EGU General Assembly 2023  

River ecosystems are superlatives in many respects. Their networks represent the largest biogeochemical nexus between the continents, oceans and atmosphere. River networks span multiple catchments, even biomes, and are highly dynamic in space and time. The world’s rivers contribute relatively little by areal extent, but their CO₂ emissions are of the same magnitude as the CO₂ sequestration flux by the world’s oceans. Rivers figure among the most heterotrophic ecosystems on Earth, metabolizing terrestrial organic carbon. Owing to their dendritic structure, the biodiversity that river networks host is exceptionally high. Finally, needless to emphasize how critical the ecosystem services are that rivers provide. Central to many of these river superlatives are microbial biofilms that abundantly coat the sedimentary surfaces of the river beds. A microbiome, encompassing all three domains of life, shapes, in conjunction with the turbulent nature of water flow, intriguing biofilm architectures. Biofilms, a hidden beauty emanating from the interactions between biology, physics and chemistry, regulate ecosystem energetics and are therefore an important linchpin between river biodiversity and biogeochemistry.

In my lecture, I will attempt to provide the state-of-the-art of global river carbon biogeochemistry and biofilm ecology. An emphasis will be given on the rivers that literally drain the roof of our planet, now at risk because of climate change. It is my hope, that soon we will appreciate the world’s river networks as we do appreciate the oceans and various terrestrial ecosystems.

How to cite: Battin, T. J.: River ecosystems: A tale of superlatives and hidden beauty, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8898, https://doi.org/10.5194/egusphere-egu23-8898, 2023.

Study of past carbon cycle perturbation events is fundamental for assessing Earth’s climatic and ecological sensitivities, and our planet’s overall biogeochemical functioning and responses. Major hindrance to our understanding is the lack of reliable CO₂ estimates from Earth’s ‘deeper’ geologic past. I will summarize my work on CO₂ reconstruction from the rock record and make the case that boron isotope values of brachiopod shells serve as a robust CO₂ proxy. I will first present evidence from culturing experiments and natural marine settings demonstrating that the boron isotope composition of recent brachiopod shells responds predictably to the coupled ocean pH and CO₂ system, and provide a calibration that enables its accurate quantification. Next, I will showcase ocean pH and CO₂ records for some of most crucial yet enigmatic events in Earth’s evolutionary history, including the Permian-Triassic mass extinction, and discuss the causes and consequences of CO₂ change and its biogeochemical impacts during extinctions and events of abrupt environmental change. Finally, I will highlight recent progress and new capabilities to lay out a roadmap towards robust record of Phanerozoic CO₂.

How to cite: Jurikova, H.: Causes and consequences of environmental perturbations through the Phanerozoic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9859, https://doi.org/10.5194/egusphere-egu23-9859, 2023.

Fire is an integral component of ecological dynamics, playing an important role in biome distribution and biomass variability. Nonetheless, fires can also pose a  threat to both ecosystems and humans, by imposing severe economic and social consequences, and potentially contributing to biodiversity loss, carbon loss and soil erosion, whose effects can last from months to years.

The Mediterranean basin is a fire-prone region where vegetation is in general well adapted to fire, with several species showing resistance to fire itself or being able to recover quickly following fire events. However, as a consequence of climate change, more intense and frequent summer hot and dry conditions are expected to occur, which can promote more frequent and severe wildfires, with return periods potentially outpacing recovery times. Understanding recovery dynamics is therefore crucial to assess the impact of changing fire regimes in ecological dynamics and stability of ecosystems. 

In our study, we use the “Enhanced Vegetation Index” (EVI), remotely-sensed by MODIS sensor with a temporal span of 22 years, to evaluate vegetation dynamics before, during and following large fire seasons. We use a mono-parametric recovery model to assess recovery times in different burn scars across the Mediterranean basin, covering different fire regimes and land cover types. We find a tendency for slower recovery in areas that burned more often, which may indicate a decrease in ecosystems’ resilience in the past 22 years.

This study was performed under the frameworks of the 2021 FirEUrisk project (funded by European Union’s Horizon 2020 research and innovation programme under the Grant Agreement no. 101003890) and of the PhD MIT Portugal MPP2030-FCT programme (Grant no.22405886350).

How to cite: Ermitão, T., Gouveia, C., Bastos, A., and Russo, A.: Assessing changes in post-fire vegetation resilience in Mediterranean basin over the past 22 years, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-412, https://doi.org/10.5194/egusphere-egu23-412, 2023.

Wildfire is a global scale ecosystem phenomenon with substantial impact on the carbon cycle, climate warming, and ecosystem resilience. Fire and the hydrological cycle are strongly interlinked, with water availability determining the amount and combustibility of fuel, and fire influencing infiltration, runoff rates and evapotranspiration. Consequently, understanding soil moisture (SM) and vegetation water content (VWC) dynamics pre- and post-fire is fundamental for predicting fire occurrence, fire severity, and ecosystem recovery. Fire can modulate SM and VWC dynamics by influencing interception of rainfall, soil porosity, plant water uptake, and runoff; however, much evidence for fire effects on the hydrological cycle is obtained at the field- to watershed-scale. Therefore, we ask the following research question: What are the effects of large-scale fire events on SM and VWC dynamics across biomes globally?

Here we use over six years of global SM, VWC and vapor pressure deficit (VPD) derived from different remote sensing datasets to investigate the effects of large-scale fires on SM and VWC dynamics. We apply a dry down framework, only analyzing consecutive observations of decreasing soil moisture, to describe post-fire response rates for SM, VWC and VPD relative to a pre-fire reference state.

We find large scale evidence that the post-fire rate of change of SM over time is more negative, indicating faster water loss. Vegetation recovery, indicated by a positive change in VWC over time, exceeds the pre-fire reference state, which suggests that post-fire recovery is predominantly faster than undisturbed seasonal vegetation growth, likely due to succession of fast-growing plant species. Furthermore, fire affects ecosystem hydrology on shorter timescales as well, reducing diurnal VWC variation over a wide range of SM and VWC conditions. Our findings confirm several trends previously only observed at smaller scales and suggest global remote sensing of SM and VWC can substantially contribute to understanding the dynamics of post-fire plant and soil water status.

How to cite: Baur, M. J., Friend, A. D., and Pellegrini, A. F. A.: Large-scale fire events substantially impact plant-soil water relations across ecosystem types, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1406, https://doi.org/10.5194/egusphere-egu23-1406, 2023.

Australia’s unprecedented fire disasters at the end of 2019 to early 2020 emitted huge amounts of carbon monoxide (CO) and fire aerosol particles to the atmosphere, particularly during the Pyrocumulonimbus (pyroCb) outbreak that occurred in southeast Australia between 29 December 2019 and 4 January 2020. It was estimated that at least 18 pyroCbs were generated during this episode, and some of them injected ice, smoke, and biomass burning gases above the local tropopause.  An unprecedented abundance of H₂O and CO in the stratosphere, and the displacement of background ozone (O₃) and N₂O from rapid ascent of air from the troposphere and lower stratosphere were found from satellite observations. Some other studies also found that the fire emissions and their long-range transport resulted in stratospheric aerosol, temperature, and O₃ anomalies after the 2020 Australian bushfires and altered the Antarctic ozone and vortex, posing great impact to local air qality and climate change.

            This study will focus on the thermodynamic state of atmosphere associated with these pyroCbs, and its impact on the change of the cloud properties and trace gases during this unprecedented Australia fires, mainly based on a new single Field of View (SFOV) Sounder Atmospheric Products (SiFSAP) and TROPOMI. SiFSAP was developed by NASA using the Cross-track Infrared Sounder (CrIS) and Advanced Technology Microwave Sounder (ATMS) onboard SNPP and JPSS-1, and will soon be available to the public at NASA DAAC. Since this product has a spatial resolution of 15 km at nadir, which is better than most global weather and climate models and other current operational sounding products, a process-oriented analysis of the dynamic transport of CO and fire plumes during this unprecedented fire disasters will be made in this study.  Based on a Principal Component Radiative Transfer Model (PCRTM) and an optimized estimation retrieval algorithm, a simultaneously retrieval is made using the whole spectral information measured by CrIS,  and the derived SiFSAP include temperature, water vapor, trace gases (such as O₃, CO₂, CO, CH₄ and N₂O), cloud properties and surface properties. Use of ATMS together with CrIS allows SiFSAP to get accurate retrieval products under thick pyroCb conditions. An algorithm to detect pyroCb based on the hyperspectral infrared sounder spectrum from CrIS will be developed and verified. In addition to SiFSAP sounding products,  CO, O₃, NO₂ from TROPOMI and O3 from OMPS will be used. The wind fields from the NASA’s Modern-Era Retrospective Analysis for Research and Applications Version-2 (MERRA-2) and ERA5 will be used to characterize the transport, and the SiFSAP temperature and water vapor profiles within and around pyroCbs will be compared with MERRA-2 and ERA5 products.     

How to cite: Xiong, X., Liu, X., Wu, W., Lei, L., Yang, Q., Zhou, D., and Laura, A.: PyroCbs from Australia Fires and its Impact Study Using Satellite Observations from CrIS and TROPOMI and Reanalysis Data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1412, https://doi.org/10.5194/egusphere-egu23-1412, 2023.

Roughly half of global fire emissions originate from savannas, and emission factors (EF) are used to quantify the amount of trace gases and aerosols emitted per unit dry matter burned. It is well known that these EFs vary substantially even within a single biome but so far quantifying their dynamics has been hampered by a lack of EF measurements. Therefore, global emission inventories currently use a static averaged EF for the entire savanna biome. To increase the spatiotemporal coverage of EF measurements, we collected over 4500 EF bag measurements of CO₂, CO, CH₄ and N₂O using an unmanned aerial system (UAS) and measured fuel parameters and fire severity proxies during 129 individual landscape fires. These measurements spanned various widespread savanna ecosystems in Africa, South America and Australia, with early and late dry season campaigns. We trained random forest (RF) regressors to estimate daily dynamic EFs for CO₂, CO, CH₄ and N₂O at 500×500-meter resolution based on satellite and reanalysis data. The RF models reduced the difference between measured and modelled EFs by 60-85% compared to static biome averages. The introduction of EF dynamics resulted in a spatial redistribution of CO, CH₄ and N₂O emissions compared to the Global Fire Emissions Database version 4 (GFED4s) with higher emissions in higher rainfall savanna regions. While the impact from using dynamic EFs on the global annual emission estimates from savannas was relatively modest (+2% CO, -5% CH₄ and -18% N₂O), the impact on local EFs may exceed 60% under dry seasonal conditions.

How to cite: Vernooij, R., Eames, T., Russel-Smith, J., Yates, C., Beatty, R., Evans, J., Edwards, A., Ribeiro, N., wooster, M., Strydom, T., Giongo, M., Borges, M., Barradas, C., Menezes, M., van Wees, D., and van der Werf, G.: Drivers of spatial and temporal variability in savanna fire emission factors, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1975, https://doi.org/10.5194/egusphere-egu23-1975, 2023.

Recent wildfire activity in semi-arid regions like western North America exceeds the range of historical records. High-resolution paleoclimate archives such as stalagmites could illuminate the link between hydroclimate, vegetation change, and fire activity in pre-anthropogenic climate states beyond the timescale of existing tree-ring records. Here we present an analysis of levoglucosan, a combustion-sensitive anhydrosugar, and lignin oxidation products (LOPs) in a stalagmite from White Moon Cave in the California Coast Range in order to reconstruct fire activity and vegetation composition across the 8.2 kyr event. Elevated levoglucosan concentrations suggest increased fire activity while altered LOP compositions indicate a shift toward more woody vegetation during the event, with the shift in vegetation preceding the increase in fire activity. These changes are concurrent with increased hydroclimate volatility as shown by carbon and calcium isotope proxies. Together, these records suggest that climate whiplash (oscillations between extreme wetness and aridity) and fire activity in California, both projected to increase with anthropogenic climate change, were tightly coupled during the early Holocene.

How to cite: Oster, J., Homann, J., de Wet, C., Breitenbach, S., and Hoffmann, T.: Linked fire activity and climate whiplash in California during the early Holocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2097, https://doi.org/10.5194/egusphere-egu23-2097, 2023.

An increase in fire-prone conditions in non-fire adapted regions is rooted in climatic and anthropogenic changes. Such pyrogeographical shifts are observable, for example, in alpine regions. In 2021, Austria, experienced a fire larger than 100 ha for the first time in a century in the Schneeberg-Rax mountain region. In depth understanding of post-fire effects on carbon cycling at such non-fire adapted sites is still scarce. To help close this knowledge gap, post-fire changes were investigated at the abovementioned site, including soil organic matter composition and soil chemical conditions. 

Samples were taken immediately after the fire, 3 months, 6 months and 12 months thereafter from four sampling sites. Selected sites consisted of 1. a pine forest affected by a crown fire, 2. a pine and beech mixed forest affected by a surface fire, and two non-fire affected controls with similar site conditions (vegetation, slope, altitude, and exposition). Samples were analyzed for pH, carbon content, elemental composition, leachable dissolved organic carbon and trace elements, organic matter composition, and environmentally persistent free radical concentrations. 

pH increased after the fire at both sites investigated. This increase was the strongest (up to 1.5 units) immediately after the fire but was still substantial 1 year after the fire. Carbon contents decreased approximately 2fold in the crown fire affected soil compared to the control soil, but remained similar between surface fire affected soil and the respective control. However, aromaticity of bulk carbon and the leachable fraction increased in both fire-affected soils, which can be related to the formation of pyrogenic carbon during the fire. Pyrogenic carbon is a highly aromatic and recalcitrant carbon pool produced during incomplete combustion of biomass. Pyrogenic carbon can also contain substantial amounts of environmentally persistent free radicals (EPFR), which can form reactive oxygen species, which can induce oxidative stress on microbiota. Our EPFR measurements showed an increase by at least 1.5 orders of magnitude of EPFR in fire affected soils. This study suggests that changes in soil carbon cycling can be expected following fires in non-adapted alpine forests. 

How to cite: Torres, M., Poyntner, C., Chaudhuri, S., Pignitter, M., Schmidt, H., Hofmann, T., and Sigmund, G.: Fire impacts on soil carbon in a non-fire adapted alpine forest, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2233, https://doi.org/10.5194/egusphere-egu23-2233, 2023.

Cave stalagmites (speleothems) are highly-valued archives of environmental information owing to their preservation of climate sensitive proxies and well-defined chronologies.  Yet the reconstruction of fire history from stalagmites is a relatively unexplored approach, with some advantages over traditional fire proxy archives.  For example, stalagmites may contain annual laminae (visible or chemical) which can be exploited for seasonal to annual proxy information with precise chronologies.  Thus stalagmites have the potential to yield annually-resolved records of fire and climate that could be used to (1) better understand the fire-climate relationship, (2) fire recurrence interval information, (3) understand ecosystem resilience and (4) inform land management policy.

The development of fire proxies from stalagmites is still in its infancy. Robust interpretations of any proxy information relies on an understanding of the environmental processes that lead to the preservation of proxies in the archive.  Cave stalagmites may record fire history via dripwater, or via the cave entrance as aerosols.  The focus here is on the transportable constituents in dripwater such as solutes, colloids and suspended matter.  A fire event produces ash (a source of leachates) and can alter soil properties (hydrophobicity, pH, organic matter etc) producing temporary enrichments (or depletions) in transported constituents via dripwater.  The resulting signal may be detected in stalagmites using high-resolution methods such as laser ablation mass spectrometry, fluorescence and infrared microscopy techniques.  Cave depth is an important factor in the preservation process with the detection of a fire signal more likely to be observed in dripwater from shallow caves (e.g. 5-10 m) owing to the potential for attenuation and mixing that may occur in deeper caves (Campbell et al., 2022).  However, owing to the karstification of carbonate rocks which host caves, there commonly exists different flow types: diffuse/slow flow through the matrix, preferential/fast flow through fractures and conduits.  Fracture (or conduit) influenced flowpaths have higher permeability and enhance rapid and deep percolation of water from the surface towards the cave.  Several studies have shown that stalagmites fed by dripwater with a fracture-flow component contain higher concentrations of soil-derived trace metals and organics indicating a stronger hydrological connection with the surface.  It logically follows that fracture-influenced flowpaths are more likely to transmit proxies for fire.  Furthermore, flowpaths may be a more important factor than cave depth in some settings, e.g., Campbell et al. (2022) presented a case study of a historical fire event recorded in a stalagmite that was located ~40 m below the surface.  

Understanding the hydrological setting of a cave system including rainfall recharge and flowpaths is valuable in the interpretation of speleothem records in general.  This contribution presents a conceptual model illustrating how these factors influence the preservation of fire proxies in stalagmites and makes recommendations for ideal sample selection for fire proxy records based on cave characteristics as well as stalagmite attributes such as morphology and colour.

Campbell. M. et al., Speleothems as Archives for Palaeofire Proxies. ESS Open Archive. July 24, 2022. DOI:10.1002/essoar.10511989.1

How to cite: Treble, P., Micheline, C., Baker, A., Liza, M., and Nevena, K.: Hydrological conceptual model for reconstructing fire history from cave stalagmites, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2932, https://doi.org/10.5194/egusphere-egu23-2932, 2023.

The Black Summer bushfires (2019-2020) cost the Australian economy over 100 billion dollars and burnt a total of 18 million hectares. In just one season, around 20% of Australia's Eucalyptus forests burnt down and billions of animals perished. Recent catastrophic fires in Australia and North America have made scientists and policymakers question how the disruption of First Nations' burning practices has impacted fuel loads. For instance, we have learnt from modern Australian Indigenous communities, historical literature, and art works that Indigenous peoples have used cultural burning to rejuvenate patches of land and preserve open vegetation for hunting and cultural purposes. The advent of British invasion brought a change in the type of fire regimes and landscape management across much of the continent, which may have led to an increase in flammable fuels in forest settings. However, the actual degree of land-cover modification by early settlers has only been often debated in the academic literature and within management stakeholders.

The quantification of past land cover is needed to address such debates. Pollen is the key proxy to track past vegetation changes, but pollen spectra suffer from some important biases e.g. taphonomy, pollen productivity, dispersal capability. Estimating past vegetation cover from sedimentary pollen composition requires to correct for productivity and dispersal biases using empirical-based models of the pollen-vegetation relationship. Such models for quantitative vegetation reconstruction (e.g. REVEALS) have yet been mostly applied in the Northern Hemisphere in the last 15 years - here we present recent applications of this methodology from Australia. We show the quantification of land cover changes through pre- and post- British invasion on multiple records (n=51) across the southeastern Australian region. This represents the first regional application of REVEALS within the Australian continent.

We provide the first empirical evidence that the regional landscape before British invasion was a cultural landscape with limited tree cover as it was maintained by Indigenous Australians through cultural burning. Our findings suggest that the removal of Indigenous vegetation management has altered woodland fuel structure and that much of the region was predominantly open before colonial invasion. The post-colonial land modification has resonance in wildfire occurrence and management under the pressing challenges posed by climate change.

