system of Switzerland was used as basis for the calculation. This database contains information on livestock numbers, the crops grown, and the direct payments received for each farm. This information was supported with different data sources from federal offices, cantons, agricultural associations, and research institutions. Balances were calculated as a soil-surface balance according to the OECD method, which includes N input via organic and mineral fertilizers, biological N-fixation, atmospheric N-deposition, and seedlings as well as N outputs via plant yields.

The regional balances showed a high variability, resulting in an average N surplus of around 105 kg N per hectare of utilized agricultural area in cantons with highly intensive livestock farming and around 16 kg N in cantons with more extensive farming practices, i.e. in mountain regions. On national scale, highest N input occurred via organic fertilizers, whereas mineral fertilizers and biological N-fixation account for around 15% of the total input each.

Our approach of calculating N balances on farm level for the whole Swiss farming system has some limitations, which are mainly due to missing or incomplete data sources.  As an example, the use of mineral fertilizers had to be estimated by application data of a rather small sample of farms (~300 farms). Nevertheless, the obtained results show that this methodology is a promising tool to gain a regional overview of the environmental status of Swiss farms. Over the years, this approach will be refined and new data (e.g. additional administrative data, satellite data) can be incorporated in order to better estimate the N balances of Swiss farms.

How to cite: Gilgen, A., Baumgartner, S., Spiess, E., and Liebisch, F.: Regionalized nitrogen balances of Switzerland, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5701, https://doi.org/10.5194/egusphere-egu24-5701, 2024.

Nitrous oxide (N₂O) is one of the most important greenhouse gases with a global warming potential of about 298 times stronger than carbon dioxide (CO₂) over a period of 100 years. From 1800 to 2023, the atmospheric concentration of N₂O has increased from 273 to 336 ppbv, whereby more than half of this rise is due to the addition of fertilisers and manure on agricultural soils. Whilst these managed, nutrient-rich soils have been relatively well studied, little is known about N₂O fluxes in nutrient-poor ecosystems (e.g., the Arctic).

Since many Arctic soils contain very low amounts of available nitrogen, in the past it has been generally assumed that Arctic soils are not a significant source of N₂O. Only recently, several studies have reported significant N₂O emissions from organic-rich Arctic soils; however, due to methodological challenges, extensive investigations on N₂O fluxes in Arctic soils have been limited. As a result, the importance of N₂O fluxes from this region to the global budget remains highly uncertain. 

With the recent advances in portable GHG analyser technology, extensive manual chamber measurements based on in-situ N₂O concentration measurements can provide novel information to close this knowledge gap. However, guidelines on measuring techniques (e.g., chamber closure time) and data quality (e.g., no flux vs. low flux) are still lacking. In this study, we provide new insights on N₂O fluxes in a nutrient-poor ecosystem and give general practical guidelines for measuring low N₂O fluxes with a portable gas analyser and manual chambers. In May, July, and September 2023, we used a portable N₂O/CO₂ analyser to measure N₂O fluxes in a thawing sub-Arctic permafrost peatland in northern Sweden. Recommendations on practical use in the field are given to support future N₂O research with portable gas analysers. 

How to cite: Triches, N. Y., Marushchak, M., Virkkala, A., Vesala, T., Heimann, M., and Göckede, M.: Advances in measuring low N2O fluxes by a portable gas analyser and manual chambers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5728, https://doi.org/10.5194/egusphere-egu24-5728, 2024.

It has been recognized recently that trees can assimilate NO₂ directly through leaf stomata. Both laboratory and field studies have measured the foliar NO₂ deposition velocity, which could be determined by some environmental factors, e.g. light irradiation intensity, ambient NO₂ concentration, and leaf characteristics. However, the NO₂ uptake capacity and allocation of foliar uptake NO₂ under these environmental factors remain unclear. To clearly understand the foliar NO₂ uptake process and refine the forest NO₂ uptake models, we conducted a dynamic ¹⁵NO₂ fumigation experiment.

We selected Fraxinus mandshurica (F. mandshurica), Pinus koraiensis (P. konraiensis), Quercus mongolica (Q. mongolica), and Larix gmenilii (L. gmenilii) saplings, four dominant tree species in temperate forests of northeastern China, as our experimental materials. Meanwhile, we chose a pair of broad-leaved and coniferous tree species (F. mandshurica and P. konraiensis) to perform fumigation experiment under dark/light irradiation and another pair (Q. mongolica and L. gmenilii) to perform fumigation experiment with soil N addition. All saplings were dynamically fumigated with 50 ppb ¹⁵NO₂ for 8 h and destructively sampled immediately after fumigation. We rinsed the samples surface with purified water, dried and grinded all samples, then measured the ¹⁵N abundance in leaves, twigs, stems and roots with EA-IRMS.

The results showed that tree saplings can absorb NO₂ under both dark and light irradiation treatments. The total ¹⁵N recovery ranged between 30 to 80% under the light condition in all species. Under the dark condition, the total ¹⁵N recovery were (29.8±9.16) % and (1.1±0.47) % for F. mandshurica and P. konraiensis, which were significantly lower than under the light condition, (59.6±5.2) % and (8.8±2.5) %, respectively. With the soil N addition, the total ¹⁵N recovery in Q. mongolica ((56.2±8.8) %) were significantly larger than non-N addition ((27.6± 4.8) %), while L. gmenilii showed the opposite result that the total ¹⁵N recovery ((31.7±7.8) %) significantly decreased, compared to that without N addition ((73.6±4.3) %). These results are likely attributed to different amount of N demand for different tree species, more N needed for Q. mongolica than L. gmenilii. Moreover, coniferous species could assimilate more N through foliar uptake than broad-leaved species, probably due to bigger leaf surface areas of coniferous trees. After 8 h fumigation, the largest proportion of ¹⁵NO₂ was recovered in leaves in all species and treatments, accounting for 60-97%, which indicates that NO₂ stays in leaves in a short-term period after foliar assimilation. However, further studies are needed to explore the transformation of foliar incorporated NO₂ to other organs in a long-term scale.

This study quantified the foliar NO₂ uptake capacity of different tree species and figured out the effects of light irradiation and soil nitrogen availability on foliar NO₂ uptake. Our results would provide references for the model estimation of canopy NO₂ uptake magnitude at a regional scale.

How to cite: Yao, M. and Kang, R.: 2152, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5816, https://doi.org/10.5194/egusphere-egu24-5816, 2024.

Chinese agriculture has long been characterized by low nitrogen use efficiency (NUE) associated with substantial ammonia (NH₃) loss, which contributes significantly to fine particulate matter (PM_2.5) pollution. However, the knowledge gaps in the spatiotemporal patterns of NH₃ emissions and the states of nitrogen management of agricultural systems render it challenging to evaluate the effectiveness of different mitigation strategies and policies. Here we explored the NH₃ mitigation potential of various strategies and its subsequent effects on PM_2.5 pollution, and their effectiveness in improving NUE of Chinese agricultural systems. We developed and used a nitrogen flow model for evaluating NUE of different crop and livestock types at a provincial scale in China. We then used the bottom-up NH₃ estimates to drive an air quality model (GEOS-Chem High Performance, GCHP) to provide an integrated assessment of four improved nitrogen management scenarios: improving NUE of crop systems (NUE-C), increasing organic fertilizer use (OUR), improving NUE of livestock systems (NUE-L) and combined measures (COMB). The total agricultural NH₃ emission of China was estimated to be 11.2 Tg NH₃ in 2017, of which 46.24% and 53.76% are attributable to fertilizer use and livestock animal waste, respectively, and emission hotspots can be identified in the North China Plain. Our results show that grain crops have higher NUE than fruits and vegetables, while high livestock NUE can be found in pork and poultry, and NUE for the entire crop and livestock systems are both better in Northeast China than the rest of China. We also found that agricultural NH₃ emissions can be reduced from 11.2 Tg to 9.1 Tg, 9.3 Tg, 9.9 Tg and 6.8 Tg, and consequently annual population-weighted PM_2.5 reductions are estimated to be 1.8 µg m^–3, 1.6 µg m^–3, 1.3 µg m^–3 and 4.1 µg m^–3 under NUE-C, OUR, NUE-L and COMB scenarios, respectively. Our results are expected to provide decision support policy making concerning agricultural NH₃ emissions.

How to cite: Luo, B. and Tai, A. P. K.: Improving Agricultural Nitrogen Use Efficiency to Reduce Air Pollution in China, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6942, https://doi.org/10.5194/egusphere-egu24-6942, 2024.

Nitrogen (N) plays an important role in mediating many aspects of permafrost carbon cycle, such as plant productivity, soil organic matter decomposition and the production of greenhouse gases. In contrast to the well-recognized effects of climate warming on soil organic carbon stocks and vulnerability, the fates and pools of soil N has received little attention in permafrost ecosystems.

Here, based on a decadal warming experiment in a permafrost ecosystem on the Tibetan Plateau, we assessed changes in soil N stocks over a 10-year time-scale, and in situ measured the majority of N-cycling processes involving biological N fixation and soil N transformation, and the preferential plant uptake of different N forms, and above- and belowground litter decomposition and N release, and N leaching losses as well as high-resolution nitrous oxide (N₂O) flux during the growing season.

Our results showed that experimental warming progressively reduced topsoil N stocks but had no effect in the deeper soils on a 10-year time-scale. The observed decline in topsoil N pools could be due to the fact that decadal warming enhanced plant N uptake and intensified N leaching and gaseous losses. Specifically, warming treatment had a negligible effect on ecosystem biological N fixation rate, but increased the above- and belowground plant N pools. Meanwhile, simulated warming accelerated belowground litter N release and soil N transformation rate, and enhanced plant uptake of organic N. However, warming intensified the topsoil inorganic N leaching losses and N₂O flux during the growing season.

These findings highlight that progressive N limitation could occur in permafrost ecosystems under continuous climate warming due to the re-allocation of N pool from soils to plants and the losses of N through leaching and gases flux, which would make the future trajectory of permafrost carbon cycle and its feedback to climate warming more complex than previously thought.

How to cite: Wei, B. and Yang, Y.: Progressive decline in topsoil nitrogen pool upon decadal warming in a permafrost ecosystem, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9564, https://doi.org/10.5194/egusphere-egu24-9564, 2024.

The joint project 'Measures to reduce direct and indirect climate-impacting emissions caused by denitrification in agricultural soils - MinDen' addresses the topics of reducing nitrous oxide emissions and improving nitrogen efficiency through modeling, the evaluation of possible mitigation measures and the evaluation of denitrification on spatial scale. Gaseous emissions from denitrification cause N losses relevant to crop cultivation and cause direct N₂O emissions from crop cultivation. Climate protection measures in crop production in the areas of fertilization, soil cultivation and crop rotation have hardly been researched with regard to the role of denitrification. Crop management that optimizes N efficiency and minimizes N emissions at the same time has therefore not yet been reliably defined. The overall objective of the present project is to identify practicable crop management measures to minimize N₂ and N₂O emissions from denitrification for arable cropping systems in Germany by improving the knowledge on denitrification-related N losses through field and laboratory studies and using it for parameterization, validation and application of simulation models. Our objectives are as follows:

• Regionalization of N losses due to denitrification in Germany based on existing models
• Determination of the effect of crop protection measures on N₂ and N₂O losses on field scale
• Testing of mitigation options on the model, laboratory and field scale, taking into account the topsoil and subsoil for different soils
• Further development of denitrification models to improve the mapping of mitigation measures using existing and new field data
• Testing of mitigation options for Germany using the improved models, taking into account yield, economic efficiency, technology requirements, N₂O emissions, N efficiency, fertilizer requirements, NH₃ emissions and nitrate leaching.

We provide an overview of the approach and the current status of the joint project, which started at the beginning of 2023.

How to cite: Stenfert Kroese, J., Buchen-Tschiskale, C., Cordes, J., Dechow, R., Dittert, K., Dix, B., Fuchs, K., Gattinger, A., Greef, J.-M., Grosz, B., Hauschild, M., Mahboube, J., Kühne, J., Mielenz, H., Potthoff, T., Scheer, C., Schulz, F., Simpson, C., Wolf, B., and Well, R.: Mitigation measures of crop cultivation to reduce climate-impacting emissions from denitrification, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10360, https://doi.org/10.5194/egusphere-egu24-10360, 2024.

Title: Drought and eCO₂ Effects on Oak Seedlings Growth, Soil Fertility, and Greenhouse Gases Fluxes

Authors: Rehab Al Mutairi, Nicholas Kettridge and Sami Ullah

Objective/Purpose:

This study explores the impact of water stress legacy and elevated CO₂ on oak seedlings' growth, stomatal conductance, soil nutrient availability, and greenhouse gas (GHGs) fluxes. The research aims to unravel the intricate interplay of these factors under controlled glasshouse conditions.

Methods/Approach:

The experiment, conducted from mid-May to August 2023 at the University of Birmingham campus, involved oak seedlings grown under ambient CO₂ and elevated CO₂ chambers, subjected to two soil volumetric moisture levels (10% for drought, 30% for non-drought). Various parameters, including oak growth, stomatal conductance, soil nutrient availability, and GHGs flux, were measured and recorded throughout the three-month period. Additional analyses, including biomass, soil extracellular enzyme activities, microbial biomass of N and C, and net N mineralization, were conducted at the experiment's conclusion.

Key Findings/Results:

The study revealed compelling insights into the response of oak seedlings to drought stress and elevated CO₂ conditions. Under drought scenarios, both under ambient and elevated CO₂  environments, oak biomass and growth were notably diminished. Particularly, the roots exhibited a substantial increase in biomass, suggesting a coping strategy in search of water and nutrient resources of the seedlings. Stomatal conductance exhibited a decline under elevated carbon dioxide (eCO₂), indicating a water-saving mechanism employed by plants. Additionally, extracellular enzyme activities were impacted by environmental conditions: a reduction was observed under drought stress. This reduction in enzyme functions aligns with a concurrent decrease in nutrient availability, highlighting a correlation between nutrient levels and enzyme activity reduction during drought conditions.

Conclusion/Implications:

The findings underscore the vulnerability of oak seedlings to drought stress, highlighting the importance of soil moisture management for their optimal growth. Additionally, the differential response between ambient and elevated CO₂  levels emphasizes the need for nuanced considerations in future climate change scenarios. These insights contribute to our understanding of ecosystem responses to concurrent drought and elevated CO₂ conditions.

Keywords:

Oak seedlings, Drought stress, Elevated CO₂, Soil fertility, Greenhouse gas fluxes, Stomatal conductance, Biomass, Microbial biomass, Net N mineralization.

How to cite: Almutairi, R.: Drought and eCO2 Effects on Oak Seedlings Growth, Soil Fertility, and Greenhouse Gases Fluxes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11614, https://doi.org/10.5194/egusphere-egu24-11614, 2024.

The biogeochemical nitrogen (N) cycle in South Africa is influenced by, and in turn influences a number of crucially important global change processes. However, the natural N cycling in South Africa is not well-understood. The “Emissions, deposition, impacts - Interdisciplinary study of N biogeochemical cycling (EDI-SA)” project is working to improve our baseline understanding of the natural biogeochemical cycling of N in non-industrialized ecosystems across South Africa. This includes quantifying N fluxes from emissions through to deposition, identifying linkages between N cycling and related species such as sulphur (S) and ozone, and evaluating ecosystem impacts. Previous work has focused on the impact of atmospheric deposition of N and S species on ecosystems at sites almost exclusively on the industrialized Highveld. This has left large gaps of knowledge in the biogeochemical cycling and ecosystem impacts, particularly within the diverse natural ecosystems found across South Africa. In order to address this gap, EDI-SA is applying a more holistic approach using measurements (from two South African Research Infrastructures; EFTEON and BIOGRIP) and modelling to investigate multiple linkages within the biogeochemical cycling of N with a focus on improving the understanding of the natural cycling. The project is applying a variable resolution sampling approach to investigate processes which occur at multiple spatial scales, and applying multiple measurement techniques including atmospheric measurements, stable isotope analysis of aerosol particles, rainwater and soil, and analysis of soil chemistry and biology. This contribution will detail the approach of this interdisciplinary project, highlight results from the first soil and air sampling campaigns, as well as the atmospheric composition modelling that assesses the relative importance and impacts of N emissions from soil across South Africa. This baseline understanding will allow future research to assess the potential changes to N biogeochemical cycling into the future in a changing climate.  

How to cite: Garland, R. M., Naidoo, M., Altieri, K., Dlamini, P., Feig, G., Jaars, K., Sekhohola, L., van Zyl, P., Muthelo, N., Leroko, J., Sakwe, P., Hamilton, T., van Niekerk, T., Bixirao Neto Marinho, P., and Smart, K.: Examining the natural nitrogen biogeochemical cycling and impacts across South African ecosystems, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12116, https://doi.org/10.5194/egusphere-egu24-12116, 2024.

Nitrogen is a fundamental plant nutrient and the most important fertilizer in modern agriculture. At the same time nitrate based nitrogen loss from agroecosystems becomes an increasing environmental problem in ground- and surface waters. The lysimeter station Brandis in Saxony, Germany, provides detailed observations of water and solute fluxes under representative agricultural landuse since 1981. Despite substantial efforts and success in regulation and assessment of fertilizer needs and the reduction of fertilization excess, the seepage water analysis reveals increasing or stagnating levels of nitrate concentration in groundwater recharge in a broad range of soil types. This apparent decoupling between input and output is evident in all soil types under investigation and raises some important questions concerning the nitrate loss in agricultural soils:

• Which part of the soil N-cycle contributes to the seepage water nitrate export?
• What are the main drivers of nitrate loss in agricultural soils?
• Can residence times of mineral fertilizer nitrogen be estimated?
• Will reduced fertilization excess lead to timely reductions in nitrate loss to the groundwater?

We investigated these questions with long-term solute balances and state-of-the-art isotope methods. Analysis of source δ ¹⁵N ratios in soil, atmospheric deposition and fertilizer in combination with a 5-year campaign of δ¹⁵N and δ¹⁸O analysis of seepage water nitrate allows a source identification with dual-isotope plots and mixing models. The results clearly show that the main source of nitrate loss with the seepage water is the soil organic matter pool in all investigated soils. Analysis of the long-term nitrogen balances and the soil samples show furthermore a substantial accumulation of fertilization excess within the upper meter of agricultural soils and indicate that the residence time of nitrogen in the lysimeters might be substantially longer than water residence times. Isotope analysis in combination with mixing model analysis suggest that the nitrate loss is mainly driven by nitrification of this nitrogen legacy in the post-harvest period. Thus, the results hold an explanation why the current regulation efforts have not yet led to the desired reductions in nitrogen loadings of seepage water fluxes. Furthermore, the apparent decoupling between nitrogen input in agricultural soils and the seepage water output makes a timely reduction of nitrate concentrations, by reductions in fertilization excess alone, in groundwater recharge unlikely.