How to cite: Mariani, M., Connor, S., Fletcher, M.-S., Haberle, S., Stevenson, J., Kershaw, P., Herbert, A., Theuerkauf, M., and Bowman, D.: Feeding the flames: how colonialism led to unprecedented wildfires across SE Australia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3238, https://doi.org/10.5194/egusphere-egu23-3238, 2023.

The Fire Weather Index (FWI) is used worldwide to estimate the danger of wildfires. The FWI system integrates meteorological parameters and empirically combines them into several moisture codes, each representing a different fuel type. These moisture codes are then used in combination with wind speed to estimate a fire danger. Originally, the FWI system was developed for a standard jack pine forest, however, it is widely used by fire managers to assess the fire danger in different environments as well. Furthermore, it is often also used to assess the vulnerability of organic soils, such as peatlands, to ignition and depth of burn. The utility of which is often questioned.

This research aims at improving the original FWI for northern peatlands by replacing parts of the original, purely weather-based FWI system with satellite-informed model estimates of peat moisture and water level. These come from a data assimilation output combining the NASA catchment model, including the peat modules PEATCLSM, and Soil Moisture and Ocean Salinity (SMOS) L-band brightness temperature observations. The predictive power of the new, peat-specific FWI (PEAT-FWI) is evaluated against the original FWI against fire data of the global fire atlas from 2010 through 2018 over the major northern peatlands areas. For the evaluation, the fires are split up in early and late season fires, as it is hypothesized that late fires are more hydrological driven, and the predictive power of the PEAT-FWI will thus differ between the two types of fires. Our results indeed indicate that the PEAT-FWI improves the predictive capability of estimating fire risk over northern peatlands in particular for late fires. By using a receiver operating characteristics (ROC) curve to evaluate the predictive power of the FWI against a random estimate, the area under the curve increases by up to 10% for the PEAT-FWI compared to the original FWI. The recent version 7 release of the operational Soil Moisture Active Passive (SMAP) Level-4 Soil Moisture Data Assimilation Product now includes PEATCLSM, thus, the proposed PEAT-FWI is straightforward to include in operational FWI products.

How to cite: Mortelmans, J., Felsberg, A., De Lannoy, G., Veraverbeke, S., Field, R., Andela, N., and Bechtold, M.: PEAT-FWI: Improving the Fire Weather Index for peatlands with Hydrological Modeling and L-band Microwave Observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3310, https://doi.org/10.5194/egusphere-egu23-3310, 2023.

Agricultural expansion and ongoing climate change are rapidly altering the fire regime of natural ecosystems along the Cerrado-Amazon biome boundary. While agricultural intensification has driven a decrease in fire ignitions in some regions, agricultural expansion has increased fire usage in other landscapes for deforestation and managing pasturelands. These contrasting patterns of fire activity across different land-use frontiers limits our ability to accurately predict where and when fires may occur, particularly under the context of climate change.

To predict fire activity with land-use transitions, we modelled fire probability as a function of the age of different land-use transitions across the Amazon and Cerrado. We investigated annual land-use and associated burned areas based on the MapBiomas Collection 6.0 and MapBiomas Fire Collection 1.0 data, respectively, from 1986 to 2020. This allowed us to quantify how the time-since conversion of native vegetation (forest, savanna, and grassland) to pasture and farming influence fire occurrence. Additionally, we explored the joint impact of land-use change and climate extremes in fire activity in terms of estimated vapor pressure deficit (VPD) and maximum cumulative water deficit (MCWD), two common measures of flammability and drought impact. 

Our results confirm that transition age is a strong predictor of fire probability. They also suggest that fire probability increases (decreases) at different rates before (after) clearing in Amazon and Cerrado. The role of climate extremes in modulating burning activity associated with land-use transitions varied by biome, post-fire land use, and the size of the burned area associated with the conversion. These findings provide insight into incorporating the effect of land-use transition age on ignition probability for fire modelling in combination with climate drivers. From an operational point of view, our results aim to contribute to environmental policies capable of sustaining ecosystem integrity at the ecotone between the Amazon and Cerrado biomes.

How to cite: Ribeiro, A. F. S., Santos, L., Uribe, M. R., Silvestrini, R. A., Rattis, L., Macedo, M. N., Morton, D. C., Randerson, J. T., Seneviratne, S. I., Zscheischler, J., and Brando, P. M.: How changes in ignition sources influence fire probability in the Amazon and Cerrado biomes: a perspective based on frontier age, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3332, https://doi.org/10.5194/egusphere-egu23-3332, 2023.

Fire alters the biogeochemical cycling of important elements, plays a role in climate change, and shapes the composition of global biological communities. Detection of past fires has long been used to reconstruct human settlement and climate records. Charcoal and phytolith abundance has been the most commonly used paleofire proxies but may only represent evidence of local fires. Chemical analyses of pyrogenic carbon (PyC) have been more recently used, but are also not without controversy. Thus far, very few intercomparisons of these proxies have been conducted. Here, the fire records contained in soil and lake sediments of Western Amazon (at lakes Ayauchⁱ, Parker, Gentry, and surrounding regions) were determined by charcoal microscopy, chemical thermal oxidation (CTO), and benzene polycarboxylic acids (BPCA) molecular biomarkers. Charcoal represented a smaller portion of PyC and, with its patchy distribution, likely indicated local or larger regional fire events. With a median value of about 15% of organic carbon, PyC via CTO oxidation was of the highest concentrations, which suggests a larger PyC detection window and lower sensitivity of reflecting regional fire. With a median value of about 3% of organic carbon, the BPCA-derived PyC distributions bore the closest resemblance to both spatial and temporal regional fire variations, established via archeological, pollen and phytolith records, thus may be a more sensitive indicator of fire over larger regional scales. Molecular ratios of BPCA molecules in Lake Ayauchⁱ soils indicated higher temperature fires (> 600°C) and suggested a history of more human occupation and human-caused fire in the Lake Ayauchⁱ region compared with the Lake Gentry & Parker region. However, our findings suggest that the use of a combination of fire proxy methods provides a fuller picture of the fire history of a region than any single approach. Establishing a better understanding the differences in the information provided by various paleofire proxies will allow a more complete understanding of the drivers, history and ecological and biogeochemical effects of fire, both regionally and globally.

How to cite: Lyu, J., Zimmerman, A., Bush, M., and McMichael, C.: BPCA-derived PyC may reflect fire signals over regional scales from the western Amazon Basin fire record, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3632, https://doi.org/10.5194/egusphere-egu23-3632, 2023.

Background:

Fires burn roughly 3% of Earth’s land surface each year and are predicted to become more frequent and severe as human-caused climate change progresses. Fires can drive ecosystem N loss by volatilizing N bound in plant biomass to the atmosphere and by leaving behind ash rich in ammonium (NH₄⁺) and organic N that can run off when it rains. While N volatilization and runoff account for a large fraction of N loss after fires, budget imbalances suggest soil emissions of nitric oxide (NO) and nitrous oxide (N₂O) may also be significant N loss pathways after fire. Identifying sources of NO and N₂O is important because NO is a precursor for tropospheric O₃ which causes high rates of asthma hospitalizations,and N₂O is a powerful greenhouse gas with 300× the warming potential of CO₂. Soil emissions of NO and N₂O are largely governed by the microbial processes of nitrification and denitrification. Under aerobic conditions typical of dry soils, nitrifying organisms such as ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) oxidize NH₄⁺ to nitrate (NO₃^-) and release NO and N₂O as byproducts. AOA and AOB process N with different efficiencies, suggesting shifts in AOA:AOB ratios may change N emissions. Specifically, AOB are dominant in soils with high NH₄⁺and pH and produce higher NO and N₂O emissions. Since such soil conditions are frequently observed after fires, we hypothesize NO and N₂O emissions will increase as AOB communities become dominant. To test this, we collected soil cores from 5 plots in the Sequoia National Park, CA over a time series starting two weeks after a high severity chaparral fire. We selectively inhibited AOA and AOB communities to measure their contributions to NO and N₂O emissions. We also measured the isotopic composition of N₂O emissions from these soils using an LGR isotopic N₂O analyzer to better understand the processes responsible for post-fire N₂O production.

Results/Conclusions

One month after the fire, soil bulk emissions of NO over 72hrs were 1.5 times higher in the burned plots (101.4 ± 22.4 µg N-NO/g soil burned; 67.1 ± 19.3 µg N-NO/g soil unburned; ±SE). Bulk soil emissions of N₂O over 72hrs were 7.5 times lower in burned plots compared to before the fire (0.0616 ± 0.04 ng N-N₂O/g soil burned; 0.463 ± 0.19 ng N-N₂O/g soil unburned; ±SE). Although the effects of fire on nitrifier communities were not significant at one month post-fire (Control: p=0.14, AOA: p=0.09, AOB: p=0.162), both AOA and AOB contributions to NO emissions increased in response to fire. Results for nitrifier contributions to N₂O emissions were highly variable and non-significant with no clear trends as all N₂O emissions were near zero. Further analysis over the time series may yield clearer results as microbial communities have more time to recover. Pairing these data with isotopic information (in progress) may yield one of the most in-depth understandings of post-fire NO and N₂O emissions to date.

How to cite: Stephens, E., Greene, A., Krichels, A., and Homyak, P.: Wildfires alter nitrifier communities and increase soil emissions of NOx but not N2O in California chaparral, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3695, https://doi.org/10.5194/egusphere-egu23-3695, 2023.

Climate change and atmospheric CO₂ levels can influence wildfire properties through separate and potentially contrasting impacts on vegetation and climate. One way to examine the sensitivity of global wildfire properties to changes in climate and CO₂ levels is using an out-of-sample experiment, such as the Last Glacial Maximum (LGM; 21 ka BP). Charcoal records show reduced burning at the LGM, when CO₂ levels were ~ 185 ppm and the climate was cooler and drier. In this analysis, we isolated out the potential effects of LGM CO₂ levels and LGM climate on the spatial patterns of global wildfire properties.

Using three statistical models, we conducted simulations of the spatial distribution of global burnt area, fire size and fire intensity under four scenarios: modern climate/modern CO₂ levels, LGM climate/LGM CO₂ levels, modern climate/LGM CO₂ levels and LGM/ modern CO₂ levels. We used outputs from three coupled ocean–atmosphere models representative of the range of simulated LGM climates. The ecophysiological effect of CO₂ levels was explicitly accounted for through vegetation inputs. Gross primary productivity (GPP) and land cover were derived for the LGM and modern climate keeping either CO₂ levels at 395 ppm (modern), or setting them to 185 ppm, using the P Model, a first-principles model of GPP which allows continuous acclimation of photosynthetic parameters to environmental variations, and the BIOME4 equilibrium global vegetation model.

Our results show a reduction in burnt area under LGM CO₂ levels, both with modern and LGM climate inputs. In the case of the warmest of the LGM climate scenarios, this reduction was of the same magnitude as the combined LGM climate/LGM CO₂ levels scenario. However, the driest and coldest LGM climate scenario produced a reduction in burnt area even with modern CO₂ levels, and the largest reduction in burnt area with LGM CO₂.  The reduction was primarily driven by changes in vapour pressure deficit (VPD). Fire size increased under LGM climates, due to changes in wind and VPD. The lower CO₂ values at the LGM had no impact on fire size. Fire intensity increased under LGM climates and LGM CO₂ levels, with both effects of similar amplitude and changes driven primarily by VPD, GPP and diurnal temperature range. 

We compared our outputs with sedimentary charcoal records from the Reading Palaeofire Database (RPD). Overall, the burnt area LGM CO₂ levels/LGM climate scenario showed the greatest agreement, though depending on how cold and dry the LGM climate was, this agreement was either equal to LGM CO₂ levels or LGM climate alone. These results suggest that whilst there was reduced global burning at the LGM, there may have been larger and more intense fires. They also highlight the importance of the ecophysiological effect of CO₂ levels on fuels, a major control of burnt area and fire intensity regardless of climate. They point to the importance of including this effect in process-based fire models, as well as the importance of accurately estimating the amplitude of projected change for different climate variables in order to increase the reliability of future projections.

How to cite: Haas, O., Prentice, I. C., and Harrison, S. P.: Examining the response of different wildfire properties to changes in climate and CO2 levels at the Last Glacial Maximum, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4520, https://doi.org/10.5194/egusphere-egu23-4520, 2023.

Recent developments in speleothem science are showing their potential for paleofire reconstruction through a variety of inorganic and organic proxies including trace metals (1) and the pyrogenic organic compound levoglucosan (2). Previous work by Argiriadis et al. (2019) presented a method for the analysis of trace polycyclic aromatic hydrocarbons (PAHs) and n-alkanes in stalagmites (3). These compounds reflect biogeochemical processes occurring at the land surface, in the soil, and in the cave. PAHs are primarily related to combustion of biomass while n-alkanes, with their potential for vegetation reconstruction (4), provide information on fuel availability and composition, as well as fire activity. These organic molecules are carried downward by infiltrating water and incorporated into speleothems (5), thereby creating the potential to serve as novel paleofire archives.

Using this approach, we developed a high-resolution stalagmite record of paleofire activity from cave KNI-51 in tropical northwestern Australia. This site is well suited for high resolution paleofire reconstruction as bushfire activity in this tropical savanna is some of the highest on the continent, the cave is shallow and overlain by extremely thin soils, and the stalagmites are fast-growing (1-2 mm yr^-1) and precisely dated. We analyzed three stalagmites which grew continuously in different time intervals through the last millennium - KNI-51-F (CE ~1100-1620), KNI-51-G (CE ~1320-1640), and KNI-51-11 (CE ~1750-2009). Samples were drilled continuously at 1-3 mm resolution from stalagmite slabs, processed in a stainless-steel cleanroom to prevent contamination.

Despite a difference in resolution between stalagmites KNI-51-F and -G, peaks in the target compounds show good replication in the overlapping time interval of the two stalagmites, and PAH abundances in a portion of stalagmite KNI-51-11 that grew from CE 2000-2009 are well correlated with satellite-mapped fires occurring proximally to the cave.

Our results suggest an increase in the frequency of low intensity fire in the 20^th century relative to much of the previous millennium. The timing of this shift is broadly coincident with the arrival of European pastoralists in the late 19^th century and the subsequent displacement of Aboriginal peoples from the land. Aboriginal peoples had previously utilized “fire stick farming”, a method of prescribed, low intensity burning, that was an important influence of ecology, biomass, and fire.  Prior to the late 1800s, the period with the most frequent low intensity fire activity was the 13^th century, the wettest interval of the entire record. Peak high intensity fire activity occurred during the 12^th century.

Controlled burn and irrigation experiments capable of examining the transmission of pyrogenic compounds from the land surface to cave dripwater represent the next step in this analysis. Given that karst is present in many fire-prone environments, and that stalagmites can be precisely dated and grow continuously for millennia, the potential utility of a stalagmite-based paleofire proxy is high.

(1) L.K. McDonough et al., Geochim. Cosmochim. Acta. 325, 258–277 (2022).

(2) J. Homann et al., Nat. Commun., 13:7175 (2022).

(3) E. Argiriadis et al., Anal. Chem. 91, 7007–7011 (2019).

(4) R.T. Bush, F. A. McInerney, Geochim. Cosmochim. Acta. 117, 161–179 (2013).

(5) Y. Sun et al., Chemosphere. 230, 616–627 (2019).

How to cite: Argiriadis, E., Denniston, R. F., Ondei, S., and Bowman, D.: Speleothem organic biomarkers trace last millennium fire history at near-annual resolution in northwestern Australia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5113, https://doi.org/10.5194/egusphere-egu23-5113, 2023.

Wildfire smoke is known as a highly absorptive aerosol type in the shortwave wavelength range. The absorption of Sun light by optically thick smoke layers results in heating of the ambient air. This heating is translated into self-lofting of the smoke up to more than 1 km in altitude per day. The main goal is to demonstrate that radiative heating of intense smoke plumes is capable of lofting them from the lower and middle free troposphere (injection heights) up to the tropopause without the need of pyrocumulonimbus (pyroCb) convection. The further subsequent ascent within the lower stratosphere (caused by self-lofting) is already well documented in the literature. Simulations of heating rates which are then converted into lofting rates are conducted by using the ECRAD (European Centre for Medium-Range Weather Forecasts Radiation) scheme. As input parameters thermodynamic profiles from CAMS (Copernicus Atmosphere Monitoring Service) reanalysis data, aerosol profiles from ground-based lidar observations, radiosonde potential temperature profiles, CALIOP (Cloud Aerosol Lidar with Orthogonal Polarization) aerosol measurements, and MODIS (Moderate Resolution Imaging Spectroradiometer) aerosol optical depth retrievals were used. 

The sensitivity analysis revealed that the lofting rate strongly depends on aerosol optical thickness (AOT), layer thickness, layer height, and black carbon (BC) fraction. We also looked at the influence of different meteorological parameters such as cloudiness, relative humidity, and potential temperature gradient. Lofting processes in the stratosphere observed with CALIOP after major pyroCb events (Canadian fires, 2017, Australian fires 2019-2020) are compared with simulations to demonstrate the applicability of our self-lofting model. We analyzed long-term CALIOP observations of Siberian smoke layers and plumes evolving in the troposphere and UTLS (upper troposphere and lower stratosphere) region over Siberia and the adjacent Arctic during the summer season of 2019 and found several indications (fingerprints) that self-lofting contributed to the vertical transport of smoke. We hypothesize that the formation of a near-tropopause aerosol layer, observed with CALIOP over several months, was the result of self-lofting processes because this is in line with the self-lofting simulations. 

We will show a detailed analysis of tropospheric and stratospheric smoke lofting rates based on simulations and observations.

How to cite: Ohneiser, K., Ansmann, A., Witthuhn, J., Deneke, H., Chudnovsky, A., Walter, G., and Senf, F.: Smoke self-lofting towards the lower stratosphere: an alternative process to pyroCb-lofting, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5429, https://doi.org/10.5194/egusphere-egu23-5429, 2023.

Wildfires burn on average 448 million hectares globally every year, releasing around 2.2 Pg of carbon (C) into the atmosphere [1, 2]. The net effect of wildfires in the C cycle goes, however, beyond emissions and involves many other interacting processes. Among those, there is a significant knowledge gap on the role of post-fire soil organic carbon (SOC) erosion as a carbon sink mechanism.

Post-fire erosive response is greatly enhanced by the direct and indirect effects of wildfires on soil and vegetation, such as the loss of protective cover and soil structure or the development of a water-repellent layer [3]. In addition, biomass and soil organic matter undergo quantitative and qualitative changes during wildfires, such as the formation of pyrogenic carbon, highly resistant to degradation. The resulting PyC and non-PyC carbon fractions, with contrasting physical properties and chemical stability, will be differently redistributed and mineralized during the erosion process [4]. Ultimately, post-fire SOC erosion will act as a carbon sink when the post-fire burial and stabilization of eroded carbon, together with the recovery of net primary production and soil organic carbon content, exceed the SOC losses during its post-fire transport [5]. All these processes have been scarcely investigated and poorly quantified to the date. In this presentation, we will provide new insights into this potential C sink mechanism, critically reviewing the state of the art and highlighting key research gaps.