How to cite: Werisch, S., Alexandra, T., and Diana, B.: Insights into nitrogen dynamics and nitrate loss from agricultural soils based on long-term lysimeter observations and a 5-year isotope measurement campaign, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12647, https://doi.org/10.5194/egusphere-egu24-12647, 2024.

Representing plant-microbe-soil organic matter interactions and their coupling with land surface processes are critical to understanding of ecosystem responses to climate change. More specifically, microbes play an important role in the nitrogen (N) cycle by providing acquisition pathways for plants and overcoming N limitation through mycorrhizal symbiosis and bacterial fixation. Even though biological nitrogen fixation acts as a primary N source for the organisms, ecosystem N availability is still strongly affected by N losses, including atmospheric volatilization.

One of the major challenges to accurately representing N availability in Earth System Models (ESM) is the representation of the atmospheric losses that are not necessarily controlled by the organisms. For instance, the conversion of soil ammonium into gaseous ammonia (i.e., volatilization) is driven by ambient environmental conditions and not directly controlled by the biological demand of plants and soil microbes. Thus, rapid losses of N via volatilization (e.g., after precipitation events) could induce feedback on soil microbial activity and plant growth by impeding biological assimilation.

Even though the representation of ammonia emissions is progressively integrated into ESMs, the focus has been mainly on parameterizing losses from agricultural or managed ecosystems. However, ammonia volatilization from natural soils occurs worldwide and can reach 9 TgN/yr, a non-negligible source, especially in alkaline drylands. Up to now, no proper representation of emissions of ammonia, applicable to unmanaged lands, has been included in ESMs and challenged by observations. In the future, these emissions are likely to follow the rising trends of nitrogen deposition and increasing precipitation due to climate change.

Here we describe a mechanistic parameterization of ammonia emissions in natural ecosystems with explicit treatment of microbes and vegetation dynamics in the fully integrated terrestrial component of the GFDL ESM, LM4.2-GIMICS-N. We apply observational constraints, including measurements of soil 15N isotope and estimates of nitrogen fluxes (BNF, nitrification, mineralization, and ammonia exchange) at different sites to reduce uncertainty in the model simulations. Finally, we examine the main drivers of ammonia volatilization across various ecosystems by considering aridity, soil pH, and nitrogen deposition as well as the key environmental conditions such as precipitation, temperature, and soil moisture.

How to cite: Beaudor, M., Shevliakova, E., Malyshev, S., and Lee, M.: Resolving nitrogen gaseous pathways in the atmosphere-plant-microbial-soil continuum in the NOAA/GFDL Earth System Modeling Framework, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13239, https://doi.org/10.5194/egusphere-egu24-13239, 2024.

Microbial N₂-fixation helps to sustain carbon accumulation in pristine peatlands and to remove CO₂ from the atmosphere. Recent work has provided evidence that this energetically costly process is not completely downregulated at sites with higher availability of reactive nitrogen (N_r). We studied nitrogen (N) cycling at three high-elevation, mainly rain-fed, Sphagnum-dominated peat bogs in the northern Czech Republic receiving medium to high amounts of reactive nitrogen (N_r) via atmospheric deposition. ¹⁵N/¹⁴N isotope ratios were determined in N_r deposition, along vertical peat profiles, and in a laboratory incubation study using fresh Sphagnum and ¹⁵N-enriched atmospheric N₂. Our objective was to assess the potential for biological N₂-fixation at the selected study sites in light of various biogeochemical parameters. Historically, all the peat bogs experienced similar changes in atmospheric N_r (mainly NO₃^--N and NH₄-N) inputs. N_r depositions at all three sites peaked between 1980 and 1990. During that time period, the highest annual depositions were close to 10 kg ha^-1 yr^-1 at the slightly more polluted site Uhlirska (UHL) than at Male mechove jezirko (MMJ) and Brumiste (BRU). Since ca. 1990, atmospheric deposition of N_r has been steadily decreasing. Living Sphagnum had variable N concentrations with similar means for all three sites (1.1, 1.0 and 0.9 wt. % at MMJ, BRU and UHL, respectively). Downcore, peat density remained nearly constant at MMJ but increased at BRU and UHL. Ash contents were below 10 wt. % at least to the depth of 20 cm. With an increasing peat depth, both N concentration and δ¹⁵N values generally increased, while C/N ratios tended to decrease. At depths > 10 cm, N/P ratio was lower at UHL than at the other two sites and remained nearly constant downcore. N/P ratio at MMJ increased from ~10 to ~20 with an increasing depth, whereas the N/P ratio exhibited a zigzag vertical pattern at BRU, reaching a value of 40 in deeper segments. The potential for biological N₂-fixation was investigated using a replicated laboratory incubation of fresh Sphagnum in a closed system following an application of 98 % enriched atmospheric N₂. The experiment lasted for 7 days. The control Sphagnum samples had δ¹⁵N values of -4.0 ‰ (BRU and UHL) and -3.7 ‰ (MMJ). At the end of the incubation, the δ¹⁵N significantly increased only in MMJ moss reaching + 70 ‰, while it remained unchanged in BRU and UHL moss. Biological N₂ fixation was thus recorded at only at MMJ, a site with the lowest N/P ratio in the topmost 2-cm thick sections. Potential N₂ fixation rates at MMJ were similar to values previously reported for Finland (Leppänen et al. 2015) but ~7 times lower than at sites located in Patagonia, Chile (Knorr et al. 2016).

References

Leppänen et al., 2015. Plant and Soil, 389, 185-196.

Knorr et al., 2016, Global Change Biology 21, 2357–2365.

How to cite: Stepanova, M., Novak, M., Cejkova, B., Buzek, F., Jackova, I., Prechova, E., Veselovsky, F., and Curik, J.: A Sphagnum incubation study using 15N-labelled atmospheric N2 reveals contrasting potential for biological N2 fixation at three medium-polluted Central European peat bogs, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15243, https://doi.org/10.5194/egusphere-egu24-15243, 2024.

Climate warming was shown to strongly affect the biogeochemical cycles in global forests, reducing soil carbon storage and accelerating soil nitrogen (N) and phosphorus cycling. In a long-term soil warming experiment in a temperate old-growth forest in Achenkirch, Austria, we recently showed faster root turnover and growth, decreases in microbial biomass, carbon use efficiency and soil carbon storage, increases in ecosystem phosphorus limitation, and varied responses of the soil N cycle in warmed plots (+4 ° C above ambient for 14 years). In this study we therefore employed natural stable isotope techniques to better understand ecosystem-level responses of the N cycle in Achenkirch, studying the abundance of ¹⁵N and ¹⁴N (expressed as δ¹⁵N values) in a wide range of soil nitrogen pools (bulk soil N, root N, microbial biomass N, extractable organic N, ammonium, nitrate) and employed isotope fractionation models to explain the patterns found dependent on soil warming. Specific N cycle processes such as mineralization, nitrification and denitrification cause substantial isotope fractionation (against the heavy stable isotope ¹⁵N), leading to ¹⁵N enrichment of the residual substrates and ¹⁵N depletion of the cumulative products, depending on the fraction on substrates consumed and the isotope fractionation factor of that process. Other processes such as diffusion, (de)sorption and depolymerization exert negligible isotope fractionation. We found a significant warming effect on the isotopic signatures of root N and the soil ammoniumpool, i.e. a ¹⁵N enrichment in these pools. ¹⁵N enrichment of tree fine roots, considered to be isotopic integrators of the plant available N pool, suggest increased soil N cycling and greater soil N losses in warmed plots causing a ¹⁵N enrichment of the soil inorganic N pool (ammonium and nitrate). The increased ¹⁵N enrichment in ammonium of warmed soils highlights an increased activity of nitrifiers, with greater fractions of ammonium oxidized to nitrate causing the observed ¹⁵N enrichment of ammonium. However, soil nitrate did not show the expected ¹⁵N depletion imparted by nitrifiers but matched or even exceeded δ¹⁵N values of soil ammonium. Isotope fractionation calculations indicated that >50% of the soil nitrate produced was lost, particularly through denitrification promoting gaseous N losses in the form of NO, N₂O and/or N₂ and less through nitrate leaching. Natural ¹⁵N abundance studies thereby hold great potential for evaluating the status quo of the complex N cycle in terrestrial ecosystems and to monitor in situ responses to climate change with minimal invasion and improved time integration.

How to cite: Wanek, W., Bachmann, M., Tian, Y., Kwatcho Kengdo, S., Heinzle, J., Inselsbacher, E., Borken, W., and Schindlbacher, A.: Long-term soil warming causes acceleration of soil nitrogen losses in a temperate forest studied by 15N isotope fractionation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15470, https://doi.org/10.5194/egusphere-egu24-15470, 2024.

Denitrification is a major component of the nitrogen cycle in soil that returns reactive nitrogen to the atmosphere. Denitrification activity is often concentrated spatially in anoxic microsites and temporally in ephemeral events, which presents a challenge for modelling. The anaerobic fraction of soil volume can be a useful predictor of denitrification in soils. Here, we provide a review of this soil characteristic, its controlling factors and its estimation from basic soil properties.

The concept of the anaerobic soil volume and its link to denitrification activity has undergone several paradigm shifts that came along with the advent of new oxygen and microstructure mapping techniques. The current understanding is that hotspots of denitrification activity are partially decoupled from air distances in the wet soil matrix and are mainly associated with particulate organic matter (POM) in the form of fresh plant residues or manure. POM fragments harbor large amounts of labile carbon that fuels local oxygen consumption and, as a result, these microsites differ in their aeration status from the surrounding soil matrix.

Current denitrification models link the anaerobic soil volume fraction to bulk oxygen concentration in different ways but take almost no account of microstructure information, such as the distance between POM and air-filled pores. Based on meta-analyses, we derive new empirical relationships to estimate conditions for the formation of anoxia at the microscale from basic soil properties and we outline how these empirical relationships could be used in the future to improve prediction accuracy of denitrification models at the soil profile scale.

How to cite: Schlüter, S., Lucas, M., Grosz, B., Ippisch, O., Zawallich, J., He, H., Dechow, R., Kraus, D., Blagodatsky, S., Senbeyram, M., Kravchenko, A., Vogel, H.-J., and Well, R.: The anaerobic soil volume as a controlling factor of denitrification , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15569, https://doi.org/10.5194/egusphere-egu24-15569, 2024.

Direct emission of the greenhouse gases methane and nitrous oxide (N₂O) constitute a significant fraction of the overall carbon footprint of wastewater treatment. Measurement methods to identify emission sources and to quantify emissions are key in mitigating these direct emissions. Nitrous oxide is formed in biological nitrogen removal process units, which are the main source of N₂O emission from wastewater treatment.

Liquid phase sensors (LPS) have recently been developed and installed at various Danish wastewater treatment plants to measure N₂O concentrations in the liquid phase of biological nitrogen removal tanks. These sensors can be used to implement adjustments on the operation of the plant (for example duration of aeration), which affects N₂O emission. In addition, LPS can be utilized to calculate N₂O emission through mass transfer modelling. However, there is a need for validation of liquid-based modelled emission rates against measurement methods, which measure direct N₂O emission rates. In this study, emission rates determined by two remote sensing methods, the tracer gas dispersion method (TDM) and Eddy covariance method (EC) were compared to LPS derived N₂O emission rates.

TDM relies on continuous, controlled release of a gaseous tracer at the source combined with downwind measurements of concentration of target gas (N₂O here) and tracer gas (often acetylene - C₂H₂).  This method is well-established, validated, and has been used to quantify fugitive emissions from various sources such as landfills, composting plants, biogas plants, etc. EC is a stationary method, which relies on high-frequency measurements of N₂O concentration and wind vector on a tower near the source. EC can be set up for continuous monitoring, while TDM as applied here is a discrete measurement method.

In the study, N₂O emission rates were measured over a period of 1.5 years at a relatively large wastewater treatment plant in the greater Copenhagen area. TDM measurements were conducted on 15 measurement days covering both periods of relatively high and low N₂O emission rates. TDM measurements were compared to LPS derived emission rates, where N₂O emission was measured using sensors in four of eight process units for biological nitrogen removal. Overall, daily average emission rates between approximately 0.38 and 13.4 kg N₂O h^-1 were measured. High emission rates of 120 kg N₂O h^-1 were observed on a day, where plant maintenance is believed to be the cause of unusual high emission. Emission rates from simultaneous TDM measurements and LPS derived values (n=43) showed good correlation (R²=0.70). On average, emission rates from TDM were 35% higher than LPS rates. The model implementation to derive LPS determined emission rates was further developed during the study, and the listed results were the final values after some correction. Several factors can explain the difference – including liquid sensor drift, which for the specific sensors tends towards lower N₂O concentration readings than actual concentrations. Continuous EC measurements showed the same emission dynamics as measured by the liquid sensors located inside the footprint of the station.

How to cite: Fredenslund, A., Kissas, K., and Scheutz, C.: Comparison of liquid phase and remote sensing measurements of nitrous oxide emission from biological nitrogen removal at a wastewater treatment facility, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16147, https://doi.org/10.5194/egusphere-egu24-16147, 2024.

Nitrate in groundwater can be converted microbially into N₂. However, the lack of anoxic conditions (oxygen concentrations < 50 μmol/L) in the aquifer linked with the limitation of microbial available organic and inorganic electron donors may lead to insufficient denitrification in aquifers and nitrate concentration above the drinking water limit of 50 mg/L can be observed. In view of the increasing drinking-water scarcity associated with climate change and the continuing increase in nitrate concentrations in near-surface aquifers, it is urgently necessary and prudent to develop practicable and cost-effective methods to reduce nitrate to harmless N₂.
Faced with the increasing nitrate pollution in groundwater, we want to develop a new cost-effective in-situ remediation technology by hydrogen/methane coupled denitrification. We hypothesize that the simultaneous injection of the two water soluble electron donors H₂ and CH₄ into groundwater may significantly enhance the rate of nitrate consumption by activation of denitrifying chemolithoautotrophic microorganisms that are already present in the groundwater.
Here we show the experimental set-up of the 2D-model aquifer (6 m x 1,8 m), the sampling strategy and show first results of the methane injection experiment. Measurements are performed along the flow direction and at several depths. Concentration profiles and stable isotope composition of methane (δ¹³C) and nitrate (δ¹⁵N) linked with oxygen concentrations shed light on the hydrogen-methane coupled denitrification potential in the model aquifer.

How to cite: Seeholzer, A. S., Wunderlich, A., Steib, R., and Einsiedl, F.: In-situ treatment of nitrate polluted groundwater by chemoautotrophic denitrification: flow-through tank experiments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16927, https://doi.org/10.5194/egusphere-egu24-16927, 2024.

Fluxes and chemical composition of precipitation is substantially changed after passing through tree canopies, particularly in the case of atmospheric nitrogen compounds, with important implications on forest nitrogen cycling. The causes of these changes, however, have mostly focused on the passive role of foliar surfaces to scavenge pollutants from the atmosphere and to ion exchange processes, while biological processes involving microbes hidden in the phyllosphere have been less investigated. We combined triple oxygen isotopes approach and molecular analyses with the aim of quantifying canopy nitrification and identify microbes responsible for it, respectively. Ten sites included in the European ICP Forests monitoring network, chosen along climate and nitrogen deposition gradients, were selected to include the two most dominant tree species in Europe (Fagus sylvatica L. and Pinus sylvestris L.). Specifically, in this study we: 1) estimated the relative contribution of nitrate derived from biological canopy nitrification vs. atmospheric deposition by using δ¹⁸O and Δ¹⁷O of nitrate collected in water samples, i.e., in the open field (bulk deposition) and underneath tree canopies (throughfall); 2) quantified the functional genes related to nitrification for the two dominant tree species in European forests by using next-generation sequence analyses. Based on the isotope approach, we found that up to 80% of the nitrate reaching the soil via throughfall derived from biological transformations in the phyllosphere, equivalent to a flux of gross canopy nitrification of up to 5.76 kg N ha^-1 y^-1. The fraction of microbiologically derived nitrate increased with raising nitrogen deposition, thus suggesting that the process can be substrate limited. Molecular analyses confirmed the presence on foliar surfaces of bacterial and archaeal autotrophic ammonia oxidisers and bacterial autotrophic nitrite oxidisers across the investigate European forests. Our study demonstrates the potential of integrating stable isotopes with molecular analyses to advance our understanding on key processes underpinning forest nitrogen cycling, which should no longer exclude microbial processes occurring in the phyllosphere.

How to cite: Guerrieri, R., Joan, J., Mattana, S., Casamayor, E., Peñuelas, J., and Mencuccini, M. and the Collaborators at the ICP Forests sites: Quantifying tree canopy nitrification across European forests, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17028, https://doi.org/10.5194/egusphere-egu24-17028, 2024.

Under the framework of Circular Economy, EU Green Deal, and UN Sustainable Development Goals the addition of organic amendments to agricultural soils is highly promoted as a cost-efficient solution to improve soil quality and agrosystem sustainability. Nonetheless, their agronomic use comes with an uncertainty of their potential to release ample plant-available N, and to emit soil greenhouse gases.

This mesocosm study investigated short-term (90 d) soil N dynamics of a loamy soil receiving four organic amendments (50 t ha^-1) (i) cow manure compost (CMC), (ii) food waste compost (FWC), (iii) used digestate substrate (UDS) and (iv) municipal sewage sludge (MSS), without and with N fertilization (160 kg N ha^-1; urea). An unamended soil mesocosm was included as a control (C). During the incubation soil NO₂-, NO₃-, NH₄+, N₂O and CO₂ were regularly monitored.

During the incubation, org. amendments did not affect NH₄⁺ availability (AUC) compared to unamended soil, except MSS treatment which had 5.7x more NH₄⁺ than C. The co-application of urea increased available NH₄⁺ by 2.9x, 4.1x, 4.4x, 4.6x, and 5.9x for MSS, UDS, CMC, FWC, and C, respectively. There was no difference in available NO₂^- among org. amendment treatments and the C, except MSS (2.4x). There was a substantial and temporal accumulation of NO₂^- (2.4x to 3.6x) when urea was co-applied with org. amendments. Co-application of urea with org. amendments increased AUC NO₃- in all treatments ranging to 2.7x from 13.6x, except MSS. Considering cum. CO₂ we did not observe any differences between org. amended treatments without and with urea. However, org. amendments increased cum. N₂O emission by 1.4x, 1.6x, and 3x, for UDS, FWC, and MSS, and reduced by 0.6x for CMC relative to C, respectively. The co-application of urea increased cum. N₂O emissions for MSS, UDS, and CMC by 6%, 65%, and 90%, respectively, and reduced by 58% for FWC, compared to the corresponding org. treatment without urea.