References

[1] Boschetti et al., 2021. Global Wildfire Information System (GWIS). https://gwis.jrc.ec.europa.eu/apps/country.profile/downloads

[2] Randerson et al., 2012. J Geophys Res. https://doi.org/10.1029/2012JG002128

[3] Shakesby & Doerr, 2006. Earth-Sci Revs. https://doi.org/10.1016/j.earscirev.2005.10.006

[4] Doetterl et al., 2016. Earth-Sci Revs. https://doi.org/10.1016/j.earscirev.2015.12.005

[5] Santín et al., 2015. Glob Change Biol. https://doi.org/10.1111/gcb.12800

How to cite: Girona-García, A., Santín, C., Vieira, D., and Doerr, S.: Which is the role of post-fire SOC erosion in the C cycle?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5803, https://doi.org/10.5194/egusphere-egu23-5803, 2023.

Anthropogenic activities and climate change are increasing the vulnerability of carbon rich peatlands to wildfires. Peat fires, which are dominated by smouldering combustion, are some of the largest and most persistent wildfires on Earth. Across the northern high latitudes, peat fires have the potential to release vast amounts of long term stored carbon and other greenhouse gases and aerosols. Consequently, peat fires can have huge implications on the carbon cycle and result in a positive feedback effect on the climate system. Peat fires also impact air quality and can lead to haze events, with major impacts on human health. Despite the importance of peat fires they are currently not represented in most fire models, leading to large underestimations of burnt area and carbon emissions in the high latitudes. Here, I present a representation of peat fires in the JULES-INFERNO fire model (INFERNO-peat). INFERNO-peat improves the representation of burnt area across the high latitudes, with notable areas of improvement in Canada and Siberia. INFERNO-peat also highlights a large amount of interannual variability in carbon emissions from peat fires. The inclusion of peat fires into JULES-INFERNO demonstrates the importance of representing peat fires in models, and not doing so may heavily restrict our ability to model present and future fires and their impacts across the northern high latitudes.

How to cite: Blackford, K., Voulgarakis, A., Prentice, C., Burton, C., and Kasoar, M.: Representing Northern High Latitude Peat Fires in the JULES-INFERNO Fire Model, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6083, https://doi.org/10.5194/egusphere-egu23-6083, 2023.

Fires constitute a key source of emissions of greenhouse gasses and aerosols. Fire emissions can be quantified using models, and these estimates are influenced by the spatial resolution of the model and its input data. Here we present a novel global model based on the Global Fire Emissions Database (GFED) modelling framework for the estimation of fuel consumption and fire carbon emissions at a spatial resolution of 500 m. The model was primarily based on observation-derived data products from MODIS, reanalysis data for meteorology, and an updated field measurement synthesis database for constraining fuel load and fuel consumption. Compared to coarser models, typically with a resolution of 0.25°, the 500-m spatial resolution allowed for increased spatially resolved emissions and a better representation of local-scale variability in fire types. The model includes a separate module for the calculation of emissions from fire-related forest loss, using 30-m Landsat-based forest loss data. We estimated annual carbon emissions of 2.1 Pg C yr^-1, of which around 24% was from fire-related forest loss. Fuel consumption was on average a factor 10 higher in case of fire-related forest loss compared to fires without forest loss. Up to now, emission estimates from our new model are based on MODIS burned area with a 500-m resolution, leading to global emissions similar to GFED4s. However, novel high-resolution burned area datasets based on the Landsat and Sentinel-2 missions reveal substantially more global burned area. Our 500-m global fire model provides a suitable framework for converting these burned area products to emissions, with the prospect of substantially higher global emissions.

How to cite: van Wees, D., van der Werf, G. R., Randerson, J. T., Rogers, B. M., Chen, Y., Veraverbeke, S., Giglio, L., and Morton, D. C.: A global model for estimating fuel consumption and fire carbon emissions at 500-m spatial resolution, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6184, https://doi.org/10.5194/egusphere-egu23-6184, 2023.

CO₂ emission from biomass burning (BB) is one of the essential elements of the global carbon budget, with its annual mean of about 2.0 PgC/year equivalent to 15 % of 2020 fossil fuel emissions. However, while a global increase in fire-prone weather is projected alongside climate change, a quantitative understanding of how much carbon will further be released due to increased fires is highly limited, which could result in large uncertainty in meeting the net zero target. Thus, in this study, we evaluate future changes in fire-prone weather based on the fire weather index (FWI) and estimate the potential fire-induced emissions on a global scale that could be induced by climate change. To this end, 28 ensembles of idealized CO₂ reduction simulations with the CESM climate model were analyzed. The results show that when CO₂ in the atmosphere is doubled (2xCO₂) from 367 ppm by 1 % per year, the additional emission due to increased fire weather could reach about 1.7 PgC/year, which corresponds to 82% of the current BB emission. Moreover, even if the atmospheric CO₂ concentration further peaks and is reduced back to 2xCO₂, the lagged response of the climate system can cause fire-prone weather and its resulting C emissions to remain higher than its previous state in many countries. These results highlight that more focus is required on the climate-fire-carbon feedback not only for more accurate future predictions but also for achieving net zero emissions in each country through a proper wildfire management strategy.

How to cite: Kim, J.-S., Kim, H.-J., and An, S.-I.: Hysteresis of fire-prone weather to CO2 forcing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6286, https://doi.org/10.5194/egusphere-egu23-6286, 2023.

Large-scale fires such as warehouse fires that have occurred in recent years or dramatic accidents like the Paris Notre-Dame Cathedral fire in 2019 have stressed the need to develop means of assessing the toxicity risks to the population and the environment of smoke plumes. A key challenge is to quickly provide the authorities with information on the areas impacted by the plume and the pollutant concentration levels to which the population is likely to be or to have been exposed. The Laboratoire Central de la Préfecture de Police (LCPP) aims to deploy a number of devices for measuring pollutants and tracers of smoke combustion during a fire. Subsequently, the application of an atmospheric dispersion model within the framework of a data assimilation approach should provide a source characterisation and a finer estimate of the concentration levels at points of interest.

To characterise the source, noticeably the released mass of pollutants and the emission height linked to a plume rise, an inverse problem method has been implemented. It is based on a Bayesian Markov Chain Monte Carlo (MCMC) technique meant to quantify the uncertainties associated with the emission estimation. Since the emission height strongly influences the atmospheric dispersion in the vicinity of the source, two approaches are used to estimate it. The first one consists in finding the emission time rate for each considered height and the second one consists in focussing on a single emission height and its associated emission time rate using a discrete distribution to describe the vertical profile. We use the Lagrangian Parallel Micro Swift Spray (PMSS) model developed by AriaTechnologies fed with meteorological fields provided by Météo-France to represent the atmospheric dispersion of smoke.

Our inverse method is applied to a large warehouse fire that occurred in Aubervilliers near Paris in 2021 using real observations. Abnormal concentrations of particulate matter were recorded, with a peak at 160 µg.m^-3, located in the centre of Paris about 6 km from the source. They were collected by the LCPP and AirParif, the local air quality agency, and are used to retrieve the emission with a quantification of uncertainties and a sensitivity analysis of model error. The resulting emission height of the source, mainly between 200 and 300 m, coincides with the terrain observation for an emission rate of less than 1000 kg/h throughout the duration of the fire. A sensitivity analysis to the initial approximation of the source (the prior) shows its importance. It suggests to improve our method by incorporating the statistical parameters of the observation error into the MCMC method.

How to cite: Launay, E., Hergault, V., Bocquet, M., Dumont Le Brazidec, J., and Roustan, Y.: Characterisation of large-scale urban fire emissions by inverse modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6777, https://doi.org/10.5194/egusphere-egu23-6777, 2023.

Wildfires are responsible for significant emissions of greenhouse gases, pollutants and aerosols. In addition to being a large source of carbon monoxide (CO) and carbon dioxide (CO2), they alone account for more than half of black carbon emissions and the majority of primary organic aerosol emissions.

Despite proactive fire suppression policies in the Northern Hemisphere (NH), allowing a decrease in fires, especially in Europe, an increase in the number of extreme fires can be noted in recent years. In the NH, this increase is mainly in Western America and boreal regions. The pollution plumes produced during extreme fires can be transported over thousands of kilometers, impacting background pollutant levels on a hemispheric scale. Thus, variability in fire intensity may explain a large part of the spatial and temporal variability of many atmospheric pollutants. For longer lived pollutants, wildfires may significantly increase background levels.

In this study, the link between extreme fire weather (high temperature), large fires and background pollution in the Northern Hemisphere is analyzed based on satellite observations. The impact of large wildfires on background levels of CO and aerosols above Europe is studied more specifically. We present the variability of fire frequency in the NH, their intensity and the related emissions using 20 years (2003-2022) of MODIS fire observations analyzed with the APIFLAME model. The link between large events and fire weather is studied using the ERA5 reanalyses and the Canadian Fire Weather Index (FWI). The related impact on the variability of total CO and AOD in the NH is analyzed using 15 years (2008-2022) of satellite observations from IASI/Metop and MODIS/Terra and Aqua, respectively. Finally, plume retro trajectories are computed in order to assess the contribution of the different geographical areas of the NH on the CO and AOD variability.

How to cite: Ehret, A., Turquety, S., George, M., and Clerbaux, C.: Variability of CO and aerosols plumes from wildfires in the Northern Hemisphere in 2008-2022 using satellite observations., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6797, https://doi.org/10.5194/egusphere-egu23-6797, 2023.

Within the framework of the project IMPOSE (Emit now, mitigate later? IMPlications of temperature OverShoots for the Earth system) six idealized emission-overshoot simulations have been performed with the Earth System Model NorESM2-LM2 and used as forcing for the 2^nd generation dynamic global vegetation model LPJ-GUESS with its fire-model SIMFIRE-BLAZE to investigate the impact of different CO₂ overshoots on global wildfire regimes.

The simulations describe a set of scenarios with high, medium, and low accumulative CO₂ emissions and each of which has a short (immediate) and a long (100 years) peak of accumulative CO₂ emissions before declining towards a baseline simulation of 1500 PgC accumulatively emitted within the first 100 years.

The results show that the height of the overshoot has an impact on global fire regimes while its duration does not seem to play a significant role 200 years after peak CO₂. Overall, we can see that changes in vegetation composition following the temperature anomaly are the main driver for changes in global wildfire frequency. While in the low overshoot scenarios burnt area has almost converged towards the baseline simulation, the extremest scenarios show the lowest burnt area at the end of the simulation period, indicating that vegetation changes, especially in low latitudes, have been most significant and/or are still ongoing.

How to cite: Nieradzik, L., Lee, H., Miller, P., Schwinger, J., and Wårlind, D.: Changes in global fire regimes under idealized overshoot scenarios, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7379, https://doi.org/10.5194/egusphere-egu23-7379, 2023.

Wildfires are becoming a growing concern in the UK, as climate change increases the occurrence and persistence of periods of hot, dry weather. Vegetation type and management play an important but contested role in UK fire risk and resilience, and questions remain over the best ways to prevent large fires developing. Remote sensing can provide vital data on fire size, severity, and recovery times, but method effectiveness is dependent on understanding specific ecosystems. This research uses ground validation of four wildfires in the UK Peak District National Park to deliver insights which improve interpretation of satellite data in wildfire monitoring. These insights are then applied to a three-year remote sensing database of large wildfires in England and Wales, to give novel results on the links between vegetation type and management, and fire size and severity. Ecosystem resilience and recovery is further explored through analysing the vegetation growth post-fire at three of the four Peak District study sites. This project therefore develops and validates remote sensing methodology in wildfire research by combining field data with satellite imagery to yield new understandings of the relationships between vegetation and fire. 

How to cite: Lees, K. and Lenton, T.: The role of vegetation in UK upland wildfires: Risk, Resilience, and Remote Sensing, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7449, https://doi.org/10.5194/egusphere-egu23-7449, 2023.

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 (Walsh, S, 2006). 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. Following 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.

The Department of Agriculture, Food and Marine is the Forest Protection authority in Ireland responsible for issuing Fire Danger Notices. These notices improve preparedness for fire responses and are based on 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.

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: Finkele, K., Flattery, P., Nugent, C., and Downes, P.: Current Operational Implementation of the Canadian Forest Fire Weather Index System in the Republic of Ireland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7853, https://doi.org/10.5194/egusphere-egu23-7853, 2023.

Keywords: Black carbon, Dissolved organic carbon, BPCAs, Mackenzie River, Beaufort Sea, Climate change

Climate change is amplified in the arctic and boreal regions. This causes higher average temperatures and less precipitation in the summer months and is resulting in longer wildfire seasons, severity, frequency and extent. This increases the relies of carbon into the atmosphere as greenhouse gases and aerosols, amplifying climate change even further. Black carbon (BC) is a fraction of organic carbon, resulting from the incomplete combustion of biomass and fossil fuels. BC may be inaccessible for biodegradation, because of its highly condensed aromatic molecular structure and therefore stores carbon on long timescales on land and in the ocean. BC is produced on land, but is transported as dissolved BC (DBC) by the rivers to the oceans, where it cycles on millennial timescales, sequestering BC. Thus, it is important to understand the significance of BC in the context of increased fires in this vulnerable region in the face of climate change.

The Mackenzie River is a major source of terrestrial dissolved organic carbon (DOC) and the largest source of sediments to the Arctic Ocean. Here, we resolve the cycling of riverine DBC from the Mackenzie River to its fate in the Beaufort Sea, and the influence of mixing with Pacific water masses entering from the Chukchi Sea. We present DBC concentration data in ocean water, which was collected on two cruises in the Beaufort Sea in 2021 and 2022 covering the outflow of the Mackenzie River.

For DBC concentrations, we digested solid phase extracts of DOC with nitric acid to oxidize BC molecules into benzenepolycarboxylic acids (BPCAs), which were then quantified on High Performance Liquid Chromatography (HPLC). We compare the concentrations of the DBC and DOC to trace the mixing of DBC river outflow with the ocean water. Since DBC originates on land and is relatively stable to biodegradation we can resolve the pathways of DBC from the Mackenzie River to the Arctic Ocean.

How to cite: Speidel, L. G., Bröder, L., Lattaud, J., Haghipour, N., Eglinton, T. I., and Coppola, A. I.: Fate of Fire altered Organic Carbon in the arctic river-to-ocean continuum: Resolving Mackenzie River Black Carbon in the Beaufort Sea, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7913, https://doi.org/10.5194/egusphere-egu23-7913, 2023.

Wildfire risk prediction relies on the often-heuristic assessment of diverse fire potential indices, fuel maps, fire weather indices and prior fire activity data. Here we present a model nowcasting daily wildfire genesis probability and expected wildfire sizes in the contiguous US.

Predictors were selected and developed to account for climate, vegetation, topographic and human effects on wildfire genesis. Climate factors are represented by multiple fuel wetting and drying processes at daily to seasonal-scale antecedences, snowpack, and wind. We use GPP to predict fuel mass and recent growth, and dominant vegetation type. Human factors include population, landscape accessibility and ignition sources such as powerlines.

The first stage of the model predicts wildfire genesis probability as a zero-inflated process with an explicit probability of fire preclusion, whilst the second stage models fire sizes according to a generalised extreme value distribution. Nonlinear effects are accounted for via global optimisation for the domain for which each variable drives changes in fire genesis behaviour and the appropriate variable transform.

The model has good predictive and explanatory power, as shown by various performance metrics and the meaningful nonlinear relationships identified in the optimisation process. We show that this method can resolve seasonal wildfire risk dynamics well over smaller ecoregions than the observational record permits, allowing us to quantify the extent to which fire risk is determined by seasonal-scale versus daily-scale effects.

How to cite: Keeping, T., Harrison, S., and Prentice, I.: A New Method for Nowcasting Wildfire Risk, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7937, https://doi.org/10.5194/egusphere-egu23-7937, 2023.

Fire processes are a complex component of the Earth System processes and their full representation has proven to be difficult to represent Earth System Models (ESM). Because of this, these processes are often simplified in fire enabled ESMs, for instance ignitions are usually modelled to increase at low population densities up to a threshold, and reduce thereafter, as suppression effects become dominant with the increase of population density. However, socio-economic, and cultural factors can play a significant role in shaping the behaviour of fire ignitions. This study aims to address this by implementing a socio-economic factor in the fire ignition and suppression parametrisation in the INteractive Fire and Emission algoRithm for Natural envirOnments (INFERNO) based on the Human Development Index (HDI). The inclusion of this factor reduced a large long-standing positive bias found in regions of Temperate North America, Central America, Europe, and Southern Hemisphere South America. This change also leads to improvements in the model representation of fire weather and anthropogenic drivers in tropical regions, by reducing the influence of population density changes. Therefore, this framework can be used to improve understanding of the anthropogenic impacts of fire in future scenarios based on different Shared Socioeconomic Pathways.

How to cite: Teixeira, J., Burton, C., Kelley, D. I., Folberth, G., O'Connor, F. M., Betts, R., and Voulgarakis, A.: Impact of socio-economic factors in burnt area for future climate scenarios, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8075, https://doi.org/10.5194/egusphere-egu23-8075, 2023.

Carbon monoxide (CO) is released during biomass burning events, resulting in decreased air quality and leading to the formation of climate forcing pollutants. An increase in wildfires has resulted in a change to the CO seasonal cycle of the North American Pacific Northwest, when comparing 2012-2018 to 2002-2011. This trend was reported using data from the Measurements of Pollution in the Troposphere (MOPITT) instrument on NASA’s Terra satellite. Similarly, an increase in summertime CO values was identified with the Fourier Transform Infrared (FTIR) spectrometer at the University of Toronto Atmospheric Observatory (TAO), over the same time period. Studies have shown correlations between wildfire smoke exposure and healthcare utilization for cardiovascular and respiratory conditions. Monthly counts of Emergency Department admissions for cardiovascular and respiratory diseases for Alberta and Ontario are investigated in relation to wildfire events in Canada and the USA. MOPITT and TAO FTIR CO columns, the Moderate Resolution Imaging Spectroradiometer (MODIS) burned area product, and provincial burned areas from Natural Resources Canada are assessed to estimate wildfire smoke exposure in the study region. This work aims to evaluate if CO can be used as a complementary tracer for health impacts from wildfire smoke exposure. 

How to cite: Flood, V., Strong, K., Buchholz, R., Magzamen, S., and Kuiper, G.: Investigating Emergency Room Visits for Cardiorespiratory Diseases in Alberta and Ontario, Canada in Relation to Wildfires, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9361, https://doi.org/10.5194/egusphere-egu23-9361, 2023.