Interestingly, co-application of urea with org. amendments reduced N₂O emission factor (EF) by 4x, 6x, 6x, and 9x, relative to org. amendments without urea, for CMC, MSS, UDS and FWC, respectively. However, the EF N₂O exceeded 1% in most cases. Treatments with urea lost substantial amounts of org. C as CO₂-equivalent emissions, for instance, UDS+U and MSS+U lost 22% and 68%, respectively.  

In conclusion, our preliminary results indicate that the co-application of org. amendments with urea-N could potentially fuel soil N₂O emissions, thus offsetting any favorable aspects of the aforementioned policies. Org. amendment, urea-N, and their interaction were significant factors (p≤0.05) driving CO₂ and N₂O emissions. The quality and composition of the amendments may stimulate soil microbial N transformations, and further investigation will elucidate the intrinsic role of soil microbes and their dynamics in regulating CO₂ and N₂O emissions from soils.

The research project was supported by the Hellenic Foundation for Research and Innovation (H.F.R.I.) under the “2nd Call for H.F.R.I. Research Projects to support Post-Doctoral Researchers”; Project #01053 awarded to P.I. Dr Georgios Giannopoulos. This project was co-implemented with industrial partner Corteva Agriscience Hellas SA.     

How to cite: Giannopoulos, G., Pasvadoglou, E., Kourtidis, G., Elsgaard, L., Zanakis, G., and Anastopoulos, I.: Co-application of organic amendments and urea-N in a loamy soil reduced the N2O emission factor but substantial amounts of organic C were lost as CO2., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17096, https://doi.org/10.5194/egusphere-egu24-17096, 2024.

Boreal forests play an important role in the global carbon (C) cycle, and their productivity is strongly limited by nitrogen availability.  Thus, understanding whether nitrogen availability in boreal forests is changing has important implications for understanding past, present, and future trends of forest growth. We utilized a unique archive of tree cores collected by the Swedish National Forest Inventory, to evaluate temporal patterns (1950-2017) of wood δ¹⁵N, which is commonly used as an indicator of N limitation. First, we focused on an area of ca. 55,000 sq. km in central Sweden to evaluate how sensitive the wood δ¹⁵N approach is to tree age and two alternative sampling methodologies: a) analysis of single trees sampled in the present, versus b) tree chronologies constructed from multiple trees of the same age sampled during different decades.  By analysing 1038 woods samples, and covering two key boreal tree species (Picea abies and Pinus sylvestris), we found strong trends of declining δ¹⁵N through time, suggestive of progressive N limitation.  We further found that temporal patterns were highly sensitive to method choice, where the multiple tree approach supported by the tree core archive showed much stronger temporal patterns than reliance on more conventional contemporary sampling approaches, where N mobility appeared to obscure temporal patterns.  We further found that temporal trends were relatively insensitive to tree age class. Using the more powerful Multiple Tree Approach, we further evaluated δ¹⁵N values from an additional 1000 P. abies and P. sylvestris wood samples covering the entire forested area of Sweden and spanning the same time period, to investigate how temporal patterns in wood δ¹⁵N varied in areas with historically high N deposition (Southern Sweden) versus low N deposition (Northern Sweden).  These data help address current debates regarding whether temporal patterns in δ¹⁵N are indicative of oligitrophication (i.e. progressive N limitation), or are instead the result of changing δ¹⁵N signatures from nitrogen deposition inputs.  

How to cite: Gundale, M., Bassett, K., Östlund, L., Fridman, J., Perakis, S., and Jämtgård, S.: Evaluating temporal patterns in wood δ15N in Swedish forests as an indicator of changing N limitation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17469, https://doi.org/10.5194/egusphere-egu24-17469, 2024.

The effect of nano fertilizers on Wheat vegetative characters

Thanawan Buacharoen¹, Yafei Guo¹, Eugenia Valsami-Jones^1*, and Sami Ullah¹

*Authors to whom correspondence should be addressed.

¹School of Geography, Earth and Environmental Science, College of Life and Environmental Sciences, University of Birmingham, Birmingham B15 2TT, UK

Wheat is the primary staple cereal in the world. It was the highest cultivation in 2018. According to the British Survey of Fertilizer Practice, total nitrogen use in Great Britain was reduced between 2021 and 2022. At the same time, the total phosphate did not change. Meanwhile, the usage of the total potash has increased compared to last year.  
Conventional fertilizer, which consists of nitrogen, phosphorous, and potassium nutrients, will release Greenhouse gas emissions. The other option to solve this problem is the nano fertilizer. Plants can easily absorb a tiny particle of nano fertilizer, reducing greenhouse gas emissions into the air. Therefore, this study focused on nano fertilizers' effect on plant growth. 

The first set of 30-day-old wheat plants was treated with amorphous calcium phosphate (nano - ACP), a potassium-bearing variant of the ACP (nano ACP - NPK) and a urea and potassium-bearing variant of the ACP (nano - UNPK). Moreover, three conventional fertilizers, which have the same nutrient quantity as same as nano fertilizers, were applied to the second set of plants to be a positive control. On the other hand, blank treatment was used to be a negative control. After harvesting the wheat plants, the shoot length and fresh weight were measured. Also, the ammonium concentration in the soil was examined with the colorimetric method. Maximum root weight was found in the wheat treated with nano–ACP (Average± SD. = 0.39±0.20). The nano ACP - NPK gave the highest value of shoot weight (Average ± SD. = 0.9 ± 0.10), number of seeds (84 seeds) and shoot length (Average ±SD.= 63.33 ± 4.29). However, the maximum ammonium concentration was found in the soil treated with nano ACP. All treatments' seed weight and shoot length differ at the P – value of less than 0.5. Our finding suggests that the nano fertilizers had enhanced vegetative characteristics compared with the conventional fertilizers.

Key word; amorphous calcium phosphate (nano - ACP), potassium-bearing variant of the ACP (nano ACP - NPK) and urea and potassium-bearing variant of the ACP (nano - UNPK)        

How to cite: Buacharoen, T., Guo, Y., Valsami - Jones, E., and Ullah, S.: The effect of nano fertilizers on wheat vegetative characters, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17865, https://doi.org/10.5194/egusphere-egu24-17865, 2024.

Intensively managed pasture systems receive large inputs of nitrogen (N) in the form of fertiliser and through the  deposition of ruminant urine, creating hot-spots for denitrification which results in variable amounts of nitrous oxide (N₂O) and dinitrogen (N₂) emitted. Here we investigated the potential of increased  irrigation frequency to reduce N₂O and N₂ emissions from an intensively managed pasture in the subtropics after ruminant urine deposition. Irrigation volumes were estimated to replace evapotranspiration and were applied either once (Low-Frequency) or split into four applications (High-Frequency). This irrigation schedule was applied 3 times over the 60 day monitoring period, and fluxes of N₂O and N₂ were  measured using the ¹⁵N gas flux method. In line with farming practice, simulated urine patches (equivalent of 80 g N m^-2 applied) were also fertilised three times with 2 g urea N m^-2 to show the combined effects of urinary and fertiliser N on N₂O and N₂ emissions. Highest N₂O emissions of up to 60 mg N₂O-N m^-2 day^-1 were observed briefly after urine deposition, decreasing thereafter, resulting in cumulative N₂O losses of 169.9 mg N₂O-N m^-2 from the Low-Frequency treatment. Denitrification was dominated by N₂, accounting for more than 89% of  N₂O+N₂ emitted. Irrigation treatments had no effect on cumulative N₂ losses of more than 2700 mg N₂-N m^-2. However, High frequency irrigation reduced cumulative N₂O losses by 35%. Our findings suggest that under conditions of high N availability, increased irrigation frequency can reduce the environmental impact (N₂O) of denitrification, but not overall N losses via this pathway. The response of N₂O emissions may further indicate that less frequent, but more intense rainfall events will shift the product ratio of denitrification towards N₂O, increasing environmentally harmful N losses from intensively managed pasture systems.

How to cite: Friedl, J., De Rosa, D., Scheer, C., Fitzgerald, M., Grace, P. R., and Rowlings, D. W.: Increased irrigation frequency reduces N2O, but not overall denitrification losses (N2O+N2) from an intensively managed pasture following ruminant urine deposition and nitrogen fertilisation., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19499, https://doi.org/10.5194/egusphere-egu24-19499, 2024.

There is limited knowledge on the N (nitrogen) cycling in winter, on the role of organic matter quality on N cycling, and on the microbes involved.

We studied Lake Viinijärvi and Lake Höytiäinen, large boreal lakes in Finland, each lake with clear-water and brown-water sides. Viinijärvi has an additional side affected by mining activities in the catchment showing higher nitrate and sulphate levels. During winter of 2021 we sampled 5 sites at the beginning and at the end of the ice-covered period. Using the Isotope Pairing Technique we incubated sediment cores with ¹⁵NO₃^- and quantified the products of 1) complete denitrification (N₂), 2) truncated denitrification (nitrous oxide, N₂O), and 3) dissimilatory nitrate reduction to ammonium (DNRA, NH₄⁺) to infer the process rates. We characterized the DOM using FT-ICR MS. We explore the genetic potential (DNA) of the sediment microbiome by using several sequencing techniques.

During winter the sediment-water interface is an active compartment. The top sediment microbiome has heterotrophic bacteria with flexible metabolism, breaking-down OM during winter despite most of the DOM is recalcitrant. Impacts of browning and mining with major differences between sites. The genetic potential of the sediment microbiome indicates more DNRA and N2O consumption in clear-waters, while in the mining-impacted site and brown-water sites the dominant pathway depends on the sediment layer with truncated denitrification in top layer, and methanogenesis and N-fixation in sub-top layer. The N₂O production (d14), that fits the genetic potential, is highest in the mining-impacted site (35-43 µmol N/m²/d), followed by the brown-water sediments (6-11 µmol N/m²/d), with the lowest rates in the clear-water sediments (0-1 µmol N/m²/d).

How to cite: Palacin-Lizarbe, C., Bertilsson, S., Siljanen, H. J., Buck, M., Kolh, L., Paul, D., Maréchal, M., Nykänen, H., Liu, T., Kiljunen, M., Aalto, S. L., Rissanen, A. J., Biasi, C., Vainikka, A., and Pumpanen, J.: Browning and mining increase the nitrous oxide production in sediments of large boreal lakes during winter, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20301, https://doi.org/10.5194/egusphere-egu24-20301, 2024.

One of the most pressing issues in intensive agriculture is how we can reduce post-harvest losses of nitrogen (N) on agricultural land. In terms of N use efficiency, the focus so far has been on optimizing the amount and timing of N fertilization, including spatially targeted application (precision agriculture). However, we must be aware that this will not be sufficient to solve the problem of N surplus. The mineralization of crop residues and soil organic matter, especially after harvest, can lead to very high mineral N concentrations in the soil, which ultimately result in high N losses, mainly in the form of nitrate leaching, but also as nitrous oxide (N₂O) if the excess N is not immobilized before winter. In crop rotations that do not allow the cultivation of a catch crop, e.g. before winter cereals, the N immobilization potential is by far not high enough to immobilize the available mineral N. In this case, a different approach than plant N immobilization is required to immobilize the excess N before winter.

Here, we present results from laboratory incubations and field trials with different soils under a wide range of conditions based on the stimulation of microbial biomass growth by readily available organic soil amendments. They show that effective immobilization of mineral N in large quantities (almost 100 % reduction of nitrate concentration in the soil) is possible for several months, even under winter conditions. A consistent picture emerges from the results, suggesting that the optimal and longest-lasting effect of N immobilization can be achieved with nitrogen-free organic compounds that are moderately available to microorganisms (i.e., within several weeks rather than a few days). If the microorganisms are offered compounds that are too readily available (extreme case: glucose), a rapid stimulating effect can be triggered, which, however, does not last long enough to immobilize N for several months due to too early remineralization. If too recalcitrant organic compounds are introduced into the soil, the utilization of the additional carbon source takes too long to lead to effective N immobilization. We can therefore say that we have taken a significant step forward in understanding the mechanisms and timing of microbial N immobilization and remobilization, which may prove key to solving the N surplus problem in agriculture. However, the extent to which such management measures can be implemented in agricultural practice also depends on the political framework conditions that make them economically feasible.

How to cite: Brüggemann, N., Zhao, K., and Reichel, R.: How can we reduce post-harvest nitrogen losses on agricultural land? Evaluating the potential of easily degradable, nitrogen-free organic soil additives, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20772, https://doi.org/10.5194/egusphere-egu24-20772, 2024.

High nitrification rates and substantial nitrogen (N) losses through nitrate leaching and N₂O emissions make current agricultural practices unsustainable, contributing to greenhouse gas emissions and environmental pollution. Synthetic nitrification inhibitors (SNIs) can be amended with N-fertilizers to reduce the conversion of ammonia to nitrate by soil nitrifiers. SNIs aim to increase agricultural nitrogen use efficiency (NUE), but they have several disadvantages (e.g., costs, ineffectiveness in the field, possible accumulation in the food chain). The use of biological nitrification inhibitors (BNIs), naturally occurring in plant root exudates, could become an alternative to SNIs. Potential BNIs should be highly specifically targeting nitrification, but for most known BNIs it is unclear if and how they affect other soil microorganisms and biogeochemical processes.

This study aimed to investigate possible off-target effects of BNIs in agricultural soils. We tested the effect of two candidate BNIs (Methyl 3-(4-hydroxyphenyl)propionate and DL-limonene) in slurry assays on soil microbial communities from a typical Austrian agricultural field (Linz, pH 6.89±0.12, fertilized with 120 kg N ha^-1 yr^-1), and compared them to a known SNI (nitrapyrin), and two further nitrification inhibitors (phenylacetylene and octyne). The slurries were incubated for eight days and CO₂ production, pH, as well as nitrate- and N₂O accumulation were measured. At the end of the incubation, we analyzed fluorescence-based enzyme activity, as well as microbial substrate use efficiency using ‘Biolog©’ assays to test the influence on general microbial activity, selected microbial soil processes, and the effectiveness of nitrification inhibition, respectively.

Our results showed that both tested BNIs significantly reduced net nitrification rates, but also affected other biogeochemical processes, even though limonene lost some effectiveness during the incubation. MHPP was heavily respired by heterotrophic microorganisms, leading to a drop in pH and heterotrophic competition for the remaining ammonium, therefore likely acting as an indirect nitrification inhibitor. Extracellular enzymes were also affected: MHPP led to increased potential β-glucosidase activity, while nitrapyrin led to a decrease in potential phosphatase activity. General soil microbial substrate use diversity seemed to be unaffected by the input of either BNIs or SNIs. Whether or not the observed off-target effects are positive and what they mean for the large-scale application of BNIs in the agricultural industry remains to be further investigated.

How to cite: Karbon, I., Madani, K., Prommer, J., Rojas, P., Giguere, A., Sedlacek, C., Sandén, T., Spiegel, H., Pjevac, P., and Fuchslueger, L.: Off-target effects of biological nitrification inhibitors on soil microbial substrate use and enzyme activity in an agricultural soil , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-21470, https://doi.org/10.5194/egusphere-egu24-21470, 2024.

Tropical rainforests play an important role in the global carbon cycle. They store massive amounts of biomass in their trees and soils, and contribute to climate mitigation by removing carbon from the atmosphere through photosynthesis. It is assumed that plant responses to rising atmospheric CO₂ concentrations may have induced an increase in biomass and thus, increased the carbon sink in forests worldwide. Rising CO₂ directly stimulates photosynthesis (the so-called CO₂-fertilization effect) and tends to reduce stomatal conductance, leading to enhanced water-use efficiency, which may provide an important buffering effect for plants during adverse climate conditions and also have implications for water resources by reducing the loss of soil moisture through transpiration. For these reasons, current global climate simulations consistently predict that undisturbed tropical forests will continue to sequester more carbon in aboveground biomass. However, several lines of evidence point towards a decreasing carbon sink strength of the Amazon rainforest in the coming decades, potentially driven by nutrient limitation, droughts or other factors. Mechanistically modelling the effects of rising CO₂ in the Amazon rainforest are hindered by a lack of direct observations from ecosystem scale CO₂ experiments. To address these critical issues, we are currently building a free-air CO₂ enrichment (FACE) experiment in an old-growth, highly diverse, tropical forest in the Brazilian Amazon and we here present our main hypotheses that underpin the AmazonFACE experiment.  We focus on possible effects of rising CO₂ on carbon uptake and allocation, phosphorus cycling, water-use and plant-herbivore interactions, and discuss relevant ecophysiological processes, which need to be implemented in dynamic vegetation models to estimate future changes of the Amazon carbon sink. We give an update on the state of the experiment construction, present the sampling strategy and discuss our approach to upscale tree-level responses to stand scale. 

How to cite: Rammig, A. and Lapola, D. and the AmazonFACE Team: AmazonFACE – A large-scale Free Air CO2 Enrichment Experiment in the Amazon rainforest , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5418, https://doi.org/10.5194/egusphere-egu24-5418, 2024.

Tropical vegetation dynamics and ecosystem carbon (C) stocks typically vary with local topography and forest disturbance history. Yet, neither remote sensing nor vegetation modeling captures the underlying mechanistic processes determining ecosystem functioning and therefore the resulting estimates often do not match field observations of vegetation C stocks, especially so in hyperdiverse tropical forest ecosystems. This mismatch is further aggravated by the fact that multiple interacting factors, such as climatic drivers (i.e., temperature, precipitation, climate seasonality), edaphic factors (i.e., soil fertility, topographic diversity) and diversity-related parameters (i.e., species composition and associated plant functional traits) in concert determine ecosystem functioning and therefore affect tropical forest C sink-strength.

Here, we propose a novel framework designed for integrating in-situ observations of local plant species diversity with remotely sensed estimates of plant functional traits, with the goal to deduce parameters for a recently developed trait- and size-structured demographic vegetation model. Plant-FATE (Plant Functional Acclimation and Trait Evolution) captures the acclimation of plastic traits within individual plants in response to the local environment and simulates shifts in species composition through demographic changes between coexisting species, in association with differences in their life-history strategies.

Our framework may be used to project the functional response of tropical forest ecosystems under present and future climate change scenarios and thus should have crucial implications for assisted restoration and management of tropical plant species threatened by extinction.

How to cite: Hofhansl, F., Hietz, P., Huber, W., Weissenhofer, A., and Wanek, W.: Landscape-scale And Spatially Explicit Representation of vegetation dynamics and ecosystem carbon stocks in a hyperdiverse tropical forest ecosystem (LASER), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5862, https://doi.org/10.5194/egusphere-egu24-5862, 2024.

Deforestation of the Amazon rainforest biome has been of considerable international concern, as extensive forest loss has negative impacts on global carbon storage, hydrological cycles and biodiversity. Ongoing climatic change is predicted to make these effects worse, as climatic models suggest that increasing temperatures will often be accompanied by decreasing precipitation. Such change would put the continued existence of the rainforest biome at risk, as moisture-demanding species would be replaced by more drought-resistant ones. Field observations already indicate that even those Amazonian forests that are not directly affected by deforestation have started to change, and that they grow faster, store less carbon and contain more lianas than before. However, field measurements can only be carried out in a limited number of sites, and these only cover a minute part of the entire Amazon biome. To get a more complete understanding of the changes within the remaining Amazonian forests, we are carrying out broad-scale analyses using Landsat imagery. We first did pixel-based compositing using all image acquisitions within a 10-year time window in order to obtain a clean cloud-free reflectance surface. Two such composites were produced for different time periods (2000-2009 and 2013-2022) in order to identify potential changes across the forested landscape. The results are expected to identify areas where significant but non-obvious changes in the structure and/or function of the forest could be happening, and thereby to facilitate in assessing the degree of threat to the ecosystem

How to cite: Gupta, R., Ruokolainen, K., and Tuomisto, H.: Using Landsat composites to document temporal change within Amazonian forest vegetation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7786, https://doi.org/10.5194/egusphere-egu24-7786, 2024.

Land-surface representations in weather and climate models simplify the characterization of vegetation as a single layer with bulk environmental conditions. This approach overlooks the vertical variability in leaf traits and environmental conditions within the canopy. This research explores the vertical variability of plant ecophysiology and environmental measurements within the Amazon tropical rainforest during daytime, specifically at the ATTO site, during the late dry season.

To characterize the canopy and its vertical variability, we categorized the canopy into three layers: the top layer (approximately the upper third of the canopy, 18-27 m), the medium layer (approximately the medium third of the canopy, 9-18 m), and the low layer (approximately the lower third of the canopy, 0-9 m) where leaf gas exchange measurements were conducted. Utilizing these layers, we developed a multi-layer model representation that calculates water and CO₂ fluxes based on within canopy on-site observations. We conducted sensitivity analyses of the rainforest multi-layer representation to discern the significance of capturing vertical variability in leaf traits and environmental conditions for deriving net fluxes of water and CO₂ of the forest.

Current results show that measured leaf traits exhibit vertical variation within the canopy, indicating larger productivity in the top layer compared to the medium and low layers. Environmental conditions, such as incoming radiation in the top layer, fluctuate due to cloud presence. Temperature peaks in the top layer and reaches a minimum at mid-canopy. This results in a non-uniform mixing of the canopy air, maintaining a stable layer within the forest canopy that can potentially affect the distribution of scalars within the canopy. Ongoing analyses explore the similarities and differences between the CO₂ exchange between the multi-layer representation and CO₂ fluxes from eddy covariance systems, as well as the sensitivity of the former to vertical variability in leaf traits and environmental conditions. By doing so, we aim to gain knowledge on the relevance (or irrelevance) of characterizing vertical variability in land-surface representations and on important processes that may not be well captured yet by land-surface representations.

How to cite: González Armas, R., Rikkers, D., de Boer, H., de Feiter, V., de Haas, S., Hartogensis, O., Mol, W., Janssens, M., Heusinkveld, B., van Heerwaarden, C., van Asperen, H., Machado, L., Quaresma, C., Bastos Görgens, E., and Vilà Guerau de Arellano, J.: Vertical Variability in Leaf Traits and Environmental Conditions: Implications for Evapotranspiration and Net Ecosystem Exchange above the Amazon Rainforest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8693, https://doi.org/10.5194/egusphere-egu24-8693, 2024.

Restoring formerly degraded ecosystems is a promising nature-based solution to mitigate climate change and ensure the provisioning of ecosystem services. Consequently, ecosystem restoration is prominent on both governmental and private agendas (e.g., the Bonn Challenge, airline carbon off-sets by planting trees). Two opposing strategies are employed to promote forest restoration: active versus passive (e.g. natural regeneration) restoration. Assessing how these two approaches influence biodiversity hot spots such as tropical rainforests is uniquely important, but the benefits and limitations of these two techniques have not been thoroughly compared.

Among all tropical moist forests globally, forests of Asia-Oceania have experienced the highest disturbance rates in the past three decades, among which Sabah, Malaysian Borneo, contains forests with past managements to strategically assess long-term forest recovery following active and passive restoration strategies.

How overall forest carbon balance, including carbon storage in the soil, is affected by active versus passive restoration, remains a blind spot not only at this site, but also globally. Given that up to half of the total carbon stored in secondary tropical rainforests can be stored belowground, and that this carbon has slower turn-over rates than above-ground vegetation, Sabah is a perfect testing ground to examine how common forest restoration influences below-ground carbon dynamics and total forest carbon balance.

To address this, we collected soil samples in 15 actively restored and 15 naturally regenerating forest plots in INFAPRO, a restoration project in Sabah. This site was severely, selectively logged for two decades and then actively restored by planting (mainly) Dipterocarpacaea (i.e., diptertocarps) seedlings more than 20 years ago. These trees associate with ectomycorrhizal fungi that mediate important soil biochemical cycles as root-inhabiting tree symbionts.

At this restoration site, active restoration enhanced tree diversity, promoted rare species, and increased above-ground carbon density in living vegetation in comparison to natural regeneration. We hypothesize that active restoration, including the planting of diptertocarps, further enhances the presence of ectomycorrhizal fungi, leading to a suppression of free-living microbial decomposition of plant litter inputs (i.e., the Gadgil effect), and an increase in total soil carbon storage. While this may increase total soil carbon storage, the more persistent fraction that is mineral-associated may decrease. This is due to slowed plant litter decomposition and thus less production of compounds that absorb onto mineral surfaces in addition to less microbial necromass inputs sticking to minerals due to the lower growth efficiency by ectomycorrhizal fungi compared to free-living microbes.

This knowledge on soil carbon storage and its persistence is a much needed contribution to holistic assessments of active restoration compared to natural regeneration. Empirical results on soil carbon analyses will be generated by the time of the EGU conference.

How to cite: Keller, N., Jilling, A., Lim, J. Y., Koh, L. P., Godoong, E., and Anthony, M. A.: The Blind Spot in active tropical forest restoration: unknown impacts on soil carbon, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10409, https://doi.org/10.5194/egusphere-egu24-10409, 2024.

The impact of elevated atmospheric CO₂ concentrations on forest productivity depends on the capacity of plants to balance the additional CO₂ with the demand for additional nutrients. One hypothesis states that plants may allocate the extra carbon belowground in producing and maintaining fine roots to alleviate nutrient limitation. In the Amazon basin, where approximately 60% of the forest is on old and weathered soil, the litter layer is an important nutrient source. In some regions, root mats growing in the litter layer can be observed, where the roots intercept the newly mineralized nutrients before they reach the soil and may bind to the mineral matrix. To improve their nutrient uptake capacity, trees can either modify their root morphology to a ‘do-it-yourself” strategy, increasing root length and branching intensity or alternatively, they can outsource the same function by investing in symbioses with mycorrhizal fungi. Additionally, fine roots can stimulate microbial decomposition of recalcitrant substrates (e.g., wood debris) by exuding low molecular weight organic compounds (LMWO) and increasing P mobilization by phosphatase activity without changing decomposition. These strategies could also vary depending on the growing depth of roots due to the different physical conditions between the organic upper and mineral layers. However, little is known about the role of trait differences in roots under higher CO₂ concentrations.

To increase our understanding of belowground responses of understory plants to elevated CO₂ concentrations, we set up an Open-Top Chamber experiment in a lowland forest in the Central Amazon. We observed that under eCO_2, root productivity did not change in the litter layer but showed a decreased pattern in the soil layer. Moreover, plants intensified root foraging in the litter layer by increasing their specific root length more than threefold under elevated CO₂. In contrast, roots in the soil mineral layer followed an “outsourcing” strategy by increasing arbuscular mycorrhizal colonization by 117%. In addition, our results showed a decrease in the organic P in litter without a change in C decomposition under higher CO₂ concentrations, suggesting a direct P mobilization.

Our results suggest that plants may plastically adjust resource acquisition strategies to increase nutrient uptake efficiency and be able to directly affect P mobilization from the litter layer. We conclude that this ability of plants to adapt their P acquisition strategies in response to eCO₂ by tackling different sources within the litter-soil continuum and maximizing nutrient acquisition represents an important mechanism to support the CO₂ fertilization effect and might affect the resilience of the Amazonian rainforest to climate change, and thus global carbon balance.

How to cite: Martins, N. and the AmazonFACE team: Multiple plant root strategies improve phosphorus acquisition under elevated CO2 in the Amazon rainforest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10719, https://doi.org/10.5194/egusphere-egu24-10719, 2024.

The Central Amazon comprises mosaics of forest ecosystems with different water dynamics and soil characteristics. The water dynamics from each ecosystem affect the evaporation signal seasonally expressed in the water isotopes (δ¹⁸O and δD). The recognition of the evaporative signal from different forest segments is essential for the development of hydrological and eco-hydrological studies in the complex Amazon biome. In this study, we used stable isotopes to evaluate how the water dynamics of different forest ecosystems affect seasonal water evaporative signals in each environment. We monitored water isotope signals from 2018-2020 in different compartments (precipitation, soil, stream, groundwater, river, lake, and flooded areas) of two non-flooded forests (clay soils - “plato” and sandy soils – “campinarana”) and three flooded forests (pristine igapó, disturbed igapó and várzea). We found that the soil water sampled by lysimeters in the upland forest seasonally expresses the isotope signal from the rainwater (Local Meteorical Water Line-LMWL) without a strong evaporative overprint. The water isotope signal from flooded forests is more variable. The isotopic composition of pristine rivers has an overlapping signal from the rain isotope signal (LMWL). However, water from the river downstream from the very large hydropower dam (Balbina) has a strong evaporative signal. During the flooded period, the water within the flooded forests has a more evaporated signal than the signal from the source (such as the river or lakes). During the non-flooded period, the water isotope signal from the soil inside the flooded forest corresponds to the rainwater signal. To the best of our knowledge, these represent the first description of the water isotope signals from the compartments in different Central Amazonian forest ecosystems. They illustrate and identify the high variation of the evaporative signal from the complex Amazon biome, knowledge that is essential to understanding how different forest ecosystems influence water recycling in the Amazon hydrological cycle.

How to cite: Durgante, F., Schöngart, J., Piedade, M. T. F., Trumbore, S., Jones, S. P., Gastmans, D., Komiya, S., Oliveira, R., Gleixner, G., Lavric, J., Moossen, H., Geilmann, H., Weiss, B., Macedo, M., Rincon, L. M., Sá, P. A. D., and Wittmann, F.: Seasonal variation of water isotopes in different forest ecosystems in the Central Amazon , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10823, https://doi.org/10.5194/egusphere-egu24-10823, 2024.

Tropical rainforests such as the Amazon are of high importance as a global carbon sink. Due to its well-known nutrient limitation, the Amazon rainforest relies heavily on rapid microbial decomposition of biomass to release freshly available nutrients for plant growth. Despite the fundamental importance of decomposers for this ecosystem, little is known about the biodiversity of such microbiomes, their functional activity, and spatial and seasonal variability. We used 16S rDNA and ITS rDNA sequencing to analyze the microbial communities of the Amazon’s terra firme and the much drier white-sand ecosystems during the dry and wet seasons in 2022. Bacterial microbiomes differed significantly between seasons, displaying lower bacterial species richness and diversity in response to seasonal drought. In contrast, fungal richness and diversity differed strongly between sites, but were less affected by seasonal variation, suggesting their hyphae network and associations with plants as potential protectors against drought effects. Fungal and bacterial communities alike showed lower abundance of taxa involved in organic matter decomposition following seasonal drought. These changes were also reflected at the functional level, with samples collected during the dry season and at white-sand sites featuring lower abundances of decomposition and denitrification pathways. Soil hydro-chemical data also emphasizes how prolonged drought may limit soil nutrient supply via local microbiomes. Our results suggest that the reduced nutrient availability and soil connectivity during drought and within the white-sand ecosystem lower microbial activity and functional redundancy, henceforth demonstrating a strong impact of ecosystem type and drought on tropical microbiomes and their functional capacities. Our results further highlight that the observed increase in droughts in the Amazon rainforest may additionally limit nutrient supply through the microbial community, limiting carbon sequestration in the ecosystem with negative consequences for the global climate system.

How to cite: Finck, J., Lange, D. F., Quesada, B., Portela, B. T. T., Ferreira, S. J. F., Andreote, F. D., Kothe, E., and Gleixner, G.: Seasonal drought reduces microbial diversity and functional richness in the Amazon, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11089, https://doi.org/10.5194/egusphere-egu24-11089, 2024.

The Amazon rainforest is of vital importance for biodiversity, regional climate, as well as global water and carbon cycling. However, over the past decades, ecosystem functions of the Amazon rainforest have diminished through a combination of increasing anthropogenic pressure in form of land-use change and intensifying natural disturbances. Recent studies suggest that unabated deforestation and climate change could tip large parts of the Amazon towards a different, savanna-like vegetation state. Although such a scenario could lead to severe impacts on the climate system from regional to global scales, a holistic assessment of the risk of large-scale Amazon forest loss due to land-use change and climate change in the 21^st century is currently lacking. 

Here, we use data from multiple CMIP6 Earth System Models under two low climate mitigation scenarios to attribute Amazon forest loss until 2100 to land-use change and climate change, applying a novel ensemble member approach. We find that around 1 mio. km² of forest will diminish by 2100, corresponding to a loss of around one fifth of the pre-industrial forest area. Historically and over the first half of the 21^st century, land-use change is the main driver of forest loss, whereas forest loss due to climate change increases non-linearly beyond 2°C global warming and even exceeds forest loss caused by land-use change by the end of the century in some models. We further find a consistent increase in the probability of abrupt (rather than gradual) forest loss with progressing deforestation and climate change. 

Overall, our results highlight that under plausible low mitigation socio-economic pathways 1) the Amazon rainforest will substantially diminish due to anthropogenic climate and land-use change and 2) the risk of forest loss due to climate change increases significantly beyond 2°C global warming. This stresses the urgent need for increased efforts to reduce deforestation and forest degradation through forest protection, conservation and sustainable land-use practices and for climate mitigation efforts in line with the Paris Agreement.

How to cite: Bultan, S., Bathiany, S., Boers, N., Ganzenmueller, R., Gyuleva, G., Moustakis, Y., and Pongratz, J.: Attributing future Amazon forest loss to land-use change and climate change, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-11932, https://doi.org/10.5194/egusphere-egu24-11932, 2024.

Nutrient resorption efficiency (RE) occurs before leaf abscission, with nutrients being actively transported via phloem through abscission zones from senescent leaves to be used in other parts of the plant. It is an essential nutrient conservation strategy for tropical plants growing on soils depleted of P (phosphorus) and other rock-derived elements (K; potassium, Ca; calcium, and Mg; magnesium), influencing nutrient cycling in these ecosystems. The environment heavily influences resorption; therefore, a better understanding of nutrient resorption processes in tropical trees, which act as a carbon sink, is important when facing the rapid climatic changes. Thus, our objective was to investigate the resorption of five macro elements (C; carbon, N; nitrogen, P, K, Ca, and Mg) and three micronutrients (Fe; iron, Zn; zinc, and Mn; manganese), and the effects of leaf longevity, foliar nutrient concentration, and canopy position in RE in a lowland forest tree community in Central Amazon. The study was conducted in two experimental plots at the AmazonFACE Program (Free-Air CO₂ Enrichment) in Manaus, Amazonas, Brazil. Two 40 m scaffolding towers in the center of the plot granting access to the canopy of the twelve tree species studied. Young, mature, and senesced leaves were collected, totaling 188 leaves, from 2018 to 2019 for nutrient laboratory analysis. We found that K, P, and N were the most resorbed nutrients (42%, 33%, and 7%, respectively), while Zn, Fe, and Ca were the most accumulated (-65%, -27%, and -21%, respectively). Additionally, we found that C, N, P, Fe, and Zn resorption positively correlated with their concentration in leaves. Likewise, P, N, Mg, K, and C resorption positively correlated with leaf longevity. On the other hand, canopy position influenced the resorption of three elements: C, K, and Zn resorption. Our results suggest that P was the scarcest nutrient stored in leaves; the higher resorption efficiencies for K and P than for N suggest higher plant internal nutrient recycling of K and P, likely due to their scarcity in the soil during leaf senescence, species with longer leaf life span are often assumed to have higher nutrient resorption efficiency than species with short leaf life span to reduce nutrient loss, species in the community studied can optimize leaf anatomy and physiology to make the best use of the variable light encountered regarding of its position on the forest vertical profile. These trends suggest that nutrient resorption from senescent leaves may be a general adaptive strategy for conserving nutrients by plants in tropical forests growing on nutrient-poor soils, which should be considered when predicting future scenarios.

How to cite: Santos, J., Garcia, S., Lugli, L. L., Aleixo, I., Domingues, T., Takeshi, B., Oliveira, A., Menezes, J., Lapola, D., and Quesada, C.: Plant nutrient resorption efficiency in a Central Amazon rainforest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12275, https://doi.org/10.5194/egusphere-egu24-12275, 2024.

CO is an indirect greenhouse gas because it reacts with OH, therefore increasing the lifetime of methane: its possible indirect radiative forcing has been estimated as larger than that of N₂O. Previous studies have indicated that temperate and boreal forests act as a net sink for CO, but the role of tropical rain forest ecosystems has not been investigated. We present the first CO flux measurements from tropical forest and forest soils, and can show that tropical rain forests are a net source of CO to the atmosphere.

During two intensive field campaigns at tropical rain forest fieldsite ZF2 (Manaus, Brazil), soil CO fluxes were determined by use of flux chambers. In addition, nighttime vertical CO concentration profiles were measured and different micro-meteorological techniques were applied to estimate ecosystem CO fluxes. Furthermore, we performed nocturnal CO concentration measurements in a seasonally inundated valley, which was hypothesized as a potential hotspot for ecosystem CO emissions.