The assessment of global burned area from remote sensing is an essential climate variable driving land surface GHG emissions and energy/water budget. Gridded 0.25° or 0.5° monthly burned area have been largely used for biosphere/atmosphere interactions modelling, while recent fire/weather analysis or model developments increasingly request fire events, defined as a fire patch with intrinsic fire spread properties. Pixel level information, the finest resolution from global burned area, defined by their burn date, can be aggregated within a spatio-temporal threshold and delineate these fire events. Uncertainties in burn date, the coarse resolution of pixel resolution, multiple ignition points, or the specified values in spatio-temporal thresholds can however lead to various final fire event delineation. Currently, three major global fire event database exist (FRY, Fire Atlas, GlobFire), mostly derived from MCD64A1 pixel level 500m-resolution burned area. We propose here a new version of FRY, based on MCD64A1 and FireCCI51 at 250m, with an updated pixel aggregation method allowing for single ignition fire patches. Fire patch morphology indicators as elongation, direction, complexity have been conserved from v1.0, with additional information as ignition points from minimum burn date from burned area and more timely-accurate hotspots (VIIRS and MCD14ML), rate of spread, fire Radiative power and burn severity, as well as fraction of land cover affected, based on user requirements. The dataset is delivered as a yearly shapefile, with an attribute table referencing all information on ignition, spread and final shape. Global comparison of major information from FRYv2.0 (fire size distribution, fire number, ROS) will illustrate the effects of increasing spatial resolution and better timing from hotspots provided in this new version, freely available for the scientific community for the period 2001-2020.

How to cite: Mouillot, F., Chen, W., Campagnolo, M., and Ciais, P.: FRYv2.0 : a global fire patch morphology database from FireCCI51 and MCD64A1, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9575, https://doi.org/10.5194/egusphere-egu23-9575, 2023.

Lightning is an important atmospheric process for igniting forest fires – often in remote locations where they are not easily suppressed – which results in potentially large emissions of many pollutants and short-lived climate forcers. Lightning also generates reactive nitrogen, resulting in the production of tropospheric ozone, the third most important greenhouse gas. Furthermore, the changing climate is expected to change the frequency and location of lightning. As such, lightning is an important component of climate models. The Canadian Atmospheric Model, CanAM, is one such climate model that did not contain an 'online' lightning parameterization. Fire ignition in CanAM was done via an unchanging climatological lightning input. In this study, we have added a new logistical regression lightning model (Etten-Bohm et al, 2021) into CanAM, creating the capacity for future lightning predictions with CanAM under different climate scenarios. The modelled lightning and fire area burned were evaluated against measurements in a historical period with good results. Then we simulate lightning and fire area burned in a future climate scenario in order to provide an estimate on how lightning and its impacts will change in the future. This study also presents the first time that CanAM’s land fire model was used online with its atmosphere to fully simulate fires in the global earth system.

Reference:

Etten-Bohm, M., J. Yang, C. Schumacher, and M. Jun : Evaluating the relationship between lightning and the large-scale environment and its use for lightning prediction in global climate models, JGR-atmospheres, 126, e2020JD033990, 2021.

How to cite: Whaley, C., Schumacher, C., Etten-Bohm, M., Arora, V., Plummer, D., Cole, J., Lazare, M., and Akingunola, A.: Lightning in a changing climate and its impacts on fire area burned, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9791, https://doi.org/10.5194/egusphere-egu23-9791, 2023.

Fires in high latitudes are becoming more critical in terrestrial ecosystem modeling. With climate warming and dry weather condition, the fires have spread more, and widespread burning has severely damaged the ecosystem. As the fire dynamics cannot be described with the mass or energy balance equations, the fire models have been developed with different input variables, linked with different vegetation models, and widely coupled with the earth system models (ESMs) or land surface models (LSMs) with different complexities of parameterization. Here, we designed a new approach using hybrid deep learning [Long Short-Term Memory (LSTM) - Artificial Neural Network (ANN)] for predicting Alaskan natural fires and aimed to understand the impacts of fires with from the NCAR community land model 5 – biogeochemistry (CLM5-BGC). This study was conducted based on fire information provided by Alaska Interagency Coordination Center (AICC), which provides the data for each fire point, start date, end date, and total burned area from 2016-2020. As the fire duration was identified as the most important in predicting the burned area, we first trained the LSTM for predicting fire duration (i.e., fire ignition and fire persistence period) with ERA5 atmospheric forcings. Also, we trained ANN to predict the burned area with both ERA5 atmospheric forcings and fire duration. Then, we combined two models (LSTM and ANN) to simultaneously predict the fire days and burned area with climate and vegetation datasets. This hybrid model has the strength to capture large fires (>10000ha), comparing the burned area from CLM5-BGC (Correlation: 0.79). When this hybrid model is coupled with CLM5-BGC, we found that the carbon fluxes changed over Alaska. In particular, total net ecosystem exchange (NEE) increased by more than two times that of only CLM5-BGC, which could primarily affect terrestrial carbon exchanges.

Acknowledgement

This work was supported by the Korea Polar Research Institute (KOPRI, PE22900) funded by the Ministry of Oceans and Fisheries and the Basic Science Research Program through the National Research Foundation of Korea, which was funded by the Ministry of Science, ICT & Future Planning (grant no. 2020R1A2C2007670) and by the Ministry of Education (2022R1A6A3A13073233).

How to cite: Seo, H. and Kim, Y.: A hybrid deep learning framework for predicting point-level Alaskan fires, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10336, https://doi.org/10.5194/egusphere-egu23-10336, 2023.

Advances in wildfire modeling have focused on refining atmospheric interactions for obvious links between local airflows, combustion dynamics, fire line advance and smoke plume transport. Yet, lasting impacts of wildfires on landscapes are linked primarily with changes in soil characteristics and alteration of ecological and hydrologic processes. Quantitative assessment of wildfire impacts requires metrics for fire-surface thermal interactions beyond qualitative surrogates such as burn severity used for ecological assessment. The highly transient and localized nature of wildfire intensity and its coarse spatial and temporal representation hinder quantitative translation of wildfire dynamics to soil heat fluxes even with the most advanced wildfire models (e.g., QuicFire, WRF-Fire, WFDS). Inspired by the pioneering works of Byram, Rothermel and Albini, we seek to derive high resolution information on fire line intensities from highly resolved fuel maps informed by fire line dynamics derived from numerical wildfire model representation. This hybrid downscaling approach (limited by the quality and resolution of fuel maps) offers a means for constraining soil surface heat fluxes at resolutions relevant to quantifying critical temperatures and duration at depth to estimate pyrolysis of soil organic carbon and the degree of soil structure alteration. Examples will be presented and discussed. 

How to cite: Or, D., Vahdat-Aboueshagh, H., Furtak-Cole, E., and A. McKenna, S.: Towards mechanistic representation of wildfire effects on soil – downscaling to quantify subsurface heat fluxes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10389, https://doi.org/10.5194/egusphere-egu23-10389, 2023.

Stalagmites provide records of past changes in climate, vegetation, and surface events, which can be identified through variability in their chemical composition over time. This variability is the result of changes in surface environmental properties, which are reflected in the physical and chemical properties of the water that percolates into the cave, ultimately affecting the composition of the speleothem calcite. Wildfires have the potential to alter soil properties and soluble element concentrations. Consequently, stalagmite compositions have been shown to respond to increases in soil nutrients, trace metal concentrations, and changes in soil/karst bedrock hydraulic conductivity. It is, therefore, likely that stalagmites, and particularly those grown in shallow caves for which transmission of the surface signal is rapid, capture the environmental effects of wildfires in their chemical and physical properties.

We analysed a stalagmite from a shallow cave in a region known to be affected by wildfires in south-west Western Australia. Fire proxies were assessed using a multi-proxy approach. This includes water isotopes via stable-isotope ratio mass spectrometry and trace element analyses via synchrotron X-ray fluorescence microscopy and laser ablation inductively coupled plasma mass spectrometry. This approach shows that the timing of known fire events coincided with a multi-proxy response in stalagmite chemistry, including increased concentrations of phosphorus, copper, aluminium, lead, and zinc, which are interpreted to be derived from leaching of ash from burned vegetation above the cave. We also identified lower and less variable peaks in phosphorus concentrations during the pre-colonisation period, suggesting that Indigenous land management resulted in more frequent but low intensity burning. This contrasted with less frequent but more intense fires associated with post-colonisation land-management. A particularly large paleo-fire identified in 1897 appears to coincide with a peak in 𝛿¹⁸O, interpreted to have resulted from evaporation of sub-surface water during the heat of the fire. This large fire was preceded by a multi-decadal dry period identified by trace element proxies. The intensity of the 1897 fire was then exacerbated by the combination of a multi-decadal drought and a transition away from cultural burning practices by Indigenous Australians, which resulted in build-up of vegetation and dry combustible material on the forest floor.

This research is a world-first demonstration of fire events recorded in stalagmites and shows their potential to provide accurate records of both fire frequency intervals and changes in climate. Further records of past fire events from stalagmites will help to understand how past fire regimes have varied with climate, land-use change and colonisation, and will help to better guide land management practices in the future.

How to cite: McDonough, L., Treble, P., Baker, A., Borsato, A., Frisia, S., Campbell, M., Nagra, G., Coleborn, K., Gagan, M., Zhao, J., and Paterson, D.: An annually resolved stalagmite record of fire frequency for the last 250 years in south west Australia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10651, https://doi.org/10.5194/egusphere-egu23-10651, 2023.

Environmental proxy archives such as tree rings, sediment cores, and ice cores are commonly used to investigate past fire regimes. Speleothems, naturally forming cave decorations mainly comprising of stalagmites, stalactites, and flowstones, have been extensively used as palaeoenvironmental archives as their physical attributes and chemical composition change with changed environment. Research has shown that cave drip water chemistry responds to fire events, and more recently, that speleothems can record past fire events due to physical and chemical processes which alter speleothem composition. These processes include changes to water stores due to evaporation, fracturing of the host rock, changed soil hydrophobicity, production of highly soluble lime, changes in soil CO₂ production, destruction of vegetation and deposition of ash above the cave. These changes can result in shifts in δ¹⁸O and δ¹³C, altered concentrations of vegetation, soil and bedrock-derived elements, and incorporation of soluble ash derived elements (including phosphorus, aluminium, copper, zinc, and lead) in speleothems (McDonough et al., 2022; Campbell et al., 2022).

Changes in speleothem chemistry are typically determined using micro-analytical techniques (such as Synchrotron X-ray Fluorescence Microscopy and laser ablation inductively coupled plasma mass spectrometry) and isotope ratio mass spectrometry. These changes can be precisely and absolutely dated via uranium-series and carbon dating, and can often be resolved at high resolution via manual counting of seasonal fluctuations in organic matter and trace element concentration. This makes speleothems, particularly those grown in shallow caves in highly seasonal climates, ideal for identifying both short-lived events such as wildfires, and longer-term changes such as shifts in climate. This novel application of speleothems as archives for coupled climate and palaeofire proxies is still in its infancy but holds great potential.

Here, we present a review of this new sub-discipline. We cover its origins in cave dripwater monitoring, discuss site and sample selection, and describe the current analytical and statistical approaches used to extract fire information from speleothems. Such records will enable land managers to develop improved methods for managing fire regimes.

How to cite: Campbell, M., McDonough, L., Treble, P., Baker, A., Kosarac, N., Coleborn, K., Wynn, P., and Schmitt, A.: Speleothems as archives for palaeofire proxies, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11016, https://doi.org/10.5194/egusphere-egu23-11016, 2023.

Emissions from vegetation fires in tropical forests have the potential to turn the global land carbon sink into a source, affect atmospheric chemistry, and hence air quality. While natural forest fires are a rare phenomenon in tropical forests of South America and are usually of rather low intensity, deforestation fires and small land clearings in systems with high fuel loads can cause intense fires and high emissions. However, the high moisture content in tropical forests causes incomplete combustion and higher emissions of carbon monoxide (CO) than of carbon dioxide. The interacting effects of land use change, fuel load and moisture on fire intensity and emissions is, however, difficult to quantify at large scales because not all of those components are readily available from Earth observations in a consistent way. 

Here, we make use of several satellite products on vegetation, fire activity and atmospheric composition to quantify the effects of land use, fuel loads, fuel moisture on fuel consumption, emission factors and hence on emissions and atmospheric trace gas concentration. First, we use observations of active fires and fire radiative power from the VIIRS and Sentinel-3 SLSTR sensors to map different fire types (forest fires, deforestation fires, small land clearing and agricultural fires, savannah fires). Second, we integrate satellite products of canopy height, above-ground biomass, leaf area index, land cover and soil moisture in a novel data-model fusion framework to estimate fuel loads and moisture in vegetation, surface litter and woody debris. We then combine in a bottom-up approach the fire types with fuel loads and moisture to estimate fuel consumption and fire emissions using default emission factors. Third, we use observations from Sentinel-5p TROPOMI and the Integrated Forecast Systems (IFS) of the Copernicus Atmosphere Monitoring Service to compare the bottom-up estimates with distributions of CO and NOx in the atmosphere, which allows optimising emissions and associated emission factors.

Our reconciled estimates of fire emissions outperform previous CO estimates e.g. from the Global Fire Assimilation System, which demonstrates an improved estimation of fire carbon emissions. The results show that the high fire intensity and emissions in tropical deforestation fires originate from the burning of high loads of woody biomass and coarse woody debris. The high fuel moisture content causes higher emission factors of CO in tropical forests than in savannah fires and hence higher absolute emissions of CO. Our new model approaches and satellite products allow to provide an integrated assessments on the effects of fuel and fire behaviour on fire emissions.

How to cite: Forkel, M., Andela, N., Huijnen, V., Wessollek, C., Awotwi, A., Kinalczyk, D., Marrs, C., and de Laat, J.: Effects of land use, fuel loads and fuel moisture on fire intensity and fire emissions in South America derived by reconciling bottom-up and top-down satellite observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11297, https://doi.org/10.5194/egusphere-egu23-11297, 2023.

Boreal forests store about one third of the world’s forest carbon and may store even more carbon in the future because of the positive effects of rising atmospheric CO₂ concentrations on photosynthesis and plant growth. However, fire frequency and severity have also been increasing in boreal forests in the last decades, which might offset their carbon sink potential. In Eastern Siberia, the dry and hot summers of 2020 and 2021 showed exceptionally high fire activity. However, even large fires that can spread for several months, eventually come to an end. This can be because of a change in the weather or because fires run out of fuels. Here, we aim to quantify the controls of fire growth in Eastern Siberia using high resolution landscape variables and hourly ERA-5 meteorological variables. We harmonized the burned area product from the Fire Climate Change Initiative and active fire product from the Visible Infrared Imaging Radiometer Suite, and derived fire perimeters from them for the period between 2012 and 2021. Along these fire perimeters, we then identified spatial changes in landscape variables (i.e. a decline in tree cover or increase in surface water) and temporal changes in hourly vapor pressure deficit and wind. By doing so, we could attribute causes of why fires stopped spreading.

How to cite: Janssen, T. and Veraverbeke, S.: Identifying the limits to fire growth in Eastern Siberia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11559, https://doi.org/10.5194/egusphere-egu23-11559, 2023.

Climate change is expected to cause prolonged and more severe droughts in Europe, increasing landscape fire occurrence. Since The Netherlands has a high population density in areas typified as ‘Wildland-Urban Interface’, a genuine risk for Dutch society arises. Landscape management, such as prescribed burning, can reduce fire risk. Prescribed burning is executed by intentionally burning the low and understory vegetation, limiting fuel for a landscape fire, under controlled conditions. In this interdisciplinary research, conducted by a team of (early career) researchers from climate science, cultural studies, hydrology, mathematics and spatial economics, we aim to assess whether prescribed burning can be used in The Netherlands as a fire risk reduction tool in natural areas with a high fire risk.

The Netherlands has a well-developed flood management system. However, it lacks such holistic approaches to landscape fire management. Landscape managers and researchers can learn from Dutch flood management by applying the secondary objective, improvement of spatial quality, to prescribed burning. In this research we assess the potential for improving spatial quality through prescribed burning, by adapting the spatial quality framework of the Dutch Room for the River project. Our framework looks at the three pillars burning effectiveness, ecological robustness, and cultural meaning at the potential prescribed burning sites. Burning effectiveness is highest in natural areas (Natura 2000 sites), with high fire risk and the presence of low vegetation. Ecological robustness measures the disturbance prescribed burning could cause in a landscape. Disturbance depends on the burning frequency and intensity, as well as on the type of vegetation that is burned and the usage of the area. In groundwater protection areas, seepage of harmful elements could cause more disturbance. These areas are therefore excluded from the analysis. From the perspective of cultural meaning, social perceptions influence the measure’s performance. Cultural significance and landscape identification provide various perspectives on fires and prescribed burning. Categorizing the different levels of engagement, based on an engagement pyramid, can deliver a basis for implementing prescribed burning.

Preliminary analyses result in a selection of 15 Natura 2000 sites in The Netherlands where prescribed burning could be feasible, varying from the Voornes Duin (14 km²) to the Veluwe (885 km²). These areas are mostly vegetated with coniferous and mixed forests. Prescribed burning potentially causes more disturbance in grasslands. However, since none of the 15 areas contain more than 24% grassland, prescribed burning could still be feasible at all locations. In the area of the Veluwe, qualitative interviews with the local population indicate support for fire management, such as prescribed burning, as they are aware of the risks imposed by landscape fires.

The final research results can contribute to the improvement of fire management in both The Netherlands and other North-Western European countries with similar vegetation and climate change effects.

How to cite: van Manen, N., Buxó, A., Egberts, L., Houwaard, L., Jacobsen, L., Keesom, J., Reijners, M., van Slooten, D., Teunisse, A., and van Tilburg, A.: Assessing the feasibility of prescribed burning as a fire risk reduction tool for The Netherlands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11992, https://doi.org/10.5194/egusphere-egu23-11992, 2023.

In high-latitude regions, larger and more frequent fires have been occurring over recent years, a tendency that is expected to continue in the coming decades due to warmer temperatures and regionally decreased precipitation imposed by climate change (IPCC,2019). Boreal wildfires in general are a significant source of CO₂ emissions, as well as other greenhouse gases and aerosols (Akagi et al. 2011; Van Der Werf et al. 2010), e.g. emissions from boreal forests between 1997 and 2016 accounted for 7.4% of the global emissions (van der Werf et al. 2017). The effects of boreal fires on future climate have not been investigated and are potentially of great importance since climate change is occurring more rapidly in those high-latitude areas. More flammable forests in addition to the large carbon-rich peatlands, will potentially lead to devastating consequences.

The overall goal of our project is to quantify the effects of high-latitude wildfire emissions on atmospheric composition as well as climate. For this purpose, simulations with the EC Earth Earth System Model (ESM) are being employed to characterize the past, present and future variability and changes of wildfires especially in high latitudes. In the results presented here, we demonstrate how the EC Earth model performs when forced with prescribed fire emissions (GFED4) and with a more detailed peat fire module developed by our team. The mean state, seasonality, and interannual variability of fire emissions and key atmospheric constituent abundances (black carbon, organic carbon, NO_x, CO, ozone, amongst others) are validated in the model, using a range of observational datasets. This validation exercise is a key step before employing the EC-Earth model for quantifying future impacts of high-latitude fires on atmospheric composition and climate.