Soil CO fluxes ranged from -0.19 (net soil uptake) to 3.36 (net soil emission) nmol m^-2 s^-1, averaging ∼1 nmol CO m^-2 s^-1. Fluxes varied with season and topographic location, with highest fluxes measured in the dry season in a seasonally inundated valley. Nocturnal canopy air profiles show consistent decreases in CO mixing ratios with height, which requires positive surface fluxes between 0.3 and 2.0 nmol CO m^-2 s^-1. Similar fluxes are derived using a canopy layer budget method, which considered the nocturnal increase in CO over time (1.1 to 2.3 nmol CO m^-2 s^-1). Using wet season concentration profiles of CO, the estimated valley ecosystem CO production exceeded the measured soil valley CO fluxes, indicating a potential contribution of the valley stream to overall CO emissions.

Based on our field observations, we expect that tropical rain forest ecosystems are a net source of CO. Extrapolating our first observation-based tropical rain forest soil emission estimate of ∼1 nmol m^-2 s^-1, a global tropical rain forest soil emission of ∼16.0 Tg CO yr^-1 is suggested. Total ecosystem CO emissions might surpass this estimate, considering that valley streams and inundated areas could serve as local CO emission hotspots. To further improve tropical forest ecosystem CO emission estimates, more in-situ tropical forest soil and ecosystem CO flux measurements are essential.

How to cite: van Asperen, H., Warneke, T., Carioca de Araújo, A., Forsberg, B., José Filgueiras Ferreira, S., Röckmann, T., van der Veen, C., Bulthuis, S., Komiya, S., P Jones, S., Botía, S., Ramos de Oliveira, L., de Lima Xavier, T., da Mata, J., de Oliveira Sá, M., Ricardo Teixeira, P., Andrews de França e Silva, J., Notholt, J., and Trumbore, S.: Tropical forests: a source of CO!, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-12352, https://doi.org/10.5194/egusphere-egu24-12352, 2024.

Land surface temperature (LST) is a dominant influence on the health and productivity of ecosystems. Deforestation in the Brazilian Amazon has led to extensive land-use transitions from forests to pastures and industrialized agriculture. This has resulted in elevated land surface temperatures, with impacts on the energy, water, and carbon cycles. Forest fragmentation increases the area of forest edges, where exposure to sunlight, wind, and bordering land-uses alters the forest microclimate. While the changes in forest edge temperature due to bordering land-use transitions is acknowledged, the magnitude of these changes between specific agricultural land management practices has yet to be determined. This case study uses a remote sensing approach to investigate forest edge temperatures in Mato Grosso, Brazil, with a primary goal of discerning how distinct agricultural practices, such as cover cropping or double cropping, can potentially mitigate adverse temperature impacts on forest edges. These findings will strengthen the understanding of forest edge temperatures, with a focus on the potential of sustainable land management, contributing to broader conservation efforts in the Amazon Rainforest. 

How to cite: Hellenkamp, S., Brando, P., and Starinchak, B.: Understanding the role of temperature in forest edges: a remote sensing approach in the Brazilian Amazon, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13403, https://doi.org/10.5194/egusphere-egu24-13403, 2024.

Spatial heterogeneity in tropical forest productivity and resulting rates of carbon uptake and storage emerge from variation in ecosystem structure and functional traits reflecting differences in climate, edaphic conditions, evolutionary history, and natural and anthropogenic disturbance histories. Yet, models poorly represent this heterogeneity. Remote sensing data provide landscape-scale measures of tropical forest heterogeneity in structure and functional traits that can be used to advance terrestrial biosphere models. To examine whether forest functional traits related to photosynthetic capacity can be used to improve predictions of tropical biomass dynamics and carbon fluxes, we parameterized the Ecosystem Demography model version 2.2 (ED2.2) using canopy traits derived from visible to shortwave infrared (VSWIR) airborne imaging spectroscopy data across an edaphic gradient in Borneo. We find significant site-level differences in relationships between SLA and foliar nutrient concentrations, suggesting that remotely sensed foliar traits can be used to capture variation in photosynthetic capacity at large, edaphically varying spatial scales. We further show that plant functional types parameterized with site-constrained trait values yield more accurate predictions of canopy demography, forest productivity and above-ground biomass dynamics than simulations that depend solely on parameterization of edaphic conditions. However, the most substantial improvements result from allowing for site-level variation in background disturbance rates in the model. Our study reveals the importance of capturing tropical forest heterogeneity in terrestrial biosphere models, particularly as it relates to nutrient availability and disturbance processes. 

How to cite: Ordway, E., Asner, G., Burslem, D., Davies, S., Lewis, S., Mohiza, M., Reuben, N., Michael, O., Oliver, P., Lan, Q., Russo, S., Xu, X., Longo, M., and Moorcroft, P.: Constraining uncertainty in terrestrial tropical carbon flux dynamics requires capturing local biogeochemical influences on structure and function, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14471, https://doi.org/10.5194/egusphere-egu24-14471, 2024.

The risk of a tipping point for Amazon forests — a perturbation threshold beyond which abrupt, irreversible (or difficult to reverse) changes in forest function and large-scale tree die-off occur — motivates much recent Amazon forest science and policy work to understand and reduce the risk. However, virtually all the science to date focuses on tipping points as a basin-wide phenomenon. To understand how large-scale tipping points may be triggered, we urgently need to study mechanisms of tipping point onsets at local-scales in pivotal forests.

 Here, we used 12+ years of observations (spread over two decades from 2001-2020) of water and energy fluxes from eddy covariance measurements, and associated ecological and meteorological observations in the eastern Amazon basin, to investigate the potential for hydrological extremes to induce a “local scale” tipping point.  We focused on forest transpiration capacity (the capacity of vegetation to convert available energy into latent heat, quantified as the ratio of transpiration to incoming radiation, T/R) because transpiration in eastern Amazon forests is the basis for precipitation recycling on which forests to the west depend.

Our observations encompassed two strong El Niño droughts, in 2002-2003 and in 2015-2016. Both events were characterized by similarly reduced rainfall; however, the 2015 El Nino was further amplified by an ongoing warming trend, which made for a hotter drought with higher atmospheric vapor demand, exacerbating the drought effects on the forest. 

This amplification of drought by warming was apparently sufficient to cause widely divergent responses to the two droughts.  The forest responded positively to the 2002 drought, with increases in canopy conductance (Gs) and in evapotranspiration, consistent with a stable forest transpiration capacity (T/R) that saw proportional increases in T in response to higher R. By contrast, the transpiration capacity (sustained through two decades of previous dry seasons and the 2002 El Nino drought) collapsed during the 2015 drought.  Notably, the forest’s ability to transpire did not return with the rain as the drought ended, but remained low for several years. Thus, we concluded that the difference between the 2002 and 2015 El Nino’s was sufficient to push the forest past a “tipping point” threshold in forest transpiration function, into an alternate state of reduced function in which it remained trapped until the forest could regenerate the canopy with new leaves.  

This discovery of the phenomenon of local-scale short-term tipping point dynamics in forest canopy function opens the door to investigating and understanding how basin-scale tipping points may emerge from local phenomena, and how careful local observations may provide early warnings of impending larger-scale forest vulnerability.

How to cite: Saleska, S., Restrepo-Coupe, N., Silva Campos, K., Alves, L., Ivanov, V., Longo, M., de Oliveira Jr., R., Silva, R., Smith, M., Tapajos, R., and Taylor, T.: Do local-scale climate tipping points exist in Amazon forests, and can they warn of impending basin-scale tipping point vulnerability?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14707, https://doi.org/10.5194/egusphere-egu24-14707, 2024.

The megadiverse system of the Amazon contributes to many local and global ecosystem processes with potential to trigger an irreversible shift in the functioning of our planet. Yet, Amazon’s biodiversity is complex and remains mostly understudied. Biodiversity distribution patterns likely affect the functioning of this crucial system, yet large scale systematic assessments are still lacking. Herein we examine how can optical remote sensing contribute to understanding biodiversity patterns in the Amazon. We use the spectral diversity approach to map the heterogeneity of spectral signatures as a proxy for heterogeneity in canopy composition using Sentinel-2 imagery over the entire basin. Our map is able to reproduce patterns of primary, secondary and deforested areas, and within the forest areas, the patterns of spectral richness and spectral turnover resemble those expected for the Amazon system, with rapid turnover in species composition closer to the waterways and more stable plant community compositions away from the waterways. We then examine whether the locations with higher or lower spectral variability correspond to different community and trait compositions. We examine the relationship between spectral richness and turnover and the presence of hyperdominant trees in the Amazon. We also examine the multivariate trait space including Specific leaf area (SLA), Leaf dry matter content (LDMC), Leaf nitrogen content (LNC), and Leaf Phosphorous content (LPC) along the gradient of spectral variability to find that trait syndromes vary along the gradient of spectral diversity. These results show that biodiversity biodiversity gradients among the Amazon may explain differences in ecosystem functioning and that approaches such as the spectral heterogeneity may start to shed some light into such relationships, especially over entire and important ecosystems like the Amazon. Further examinations of these processes and relationships are therefore required and will contribute to our better understanding of the feedbacks between biodiversity and earth system processes.

How to cite: Santos, M. J. and Villamaina, D.: Biodiversity-mediated ecosystem functioning in the Amazon: a remote sensing approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-14880, https://doi.org/10.5194/egusphere-egu24-14880, 2024.

The Amazon Tall Tower Observatory is located in the central Amazon (S 02 08.9°, W 059 00.2°) inside the Uatumã Sustainable Development Reserve and has been monitoring continuously the atmospheric composition since 2013. The site is set up with two measurement towers of 80 meters and a tall tower of 325 meters for continuous monitoring of trace gases and aerosols. The surface influence (hereafter footprint) of the research station covers a large area to the east and northeast with the fetch extending for hundreds of kilometres, overlapping with the main branch of the Amazon River reaching the city of Belém (during the dry season) and large swaths of primary forest over the Amapá state (during the wet season).  We have analysed trends in fire counts (using MODIS thermal anomalies) and burned area (GFED4 and GFED5, Global Fire Emission Database 4th and 5th version) over the last two decades (2000-2023) inside the ATTO footprint and found that both show increasing and significant trends for the months of June (14,68 fire counts/year) July (42,23 fire counts/year), August (59,6 fire counts/year) and September (148,6 fire counts/year). Spatially, fires are located on easternmost part of the footprint and there is no evidence of a spatial trend approaching ATTO. Interestingly, in October the mean longitude of the fire counts over the period of interest shows a trend migrating from -56°W to -54°W, but with no significant trend in fire counts. We complement these results by analysing mole fractions of carbon monoxide (a proxy for biomass burning) at ATTO for an overlapping period (2013-2023). In addition, we provide links to the environmental drivers explaining these trends and spatial patterns. Observing biogenic greenhouse gases enhances our understanding of the Amazonian rainforest’s carbon budget, influenced by climatic conditions, land use alteration and other anthropogenic impacts.  

How to cite: Dajti, G., Urquiza, D., van Asperen, H., Jones, S., Komiya, S., Lavric, J., Hantson, S., and Botía, S.: Fire trends on ATTO footprint over the last two decades, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15363, https://doi.org/10.5194/egusphere-egu24-15363, 2024.

Nitrogen oxides (NOx = NO and NO₂) are chemical compounds that affect and control the abundance of ozone (O₃) and hydroxyl radicals (OHx = OH and HO₂), the main oxidizing agents in the atmosphere. In pristine environments, these oxidizers react with biogenic volatile organic compounds (BVOCs), such as isoprenes, to produce oxidized secondary organic products. Further reaction with NOx leads to the formation of nitrates. Nitrates deposit on surfaces and grow aerosol particles which eventually act as cloud condensation nuclei. This makes NOx an important atmospheric component, even in low concentrations. Therefore, NOx measurements are being made at the Amazon Tall Tower Observatory (ATTO) research site in the central Amazon forest basin, a pristine region.

Here we present the measurements of NO, O₃ and meteorological parameters collected at the Walk-up tower, at a height of approximately 40 m, just above the canopy.  

How to cite: Monteiro, C., Tsokankunku, A., Harder, H., and Wolff, S.: NO and O3 mixing ratios above the canopy in the rainforest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-16499, https://doi.org/10.5194/egusphere-egu24-16499, 2024.

Phosphorus (P) is a key driver of terrestrial productivity. However, the lack of spatial data on various P forms in soils hinders the large-scale application of process-based vegetation models. To address this, we used a model selection approach based on Random Forest regression models to predict different P forms (total, available, organic, inorganic, and occluded P) in the pan-Amazon region. Our models were trained and tested using data from 108 sites of the RAINFOR network, including soil group and textural properties, geolocation, nitrogen (N) and carbon (C) contents, terrain elevation and slope, soil pH, and mean annual precipitation and temperature. The models were then applied to several spatially explicit datasets to predict the target P forms. The resulting maps depict the distribution of total, available, organic, inorganic, and occluded P forms in the topsoil profile (0 - 30 cm) at a spatial resolution of 5 arcminutes. Our models achieved a good level of mean accuracy (77.37 %, 76,86 %, 75.14 %, 68.23 %, and 64.62% for the total, available, organic, inorganic, and occluded P forms, respectively). Our results reveal a clear gradient of soil development and nutrient content, with the mapped area generally exhibiting very low total P concentration status. Total N was the most important variable for predicting all target P forms. Despite some gaps in the training and testing data, most of the area could be mapped with a good level of accuracy. Our maps can aid in the parametrization and evaluation of process-based terrestrial ecosystem models and promote the testing of new hypotheses about P availability and soil-vegetation feedbacks in the pan-Amazon region.

How to cite: Darela-Filho, J. P., Rammig, A., Fleischer, K., Reichert, T., Lugli, L. F., Quesada, C. A., Hurtarte, L. C. C., de Paula, M. D., and Lapola, D. M.: Mapping Phosphorus Forms in the Pan-Amazon Region: A Machine Learning Approach, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18326, https://doi.org/10.5194/egusphere-egu24-18326, 2024.

The response of plants to increasing atmospheric CO₂ concentration depends on several factors such as life history of specific species, availability of water, nutrients and light, and the ecological context that the plants are found. Although several experiments with elevated CO₂ (eCO₂) have been done worldwide, none was performed in the Amazon forest understory focusing in a community growing naturally. The understory of the central Amazon is limited by both light and phosphorus. Understanding how such ecosystem responds to eCO₂ is important to foresee how the forest will function in the future. Also, quantifying the response of this forest compartment helps to constrain Ecosystem Models that compute carbon and water fluxes.

For this study, we used the open-top chamber (OTC) approach, with a CO₂ enrichment of +250 ppm above the ambient concentration. Eight OTC were installed (4 with ambient CO₂ and another 4 with eCO₂) in the understory of a natural forest in the Central Amazon, approximately 70 km from Manaus city. The eCO2 experiment started in November 2019 and, after 120 days, we quantified the average community response of the following photosynthetic parameters: light saturated carbon assimilation rate (A_sat), stomatal conductance (g_s), transpiration rate (E), intrinsic water use efficiency (iWUE), apparent quantum yield (Φ), light compensation point (LCP), maximum carboxylation capacity (V_cmax), maximum electron transport rate (J_max). After 240 days of treatment, we quantified mean individual leaf production and accumulated leaf production, leaf area (Lf_area). After 300 days, we quantified the increment in base diameter (BD), height (H_t) and relative growth rate (RGR).

Under eCO₂, we observed increases in A_sat (67%), J_max (19%), Φ (56%), and iWUE (78%), in agreement with the hypothesis that plants near the light compensation point respond strongly to eCO₂. We also detected an increase in Lf_area (51%) and BD (65%), indicating that the extra primary productivity was not allocated to growth in height, but to supporting more light intercepting organs (leaf and conducting tissues). No detectable changes were observed for the other variables.

Apart from the expected increase in assimilation rates, understory plants in Central Amazon responded positively to eCO₂ by increasing their ability to capture and use light (leaf size, Φ, and J_max). The increment in leaf area while maintaining E rates signifies that this forest compartment will increase its contribution to the whole forest water fluxes to the atmosphere. That might be related to the prevailing acquisitive strategy necessary for competing for phosphorus brought by water flow through plants. As a possible consequence, this forest might be less resistant to extreme drought associated with El Niño years.

Funding: Coordination for the Improvement of Higher Education Personnel - CAPES (grants 312589/2022-0) and São Paulo Research Foundation-FAPESP processes numbers (2022/07735-5) and (2015/02537-7). 

How to cite: Domingues, T., Damasceno, A., Garcia, S., Aleixo, I., Menezes, J., Pereira, I., De Kauwe, M., Ferrer, V., Fleischer, K., Grams, T., Santana, F., Hartley, I., Kruijt, B., Lugli, L., Martins, N., Norby, R., Portela, B., Rammig, A., Quesada, C., and Lapola, D. and the AmazonFACE team: Amazonian understory response to elevated CO2, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-18954, https://doi.org/10.5194/egusphere-egu24-18954, 2024.

In the context of global warming and rapid increase of population particularly in West Africa where forest ecosystems are threatened by land use conversion, understanding the biophysical variables influencing the ecosystem respiration (Reco) becomes vital for predicting the carbon balance in response to climate change. Using the Eddy Covariance method, and without an automatic chamber system, a key step to determine Reco is to use nighttime Net Ecosystem Exchange (NEE) data to establish a functional relationship using Reco main driver’s as an input.  However, to ensure that the input variable(s) used in this relationship is the most relevant governing this process, especially in tropical regions where both data and studies are scarce, it remains therefore an important prerequisite to examine the relative importance of potential drivers. This prior analysis is especially needed because: (1) the main driver may differ according to the climate and locations; (2) collinearity between some potential drivers could be a complex issue in identifying the main one; (3) the scale of influence of these drivers on the nighttime CO2 emission at some sites is still unknown. In our study, we therefore investigated the relative importance and scale of influence of soil moisture (Hsoil) and temperature (Tsoil) at different depths on the nighttime NEE. Since variations of the net CO2 flux exchanged can differ from one site to another, in this study we used data acquired from 2008 to 2017 above two contrasted ecosystems: a mixed culture (Nalohou, lat. 9.74^°N, long. 1.60^°E) and an open clear forest (Bellefoungou, lat. 9.79°N, long.1.72°E) located in Sudanian climate, Northern Benin. Both sites belong to the AMMA-CATCH (African Monsoon Multidisciplinary Analysis-Coupling of the Tropical Atmosphere and Hydrological Cycle) observatory. Two methods have been then deployed: the first one which is the Mutual Information, was used to identify the relative importance of Hsoil and Tsoil in controlling the nighttime NEE; the second one, the wavelet transform allows determining the scales of influence of these variables on nighttime NEE. We found that periodicity of nighttime NEE response to the two variables differs according to the season.  Soil moisture appears as the most important variable in the nighttime NEE variation whatever ecosystems and seasons analyzed. During wet seasons, nighttime NEE response to soil moisture exhibits a periodicity lower than 64 nights with synchronization every 07 nights, while this synchronization can extend from 12 to 14 nights during the dry season. This fast response of nighttime CO₂ emissions to soil moisture during the wet season results from a significant increase in precipitation. During the dry seasons, without precipitation, soil moisture decreases, and this reduces the water available to plant growth and microorganism activity, thus reducing the amount of CO2 emitted. Moreover, sporadic rainfall events rewet the soil, leading to spontaneous CO2 emissions. Soil temperature is secondary in importance, but its impact can vary; it is less relevant during the dry season, or more redundant in the wet season, for both sites. It is also out of phase with nighttime CO2 emissions regardless of the season.

How to cite: Koukoui, R., Mamadou, O., Houénou, D. F., Heinesch, B., Cohard, J.-M., Bousso, M., Peugeot, C., and Kounouhéwa, B.: Assessing the relative importance of soil moisture and temperature on the nighttime CO2 flux: two contrasted ecosystems study cases in West Africa, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19868, https://doi.org/10.5194/egusphere-egu24-19868, 2024.

The Congo basin is home to the second largest tropical forest in the world Therefore, it plays a crucial role in the global carbon cycle. Yet very few field based data on related processes exist. Gaining knowledge on a species level is also crucial for understanding these ecosystems. Leaf chamber measurements allow to measure photosynthetic capacity on a leaf level and by so, quantify the photosynthetic capacity of individual species. Moreover, they allow to quantify a plant´s reaction to environmental parameters such as light, atmospheric CO₂ concentration and temperature. Such data is crucial to improve the calibration and robustness of global vegetation models. These models are key tools to estimate the global carbon budget and ecosystem responses to climate change as a part of the Intergovernmental Panel on Climate Change exercises.

To date, no such data exists for the forests of the Congo Basin which prevents us to properly understand forest dynamics and resilience to global changes.In this research, we quantify leaf level carbon uptake and its response to light, CO₂ and Temperature for dominant tree species within the footprint of the CongoFlux tower in Yangambi (DR Congo).

As such, we deliver the first in-field leaf-level photosynthetic parameters dataset for a lowland tropical forest of the Congo Basin. Doing this, we explore the controls of interspecific variation in photosynthetic capacity including plant guild, species and vertical canopy position. Our study takes place at the research site of CongoFlux, Yangambi (DR Congo).

How to cite: Sibret, T., Peaucelle, M., Meunier, F., Bauters, M., Ellsworth, D., Crous, K., Boeckx, P., and Verbeeck, H.: Quantifying the photosynthetic capacity of dominant tree species in a humid lowland tropical forest of the Congo Basin, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-19990, https://doi.org/10.5194/egusphere-egu24-19990, 2024.

Lianas (woody vines) are an iconic feature of tropical forests as they represent on average 25% of all woody stems. Lianas are structural parasites that use the stems of self-supporting plants to reach the top of the canopy. From there, they strongly compete with trees for above- (light) and below-ground (water nutrients) resources. Despite their importance, lianas are completely neglected by terrestrial models. To fill this gap, we developed the first mechanistic representation of lianas in a state-of-the-art vegetation model, the Ecosystem Demography model version 2 (ED2.2). Model simulations revealed the critical role of liana for forest biogeochemical cycles (e.g., tree gross and net productivity decreases when lianas are present with the magnitude of the reduction varying with liana abundance) but also for the energy balance (e.g., lianas increase forest albedo and buffer the microclimate of forest understorey). 

In addition, we used a combination of terrestrial lidar scanning and a meta-analysis of field and drone observations of tree shape and structure to evaluate the impacts of lianas on tree allometries. In total, we gathered 45,000+ observations of individual tree height, 1.000+ observations of tree crown areas and 150+ tree quantitative structure models over more than 40 sites spread over the tropics, together with liana infestation levels. Those datasets converged to identify a key role of lianas on the shape and structure of tree in tropical forests, independently of the tree species. Liana heavy infestation was responsible for a strong reduction of tree height (-10.7%), crown area (-12.6%), branch length (-45.9%), and overall aboveground carbon stocks (-19.6%). We estimated the global potential liana impact on aboveground tree carbon stocks to be 13.5 Tg over the tropics, or about 7% of the total tropical forest biomass.

How to cite: Verbeeck, H., Krishna Moorthy, S. M., Calders, K., and Meunier, F.: Investigating the impact of lianas on global tropical forests, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20160, https://doi.org/10.5194/egusphere-egu24-20160, 2024.

A new carbon flux tower has been established in the tropical rainforest of Ghana to measure carbon fluxes as well as emissions of biogenic volatile organic compounds. African tropical forests constitute about 20% of Global Tropical Forest cover but have been understudied due to a lack of in-situ observations. The establishment of GhanaFLUX in the Bia-Tano forest reserve in western Ghana will help to fill this gap, allowing in-depth assessments of carbon sequestration and storage in African forests. Here, we present a snapshot of the facilities available at GhanaFLUX, and measurements taken in the first year of operation. We show time series analysis of carbon dioxide and meteorological datasets obtained from GhanaFLUX, highlighting the seasonal variations in these observations. We also share some of our experiences and challenges during the establishment and operation of the flux site to guide researchers who are planning to set up new sites in challenging environments like rainforests. 

How to cite: Otu-Larbi, F., Mensah, C., Agyemang Prempeh, N., Kumi, N., and Kyere-Boateng, R.: GhanaFLUX: Meauring carbon fluxes in an African Rainforest, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20858, https://doi.org/10.5194/egusphere-egu24-20858, 2024.

The inner ear of fish contains calcium carbonate (CaCO₃)-based crystals called otoliths, which play an essential role in hearing and balance. During otolith formation, new calcium carbonate is deposited in layers on the surface of the existing part and the part is no longer affected by metabolism. This feature means that each layer of the otolith retains the trace element ratios and isotope ratios it had at the time of formation. By analysing this preserved information, it is possible to make estimates about the environment and habitat at that time.

The stepwise acid dissolution method has been used in several studies as a technique for analysing the radiocarbon isotope ratios preserved in otoliths. In this method, phosphoric acid is used to dissolves the otolith from the outermost to the innermost layers. It has the advantage that a large amount of carbon can be collected from a single otolith, compared to the mechanical methods for the calcium carbonate sampling from each layer of the otolith.

However, this method involves dissolving the otolith in acid and the pattern of dissolution cannot be controlled minutely by the experimenter. Pacific cod (Gadus macrocephalus) otolith used by us is flattened and the dissolution pattern of such otoliths is not yet known. Furthermore, no direct observation of the otolith dissolution process has been made in relation to previous studies.

In this study, we dissolved three Pacific cod otoliths in phosphoric acid to directly confirm the process of otolith dissolution in the stepwise acid dissolution method. We removed each otolith from the acid one or more times during the dissolution process, weighed it and observed the change in the shape of the otolith and the layer structure exposed on the otolith surface. As the dissolution progressed and the otoliths became smaller, we polished them to check that the internal layered structure had not been destroyed by acid penetration.

As a result, we found that the serrated structures present on the outer edges of the otoliths are maintained when they are dissolved from the outside by acid. We also confirmed that acid dissolution from the outside does not destroy the inner layer structure, even microstructures such as daily rings. The validity of the stepwise acid dissolution method would be strengthened by these results. On the other hand, the otoliths were thinner as a result of acid dissolution, exposing the more inner layers on the flat surface. This is due to the thin vertical thickness of the flattened otoliths. This observation suggests that the collected carbon may be mixed with the carbon collected from more inner layer. This carbon mixing is able to be taken into account with future work. In addition, care should be taken when using this method near the nucleus, as the final stage of dissolution results in multiple holes in the otolith.

How to cite: Aonuma, K., Yokoyama, Y., Miyairi, Y., Chimura, M., Hamatsu, T., Sakai, O., and Plaza, G.: The dissolution pattern of the flattened otolith of Pacific cod using the stepwise acid dissolution method, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-416, https://doi.org/10.5194/egusphere-egu24-416, 2024.

Natural organic matter (NOM) is a complex mixture of thousands of organic molecules that reflects environmental conditions and chemical transformations occurring nowadays or in the past. Fourier transform mass spectrometry (FTMS) resolves isobaric constituents and it is widely applied to obtain aquatic, terrigenous and aerosol NOM fingerprints. Traditionally, comparison of mass peak intensities is used to make a distinctive conclusion about samples behavior, but it has the limitation of omitting structural information on the corresponding ions. Due to the stochastic character of NOM synthesis, drastically different samples may appear as resembling, which hampers mechanistic study of NOM dynamics and its attribution to the source. Here we present how implementation of chemical and isotopic tagging in combination with FTMS helps to overcome this issue. The developed approach provides an upper boundary for the presence of specific structural features, e.g. functional groups, in individual NOM components. This facilitates a clear distinction between different NOM samples, which would share isobaric ions, and provides insights on isomeric complexity of these ions. The advantages of the method were demonstrated on two sets of samples. Firstly, we collected permafrost peat cores from different depths in the European Arctic region, which varied in corresponding botanical conditions, peat degradation and oxidation states. Selective deuteromethylation and bromination coupled to FTMS enabled to capture structural differences between shared ions, which differed in carboxylic functionality and aromaticity. Surprisingly, structural differences were found for ions, which abundance positively correlated with peat characteristics and geo-temporal conditions. The second set included aerosol particles collected in marine, rural and urban areas. Application of in-source H/D exchange for FTMS analysis of extracted NOM enabled to enumerate functional groups in shared ions and point molecular constituents with similar and distinct structural features. The observed trends serve to better understand aerosol formation processes and accompanied conventional formula-based statistical analysis including better understanding of Kendrick mass defect series.

How to cite: Zherebker, A., Babcock, O., Vasilevich, R., and Giorio, C.: From sediments to the atmosphere: a mass spectrometry approach revealing structural dissimilarities of common NOM components, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-815, https://doi.org/10.5194/egusphere-egu24-815, 2024.

Forest fires are among the most influential disturbances in ecosystems and have varying effects on the soil depending on fire intensity and biomass consumption. The significant decline in biodiversity in European forests due to centuries of non-sustainable forest management, combined with worsening drought from climate change, has greatly increased vulnerability to wildfires. Incomplete combustion during fires leads to the formation of black carbon (BC), a group of substances known for their persistence in soil. However, studies suggest that medium-condensed BC species may have lower chemical and spatial stability and are therefore potentially more mobile and consequently only serve as temporary carbon sinks.

In order to assess the mobilization of BC, we investigate short-term changes in BC under field conditions, particularly of the low-condensed BC, and call into question the established concept of the general stability of BC pools. We investigated the dynamics of BC alterations during the post-fire period within one winter, following a late summer forest fire. We selected two comparable sites featuring spruce-dominated forest stands with different geologic parent material and weather conditions, particularly with respect to the amount of precipitation during the observation period. We sampled soil profiles down to 40 cm depth shortly after the fire event in late summer and after a 6-month period in late spring. After performing density fractionation to separate the mineral associated organic matter (MAOM) from particulate organic matter (POM), we analysed the BC content in the MAOM fraction using benzene polycarboxylic acids (BPCA) analysis.

The results show a high content of low to medium condensed BPCAs directly after fire, which decreased, especially the medium condensed BPCA marker, during the observation period. Taking into account the fast change in medium BPCA values in the MAOM fraction, we conclude that the general assumption that BC is in principle a stable, long-term carbon sink needs to be addressed more carefully.

How to cite: Donnerhack, O., Liebmann, P., Maurischat, P., and Guggenberger, G.: Post fire Black Carbon alteration: Rapid changes in a supposedly inert pool, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1109, https://doi.org/10.5194/egusphere-egu24-1109, 2024.

Oxidation of pyrites plays a key role in global chemical and climatic cycles. In particular, interaction of sulfuric acid produced through this process with carbonates releases CO₂ to the atmosphere. This CO₂ source counterbalances the CO₂ consumed during silicate weathering in river basins, and hence, may influence earlier-suggested linkage between silicate weathering and global cooling events. In this study, we have investigated the dissolved major ions and sulfur isotopes of Indus headwaters to quantify the net effect of sulfide oxidation on the CO₂ budget. This research is an attempt to evaluate the coupling between global Cenozoic cooling event and Himalaya weathering - ­a hypothesis which overlooked the CO₂ supply via sulfide and organic oxidation. Towards this, we have employed sulfur isotopes (δ³⁴S) as a proxy for riverine sulfate sources, mainly due to its distinct composition for the two major end-members [pyrite (~ -12 ‰) and gypsum (~ 17 ‰); [1]]. The average sulfate concentrations for the Indus headwaters are found to be higher than the regional rainfall, global average for rivers, and other major Himalayan rivers (e.g., Ganga and the Brahmaputra). Consistently, the mean δ³⁴S for the Indus headwaters is also depleted with respect to that reported for the Ganga (~ 2 ‰) and Brahmaputra (~ 4 ‰) outflows [1-5]. Also, the sulfur isotopic values for the Indus headwaters are systematically depleted by 3 to 4 ‰ than that reported earlier for Indus mainstream [3]. These lighter δ³⁴S values for the headwaters hint at relatively higher sulfide oxidation in the northwestern (NW) Himalaya compared to central and eastern Himalayas. Also, these processes are found to be more intense in the mountainous regions than in the floodplains. These observations are consistent with the basin lithology dominated by Paleozoic carbonates and organic-rich shales, and higher glacial coverage. Estimation of sulfide-derived cations from carbonate weathering and silicate-derived cations indicate that the chemical weathering in the Indus headwaters serve as a net source of CO₂ to the atmosphere. This finding is in contrast with previous suggestion of significant CO₂ removal during the Himalaya weathering and hence, challenges the role of land surface processes in the NW Himalaya in regulating the Cenozoic cooling event.

References

[1] Burke et al., (2018), Earth Planet. Sci. Lett., 496, 168-177.

[2] Chakrapani et al., (2009), J. Asian Earth Sci., 34, 347-362.

[3] Karim and Veizer, (2000), Chem. Geol., 170, 153-177.

[4] Kemeny et al., (2021), Geochim. Cosmochim. Acta, 294, 43-69.

[5] Turchyn et al., (2013), Earth Planet. Sci. Lett., 374, 36-46.

How to cite: Rout, R. K., Tripathy, G. R., Das, S., and Rai, S. K.: Net CO2 release during chemical weathering in the north-western Himalaya: A dominant role of pyrite oxidation, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1180, https://doi.org/10.5194/egusphere-egu24-1180, 2024.

In the past decade, the size, frequency, and severity of wildfires have increased around the world, especially in forests of the western United States, where ecosystems are dominated by dry conifer forests. It is known that fires can greatly affect not only air quality, climate, forest, and fauna, but also soil. The heat from fires can alter soil chemistry and change soil water repellency (SWR). SWR can reduce soil infiltration, which can increase surface runoff, erosion, and the potential for flooding and mud and debris slides. The increased frequency and intensity of western U.S. wildfires due to the rapidly changing climate poses an important question: What are the short- and long-term effects of wildfires on soil’s hydrologic responses, including SWR, and what is the role of fire-induced chemistry in SWR?

In the summer and fall of 2021 and 2022, there were four mega-wildfires (Caldor, Dixie, Beckwourth Complex, and Mosquito) in the Eastern Sierra Nevada mountains (California, USA). These wildfires provided us an opportunity to collect post-fire soil and ash samples and study the effects of fires on the physical and chemical properties of soils. We collected over 80 samples and performed multiple water-droplet penetration time (WDPT) tests in the field and, in the laboratory, apparent contact angle (ACA) measurements with the goniometer technique. For all four fires, a significant increase in SWR was observed between unburned and burned soils, with WDPT increasing from <1 s to 600 s (maximum measured value) and ACA values increasing between 1.1 and 9 times (p-value < 0.001). Our WDPT and ACA measurements of the samples collected 6 months and 1 year after the 2021 megafires (Dixie, Caldor, and Beckwourth Complex megafires) showed no significant changes in SWR for unburned and burned soils. The chemical analysis of organic constituents of unburned and burned soils with ultra-high-resolution mass spectrometry (thermogravimetry atmospheric pressure photoionization in combination with Fourier transform ion cyclotron resonance mass spectrometry or TG APPI FT-ICR MS) suggests that burned soils became water-repellent due to the formation and/or deposition of aromatic organic species (e.g., polycyclic aromatic hydrocarbons or PAHs) on the soil surface during fires. We found a positive correlation (R² = 0.813) between the ACA values of analyzed fire-affected samples and aromaticity derived from the TG APPI FT-ICR MS spectra.

These results of our research highlight the importance of future research on the chemical composition of post-fire soils and the need to study the long-term effects of fires on soil properties.

How to cite: Samburova, V., Schneider, E., Rüger, C., Sion, B., Friederici, L., Raeofy, Y., Berli, M., Bahdanovich, P., Moosmüller, H., and Zimmermann, R.: Soil chemistry and hydrophobicity caused by four 2021-22 western U.S. megafires., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1546, https://doi.org/10.5194/egusphere-egu24-1546, 2024.

Recently, wildfire activity and intensity in the western U.S. have greatly increased, mainly due to a warming climate, population growth, land use changes, and fuel accumulation. Disastrous effects during fires include loss of human lives and infrastructure, ecosystem disturbances, and emissions of carbon dioxide and air pollutants. In addition, wildfires modify physical and chemical soil properties and can cause Fire-Induced Soil Hydrophobicity (FISH), which reduces water infiltration into the soil and accelerates runoff during precipitation events. This may induce cascading disasters including flooding, landslides, and deterioration of water quality. To predict and mitigate such disasters, FISH is generally quantified at a few fire-affected locations using a manual infiltration test. However, this limited spatial coverage poorly represents FISH on a watershed scale as needed for prediction and mitigation purposes.