IPCC,2019: Jia, G., E. Shevliakova, P. Artaxo, N. De Noblet-Ducoudré, R. Houghton, J. House, K. Kitajima, C. Lennard, A. Popp, A. Sirin, R. Sukumar, L. Verchot, 2019: Land–climate interactions. In: Climate Change and Land: an IPCC special report on climate change, desertification, land degradation, sustainable land management, food security, and greenhouse gas fluxes in terrestrial ecosystems [P.R. Shukla, J. Skea, E. Calvo Buendia, V. Masson-Delmotte, H.-O. Pörtner, D.C. Roberts, P. Zhai, R. Slade, S. Connors, R. van Diemen, M. Ferrat, E. Haughey, S. Luz, S. Neogi, M. Pathak, J. Petzold, J. Portugal Pereira, P. Vyas, E. Huntley, K. Kissick, M, Belkacemi, J. Malley, (eds.)]. In press.

Akagi, S.K. et al., 2011: Emission factors for open and domestic biomass burning for use in atmospheric models. Atmos. Chem. Phys., 11, 4039–4072, doi:10.5194/acp-11-4039-2011.

Van Der Werf, G.R. et al., 2010: Global fire emissions and the contribution of deforestation, savanna, forest, agricultural, and peat fires (1997–2009). Atmos. Chem. Phys., 10, 11707–11735, doi:10.5194/acp-10-11707-2010.

Van Der Werf, G.R. et al., 2010: Global fire emissions and the contribution of deforestation, savanna, forest, agricultural, and peat fires (1997–2009). Atmos. Chem. Phys., 10, 11707–11735, doi:10.5194/acp-10-11707-2010.

How to cite: Boleti, E., Blackford, K., Myriokefalitakis, S., and Voulgarakis, A.: High-latitude wildfires, atmospheric composition, and climate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12559, https://doi.org/10.5194/egusphere-egu23-12559, 2023.

Fire-enabled dynamic global vegetation models (DGVMs) can be used to study how fire activity responds to its main drivers, including climate/weather, vegetation and human activities, at coarse spatial scales. Such models can also be used to examine the effects of fire on vegetation, and, when embedded in Earth system models, investigate the feedback of fire on the climate system. Thus they are valuable tools for studying wildfires. Accordingly, the Fire Model Intercomparison Project (FireMIP) was established to evaluate and utilise these models using consistent protocols.

Here we present the second round of FireMIP simulations to focus historic wildfire drivers (1901 to present). A six-member ensemble of simulations from fire-enabled DGVMs was compared to remotely-sensed burnt area observations and to the previous round of historical FireMIP simulations. We found that the model skill when simulating spatial patterns of burnt area shows modest improvements compared to the previous FireMIP round, and that the simulations mostly reproduce the decreasing trend in global burnt area found over the last two decades. However, whilst the broad global patterns are reasonable, there are considerable discrepancies with regards to regional agreement and timing of burnt area. Furthermore, the models show diverging trends in the pre-satellite era.

To investigate further and inform future model development, we explored the residuals between simulated burnt area from the FireMIP models and remotely-sensed burnt area as a function of climate, vegetation, anthropogenic and topographic variables using generalised additive models (GAMs). We found some common responses across the models, with many over-predicting fire activity in arid/low productivity areas and all models under-predicting at low road density. However, with respect to other variables, such as wind speed and cropland fraction, the models residuals showed divergent responses. It is anticipated that these results should aid further development of global fire models in terms of driving variables, process representations and model structure.

How to cite: Forrest, M., Burton, C., Drüke, M., Hantson, S., Li, F., Melton, J., Nieradzik, L., Rabin, S., Sitch, S., Yue, C., and Hickler, T.: Causes of uncertainty in simulated burnt area by fire-enabled DGVMs, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12604, https://doi.org/10.5194/egusphere-egu23-12604, 2023.

Due to its strong connection with meteorological conditions and vegetation structure, fire activity is affected by anthropogenic climate change. As a direct effect, climate regulates fuel moisture, so warmer and drier conditions are linked to higher fuel flammability, increasing fire risk. We use data from ERA5 and different CMIP6 models to build a database of fuel moisture (for both live and dead fuels) under real conditions (factual) and modified conditions without the influence of global warming (counterfactual). We then calculate the rate of spread of some observed wildfires in the Iberian Peninsula from 2001 to 2021, from both factual and counterfactual data. We find that climate change influence is already noticeable and significant. We also identify the areas most vulnerable to the impacts of climate change and the time of the year when these impacts are strongest. 

How to cite: Senande-Rivera, M., Insua-Costa, D., and Míguez-Macho, G.: Quantifying the direct influence of climate change on the rate of spread of wildfires in the Iberian Peninsula, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12731, https://doi.org/10.5194/egusphere-egu23-12731, 2023.

Tropospheric ozone (O₃) is a key greenhouse gas and pollutant that is receiving increasing attention globally.  While there are many sources of tropospheric O₃, precursors from human activity (Anthro) and open biomass burning (BB) are the only ones that can be controlled. As such, it is crucial for policymakers to understand the relative contributions of the two. However, determining the contribution of O₃ can be challenging as it cannot be directly observed. It must be calculated by chemical transportation model (CTM) simulation which could be biased for unreal emission inventory, or estimated by real observations that assumes too simple chemical and transportation processes.

In this paper, we propose a solution by developing a deep learning (DL) model that combines both CTM simulations and observations. The DL model is able to learn a generalized relationship between unobservable O₃ contribution from Anthro or BB sectors and observable mixing ratio of tracers simulated by CTM with full chemistry and transportation processes. The DL model then, when applied to observed tracers, could avoid the bias from model to provide an accurate estimation of the contributions in reality.

Our results indicate the contribution from BB to tropospheric remote ozone mixing ratio is no larger than that from Anthro emission from a global perspective, even when uncertainties are deliberately tuned to bias BB. Therefore, the reduction of anthropogenic emissions should be the top priority for controlling global background O₃ levels, at least for the time period of 2016-2018 studied.

How to cite: Ma, C., Cheng, Y., and Su, H.: Biomass Burning Contributes Less to Remote Tropospheric Ozone than Human Activity, Indicated by a Deep Learning Approach, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13307, https://doi.org/10.5194/egusphere-egu23-13307, 2023.

Tropical savannas and grasslands are the most frequently burned biome in the world, and fire constitutes an important part of the ecosystem. In this ecosystem it can have both rejuvenating and destructive effects, depending on several factors including fuel conditions, weather conditions, and time of year. For centuries humanity has used fire in these landscapes for hunting, land clearance, agriculture, and most recently carbon offsetting. Land managers in locations with a monsoonal climate and frequent fire regimes such as tropical savannas use prescribed burning as a management tool in the ‘early dry season’ (EDS) shortly after the last rains of the year. Fires at this time tend to be cooler, restricted to surface level and less severe, meaning they can be controlled more easily and tend to go out at night without external input. Commonly a specific, fixed date is used to indicate when this window of safe burning has expired, set based on experience of the local or regional authority. In this work, we have defined a method of determining when this window expires on the basis of active fire hotspot data from the twin MODIS instruments from 2001 through to 2021. By using the relationship between day and night-time active fire detections, we set a flexible date for the transition between the early and late dry seasons in fire-prone savannas globally in the five major tropical savanna regions - Northern & Southern hemisphere South America (NHSA & SHSA), Northern & Southern hemisphere Africa (NHAF & SHAF), and Australia (AUST). The variability across each region was high (lowest mean standard deviation annually was 24 days in NHAF and highest was 56 in AUST). The fraction of area burned in the late dry season ranged from 15% (SHSA) to as high as 85% (AUST) on average, with many parts of Africa and Australia especially showing a significant skew towards the late dry season. This suggests potential for implementation of prescribed burning programmes to increase the amount of desirable fire in the global savanna ecosystems.

How to cite: Eames, T., Russell-smith, J., Yates, C., Vernooij, R., and van der Werf, G.: Seasonal skew of tropical savanna fires, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13544, https://doi.org/10.5194/egusphere-egu23-13544, 2023.

Even though wildfires are an important ecological component of larch-dominated boreal forests in eastern Siberia, intensifying fire regimes may induce large-scale shifts in forest structure and composition. Recent paleoecological research suggests that such a state change, apart from threatening human livelihoods, may result in a positive feedback on intensifying wildfires and increased permafrost degradation [1]. Common fire-vegetation models mostly do not explicitly include detailed individual-based tree population dynamics. However, setting a focus on patterns of forest structure emerging from interactions among individual trees in the unique forest system of eastern Siberia may provide beneficial perspectives on the impacts of changing fire regimes. LAVESI (Larix Vegetation Simulator) has been previously introduced as an individual-based, spatially explicit vegetation model for simulating fine-scale tree population dynamics [2]. It has since been expanded with wind-driven pollen dispersal, landscape topography, and the inclusion of multiple tree species. However, until now, it could not be used to simulate effects of changing fire regimes on those detailed tree population dynamics.

We present simulations of annually computed tree populations during the past c. 20,000 years in LAVESI, while applying a newly implemented fire module. Wildfire ignitions can stochastically occur depending on the monthly fire weather. Within the affected area, fire intensity is mediated by surface moisture. Fire severity depends on the intensity, with scaled impacts on trees, seeds and the litter layer. Each tree has a chance to survive wildfires based on a resistivity estimated from its height and species-specific traits of bark thickness, crown height, and their ability to resprout. The modelled annual fire probability compares well with a local reconstruction of charcoal influx in lake sediments. Simulation results at a study site in Central Yakutia, Siberia, indicate that the inclusion of wildfires leads to a higher number of tree individuals and increased population size variability compared to simulations without fires. In the Late Pleistocene forests establish earlier when wildfires can occur. The new fire component enables LAVESI to serve as a tool to analyze effects of varying fire return intervals and fire intensities on long-term tree population dynamics, improving our understanding of potential state transitions in the Siberian boreal forest.

References:

[1] Glückler R. et al.: Holocene wildfire and vegetation dynamics in Central Yakutia, Siberia, reconstructed from lake-sediment proxies, Frontiers in Ecology and Evolution 10, 2022.

[2] Kruse S. et al.: Treeline dynamics in Siberia under changing climates as inferred from an individual-based model for Larix, Ecological Modelling 338, 101–121, 2016.

How to cite: Glückler, R., Gloy, J., Dietze, E., Herzschuh, U., and Kruse, S.: Simulating wildfire impacts on boreal forest structure over the past 20,000 years since the Last Glacial Maximum in Central Yakutia, Siberia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13603, https://doi.org/10.5194/egusphere-egu23-13603, 2023.

During the last decade, the world faced record-breaking giant fires as observed in Australia and California, a trend that is expected to increase in the forthcoming years due to climate change (Palinkas, 2020; Sharples et al., 2016; van Oldenborgh et al., 2021). In addition to their large ecological impacts, wildfires are more and more regarded for their potential threat to human health through air pollution (Xu et al., 2020). However, water pollution resulting from wildfires represents an underestimated pathway for wildfires-induced health risk (Abraham et al., 2017). This latter impact is related to the heat generated by wildfires that can propagate towards several centimeters in the soil and transform/destroy soil components. In addition to weakening soil physical stability, such transformation/destruction can change the speciation of potentially toxic elements (PTEs) that are associated with these soil components, leading to enhanced mobility towards waterways (Abraham et al., 2017; Terzano et al., 2021). One notable PTE is chromium, which is naturally present in soils mostly as trivalent Cr(III), but can represent an environmental and health issue when occurring as hexavalent Cr(VI). Recent studies reported Cr(III) oxidation to Cr(VI) upon laboratory-heating of Cr(III)-doped Fe-oxyhydroxides (Burton et al., 2019a; 2019b). Besides, Cr(III) oxidation to Cr(VI) upon controlled heating was also demonstrated for different types of soils (Burton et al., 2019b; Rascio et al., 2022; Thery et al., 2023). All these considerations suggest a significant effect of wildfires on Cr(III) oxidation to Cr(VI) in soils, with a possible influence on Cr mobility that could further impact freshwater quality. This risk of freshwater Cr(VI) pollution is expected to particularly concern ultramafic catchments because of the related occurrence of Cr-rich soils.

We have tried to address this question by performing laboratory-heating of several soils types (Ferralsols, Cambisols and Vertisols) developed on various geological settings (ultramafic, mafic and volcano-sedimentary) in New Caledonia, a French overseas territory which is a good representative of wildfires-threatened tropical ultramafic catchments (Toussaint, 2020). The results obtained revealed a significant influence of soil heating on Cr(III) oxidation to Cr(VI), followed by an enhanced Cr(VI) mobility, in all soil types. However, the magnitude of Cr(III) to Cr(VI) oxidation and Cr mobility depended on the actual nature of the soil, Ferralsols showing the highest Cr(VI) release compared to Cambisols and Vertisols. These differences were further interpreted on the basis of the changes in Cr speciation (including redox) induced by laboratory-heating of the investigated soils, as revealed by synchrotron-based X-ray absorption spectroscopy analyses. Finally, a simple risk assessment relying on the hypothesized concentration of suspended particulate matter (SPM) issued from burned soils in the related waterways allowed to emphasize a risk of wildfires-induced freshwater Cr(VI) pollution for ultramafic catchments composed of Ferralsols (Thery et al., 2023). Beyond the single case of New Caledonia, the results of this study point to the need to foster collaborative studies in order to further evaluate this risk of wildfires-induced freshwater Cr(VI) pollution at tropical ultramafic catchments on a global scale.

How to cite: Juillot, F., Thery, G., Quantin, C., Bollaert, Q., Meyer, M., Quiniou, T., Jourand, P., Ducousso, M., Fritsch, E., and Morin, G.: Wildfires, chromium and freshwater quality at tropical ultramafic catchments : A prospective study on laboratory-heated soils from New Caledonia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13941, https://doi.org/10.5194/egusphere-egu23-13941, 2023.

Biomass burning releases numerous aerosol particles into the air, influencing the radiative budget by scattering or absorbing solar radiation and by influencing cloud properties through acting as cloud condensation nuclei. These aerosol particles contain black and organic carbon and can be transported over large distances, reaching also pristine environments such as the Arctic. Due to the rising global temperature the fire activity has increased, and record-breaking black carbon concentrations have been observed in the Arctic (Stohl et al., 2007). Biomass burning events reaching the Arctic have been observed to increase the aerosol number concentration by about one to two orders of magnitude (Lathem et al., 2013). Although a lot of attention has been drawn to the physical characteristics of fire plumes, changes in chemical composition, specifically in the Arctic, are studied to a lesser extent. In this study we report molecular-level information on the chemical characteristics of biomass burning aerosol particles measured during different plumes reaching the island of Svalbard during 2020. These measurements were part of the year-long NASCENT (Ny-Ålesund aerosol cloud experiment; Pasquier et al., 2022) campaign, and were conducted using a filter inlet for gases and aerosols coupled to a high-resolution time-of-flight mass spectrometer (FIGAERO-CIMS) using iodide as reagent ion. We use the particle-phase levoglucosan, a well-known tracer for biomass burning released from cellulose combustion, obtained from the FIGAERO-CIMS to identify biomass burning events, and will discuss the chemical characteristics of the properties of the events compared to non-events and implications for aerosol radiative and hygroscopic properties. In addition to a better understanding of the chemical composition of aged fire plumes reaching the Arctic, our study will also give insights on the time scales on which the background Arctic air can be disturbed by fire activity. 

References:
Stohl et al., Atmospheric Chem. Phys., 7, 511–534, 2007
Lathem et al., Atmospheric Chem. Phys., 13, 2735–2756, 2013
Pasquier et al., Bull. Am. Meteorol. Soc., 103, E2533–E2558, 2022

How to cite: Gramlich, Y., Siegel, K., Haslett, S. L., Krejci, R., Zieger, P., and Mohr, C.: Impact of biomass burning on the chemical composition of Arctic aerosols using mass spectrometry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14211, https://doi.org/10.5194/egusphere-egu23-14211, 2023.

We present the first continuous Holocene fire record of Iceland from a lacustrine archive in the northeast region. We use pyrogenic PAHs (polycyclic aromatic hydrocarbons) to trace shifts in fire regimes, paired to a continuous record of n-alkanes, faecal sterols, perylene, biogenic silica, and ¹³C, as proxies for soil erosion, lake productivity, and human presence.

Paleoclimate research across Iceland provides a template for changes in climate across the northern North Atlantic. The role of orbitally driven cooling, volcanism, and human impact as triggers of local environmental changes, such as fire and soil erosion, is debated. While there are indications that human impact could have reduced environmental resilience in a context of deteriorating climatic conditions, it is still difficult to resolve to what extent human and natural factors affected Iceland landscape instability, due also to a lack of data on natural fire regime prior and during human colonisation.

Pyrogenic PAHs can be formed during the incomplete combustion of biomass initiated by humans or natural wildfires. Factors such as fire temperature, biomass typology, and source distance can strongly affect pyrogenic PAH molecular weight and spatial distribution.
Faecal sterols/stanols and their ratios have been used in archaeological and paleoclimate studies to detect human and/or livestock/herbivore waste. The absence of large herbivorous mammals and humans in Iceland prior to settlement means that increases in the occurrence of faecal sterols and bile acids over natural background values should mark the arrival of humans and associated livestock in the catchment, which could be traced regionally.

Our results indicate that the Icelandic fire regime during the Holocene followed four main phases. Among these, a very long period centred around the Holocene climatic optimum (ca 9.5 – 4.5 ka BP) was characterised by a generally low frequency fire regime, both in the lake catchment as in the whole north-eastern Iceland. This same period was also marked by relatively low background levels of faecal sterols/stanols. At 4.5 ka BP a new phase started, with a general increase of all PAHs values. According to both our PAH and sterol data, there is no apparent human signal around the 9th century C.E., where an increase in man-made fires would likely be expected in connection to the historical data of Viking colonisation of Iceland (870s C.E.), suggesting that fire regimes have primarily been controlled by natural factors.
In addition, the pyrogenic PAHs record also differs from the trend of a general stepwise climatic “deterioration” previously highlighted by other lake proxies throughout Iceland, linked to decreasing summer insolation and related cooling, as highlighted also by our other proxies.

A comparison to recent palynological data from a nearby site and to δD data from the NW region suggest shifts in NAO regimes as the main forcing behind shifting fire regimes in Iceland. Changes in precipitation regimes would have determined shifts in the composition of the regional vegetational community, increasing fuel availability and flammability with decreasing precipitation, leading to widespread low temperature fires, easily trigged by frequent volcanic episodes.