Watershed-wide, high-resolution monitoring of FISH is only practical using airborne or satellite-based remote sensing, for example utilizing solar reflectance spectra to characterize and monitor physical and chemical properties of fire-affected soils. Such spectra depend on light scattering and absorption at the soil surface. For this study, we have sampled ash, burned, and unburned soils, fresh (0 month), 1 year, and 2 years after three recent California (US) megafires: the Dixie (2021, 3,890 km²), Caldor (2021, 897 km²), and Beckwourth Complex (2021, 428 km²) fires. We studied the optical, chemical, and physical properties of all our samples. Optical hyperspectral reflectance spectra (350–2,500 nm) were obtained using natural solar (blue sky) illumination and a spectroradiometer (ASD FieldSpec3), operated in reflectance mode.  For all three fires, the results show that 700 nm wavelength reflectance of ash samples collected 1 and 1.5 years after the fire decreased between 36% and 76% compared to that of samples collected right after the fires. Additionally, significantly higher visible reflectance has been found for unburned compared to burned soil samples in each fire region that was studied. Fourier-transform infrared (FTIR) measurements were used to characterize the carbonate content of soil and ash samples demonstrating a positive relationship between carbonate content and visible reflectance, indicating a possible contribution of carbonate to the reflectance of soil/ash samples.

How to cite: Raeofy, Y., Samburova, V., Berli, M., Sion, B., and Moosmüller, H.: Hyperspectral Reflectance of Pre- and Post-Fire Soils: Toward Remote Sensing of Fire-Induced Soil Hydrophobicity, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1595, https://doi.org/10.5194/egusphere-egu24-1595, 2024.

Dissolved organic matter (DOM) is a major carbon pool and considered the most bioavailable and most mobile fraction of organic matter. DOM is generally defined as the organic matter passing a filter pore size of 0.2 or 0.45 µm, and this size cut off means that DOM not only contains dissolved molecules but also colloidal objects and aggregates up to a few hundred nanometres. The properties of this colloidal DOM fraction, such as for example size, shape, and surface charge, will affect its actual bioavailability and mobility in the environment. Although previously not well studied, there has recently been a growing interest in this colloidal fraction of DOM.

We have studied DOM extracted by water from a boreal spruce forest soil, filtered through a 0.2 µm pore size. By using a combination of spectroscopy techniques, such as NMR, and light (SLS, DLS), X-ray (SAXS) and neutron (SANS) scattering techniques, we can access chemical and physical information on both the molecular and colloidal fractions of DOM.

Our results show that the colloidal DOM has a homogenous chemical composition, and that carbohydrates is the dominating chemical component in both the colloidal and molecular DOM. The colloids have a mass fractal structure which does not change upon dilution and they are electrostatically stabilised against aggregation. In a lab scale study, we investigated the bacterial decomposition of this DOM during a two-month incubation. The molecular fraction of DOM was quickly decomposed. However, no change was observed for the colloidal DOM, constituting ca. 50% of the carbon, indicating that it persisted bacterial decomposition.

Our results suggest that colloidal properties could be an important but hitherto overlooked aspect to the central question of what dictates organic matter reactivity and persistency in different environments and across different time scales. Our current work extends from soil solution to aquatic ecosystems, to assess the ubiquity of the colloidal fraction of DOM.

How to cite: Andersson, E., Tranvik, L., Groeneveld, M., Tunlid, A., Persson, P., and Olsson, U.: Bacterial decomposition of dissolved organic matter: including the colloidal perspective, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-1957, https://doi.org/10.5194/egusphere-egu24-1957, 2024.

Biochar can increase long-term soil organic carbon (SOC) storage due to its polyaromatic structure. In addition to the recalcitrant carbon (C) contained in the biochar itself, biochar can also increase SOC storage by adsorption or organic matter on its surfaces, and reduced decomposition rate of native SOC (negative priming). Limited number of studies have looked at how biochar affects decomposition and stabilization of fresh C inputs, and native SOC decomposition. To fill this knowledge gap, we conducted a laboratory incubation study, where we followed the fate of added ¹³C-labeled glucose in a fine-textured agriculturally used soil (Stagnosol) amended with two different biochar levels corresponding to 15 and 30 Mg ha^-1 in field conditions. Biochar addition reduced mineralization of SOC and added ¹³C glucose, while increasing microbial biomass and microbial carbon use efficiency (CUE). Most of the added biochar, as well as remaining ¹³C were found in the free particulate organic matter (POM) fraction after 6 months, indicating that added ¹³C glucose was preserved within the biochar particles. Our closer study of ¹³C amino sugar fraction extracted from the biochar particles revealed that the microbes that had efficiently grown on the added ¹³C glucose in the presence of biochar, were retained as dead microbial residues inside the biochar pores. This microbial route could provide a way for additional formation of rather recalcitrant C in the form of microbial residues in the presence of biochar, which could with time contribute to building SOC stock in biochar amended soils beyond the C present in biochar itself. We found that biochar also increased the portion of occluded POM in the treatments without ¹³C glucose addition, demonstrating that increased soil occlusion following biochar addition reduced SOC mineralization. The effects were found to be dose-dependent, i.e. higher biochar application rate resulted in lower mineralization rate of native SOC and of added ¹³C-glucose.

How to cite: Karhu, K., Kalu, S., Seppänen, A., Mganga, K., Sietiö, O.-M., and Glaser, B.: Biochar enhanced microbial carbon use efficiency, while reducing mineralization of added and native soil organic carbon, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2117, https://doi.org/10.5194/egusphere-egu24-2117, 2024.

Elevated concentration levels of geogenic ammonium in groundwater arise from the mineralization of nitrogen-containing natural organic matter in various geological settings worldwide, especially in alluvial-lacustrine and coastal environments. However, the difference in enrichment mechanisms of geogenic ammonium between these two types of aquifers remains poorly understood. To address this knowledge gap, we investigated two representative aquifer systems in central Yangtze (Dongting Lake Plain, DTP) and southern China (Pearl River Delta, PRD) with contrasting geogenic ammonium contents. The use of optical and molecular characterization of DOM combined with hydrochemistry and stable carbon isotopes has revealed differences in DOM between the two types of aquifer systems and revealed contrasting controls of DOM on ammonium enrichment. The results indicated higher humification and degradation of DOM in DTP groundwater, characterized by abundant highly unsaturated compounds. The degradation of DOM and nitrogen-containing DOM was dominated by highly unsaturated compounds and CHO+N molecular formulas in highly unsaturated compounds, respectively. In contrast, the DOM in PRD groundwater was more biogenic, less degraded, and contained more aliphatic compounds in addition to highly unsaturated compounds. The degradation of DOM and nitrogen-containing DOM was dominated by aliphatic compounds and polyphenols and CHO+N molecular formulas in highly unsaturated compounds and polyphenols, respectively. As DOM degraded, the ammonium production efficiency of DOM decreased, contributing to lower ammonium concentrations in DTP groundwater. In addition, the CHO+N(SP) molecular formulas were mainly of microbial-derived and gradually accumulated with DOM degradation. In this study, we conducted the first comprehensive investigation into the patterns of groundwater ammonium enrichment based on DOM differences in various geological settings.

How to cite: Xiong, Y.: Characteristics of Dissolved Organic Matter Contribute to Geogenic Ammonium Enrichment in Coastal versus Alluvial-lacustrine Aquifers, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3292, https://doi.org/10.5194/egusphere-egu24-3292, 2024.

Natural organic matter (NOM) was widely investigated in natural waters, sea water, river water, lake water, groundwater. The highest molecular resolution of NOM can be achieved by Fourier-transform ion cyclotron resonance mass spectroscopy (FT-ICR-MS). This analytical tool generates molecular formulas (MF) for thousands of NOM components. By coupling liquid chromatography to FT-ICR-MS insights into the polarity (hydrophilic versus hydrophobic) of NOM compounds can be achieved.

Anthropogenic inputs have an imprint on NOM and it changes its overall composition. Aquaculture is one of the fastest growing sectors of food production by covering over 8 Mio ha. The consequences of fish farming for the organic matter quality in fish pond waters and sediments are poorly understood. Here we investigated the stages of pollution by comparison the water extractable organic matter (WEOM) in the sediment at the main site of fish feed application and open water sediments at different distances (transect) to the feeding site.

Full profile HPLC-FTICR-MS chromatograms were segmented into approx. one-minute wide segments between 10 and 15 Min (five segments), the main eluting region of WEOM. MF were calculated for the mass range 150 - 1000 Da with an error threshold of 1 ppm using in-house software considering the following carbon (C), hydrogen (H), oxygen (O), nitrogen (N) and sulphur (S) elements: ¹²C_0–60, ¹³C_0–1, ¹H_0–122, ¹⁶O_0–40, ¹⁴N_0–8, ³²S_0–3, and ³⁴S_0–1.

For all retention times, N3, N4, N5, N6, N7 (CHNO) MF with 0.2 < O/C < 0.5 and 1.5 < H/C < 2.0 showed relative higher intensities in the feeding center compared to the distant sites. For some MF like C₂₀H₃₇N₅O₇, C₂₂H₃₉N₅O₇, C₂₄H₄₂N₆O₁₀ the intensity was more than five times higher in the center compared to open water site. Such components can be suggested to be oligopeptides (Leu-Asn-Thr-Ile, Glu-Pro-Lys-Ile, Leu-Leu-Asp-Ser-Gln as possible isomeric solutions). The sediment in the feeding center exhibited a prevalence of CHNOS and CHOS2 MF, whereas N1, N2, CHOS1, and CHO displayed relatively uniform intensities along the transect, with some instances of slightly higher intensities observed away from the feeding site. The number and abundance of CHNOS MF decreased with increasing retention time (decreasing polarity). Notably, these compounds appear to be inherently hydrophilic, characterized by predominantly low molecular weights (< 400 Da).

The results obtained suggest the following biogeochemical processes: Initially, the protein-rich fish feed undergoes hydrolysis, leading to the formation of oligopeptides. Subsequent partial desamination of these molecules facilitates their interaction with inorganic sulphides, resulting in the formation of CHNOS MF. Notably, the component C₈H₁₃N₁O₃S₁, exhibiting a five-fold intensity at the feeding site, appears to correspond to one of the possible metabolites (Sulfanylpropanoyl-proline).

The results indicate a potential overfertilization with easily biodegradable protein-rich substances. The WEOM quality seems highly affected by additional input of CHNO, CHNOS and CHOS.

How to cite: Herzsprung, P., Waldemer, C., Koschorreck, M., and Lechtenfeld, O.: NOM quality differences in sediments of land based aquacultures – insights by liquid chromatography-high resolution mass spectrometry, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3355, https://doi.org/10.5194/egusphere-egu24-3355, 2024.

Deepwater formation in the North Atlantic Ocean is a major gateway for dissolved organic matter (DOM) transport into the deep ocean. Despite focusing on vertical mixing, lateral transport of DOM from productive shelf regions is underexplored. Previous research suggested substantial offshore DOM transport on the Irish and Hebrides Margin via the bottom Ekman Drain. Our in-depth bottom water DOM analyses of carbon isotopes in combination with ultrahigh-resolution mass spectrometry (FT-ICR-MS) indicated that downwelling in this region leads to higher DOM concentrations (by 7–11 μM) and younger radiocarbon ages (by 190–330 yrs) compared to DOM of the central Northeast Atlantic at similar depths. During downslope transport, conservative mixing shapes the molecular composition of recalcitrant DOM, while minor particulate organic matter degradation contributes to producing less-refractory DOM with terrigenous signals. Consequently, the bottom Ekman transport emerges as a rapid and efficient channel for transporting fresh DOM into the deep North Atlantic Ocean, acting as a crucial carbon sink for atmospheric CO₂.

How to cite: Wei, B., Seidel, M., Mollenhauer, G., Grotheer, H., Wendt, J., Dittmar, T., and Holtappels, M.: Rapid lateral transport of fresh dissolved organic matter to the deep ocean in the NE Atlantic, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3667, https://doi.org/10.5194/egusphere-egu24-3667, 2024.

Cold seeps and cold water corals (CWCs) coexist on Northern Norway's continental shelf at the Hola trough between Lofoten and Vesterålen. Here, cold seeps release methane from the seabed, yet only a limited amount reaches the atmosphere. The remaining methane dissolves and disperses in nearby seeps. Methane is unreactive for most microorganisms in the water column, yet it is a unique energy and carbon source for methane-oxidizing bacteria (MOB). MOBs metabolize methane and release carbon dioxide as the end product of oxidation. Increasing carbon dioxide may constrain pH-sensitive CWCs in the region. We investigated the biogeochemistry of carbon, carbon isotopes, nutrients, dissolved organic matter (DOM) compositions and microbial diversity through water column profiles and water samples collected in June 2022. Preliminary results indicated that elevated methane increases dissolved inorganic carbon concentrations and modifies carbon isotopic compositions. Additionally, DOM compositions implied a positive correlation between prokaryotic diversity and protein-like DOM components at cold seeps and the entire water column near CWCs, suggesting analogous microbial modifications. Our preliminary conclusion suggests cold seeps and CWCs symbiotically coexist in Northern Norway continental shelves; however, enhanced water temperatures and consequent increase in methane release at cold seeps may mitigate the functioning of CWCs in future.

This study is supported by the Research Council of Norway, project number 320100, through the project EMAN7 (Environmental impact of Methane seepage and sub-seabed characterization at LoVe-Node 7).

How to cite: Sert, M. F., Dølven, K. O., Petters, S., Kekäläinen, T., Jänis, J., Corrales-Guerrero, J., and Ferré, B.: Carbon cycling in coexisting marine ecosystems: Cold seeps and coral reefs in Northern Norway, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-3890, https://doi.org/10.5194/egusphere-egu24-3890, 2024.

As a vital component of the global carbon cycle, the ocean’s biological carbon pump determines the amount of carbon fixed by primary production in the surface waters. The efficiency of this biological pump is closely interconnected with the nitrogen cycle, which regulates nutrient inventory and primary productivity rates. Additionally, the structure of the upper ocean ecosystem influences the efficiency of the biological pump by determining how much fixed carbon is exported to the deep ocean. Compound-specific nitrogen isotope (δ¹⁵N_AA) is a novel proxy that could provide valuable insights into both aspects of these questions. The δ¹⁵N_AA could unravel isotopic information of source nitrogen and show δ¹⁵N changes associated with trophic processes. This study generates sedimentary δ¹⁵N_AA, as well as bulk sediment δ¹⁵N and organic δ¹⁵N records from a western equatorial Pacific site (MD10-3340) covering the last 140 kyr. Our results demonstrate an overall agreement among three proxies, all indicating distinct precessional variations in source nitrate δ¹⁵N and potential changes in nutrient inventory. More importantly, the δ¹⁵N_AA signatures suggest an inverse relationship between animal trophic activity in the surface water and the degradation of organic matter precipitating through the water column. Higher ecosystem trophic position is found during glacial periods, accompanied by inactive organic matter recycling, which implies a greater potential for carbon burial in deep reservoirs. Together, we suggest that the δ¹⁵N_AAsignatures can provide a detailed picture of carbon cycle coupled with nitrogen cycle.

How to cite: Li, C., Jian, Z., and Dang, H.: Efficiency of Biological Carbon Pump: Insights from Compound-Specific Amino Acid δ15N, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5444, https://doi.org/10.5194/egusphere-egu24-5444, 2024.

DOM from peatlands is a collection of complex molecules, but also a significant source of carbon to aquatic pathways. It has a wide impact on aquatic ecosystems, providing an energy source for microbes and buffering capacity for water chemistry changes. The composition of DOM in drinking water reservoirs also impacts on chemical and energy demands of treatment processes, and is an area of growing concern for UK drinking water providers.

DOM was extracted from water collected from peatland headwater streams and reservoirs in the UK. The DOM was analysed with elemental analysis and FT-ICR MS to determine how the composition changes as water moves through the catchment. A combination of spatial and temporal sampling strategies allowed seasonal and catchment characteristics to be investigated (from 2018-2021, and 53-61°N).

There were significant trends in DOM composition metrics across a north/south gradient, with higher lipid content, and lower carbohydrate and peptide content in northern sites than southern sites. Samples collected in 2021 had several significant composition differences to other years. Monthly sampling showed the largest changes in DOM composition coincided with the end of the growing season (September in the UK).

These results show variable DOM in headwaters can be, and how reservoirs act to buffer the most extreme changes, resulting in more stable DOM compositions in reservoirs. Understanding how DOM composition is impacted by season, climate and catchment characteristics will have important ramifications for drinking water providers, and will help catchment managers plan land use changes and timing of water draw-off from peatland reservoirs.

How to cite: Moody, C., Bell, N., Mackay, L., and Kitson, E.: Temporal and spatial changes in DOM revealed by FT-ICR MS, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-5586, https://doi.org/10.5194/egusphere-egu24-5586, 2024.

The binding properties of dissolved organic matter (DOM) play a crucial role in the biogeochemical cycles of trace metals and carbon. The composition of DOM is anticipated to exert influence over the magnitude and distribution of the intrinsic ion binding affinities that occur over a continuum of values, referred to as the affinity spectra. These spectra encompass many different organic acid groups that contribute to the nuanced binding characteristics of DOM. The total proton binding capacity represents the maximum sites available for other chemical species that may compete with protons for the same DOM binding sites, particularly in the case of metals. Consequently, the study of proton binding by DOM becomes the initial step to investigate deeper into metal binding mechanisms. Here, we research the variability in proton binding exhibited by DOM extracted from the Ebro and Mero Rivers (NNE and NW of Spain), and at the Atlantic Ocean and Mediterranean Sea. Our approach combines the non-ideal competitive adsorption (NICA) isotherm, offering insights into chemical binding on heterogeneous ligands, with the Donnan electrostatic model, which accounts for polyelectrolytic effects, i.e., the non-specific binding. This methodology enables us to pinpoint potential shifts in DOM binding affinities and derive a comprehensive set of intrinsic binding parameters for DOM. Importantly, these parameters are thermodynamically consistent and remain independent of the specific conditions of the samples, enhancing the extrapolation to future environmental changes.

Acknowledgements: Authors thank Agencia Española de Investigación for the financial support through the research projects PID2020-117910GB-C21 and -C22/AEI/10.13039/501100011033. P.L. acknowledges current support from the Ministerio de Ciencia, Innovación y Universidades of Spain and University of Lleida (Beatriz Galindo Senior award number BG20/00104)

References:

[1] Lodeiro, P., Rey-Castro, C., David, C., Humphreys, M. H., Gledhill, M., 2023. Proton Binding Characteristics of Dissolved Organic Matter Extracted from the North Atlantic. Environmental Science & Technology 57, 21136–21144.

[2] Waska, H., Brumsack, H.-J., Massmann, G., Koschinsky, A., Schnetger, B., Simon, H., Dittmar, T., 2019. Inorganic and organic iron and copper species of the subterranean estuary: Origins and fate. Geochimica et Cosmochimica Acta 259, 211–232.

[3] Heerah, K. M.,  Reade, H. E., 2023. Towards the identification of humic ligands associated with iron transport through a salinity gradient. Scientific Reports 12:15545.

How to cite: Lodeiro, P., Macedo, J. C. A., David, C., Rey-Castro, C., Puy, J., Martínez-Cabanas, M., Herrero, R., Sastre de Vicente, M. E., and Barriada, J. L.: Variations in binding properties of dissolved organic matter along river-ocean continuum, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6501, https://doi.org/10.5194/egusphere-egu24-6501, 2024.

Rivers play a key role in the global carbon cycle by transferring organic carbon (OC) from the terrestrial biosphere to marine sediments, which act as an important long-term carbon sink. Associations between biospheric OC and mineral phases can alter OC stability and hydrodynamic properties, thereby influencing its transport and storage patterns within a river basin and dictating the fate of terrestrial biospheric OC discharged to the ocean. While research has mainly investigated the formation of these associations within soils, open questions remain on how these interactions evolve over space and time.

The Fraser River Basin in British Columbia, Canada drains regions with distinctive lithological and climatic gradients allowing the simultaneous study of leaf-wax-specific isotopic compositions (δ²H, δ¹³C) and inorganic geochemical signatures (εNd) of sediments as tracers of the provenance of biospheric OC and detrital mineral phases, respectively. In addition, bulk radiocarbon (D¹⁴C) serves as a tool to constrain biospheric OC residence times. Here, to investigate seasonal variations in the geochemical signatures of OC and its mineral host in sediments exported by the Fraser River to the Strait of Georgia using samples from a time-series sediment trap deployed cover the course of a year adjacent to the river mouth.

Both εNd and D¹⁴C follow a seasonal pattern by which aged OC (-176 to -140‰) is mostly transported during high discharge events such as the freshet in June and heavy rainstorms occurring in the upper basin in fall. During the former event, the geochemical signature (ε_Nd: -9.2 to -7.2) points towards the Coastal Range affecting the detrital mineral composition more strongly, which shifts towards a greater proportion of Rocky Mountains-sourced sediment (ε_Nd: -11.7 to -9.1) during the second high discharge event. Biomarker specific δ2H will further elucidate the extent to which the provenance of biospheric OC coincides with the mineral detrital load. Further, comparison with geochemical signatures of fluvial sediments within the Fraser basin, together with corresponding signatures in river-proximal sediments deposited in the Strait of Georgia allow for OC-mineral interactions to be assessed from a source-to-sink perspective.

This coupled investigation of organic and inorganic tracers provides new insights into terrestrial organic carbon export and the role of organo-mineral interactions on riverine organic carbon dynamics. These findings also have important ramifications for the interpretation of sedimentary archives.

How to cite: Gallarotti, N., Peucker-Ehrenbrink, B., Johannessen, S., Bröder, L., Wijker, R., Voss, B., Haghipour, N., and Eglinton, T.: Spatio-temporal dimensions of organic carbon-mineral interactions in a source-to-sink system, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6516, https://doi.org/10.5194/egusphere-egu24-6516, 2024.

Dissolved organic matter (DOM) is diverse in composition and serves as substrate for microbial metabolism. Within subterranean estuaries (STEs), DOM is introduced from different sources along the groundwater flow paths. These different DOM sources make it challenging to disentangle degradation pathways, especially in high-energy beaches with dynamic porewater advection and changing redox conditions. We performed sediment incubations in flow-through reactors (FTRs) to investigate how DOM from different sources is transformed by STE microbial communities. We used sediment and groundwater from the STE of a high-energy beach on Spiekeroog Island (Germany). Intertidal beach sediments were incubated for 13 days in FTRs with groundwater of low (~1.6) and high salinity (~29.1) as marine and terrestrial endmember, respectively, in triplicate setups, and additional control FTRs with artificial seawater of respective salinities. The FTRs ran under oxic conditions with recirculating advective flow. Porewater samples were taken daily for quantification of dissolved organic carbon (DOC) and nutrient concentrations, and samples from the start and the end of the incubation were taken for the analysis of microbial community composition, microbial cell numbers, and DOM composition. DOM samples were isolated through solid phase extraction and molecularly characterized via ultrahigh-resolution Fourier-transform ion cyclotron resonance mass spectrometry. Over the course of the incubation, DOC concentrations increased, presumably from sediment leaching and potentially also by primary production in light-exposed parts of the setup, as oxygen concentrations also increased. The DOM composition of the porewater samples at start and end of the incubation was highly diverse, with a total of up to 2900 different molecular formulae detected in each sample. As expected, the low salinity porewater had a more terrestrial DOM signature with a higher proportion of aromatic compounds compared to the DOM in the high salinity porewater. In all setups, the DOM composition changed significantly from start to end. We observed an increase in DOM lability in both endmember setups indicating the mobilization of fresh DOM from sediments and/or microbial activity, including primary production. Interestingly, the changes observed were similar for both DOM endmembers. Our results indicate that the microbial communities of the high-energy beach STE thrive on a similar fraction of DOM, independent of its source.

How to cite: Abarike, G., Brick, S., Engelen, B., and Niggemann, J.: Different dissolved organic matter (DOM) sources sustain microbial life in beach subterranean estuary, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-6629, https://doi.org/10.5194/egusphere-egu24-6629, 2024.

The increased frequency and intensity of climate extremes challenges vineyards to adapt and mitigate to ensure the survival of grape vines (Vitis vinifera) to meet the growing demand for quality wine.  Regenerative Viticulture (RV) is a novel approach with a strong focus on increasing soil carbon (C) stocks to regenerate vineyard soil that is largely degraded and in poor health.  When soil health and fertility is low, this impacts vine health and reduces its ability to fight disease and pests and withstand extreme climatic events. We hypothesised that biochar would increase nitrogen (N) cycling and retention and that these would differ in relation to the distinct physiochemical properties of the two vineyard soils.   Conscious of contributing to a sustainable circular economy, we utilised viticulture industry waste to produce biochar’s to compare with standard pine biochar.  Biochar was produced with three feedstocks at different pyrolysis temperatures, grape marc (475°C), vine pruning (450°C) and pine (600°C).  Soil (0 - 10 cm depth) was collected from under vines from vineyards at the South Burnett (heavy texture) and Granite Belt (sandy texture) regions in Queensland, Australia. We used a novel ¹⁵N natural abundance approach in a laboratory incubation experiment to investigate the potential of using biochar, a C-dense material produced by high temperature pyrolysis of organic materials in limited oxygen conditions as a suitable climate smart RV method for vineyard soils.  A short three-day laboratory incubation followed by microdiffusion was conducted to quantify the impacts of the three biochars on N transformations in the two soils.  Soil moisture was controlled at 60% and 90% water holding capacity (WHC) and biochar applied at 0% and 10% (w/w), with samples harvested on incubation days 0 and 3. Preliminary results indicate that in the short term for both experimental soils, biochar stimulated microbial activity, increased N availability and water use efficiency and reduced N loss through denitrification.  The results indicate that fungicides use in vineyards impacted the underlying soil health and microbial communities and influencing N cycling.  For the long term impact, the potential to use biochar for increase biodiversity and ecosystem recovery as a climate smart RV method in vineyards needs to be trialled in the field.  This is to establish the long-term effects of C accumulation and improved N cycling on soil health, biodiversity, vine resilience under extreme natural weather events, and on wine grape quality and quantity.

How to cite: Kingston, K., Xu, Z., Pratt, C., Mackey, B., Petrie, P., and Li, Y.: Using a novel N-15 natural abundance approach to quantify soil nitrogen transformations in biochar-treated vineyard soils., EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7088, https://doi.org/10.5194/egusphere-egu24-7088, 2024.

The presence of organic molecules containing sulfur-sulfur bonds was identified in both water columns and sediments of natural aquatic systems. While processes leading to formation of these compounds were intensively studied during recent decades, the kinetics and mechanisms of reactions responsible for their decomposition remain poorly understood. This study focuses on the kinetics and products of the reactions of dimethyl disulfide, dimethyl trisulfide, and cyclic polysulfide lenthionine (1,2,3,5,6-pentathiepane) with hydrogen sulfide at the pH and temperature ranges typical of environmental conditions. The findings reveal that under environmental conditions (pH≥5), the overall reaction rates are primarily controlled by the reaction of bisulfide anion (HS^-) rather than hydrogen sulfide. The activation energy and the order of the reaction with respect to bisulfide anion is dimethyl disulfide < dimethyl trisulfide < lenthionine, while the order of the reaction with respect to organosulfur compounds is lenthionine < dimethyl trisulfide < dimethyl disulfide. The rates of the reactions between linear dimethyl polysulfides with bisulfide anion were found to be higher than the rates of their reactions with cyanide and hydroxyl anions, but lower than the rates of their photodecomposition. These results suggest that rapid decomposition of organosulfur compounds in sulfidic aphotic natural aquatic systems should be controlled by HS^- decomposition pathway. Products of the decomposition of dimethyl disulfide and dimethyl trisulfide include methanethiol, higher dimethyl polysulfides, and inorganic polysulfides. The cyclic polysulfides were shown to be more stable than their linear analogs, resulting in their preferential preservation during the maturation process.

How to cite: Zweig, I. and Kamyshny, A.: Reactivity of hydrogen sulfide toward organic compounds with sulfur-sulfur bonds, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7317, https://doi.org/10.5194/egusphere-egu24-7317, 2024.

Radiocarbon (¹⁴C) measurements provide a powerful tool to deconvolute sources and dynamics of organic matter in the environment. However, interpretation of conventional bulk-level ¹⁴C data is challenging due to the myriad components comprising organic matter in soils and sediments. Thermally ramped oxidation provides one approach for overcoming this limitation, and involves subjecting a sample to gradually increasing temperatures, serially oxidizing the OC to CO₂. Collected over prescribed temperature ranges ('thermal fractions'), this CO₂ is then analyzed for ¹⁴C content using accelerator mass spectrometry (AMS). While effective, current ramped oxidation methods are mostly 'offline', involving manual collection and subsequent AMS analysis of evolved CO₂, hindering sample throughput and reproducibility.

Here, we introduce a compact, online ramped oxidation (ORO) setup in which CO₂ from discrete thermal fractions is directly collected and measured for ¹⁴C by AMS equipped with a gas ion source. The setup comprises two modules: (i) an ORO unit with two sequential furnaces - the first, ramped from room temperature to 900 °C, holds the sample; the second, maintained at 900 °C, includes a catalyst ensuring complete oxidation to CO₂; and (ii) a dual-trap interface (DTI) collection unit with two parallel molecular sieve traps alternately collecting and releasing CO₂ from a given fraction for direct injection into the AMS.

Preliminary results indicate reproducible data, evident in both thermograms and F¹⁴C results. Analysis of natural reference samples reveals that measured ¹⁴C values and their associated uncertainties align with those reported in the literature using conventional “off-line” ramped oxidation methods, affirming the utility of the new ORO-DTI-AMS setup.

Our goal is to apply this new method for comprehensive investigation of a range of natural samples, with a particular focus on the improved understanding of the fate of OC held in permafrost soils in the context of on-going climate and carbon cycle change in high latitude ecosystems.

How to cite: Bolandini, M. A., De Maria, D., Haghipour, N., Wacker, L., Hemingway, J. D., Eglinton, T. I., and Bröder, L.: Towards an online ramped oxidation approach for thermal dissection and serial radiocarbon measurement of complex organic matter, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7593, https://doi.org/10.5194/egusphere-egu24-7593, 2024.

Subterranean estuaries underlying high-energy beaches are efficient turnover sites for dissolved organic matter (DOM) and nutrients from marine and terrestrial waters. In addition, leaching of beach wrack during tidal inundation and precipitation can contribute to DOM and nutrient loads. However, the combined impact of diverse environmental settings on the release of DOM and nutrients from beach wrack has so far not been studied, although e.g., salinity oscillations and temporary exposure to sunlight are common in high-energy beach subterranean estuaries. Here, we present the results of an extensive beach wrack leaching experiment taking beach wrack type, age, sunlight exposure, and leaching matrix into consideration. A combination of UVA irradiation, advanced wrack age, and leaching by low-salinity artificial rainwater resulted in high dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) releases of mmoles- to moles per kg dry weight in the macroalga Fucus sp. Furthermore, jellyfish wrack released millimoles of TDN in artificial seawater incubations. Ultra-high-resolution analyses of DOM revealed a prevalence of molecular formulae resembling biochemical building blocks such as sugars, amino acids, and vitamins, indicating that the released DOM could be of substantial nutritional value for the heterotrophic microbial communities on and near beach wrack. An interesting finding was the high abundance of aromatic and humic-like DOM released from macroalgal beach wrack, which may impact typically used marine and terrestrial source- and sink proxies. As such, beach wrack DOM and nutrients could further complicate biogeochemical distribution patterns in the subterranean estuary.

How to cite: Waska, H. and Banko-Kubis, H.: Experimental comparison of dissolved organic matter and nutrients leached from beach wrack by sea- and rainwater: A nutritional boost for the sandy beach subterranean estuary, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-8750, https://doi.org/10.5194/egusphere-egu24-8750, 2024.

Carbonate-associated organic matter (CAOM) is the organic matter associated with carbonate minerals, and a survey of carbonate-rich surface sediments suggests that it is incorporated at a consistent amount scaling with the internal surface area of the carbonate grains. As the carbonate sediment is sensitive to changes in saturation state due to benthic biogeochemical processing, we predicted that CAOM could exhibit interesting biogeochemical cycling, based on its potential to bridge particulate and dissolved pools of organic matter. Here, we report on a study in a seagrass meadow in central Florida Bay, USA. We utilize a combination of inorganic stable isotope (C, S, O) and high resolution mass spectrometry (21T FT ICR-MS) techniques to explore the carbon and sulfur cycles here, with a particular emphasis on dissolved organic matter (DOM) characterization. CAOM is examined similar to standard solid phase extraction (SPE-DOM) methods, after first washing carbonate sediment and dissolving it incompletely under a mild hydrochloric acid treatment. The δ³⁴S and δ¹⁸O of sulfate, as well as the δ¹³C of dissolved inorganic carbon (DIC), suggest that the promotion of sulfide oxidation in the seagrass rhizosphere drives rapid carbonate dissolution and re-precipitation cycles. Sulfide oxidation, as well as elevated sulfide concentration, promotes sulfurization of CAOM, which is more sulfurized than porewater and surface water, as 42% of CAOM formulas vs 28% of surface water are sulfurized. Furthermore, a substantial quantity of molecular formulas present in the overlaying surface waters (90% of formulas, 97% by relative abundance) are also present in CAOM. Despite the CAOM sample containing nearly twice the number of formulas compared to surface water, due in part to its higher dissolved organic carbon concentration, these shared formulas make up 75% of the abundance of CAOM formulas. We argue that repeated coupled sulfur and inorganic carbon cycles, intensified by seagrasses, leads to increased sulfurization and release of CAOM, affecting DOM quality in the broader aquatic system. We estimate that approximately 9% of the particulate organic carbon (POC) stored in the sediments of this site are CAOM. Our results suggest that CAOM here is a form of “dissolvable” organic carbon which cycles much more rapidly than POC more broadly.

How to cite: Zeller, M., Van Dam, B., McKenna, A., Lopes, C., Osburn, C., Fourqurean, J., John, K., and Böttcher, M.: Carbonate-associated organic matter: A form of “dissolvable” organic matter?, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10047, https://doi.org/10.5194/egusphere-egu24-10047, 2024.

The balance between remineralization and sedimentary burial of terrestrial organic carbon (OC_terr) in large river-dominated marginal seas influences atmospheric CO₂ inventory on a range of timescales. Here we systematically investigate the evolution of OC_terr along the river-estuary-coastal ocean continuum for three fluvial systems discharging to the Chinese marginal seas. The ¹⁴C-depleted characteristics of bulk OC and molecular components of riverine suspended sediments and marine sediments suggest that the Chinese marginal seas are a significant sink of pre-aged OC_terr. Lower plant-wax fatty acid ¹⁴C contents suggest selective degradation of labile OC within estuaries, resulting in apparent aging of OC_terr, followed by an apparent rejuvenation in OC_terr in shelf sediments, the latter likely reflecting inputs from proximal sources that contribute younger OC_terr. This selective degradation, aging and rejuvenation of OC_terr along the continuum confounds the use of plant wax lipid ¹⁴C to constrain lateral transport times, and sheds light on more complex OC_terr dynamics in marginal seas.

How to cite: Yu, M., Eglinton, T., Hou, P., Haghipour, N., Zhang, H., Wang, Z., and Zhao, M.: Apparent Aging and Rejuvenation of Terrestrial Organic Carbon Along the River-Estuary-Coastal Ocean Continuum, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-10209, https://doi.org/10.5194/egusphere-egu24-10209, 2024.

We know that the concentrations of CO₂ and DIC in the subsurface are often magnitudes higher than in the soil zone, and therefore we need to understand this reservoir and its vulnerability to change. Understanding the critical zone in the context of CO₂ input, cycling dynamics, and export is essential as this carbon is particularly vulnerable to changes in water table rise which may result in rapid release of CO₂ into the atmosphere. Cave environments provide an accessible natural window into the critical zone as they connect meteoric water, soils, the unsaturated vadose zone, and saturated zone. We conducted a two year monitoring campaign at Milandre cave in northern Switzerland, analyzing pCO₂, d¹³CO₂, and ¹⁴CO₂ at various environmental interfaces, including the soil zone, within the epikarst, and in the cave itself. Forest soils maintained stable, modern ¹⁴C signatures and low d¹³C indicating year-round contribution of CO₂ from C3 tree and plant root respiration. Conversely, meadow soils exhibited notable seasonality in F¹⁴C, suggesting a dominance of respiration from older soil pools in the winter months. Distinct variations in CO₂ concentrations were observed within the cave, influenced by temperature driven ventilation dynamics. Keeling plot analysis revealed a consistent contributing endmember of C3 vegetation. However, similarities between the F¹⁴C of the meadow soils and cave CO₂ suggests a significant contribution of meadow soil CO₂ into the cave. These findings offer vital insights into the nuanced dynamics of CO₂ sources and cycling processes within the critical zone of Milandre Cave, shedding light on the influences of seasonal variation and ecological influences of critical zone carbon and the export of carbon from terrestrial ecosystems.