How to cite: Ardenghi, N., Miller, G. H., Geirsdóttir, Á., Harning, D. J., Raberg, J. H., Thordarson, T., and Sepúlveda, J.: Regional precipitation variability modulates Holocene fire history of Iceland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15549, https://doi.org/10.5194/egusphere-egu23-15549, 2023.

Peatlands are globally important carbon sinks and stores. Climate change threatens to alter carbon cycling in some regions of the Northern Hemisphere, causing them to become net sources of atmospheric carbon, exerting a positive feedback upon global climate. Furthermore, enhanced drying, increased human activity and vegetation succession in response to a warming climate have increased the frequency of wildfires in some peat-bearing regions, including areas underlain by permafrost. Such events can cause thousands of years’ worth of formerly stable carbon to be rapidly released into the atmosphere, imparting further climate warming.

The future response of peatlands to climate warming and wildfire remains uncertain, and as a result peatlands are rarely included in Earth System Models, despite their importance in the global carbon system. Understanding how changes in climate and anthropogenic activity in the past affected peatland ecosystem functioning will improve our understanding of how these sensitive ecosystems may respond to future projected changes and thus reduce this uncertainty.

Our project aims to assess how warming, drought and wildfire have impacted the resilience of peatlands and permafrost in the Northern Hemisphere over the past c. 2000 years. Several peat cores spanning a latitudinal gradient covering several regions including Russia, Poland, the Baltic states and Scandinavia will be analysed using multiple palaeoecological proxies at high resolution to reconstruct past changes in wildfire frequency, hydrology and vegetation. This will allow us to define baselines and threshold values for ecosystem shifts relevant to future projected changes in climate.

How to cite: Andrews, L., Słowiński, M., Roberts, H., Marcisz, K., Kołaczek, P., Halaś, A., Łuców, D., and Lamentowicz, M.: Identifying tipping points and threshold values for ecosystem functioning in northern peatlands during the climate crisis (PEATFLAMES), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15670, https://doi.org/10.5194/egusphere-egu23-15670, 2023.

The Northwest of the Iberian Peninsula is one of the European regions with the highest frequency of forest fires. However, in the last decade fires in this region have burned larger areas and later in the fire season. Assessing the damage caused by fire and the pollutants released in the burning process is important to understand the effects on ecosystems and the carbon cycle, the recurrence of fires, and the effect on human health. In this work, we performed the estimation of emissions released in Galicia (Northwest Spain) in the last six years combining existing ESA CCI products. To quantify the area burned, we used the products from the Burned Area Algorithm developed within the Fire Climate Change Initiative (FireCCI) project. Then, the characterization and quantification of the total biomass were obtained from the Biomass CCI project at 100 m resolution by extracting the mean biomass by vegetation type from CORINE Land cover 2018. The burning efficiency factor was fitted using burn severity estimates from the dNBR calculation on the Sentinel-2 data. The emissions factors were selected from the literature. Our results show that during the last few years, there is a positive trend of annual emissions in Galicia. The sporadic maximums were registered in the years 2017 and 2022 when the climatic conditions aggravated the fire behaviour. In addition, Galicia is the region of Spain that registers the highest average estimates of emissions from fires since a high percentage of the affected area is occupied by pine and eucalyptus forests. These emissions contribute to a drastic decrease in air quality influencing the climate and affecting public health. Finally, we verified that adapting the burning efficiency factors to the specific conditions of the affected ecosystem generates more precise emission estimates.

How to cite: Oliva, P. and Quishpe, C.: Temporal analysis of wildfire emissions in the Northwest of Spain using ESA CCI data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16152, https://doi.org/10.5194/egusphere-egu23-16152, 2023.

Wildfires play an essential role in the biogeophysical cycles of different world ecosystems, from dry savannas to humid wetlands. During the last decades, fire regimes of several global regions began to present significant alterations due to climate change and human land-use pressure. The South American Gran Chaco ecoregion contains one of the most important reservoirs of native forests and biodiversity in the world, including the largest continuous dry tropical forest and some of the most extensive wetlands. The area presents a marked precipitation gradient from the East (wet) to the West (dry), which is manifested in vegetation (from wetlands to dry forests and shrublands). In this work, we mapped natural vegetation with the European Space Agency (ESA) Climate Change Initiative (CCI) medium-resolution land cover maps (MRLC v2.0.7; annual - 300m) and fires with the ESA CCI Fire product (FireCCI51; monthly - 250m) in the Gran Chaco between 2001 and 2019 to establish the past and current effects and dynamics of fires in the area (which are primarily human ignited). To assess the region’s climatology, we used the ERA5 bias-corrected reanalysis dataset (WFDE5; daily - 0.5º). Our results highlight the distinct dynamics of fires in the wet and dry areas of the Gran Chaco, showing two fire seasons - summer and winter - in the wet areas (where grasses predominate) and one fire season - winter - in the dry areas (where shrubs and trees are more abundant). Examining the correlations between annual rain anomalies and burnt area, we find that precipitation anomalies have different effects in dry and wet areas throughout the region’s precipitation gradient. Correlations change from positive in the drier areas to negative in the wetter areas. These results may reflect that summer and winter fires do not have the same drivers and the key role of the available biomass limiting the fire expansion. Since biomass is more dependent on precipitation in dry areas compared to wetter ones, the correlation of winter fires with precipitation is positive in the drier regions. The negative correlations obtained in the summer season could be explained by the fact that summer fires essentially occurred in the wetter part of the Chaco and are intended (through human ignition) to increase the grasslands’ productivity; this practice could be more frequent during negative precipitation anomalies compared to positive ones. Further analysis will try to confirm these findings with biomass satellite data.   

How to cite: San Martin, R., Ottle, C., and Sörensson, A.: Characterizing the fire regime evolution and land-use change in the Dry and Wet Chaco between 2001 and 2019, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16241, https://doi.org/10.5194/egusphere-egu23-16241, 2023.

Recent years have seen rapid climatic changes in Central Asia, particularly Mongolia. An increase in the thickness of the active layer above permafrost and considerable changes to the vegetation structure are likely outcomes of the long-term temperature rise and precipitation changes. The management of future habitats or the biodiversity of northern Mongolia faces significant difficulties from rising temperatures, prolonged and frequent droughts, and gradual permafrost degradation. Our knowledge of the historical processes involved in permafrost degradation and the ensuing ecological effects is still mostly incomplete. These connections may be used to explain changes in the fire regime, permafrost melting, and plant distribution in the Khentii mountains region. Therefore, based on a multiproxy study of peat archive data, we provide the first high-resolution fire history from northeastern Mongolia over the last 1000 years (micro- and macroscopic charcoals, charcoal size classes and morphotypes, peat geochemistry). We examined microscopic and macroscopic charcoal particles as a proxy for fire activity. We also tracked changes in regional and local plant composition using pollen data. To investigate how changes in fire regimes and the climate affect the functioning of the peatland ecosystem, we also conducted a geochemical analysis.

Additionally, to better comprehend the changes in earlier fire regimes and fire-vegetation connections, we employed the morphotypes of macrocharcoal to pinpoint vegetation burning. This study's primary objective is to evaluate the impact of human behavior, vegetation, and prolonged droughts on the incidence of fire regime transitions during the past 1000 years in Central Asia permafrost marginal zone (Mongolia). The findings showed that most of the fires in the area were probably started by natural causes, presumably connected to heatwaves that resulted in prolonged droughts. We have established a connection between increased fires and the local weather phenomena known as "dzud", a catastrophic confluence of winter snowfall and droughts that impacts fire intensity.

The study is the result of research project No. 2017/01/X/ST10/01216 and 2018/31/B/ST10/02498 funded by the Polish National Science Centre.

How to cite: Słowiński, M., Obremska, M., Avirmed, D., Woszczyk, M., Adiya, S., Łuców, D., Mroczkowska, A., Halaś, A., Szczuciński, W., Kruk, A., Lamentowicz, M., Stańczak, J., and Rudaya, N.: History of fire regime shifts during the last 1000 years in Northeastern Mongolia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16504, https://doi.org/10.5194/egusphere-egu23-16504, 2023.

Polycyclic aromatic hydrocarbons (PAHs) are molecules produced during incomplete combustion of organic matter and have been increasingly utilized as paleo-proxies for wildfires. More recently, their incorporation from drip water into speleothems has been utilized in conjunction with the stable isotopic and trace elemental measurements of host carbonate and fluid inclusions in order to assess a coupled record of fire and hydroclimate. Numerous studies have focused on cave systems in the Southwestern U.S., which has experienced highly variable hydroclimate and massive wildfires with past climate changes. Here, we present a PAH record covering ~19-11.5 ka obtained from a precisely dated and well-studied ML-1 stalagmite obtained from McLean’s Cave in the central Sierran foothills, CA. Total concentrations of four-ring PAHs reach maximum values from ~16.8-15 ka, associated with the first stage (1a) of Heinrich Stadial 1 (HS1) interval – this is interpreted as increased levels of soil PAHs produced from regional wildfires. Covariance of isomeric diagnostic ratios with total concentration indicates a shift in the nature of the associated fires, separating effects of PAH mobility in altered soils as well as shifts in soil water transport, stalagmite growth rates, and precipitation amounts. Paired climate signals from independent regional proxies are discussed, as well as factors affecting the interpretation of PAH signals in speleothems. Considerations and methods using small (~1g) speleothem samples are presented, with a focus on simultaneous extraction of useful paleoenvironmental information from other molecular biomarkers entombed within speleothems.

How to cite: Smolen, J., Montañez, I., and Hren, M.: Fire, Work with Me: A PAH record from a Southwestern US speleothem, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16912, https://doi.org/10.5194/egusphere-egu23-16912, 2023.

Fire is a major disturbance in the boreal forests of the high northern latitude. Fire extent and severity have been increasing in recent decades, and the occurrence of overwintering ‘zombie’ fires has been linked to recent fire extremes. Overwintering fires are fires which were seemingly extinguished at the end of the boreal fire season yet smolder during winter to re-emerge as a flaming fire in the subsequent spring. So far, overwintering fires have only been investigated using satellite imagery. Here, for the first time, we show preliminary results from a field campaign that measured in situ impacts of fires that overwintered from 2014 to 2015 in the Canadian Northwest Territories. We measured among other the burn depth in organic soils, and characterized micro-topography. We also qualitatively assessed how fires may have overwintered. We compared nine overwintering fire sites, which burned during both 2014 and 2015, with six sites that only burned in 2014 and five nearby unburned sites. The average burn depth (±SD) of the overwintering fires was 6.8 ± 1.6 cm and significantly deeper compared to 6.1 ± 1.2 cm in the single fire sites (P < 0.01). Somewhat surprisingly, the majority of overwintering fires occurred in mesic sites with large productive trees. Only two overwintering sites were sampled in mesic-subhygric to subhygric sites dominated by black spruce (Picea mariana). The unburned control sites often featured a micro-topography of hummocks and hollows. This micro-topography was leveled in overwintering fires sites because of severe burning in organic soils. In overwintering sites, most of the organic layer was consumed. This may have led to prolonged smoldering in the root systems of trees. Our results are the first to quantify the burn depth of overwintering fires, and also show that overwintering does not only happen through deep smoldering in organic soils, yet can also occur from smoldering in tree boles and root systems of burned and fallen trees.

How to cite: Hessilt, T. D., Veraverbeke, S., Ogden, E., Paul, J., Turetsky, M., van Gerrevink, M., Alfaro-Sanchez, R., Melnik, O., Scholten, R. C., and Baltzer, J.: First results of a field campaign focused on overwintering zombie fires, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17450, https://doi.org/10.5194/egusphere-egu23-17450, 2023.

Cropland suitability, a process of evaluating the capability of a piece of land in relation to the growing conditions of a given crop, is highly essential for agricultural planning. Projected changes in the future climate are expected to significantly affect the agricultural sector, notably agricultural production which include cropland suitability. Although, previous studies have shown Solar Radiation Modification (SRM), which involves the injection of sulfur into the stratosphere to reduce insolation of the sun and cool the planet, could mitigate the impact of climate change (hereafter GHG) on agricultural production, however there is still a lack of understanding on how Stratospheric Aerosol Injection (SAI) intervention (an SRM technique) will affect cropland suitability in West Africa. The present study examines the impact of GHG and SAI on Legumes (Cowpea, Soyabean and Groundnut) and Root and Tuber (Cassava, Potato and Yam) suitability and planting season over West Africa. The Stratospheric Aerosol Geoengineering Large Ensembles (GLENS) simulation for the historical, GHG and SAI experiments for the period 1980-2009 and 2060-2089. Ecocrop, a crop suitability model was used to investigate the impact of GHG and SAI on the over West Africa owing to their economic importance to the region. Our findings shows while SAI offset the impact of GHG on temperature it leads to a reduction in rainfall over West Africa. Crop suitability decreases northwards over the region. SAI intervention will lead to an increase (over 12%) in highly suitable area for Cassava and Potato compared to GHG but leads to 3% decrease compared to historical period. In contrast, SAI results in decrease (6%) in suitable area for Legumes when compared to GHG impact over West Africa. In addition, SAI intervention will lead to a 1-2month early planting season for all legumes crops and Yam over West Africa but delay of about 2months for Cassava and Potato. The study will assist to improve our understanding on SAI intervention at mitigating GHG impact on Legumes and Root & Tuber crop production over West Africa. It will also help inform policy maker in their decision making of adaptation strategies to ensure food security and zero hunger and healthy nutrition in West Africa.

How to cite: Egbebiyi, T. S., Lennard, C., Pinto, I., Odoulami, R., Wiolski, P., Tilmes, S., and EGBEBIYI, T. S.: How will Solar Radiation Modification affect Cropland Suitability in West Africa?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-703, https://doi.org/10.5194/egusphere-egu23-703, 2023.

Atmospheric aerosols can scatter and absorb the incident solar radiation, and thus impact the land carbon cycle by perturbating the radiation required for photosynthesis. Atmospheric aerosols inhibit the carbon uptake by terrestrial ecosystems through reducing the total amount of incident radiation, while the increased proportion of diffuse irradiance is known to promote photosynthesis. In the past few decades, with the rapid industrialization and urbanization, China has suffered from frequent haze pollution episodes, which have brought up severe environmental problems and ecological impacts. Here, we use a regional climate model, WRF-Chem, along with the offline driven Simplified Simple Biosphere Model (SSiB4) to investigate the impact of aerosol radiation effects on land biosphere carbon uptake capacity. The results show that the current aerosol loading has led to significant decrease in the incident solar radiation in China, which severely suppresses the gross primary production (GPP) and net primary production (NPP). Then, we assessed the influences of stringent emission and pollution control policies on terrestrial ecosystem carbon fluxes. By comparing the simulation results based on China’s ambitious carbon neutrality policies with the reference scenario with negligible emission control, we found that the carbon neutrality scenario with rigorous pollution control increases the incident solar radiation and thereby enhancing the carbon uptake of land biosphere. Under the current state of aerosol loading, the decrease of total amount of incident radiation dominates the suppression of terrestrial carbon uptake, while aerosol diffuse fertilization effect can only partly offset the inhibition of decreased solar radiation on plant photosynthesis. Our findings improve the understanding of the interactions between aerosol pollution and the land carbon cycle, and suggest an appreciable ecological benefit and a potential terrestrial carbon sink enhancement of stringent emission and pollution control actions.

How to cite: Li, L., Qiu, B., Huang, X., Guo, W., Miao, X., Chen, J., Ni, Y., and Tian, X.: Aerosol-induced radiation effect and the potential influence of stringent emission control on terrestrial carbon uptake in China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3775, https://doi.org/10.5194/egusphere-egu23-3775, 2023.

A major limitation in modeling global O₃ vegetation damage has long been the reliance on empirical O₃ sensitivity parameters derived from a limited number of species and applied at the level of plant functional types (PFTs), which ignore the large interspecific variations within the same PFT. Here, we present a major advance in large-scale assessments of O₃ plant injury by linking the trait leaf mass per area (LMA) and plant O₃ sensitivity in a broad and global perspective. Application of the new approach and a global LMA map in a dynamic global vegetation model reasonably represents the observed interspecific responses to O₃ with a unified sensitivity parameter for all plant species. Simulations suggest a contemporary global mean reduction of 4.8% in gross primary productivity by O₃, with a range of 1.1%-12.6% for varied PFTs. Hotspots with damages > 10% are found in agricultural areas in the eastern U.S., western Europe, eastern China, and India, accompanied by moderate to high levels of surface O₃. Furthermore, we reveal an inherent plant sensitivity spectrum for O₃ which is highly linked with plant leaf trait trade-off strategy, revealing high risks for fast-growing species with low LMA, such as crops, grasses and deciduous trees.

How to cite: Ma, Y., Yue, X., Sitch, S., Unger, N., Uddling, J., Mercado, L., Gong, C., and Feng, Z.: Trait-based ozone plant sensitivity to assess global vegetation damage risks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3823, https://doi.org/10.5194/egusphere-egu23-3823, 2023.

Ozone (O₃) is a toxic oxidative air pollutant with significant detrimental effects on natural vegetation and crop species. Free-air controlled exposure (FACE) facilities provide an ideal tool for O₃ effect studies, producing realistic results. The O₃ Free-Air Controlled Exposure (FO₃X - FACE) facility, located in Sesto Fiorentino, Italy, and established in 2015, is an AnaEE (Analysis and Experimentation on Ecosystems) European research platform. The facility permits the exposure of plants to three levels of O₃ concentrations (1.0, 1.5, and 2.0 times the ambient concentration, denoted as AA, x1.5AA, x2.0AA, respectively), with main environmental variables continuously monitored. Over the years, the accumulated exposure over 40 ppb hourly concentrations (AOT40) was calculated and used as an exposure-based O₃ index. The stomatal conductance (g_sto) model, based on the multiplicative algorithm, was used to parameterize the g_sto of 12 species (7 deciduous: Oxford poplar, Quercus robur, Quercus pubescens, Sorbus aucuparia, Alnus glutinosa, Vaccinium myrtillus, I-214 poplar, and 5 evergreens: Quercus ilex, Phillyrea angustifolia, Arbutus unedo, Pinus halepensis, Pinus pinea), in order to calculate the hourly stomatal O₃ flux (F_st), and thus the phytotoxic O₃ dose above an hourly threshold y of uptake (y = 1, POD₁) used as a flux-based O₃ index. Our studies have evaluated the effect of O₃ in gas exchange parameters as light-saturated photosynthesis (A_sat / R² POD₁ = 0.46 vs. AOT40 = 0.20) and stomatal conductance (g_sto /R² POD₁ = 0.18 vs. AOT40 = 0.18), as well as for the induction of specific visible foliar injury (VFI / R² POD₁ =0.40 vs. AOT40 = 0.32) and biomass loss (B_loss / R² POD₁ = 0.50 vs. AOT40 = 0.22). We demonstrate that species-specific flux-based O₃ index POD₁ is more relevant compared to the exposure-based O₃ index AOT40, showing the importance of comprehending the mechanism of O₃ damage to plants after the uptake through stomata. Our research has also been improving the derivation of experimentally based critical levels (CLs) for the protection of forests and crops vegetation from O₃ damage.

How to cite: Baesso Moura, B., Manzini, J., Hoshika, Y., and Paoletti, E.: Ozone damage in plants: 7 years of study in a free-air experimental facility (FO3X), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5157, https://doi.org/10.5194/egusphere-egu23-5157, 2023.

How to cite: Lin, Z.: Water-food-energy nexus: Progress, challenges and prospect, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5313, https://doi.org/10.5194/egusphere-egu23-5313, 2023.

Air pollution is one of the most important environmental problems in China. As a major air pollutant, ozone (O₃) will endanger human health and terrestrial ecosystems. It is of great practical significance to obtain a continuous full-coverage dataset of ozone with high spatio-temporal resolution to conduct mechanism research from its causes, development, diffusion, impact and other aspects. In this study, a 3-stage machine learning model was developed through multiple data fusion, and the LightGBM method is used to obtain the hourly spatio-temporal distribution dataset of the O₃ concentration in China from 2013 to 2020, with a resolution of 0.25 °× 0.25°. We first revise the meteorological reanalysis data using ground observation and propose a data fusion algorithm to achieve the ground level distribution of ozone, which combines ground observation of pollutants, population data, revised reanalysis meteorological conditions, reanalysis of radiation, land and vegetation data, emission inventory and results of chemical transport model simulation.  In addition, due to the common phenomenon that the previous prediction models underestimate the extreme value of the pollution periods,therefore, we redefined the heavy pollution event and assimilated it into the 0.25 grid by using the synthetic minimum oversampling technique (SMOTE) method to improve the model performance during the extreme pollution periods.

Our model, with the 10-fold CV result of R² = 71% and RMSE= 25.1μg·m^-3, and our hourly O₃ concentration results are spatially and spatially continuous with a similar distribution compare to the observation, which proves the reliability of our model. With higher time resolution, various exposure response indicators can be obtained. AOT40 calculated by high-resolution hourly ozone concentration further, which is far more accurate than it when directly predicted by daily indexs modeling.

In addition, based on the distribution of AOT40, we assessed the agricultural damage and ecological damage caused by the change of surface ozone pollution during 2013-2020. Our estimation considered the planting area and phenological period of crops that the overestimation of crop RYL in the region can be avoided. The annual avrage production loss of wheat, rice and maize in China from 2013 to 2020 is 55.0, 57.4 and 23.6 Mt, respectively. Besides, The loss of gross primary productivity was also estimated. During 2013-2020, the ozone pollution in China caused an annual average loss of 2.1%, and the loss in the south was much higher than that in the north.

How to cite: Liu, L., Geng, G., Zhong, J., Liu, Y., Xiao, Q., Zhang, X., and Zhang, Q.: Near Real-Time Distribution of Ozone in China from 2013 to 2020 and Agricultural Impacts, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6562, https://doi.org/10.5194/egusphere-egu23-6562, 2023.

Atmospheric aerosols can strongly affect vegetation through their cooling effect and changing diffuse radiation. The changes of vegetation further alter the climate through biophysical and biochemical feedbacks. Previous studies either investigate aerosol impacts in offline simulations to understand the vegetation response, or in fully coupled simulations to quantify the full impacts on the climate, including through atmospheric physics. So far there has been no experiment designed to separate the aerosol-induced vegetation-climate feedback from the aerosol impact itself. Existing studies on vegetation-climate feedbacks (not necessarily due to aerosol) often prescribe vegetation properties, so that the climate altered by vegetation can no longer affect the vegetation, leading to an incomplete feedback estimation. To quantify the full vegetation-climate feedback due to aerosols, we propose a new modeling framework in coupled Earth system models (ESM). In this new framework, the atmosphere module simulates the climate under both preindustrial and historical aerosol scenarios at each time step. The climates simulated under the two scenarios are both passed to the land surface module. All processes in the land surface module are separated into an organic (vegetation, part of soil) and an inorganic (energy budget, hydrology) part. The organic part is driven by the preindustrial aerosol climate, while the inorganic part is driven by the historical aerosol climate and affected by the organic part. The land surface processes provide the feedback variables for atmosphere to simulate the next time step. The feedback can be evaluated by comparing this experiment to fully coupled simulations under preindustrial and historical aerosol scenarios. Here we first introduce this framework and apply it to IPSL-CM6A-LR ESM. This new framework can have more general usages and provide opportunities to understand the land surface feedbacks in the Earth system.

How to cite: Zhang, Y., Ciais, P., Li, L., and Boucher, O.: A new modeling method to quantify aerosol-induced vegetation-climate biophysical feedbacks, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7323, https://doi.org/10.5194/egusphere-egu23-7323, 2023.

Tropospheric Ozone (O₃) is a secondary pollutant with a positive radiative forcing and many negative effects on air quality, human health and ecosystems at different scales. In fact, O₃ acts as a strong oxidant in plants, negatively impacting many cellular and molecular processes, such as modifying rubisco activity, reducing stomatal conductance and inducing early leaf senescence. Furthermore, when the O₃ levels at the surface are high (typically above 40 ppb), these combined effects may decrease the photosynthetic carbon gains, mainly detectable at the leaf level but also important at the tree and stand scales. In this study, we intend to evaluate the effects of O₃ on Gross Primary Production (GPP) at four European forest sites (Belgium, France and Italy) using local measurements, both for O₃, eddy-covariance (GPP) and meteorological variables (including air temperature (TA), relative humidity (RH), vapour pressure deficit (VPD), short-wave radiation (SW), wind and precipitation). We first applied a series of statistical analyses to identify the impact of O₃ and meteorological variables on GPP for each site. In a second step, we used a process-based model that simulates GPP using the Farquhar equations parameterised for each site to quantify O₃-induced GPP reductions. Our results showed that the dominant meteo factor is site dependent. The SW appears to be the most important variable for predicting GPP at all sites, contrary to TA and VPD. The Belgium and Italian sites show a correlation of 0.51(0.55) for TA and 0.38(0.48) for VPD, respectively. Whereas in the French site, the TA correlation of 0.55 exceeds the VPD correlation of 0.38. Consequently, the GPP reduction varies along the different sites. This study shows the necessity of long-term monitoring datasets to understand better the O₃ impacts at several ecosystems combined with process-based models.

How to cite: Vieira, I., Meunier, F., Sitch, S., Brown, F., Gerosa, G., Janssens, I., Boeckx, P., Bauters, M., and Verbeeck, H.: Multi-site analysis of the impact of surface ozone on European forests, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9331, https://doi.org/10.5194/egusphere-egu23-9331, 2023.

The impact of elevated ozone concentration on crop yield, like wheat, plays a significant role yet is poorly studied in Asian countries like China and India. We have developed, calibrated, and tested a mechanistic photosynthetic-stomatal conductance canopy model (DO3SE-crop) with an integrated ozone module (Anet-gsto+O3) for the region of Xiaoji, China. The key component of the model development involves phenology, leaf scale processes, leaf-to-canopy upscaling, and carbon allocation. The calibrated model for Xiaoji simulated the difference in yield losses for ambient and elevated ozone treatments for the years 2008 for four cultivars (Y2, Y15, Y16, Y19), ranging from 21-24%, compared with the observed dataset, giving R2 of 0.74 and RMSE of 0.003. The model was tested for 2009 and gave yield losses of 24-27%, with R2 of 0.60 and RMSE of 0.12, against the observed dataset. Further, our findings suggest that the difference in yield loss is due to the early decline in carbon assimilation in elevated treatment.This happens because of the early senescence in elevated treatment, which brings leaf senescence forward by 9-11 days.

How to cite: Pande, P., Bland, S., Booth, N., Cook, J., and Emberson, L.: The development and application of a mechanistic photosynthetic-stomatal conductance canopy model (DO3SE-crop), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10119, https://doi.org/10.5194/egusphere-egu23-10119, 2023.

The productivity of terrestrial ecosystems is determined, among other things, by solar radiation and its degree of scattering can increase or reduce it. The intensity of scattering is determined by the optical properties of the atmosphere due to the presence of particles suspended in the atmosphere, i.e. clouds and aerosols. Additionally, the amount of these substances and also the physical properties affect the radiation transfer and thus the plants ability of CO2 absorption. In the presented research, an attempt to quantify the impact of the different types of aerosols presence in the atmosphere on the amount of gross ecosystem production (GEP) in a transitional peatland in northwestern Poland was made. Three classes of cloudiness were assumed in the simulations: cloudless, medium and full cloud conditions, and an atmosphere-ecosystem model was used to assess the peatland productivity under these conditions. It was found that changes in the physical parameters of aerosols in the atmosphere can both increase and decrease the amount of CO2 uptake by peatlands by up to 8.2% and 6%, respectively. Thus, the research is extremely relevant to the global carbon balance, as peatlands are one of the largest reservoirs of organic carbon in the biosphere.

How to cite: Harenda, K., Markowicz, K., Poczta, P., Stachlewska, I., Bojanowski, J., Czernecki, B., Mac Arthur, A., Schüttemeyer, D., and Chojnicki, B.: Can the atmospheric aerosol impact on the functioning of a peatland?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12046, https://doi.org/10.5194/egusphere-egu23-12046, 2023.

Solar climate intervention using Stratospheric Aerosol Injection (SAI) is a proposed method of reducing global-mean temperatures to temporarily offset some of the effects of global warming while we cut greenhouse gas emissions and remove CO₂ from the atmosphere. While the scientific, moral, and ethical questions surrounding solar geoengineering are undoubtedly complex, rigorous and unbiased information on its advantages and pitfalls will help us make better decisions in the future. Recent research has shown that some of the negative physical side-effects of SAI can be moderated by designing a better intervention strategy. I will present a comparison between a previously published ensemble of climate model simulations using the Community Earth System Model 2 (CESM2) and a new ensemble using the United Kingdom Earth System Model 1 (UKESM1). This set of simulations is based on a moderate greenhouse gas emission scenario and start injection of stratospheric aerosols in year 2035 to keep the global-mean surface temperature at 1.5 degrees above preindustrial. The injection occurs at four different latitudes and a controller algorithm is used to maintain the latitudinal gradient and inter-hemispheric difference in surface temperature, thus moderating the side effects of previous injection methods. We compare the behavior of the algorithm between the two models, as well as the climate response, with a particular focus on tropical precipitation.

How to cite: Henry, M., Haywood, J., and Jones, A.: Towards a better understanding of the physical risks and tradeoffs of solar geoengineering., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12811, https://doi.org/10.5194/egusphere-egu23-12811, 2023.

Sugarcane a vitally important crop across many tropical and subtropical regions. São Paulo (SP) state, Brazil the largest single regional producer of both raw sugar and the production of bioethanol has experienced large-scale conversion of pasture to sugarcane production in recent decades. This predominantly rain-fed agricultural area is exposed to seasonal drought and periodic high tropospheric ozone (O₃) pollution at levels known elsewhere to be detrimental to plant productivity. Given the large current extent, and planned expansion of sugarcane production to meet global demand for ‘green’ biofuels there is a pressing need to characterize the risk of current tropospheric O₃ to the sugarcane industry. This is a key step towards limiting the O₃ yield gap under future climate and land use change scenarios. In this study, we therefore sought to a) derive realistic sugarcane O₃ dose response functions across a full range of O₃ exposure and b) model the implications of this observed O₃ response across the globally important production area of SE Brazil.

We found a significant and substantial impact of O₃ on a range of sugarcane cultivars, including a number of commercially relevant varieties. When combined with biologically relevant predictions of O₃ exposure across Brazil this allows us to predict the current regional impact of O₃ on sugarcane production. We find that up to 25 million tonnes of total crop productivity a year may be lost across São Paulo alone due to the direct impacts of O₃ exposure – but that substantial differences in O₃ sensitivity of different cultivars highlights the need for future work to elucidate the true impacts of O₃ in this important tropical cropping system.

How to cite: Cheesman, A., Brown, F., Ribero, R., Folberth, G., Hayes, F., Moura, B., Paoletti, E., Hoshika, Y., Cernusak, L., Osborne, C., and Sitch, S.: Characterizing the O3 yield gap in the sugarcane production of SE Brazil, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14543, https://doi.org/10.5194/egusphere-egu23-14543, 2023.

Fire emissions include the ozone precursor NOx, which is often the limiting precursor in remote locations such as the tropical forests. In fact, interannual variability in tropical fire activity, which depends on meteorology and human activity, is highly correlated with variability in surface ozone concentration over the tropics. Additionally, drought years in Asia and South America show consistently higher fire activity and surface ozone concentrations compared to years without droughts. Since surface ozone is known to decrease plant productivity, higher ozone concentrations during drought events may reduce strength of the land carbon sink. On the other hand, drought events may protect plants from ozone damage by causing a decrease in stomatal conductance. Thus, the net impact will be the balance of these opposing effects, and will likely vary by region. As climate change may increase the frequency of drought events in the tropics, an understanding of present-day relationships between drought events, fire activity and surface ozone concentrations will help inform of current and future risks of plant-ozone damage in the tropics.

Using climate model predictions of surface ozone concentration from 1996 – 2015, we show that annual mean ozone concentrations over the Amazon are up to 10 ppb higher during drought years compared to years without drought due to variability in fire activity. We then use a land surface model to show that net primary productivity loss due to plant-ozone damage in the Amazon is largest during drought years at the basin scale. The majority of the productivity loss occurs around the arc of deforestation in the Southern Hemisphere, whereas a reduction in stomatal conductance protects the Northern Hemisphere Amazon from ozone damage during drought years. Given that the interannual variability in carbon lost from plant-ozone damage is predicted to be of similar magnitude to that from direct fire emission (~ 200 Tg C), we highlight a need to consider plant sensitivity to ozone, especially for agriculture and secondary forests in the arc of deforestation. 

How to cite: Brown, F., Sitch, S., Folberth, G., and Cheesman, A. W.: Interannual variability in ozone damage to tropical forests, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15314, https://doi.org/10.5194/egusphere-egu23-15314, 2023.

Tropospheric ozone (O₃) reduces plant productivity by entering leaves, generating reactive oxygen species and causing oxidative stress which in turn increases respiration, decreases photosynthesis, plant growth, biomass accumulation, and consequently reduces the land carbon sink. Tropical forests are potentially most vulnerable to future O₃ scenarios given their high productivity, generally high stomatal conductance and environmental conditions conducive to O₃ uptake (eg precursor emissions during biomass burning).

Here we present the first comprehensive set of measurements of O₃ effects on plant physiology and biomass accumulation in tropical forests. We exposed twelve tropical tree species to elevated O₃ concentrations in Open Top Chambers (OTCs) based at the James Cook University O₃ experimental facility in Cairns, Australia, from which we generate O₃ dose-response functions for each species. We test the importance of Leaf Mass per unit Area (LMA) as an indicator of O₃ sensitivity.

We use these relationships to parameterize the global land-surface model JULES, and apply the model over the pan-tropical region using contemporary near-surface O₃ concentration fields. For the first time we quantify the impact of O₃ on contemporary tropical productivity.

How to cite: Sitch, S., Cheesman, A. W., Brown, F., Artaxo, P., Cernusak, L. A., Folberth, G., Hayes, F., Hill, T., Mercado, L., and Uddling, J.: Ozone impacts on tropical forest productivity, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15707, https://doi.org/10.5194/egusphere-egu23-15707, 2023.

For over 30 years scientists and engineers have theoretically pondered whether it was possible to mitigate global warming by atomising seawater over the ocean in a bid to favourably manipulate aerosol-cloud-radiation processes. Given the current plight of the coral ecosystem of the Great Barrier Reef, marine cloud brightening is under considereation as a regional strategy to reduce environmental stress on coral reefs during marine heatwaves. Atmospheric, biogeochemical and ecological modelling suggest that the potential exists to reduce light and thermal stress during marine heatwaves causing coral bleaching. Results from recent field campaigns, the first to empirically test the concept of marine cloud brightening, support the foundational assumptions. From its inception the research program has involved consultation and participation of indigenous traditional custodians of the reef and has proceeded within the regulatory oversight of one of the world’s most actively managed marine estates. This talk will give an overview of the Australian research program including the scientific basis which underpins it and a summary of the most recent results and future directions.

How to cite: Harrison, D.: Marine cloud brightening, could it mitigate coral bleaching on the Great Barrier Reef?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17057, https://doi.org/10.5194/egusphere-egu23-17057, 2023.

Both the quantity and quality of radiation could be altered by aerosols and cloud, and thus changing ecosystem carbon and water fluxes, as well as their coupling relationship. Although the importance of radiation quantity to ecosystems has been well studied, how radiation quality (characterized by diffuse radiation fraction, the proportion of diffuse to total radiation, K_d) affects ecosystem carbon and water cycles remains unclear due to the lack of diffuse radiation observations. In this work, taking advantage of a newly derived K_d dataset, we comprehensively explored the impact of K_d on ecosystem carbon uptake (net ecosystem exchange, NEE), carbon flux (gross primary production, GPP), water flux (evapotranspiration, ET), and water-use efficiency (GPP/ET, WUE) based on measurements at 201 global FLUXNET sites. We found that diffuse radiation is more efficient to improve NEE, GPP and ET than direct radiation at the same radiation level for all vegetation types, leading to increased ecosystem carbon uptake and water loss with K_d at the low and middle K_d levels. Furthermore, the enhancement of GPP is stronger than ET, leading to improved ecosystem WUE by diffuse radiation. By separating radiation into diffuse and direct components, we found that diffuse radiation is the most important factor for GPP, while ET is more dominated by direct radiation, indicating the complex process underlying the response of WUE to changes in K_d. This research helps improve our understandings of the responses of ecosystem carbon and water cycle to aerosol/cloud changes.

How to cite: Wang, B. and Yue, X.: Relationships between radiation quality and ecosystem carbon and water fluxes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17190, https://doi.org/10.5194/egusphere-egu23-17190, 2023.

Ozone pollution and climate change are extremely likely to threaten future crop production in important agricultural regions around the World with the Mediterranean, South and East Asia and mid-West US being particularly at risk with implications for food security. Modelling methods used to assess risk of ozone pollution have developed in recent years away from empirical approaches based on dose-response relationships towards more process-based models. The DO3SE-Crop model has developed from an ozone deposition and effects model (having used flux-response relationships to assess damage) to a crop model capable of assessing the effect of ozone on photosynthesis and carbon allocation. Working within the AgMIP-ozone activity, DO3SE-Crop has been calibrated and evaluated against experimental ozone fumigation datasets for wheat cultivars from Spain (Mediterranean Europe), China and India and is able to assess the influence of climate variables on crop growth and yield as well as the effect of ozone on instantaneous photosynthesis and senescence. We find that the ozone effect on senescence is the primary determinant for yield loss in wheat. We are further developing the model to assess ozone effects on nutritional quality since we know that ozone is an important limiter of translocation of nitrogen to the grains. The establishment of DO3SE-Crop will allow assessments of the future impacts resulting form the combined effects of ozone and climate change on supply and nutritional aspects of food security. Importantly, this can include an assessment of the yield improvements between current and near- to mid-term future conditions for a range of adaptation options proposed for wheat in response to climate change including management of irrigation, growing season and development of new varieties from crop breeding with targeted physiological traits such as enhanced gas exchange and improved water use efficiency.

How to cite: Emberson, L., Bland, S., Pande, P., Cook, J., Booth, N., and Pandey, D.: Understanding the combined effects of ozone pollution and climate change on crop yield and nutritional quality, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17374, https://doi.org/10.5194/egusphere-egu23-17374, 2023.

Moisture is a key factor governing soil nitrogen (N) biogeochemistry; it controls microbial activity and, therefore, the cycling of N. Ongoing climate change is altering precipitation regimes, increasing the frequency and intensity of droughts with implications for ecosystem N retention and loss. In particular, wetting dry soils can produce large emission pulses of nitrous oxide (N₂O), a potent greenhouse gas, but the mechanisms governing the N losses remain elusive. Especially because denitrification, arguably the most important process producing N₂O, is thermodynamically unfavorable in dry soils. Disentangling how drought can alter the balance between ecosystem N retention and loss is further challenged by the multiple biotic and abiotic processes that interact to control N availability and emissions, requiring multiple analytical approaches.

To advance understanding of N cycling in dry soils, we studied drylands in southern California that can experience >6 months without rain and whose contrasting soils developing under shrub canopies (soils known as “islands of fertility”), or in the bare interspaces between shrubs, allow us to interrogate biotic–abiotic interactions. Using isotopologues of N₂O coupled with chloroform fumigations to slow microbial activity, we found that N retention and loss trade off as dry conditions intensify. In particular, N₂O emissions were undetectable from soils in the interspaces between plants, but exceeded 1000 ng N-N₂O m^-1 s^-1 in islands of fertility, rivaling emissions observed in global hotspots like tropical forests and temperate agroecosystems. Despite the hot and dry conditions, isotope tracers and natural abundance isotopologues of N₂O indicated NO₃^- was reduced to N₂O within 15 minutes of wetting dry desert soils, and that both denitrification and N₂O reduction to N₂ contributed to the observed patterns, with δ¹⁵N^SP-N₂O values averaging 12.8 ± 3.9 ‰. Consistent with isotope values, fumigating soils in the lab with chloroform decreased NO₃^--derived N₂O emissions by 59%, suggesting denitrifiers were able to reduce NO₃^- immediately after wetting these summer-dry desert soils. In contrast to NO₃^-, the ¹⁵N-NH₄⁺ tracer was not found in N₂O, suggesting nitrification is not an important pathway governing N₂O emissions in these systems. Despite the hot and dry conditions known to make denitrification thermodynamically unfavorable in many drylands, denitrifiers can endure through hot and dry summers and are key to producing the surprisingly large N₂O emissions when dry desert soils wet up.

How to cite: Homyak, P.: Denitrification in dry soils: Unexpected N emissions under environmental extremes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2124, https://doi.org/10.5194/egusphere-egu23-2124, 2023.

During the last decades, large areas of grassland were converted to cropland across Europe, mainly due to the increasing demand of cropland following the expansion of biogas plant production (e.g. maize). However, the conversion to cropland bears a risk of nitrous oxide (N₂O) emission due to enhanced nitrogen (N) mineralization. Until now, knowledge about N₂O production pathways due to grassland conversion and in particular N₂O reduction to N₂ is very limited (Buchen et al., 2018), even though understanding of N₂O processes and identification of sources are needed in order to devise mitigation options.

N₂O samples were collected periodically from manual chambers following chemical and mechanical conversion from permanent grassland to cropland (maize) at two sites with different texture (clayey loam and sandy loam) and fertilization regime (with and without mineral N-fertilization) in north-western Germany (Helfrich et al., 2020). Samples were analysed for natural abundance stable isotope signatures of soil-emitted N₂O (δ¹⁵N^bulk_N2O, δ¹⁸O_N2O and δ¹⁵N^SP_N2O = intramolecular distribution of ¹⁵N in the N₂O molecule) by isotope ratio mass spectrometry (IRMS) and dual-isotope of N₂O isotopic signatures (plotting δ¹⁵N^SP_N2O vs. δ¹⁸O_N2O) were used for data evaluation (Lewicka-Szczebak et al., 2017). Although, isotopic signatures were very variable throughout the year at both sites, the clayey loam site exhibited a close correlation between δ¹⁵N^sp_N2O and δ¹⁸O_N2O suggesting that values were mainly controlled by N₂O reduction to N₂. At the sandy loam site this pattern was less pronounced, possibly because processes other than bacterial denitrification (e.g. fungal denitrification and nitrification) also significantly influence isotopocule values. Altogether, bacterial denitrification was found to be the most important process following grassland conversion to maize cropping.

References:

Buchen, C., Lewicka‐Szczebak, D., Flessa, H., Well, R., 2018. Estimating N₂O processes during grassland renewal and grassland conversion to maize cropping using N₂O isotopocules. Rapid Communications in Mass Spectrometry 32, 1053-1067.

Helfrich, M., Nicolay, G., Well, R., Buchen-Tschiskale, C., Dechow, R., Fuß, R., Gensior, A., Paulsen, H., Berendonk, C., Flessa, H., 2020. Effect of chemical and mechanical grassland conversion to cropland on soil mineral N dynamics and N₂O emission. Agriculture, Ecosystems & Environment 298, 106975.

Lewicka-Szczebak, D., Augustin, J., Giesemann, A., Well, R., 2017. Quantifying N₂O reduction to N₂ based on N₂O isotopocules – validation with independent methods (helium incubation and ¹⁵N gas flux method). Biogeosciences 14, 711-732.

How to cite: Buchen-Tschiskale, C., Lewicka-Szczebak, D., Nicolay, G., Helfrich, M., Flessa, H., and Well, R.: Which N2O production processes are relevant when converting from grassland to cropland?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2623, https://doi.org/10.5194/egusphere-egu23-2623, 2023.

Soil denitrification is known to be affected by incorporation of crop residues due to supply of reductants and oxygen (O₂) consumption by decomposition. The formation of anoxic microsites where denitrification can occur thus depends on quality, particle size and spatial distribution of incorporated residues in interaction with physical and chemical soil properties. Current biogeochemical models typically assume homogeneity of soil layers and thus don’t consider the size and distribution of crop residue particles. Until now, dinitrogen (N₂) and nitrous oxide (N₂O) fluxes related to residue incorporation patterns have been rarely studied and are poorly represented by current models. Here we present synergetic concepts and results of two projects addressing the spatial modelling of anoxic hot-spots („Modeling the impact of liquid organic fertilization and associated application techniques on N₂O and N₂ emissions from agricultural soils”, MOFANE) and measures to mitigate denitrification in soil („Measures to reduce direct and indirect climate-impacting emissions caused by denitrification in agriculturally used soils”, MinDen).

To test the incorporation of harvest residues and catch crops on denitrification, a full-factorial laboratory incubation will be carried out in MinDen, assessing incorporation methods and pre-crushing of catch crops, and how these interact with soil type and water content.

Based on a static model to take into account spatial hot-spots induced by liquid manure (Baral et al., 2016)  a dynamic model was developed in MOFANE and tested using lab experiments (Grosz et al., 2022). This model can also be applied to evaluate the aforementioned crop residue effects.

We present a conceptual model of denitrification in dependence of size and distribution of crop residues, soil type, soil moisture and soil structure. It predicts that pre-shredding and homogenous incorporation favours denitrification at low gas diffusivity given by high moisture and/or high clay content or bulk density, since small organic hot-spots suffice to create anoxia. For high gas diffusivity (e.g. due to sandy texture and/or dry conditions) it predicts that denitrification is favoured if incorporated crop residues are large, since anoxic microsites can only develop if the size of organic hot-spots is large enough so that the O₂ sink strength exceeds O₂ diffusion from the atmosphere.

Scenarios of the conceptual model will be tested using the dynamic hot-spot model and results will be presented.

Baral, K.R., Arthur, E., Olesen, J.E., Petersen, S.O., 2016. Predicting nitrous oxide emissions from manure properties and soil moisture: An incubation experiment. Soil Biology & Biochemistry 97, 112-120.

Grosz, B., Kemmann, B., Burkart, S., Petersen, S.O., Well, R., 2022. Understanding the Impact of Liquid Organic Fertilisation and Associated Application Techniques on N2, N2O and CO2 Fluxes from Agricultural Soils. Agriculture 12, 692.

How to cite: Well, R., Dechow, R., and Grosz, B.: Hot-spots of denitrification in soil depending on crop residue and liquid manure incorporation – models and experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3413, https://doi.org/10.5194/egusphere-egu23-3413, 2023.

EGU General Assembly 2023

23-28 April 2023

THE EFFECT OF FERTILISATION AND CROPS ON NITROGEN SEQUESTRATION BASED ON MICROBIAL ANALYSIS AND N₂O EMISSIONS

Laura Kuusemets¹, Ülo Mander¹, Jordi Escuer Gatius², Alar Astover ², Mikk Espenberg¹

¹ University of Tartu, Institute of Ecology and Earth Sciences, Vanemuise 46, 51014 Tartu, Estonia

² Estonian University of Life Sciences, Institute of Agricultural and Environmental Sciences, Kreutzwaldi 5, 51014 Tartu, Estonia

Contact: laura.kuusemets@ut.ee

Nitrogen (N) is an essential nutrient in crop production as N is used to make amino acids (make the proteins that construct cells), is one of the building blocks for DNA, and is a significant component of chlorophyll (photosynthesis). The input of N in the form of fertilisers increases crop yield. On the other hand, agricultural nitrogen inputs can cause N leaching and the loss of biologically active N to the atmosphere, contributing to global warming. Thus, excessive and inefficient use of N fertiliser results in enhanced crop production costs and pollution of water bodies and the atmosphere. Agricultural landscapes are an important source of nitrous oxide (N₂O), a highly active greenhouse gas and stratospheric ozone depleter. The main objectives of the study were to evaluate whether and how different crop species and fertilisation norms affect nitrous oxide (N₂O) emissions and soil microbiome using the closed chamber method and quantitative polymerase chain reaction (qPCR) analysis.

The study was done in the IOSDV (International Organic Nitrogen Long-term Fertilisation Experiment) experimental field located in the southern part of Estonia. The crop species studied were barley (cultivar “Elmeri”), sorgo (cultivar “Susu”), and wheat (cultivar “Mistral”). The fertiliser treatment is constituted of mineral nitrogen fertilisation and fertilisation with farmyard manure. Three nitrogen fertiliser treatment rates were used: 0, 80 and 160 kg ha⁻¹. Samples were collected over seven months, from April 2022 to October 2022. qPCR was used to quantify the abundance of bacteria- and archaea-specific 16S rRNA, nitrification (bacterial, archaeal and comammox (complete ammonia oxidation) amoA) denitrification (nirK, nirS, nosZI and nosZII) and dissimilatory nitrate reduction to ammonium (DNRA; nrfA gene) marker genes from the soil samples.

The results of this study indicate that different fertilisation influence N₂O emissions and the highest N₂O emissions are emitted from the highest N fertilizer treatment (160 kg ha⁻¹). On average, sorgo fields fertilised with farmyard manure had slightly higher N₂O emissions compared to fertilisation with mineral fertiliser. In addition, on average, the highest and smallest N₂O emissions occurred with wheat and barley, respectively. The N₂O emissions among all crop species decreased during drought in the summer. The preliminary microbial analysis shows that nitrification was the primary process resulting in N₂O emissions, but the different groups of nitrifiers showed different trends under different fertilisation and crops.

How to cite: Kuusemets, L.: The effect of fertilisation and crops on nitrogen sequestration based on microbial analysis and N2O emissions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4359, https://doi.org/10.5194/egusphere-egu23-4359, 2023.

Ammonia oxidation contributes to global N₂O emissions both by direct production and by fueling denitrification (provision of nitrite or nitrate to denitrifiers). Urea or ammonia-based fertilizers account for approximately 70% of annual nitrogen fertilizer inputs globally. This means that the subsequent coupling processes driven by ammonia oxidation are of great significance to N₂O emissions. However, for this important source of N₂O production, direct evidence at the process- and microorganism- level is highly lacking, leading to that the systematic mechanism of the coupling processes and microbial activities in response to environmental changes (especially O₂ changes) remains unknown. Here, we investigated ammonia oxidation, other soil N transformation processes, N₂O emissions and related environmental changes (e.g., O₂ consumption) and microbial activities in a calcareous upland soil in Northern China, which has a strong ammonia oxidizing rate and is a global N₂O hotspot, by combining field observations, microcosm, molecular and isotope techniques. The results showed that the soil has a far (5-30 times) higher nitrification potential and gross nitrification rate than other cropland soils in the world. The strong ammonia oxidation led to rapid O₂ consumption and NO₂^- accumulation in soil matrix, causing strong emission peaks of N₂O, which was in line with the N₂O yield from denitrifiers. The N₂O ¹⁵N site preference and ¹⁵N labeling data further revealed a major role of nitrification-induced denitrification in high N₂O emissions. A higher AOB/AOA gene abundance ratio correlated the higher nitrification potential, higher NO₂^- transition and higher N₂O emissions. A coupling expression of nitrifying and denitrifying genes (amoA, narG, nirS, nirK, nosZ) and a significant structural alteration of the soil microbiota along with the O₂ consumption driven by ammonia oxidation linked to higher N₂O emissions. All the evidence points to ammonia oxidation-linked denitrification being the major process generating N₂O. In consequence, reducing N surplus, slowing down nitrification rate using nitrification inhibitors, and avoiding high ammonium microzones using slow-release or organic fertilizers are main measures to reduce N₂O emissions per unit of urea or NH₄⁺-based N input in intensively managed alkaline soils globally.

How to cite: Ju, X. and Song, X.: Ammonia oxidation as the engine to induce denitrification to produce N2O in alkaline agricultural soils, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4780, https://doi.org/10.5194/egusphere-egu23-4780, 2023.

Denitrification is a key process in the global nitrogen (N) cycle, causing nitrous oxide (N₂O) and dinitrogen (N₂) emissions. Even though denitrification is assumed to be a major N loss pathway from agroecosystems, field-scale estimates of both N₂O and N₂ are scarce, reflecting methodological difficulties in measuring and upscaling N₂ emissions. Mechanistic biogeochemical models allow estimates of seasonal denitrification losses at the field scale, extrapolating important yet often limited experimental results. However, such predictions rely mostly on N₂O data, meaning that the lack of N₂ data hinders the validation of overall denitrification rates, which remain a major uncertainty for N budgets.

This study investigated denitrification losses and N budgets in two subtropical sugarcane systems using Agricultural Production Systems sIMulator (APSIM) with unique datasets of both N₂O and N₂ emissions measured in the field with the ¹⁵N gas flux method and upscaled over the growing season. Five key soil N parameters in APSIM were identified as influential on N₂O and N₂ emissions via global sensitivity analysis, followed by generalised likelihood uncertainty estimation to determine their posterior distributions using (i) both N₂O and N₂ data and (ii) N₂O data only.

For both approaches, the calibration of APSIM led to larger denitrification (N₂O+N₂) losses and a shift towards N₂ compared to the use of default parameters. Simulated N₂O emissions did not differ between the different calibration approaches. However, simulated N₂ emissions were larger and agreed better with the observed values when calibrated with both N₂O and N₂ consistently across sites. This approach also improved the simulation of fertiliser N losses via denitrification, leaching and runoff, compared to the observed fertiliser ¹⁵N loss at harvest.

These findings indicate that biogeochemical models commonly used with default soil N parameters or calibration limited to N₂O data are likely to underestimate denitrification losses, producing a bias in simulations of N budgets. Our findings also highlight the importance to integrate in-situ measurements of N₂O and N₂ in simulation exercises, and demonstrate how innovative isotope methods can be used to inform biogeochemical models, ensuring more accurate N budget estimates across scales.

How to cite: Takeda, N., Friedl, J., Rowlings, D., Scheer, C., Haas, E., Kraus, D., and Grace, P.: Importance of in-situ measurements of both N2O and N2 emissions to calibration of biogeochemical models to simulate N budgets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4849, https://doi.org/10.5194/egusphere-egu23-4849, 2023.

Rice field has been traditionally considered as a nonpoint source of reactive nitrogen (N) for the environment, while it, with surrounding ditches and ponds, also contributes to receiving N inputs from atmosphere and waterbodies and intercepting N outputs from rice field. However, due to the paucity of multi-site, long-term observation and control experiment data, as well as robust process-based model for nitrogen budget, a comprehensive assessment of the N source (i.e., outputs > inputs) or sink (i.e., inputs > outputs) of rice field for the environment, from site to regional scale, is lacking. Here, a 2-year systematic observation and process-based simulations of N budget across China, covering typical annual rice cropping systems including single rice, double rice and rotation, were conducted to identify the roles of rice field in nitrogen cycling in China. The cost-benefit analysis for shifting China’s rice fields from nitrogen source to sink in different climatic scenarios (wet, normal and dry year) by innovative agricultural management, without compromising crop yield or soil fertility, were further evaluated. Rice fields, with surrounding ditches and ponds, perform as a nitrogen sink for atmosphere but a source for waterbody, which was confirmed by both the observational data and regional assessment by process-based model, regardless of rice types or climatic scenarios. With the adoption of sustainable N and water regulation measures, single rice field across China could be shifted to N sink (12.9-29.9 kg N ha^-1) while the N source of double rice would be reduced by 51%-66%. For middle rice field (rotation with other crops), N sink would be achieved in dry year, while 31%-55% would shift to sink in wet and normal year. However, with such great benefits, the costs only accounted for 41%-49% of the expenditure for waste water treatment. Furthermore, through sorting all the measures and adopting economic ones (lower cost with higher benefit) in priority, we found that rice fields across China have great space for source-to-sink regulation with zero cost, which means the benefits would exceed the regulation costs, and even achieve overall N sink in dry year. Together these findings help us to update scientific knowledge to the role of rice fields in ecosystems, as well as highlight the significance and possibility for achieving environmental-friendly rice field, by improving agricultural management technologies.

How to cite: Huang, W., Jiang, W., and Zhou, F.: Shifting China’s rice fields from nitrogen source to sink by innovative agricultural management, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5282, https://doi.org/10.5194/egusphere-egu23-5282, 2023.

Population keeps growing so as the need for food production. The increase in energy prices is putting a lot of pressure in energy intensive industrial processes such as the production of fertilizers. Farmers need to fine-tune the amount of fertilizer needed by the soil, so that they do not add in excess, elevating costs and polluting the environment, or do not fall short, suffering sub-optimal crop yields.

This work reports the fabrication and characterization of a low-cost device for the continuous monitoring of the concentration of plant nutrients based on ion-selective electrodes and textile threads that work in direct contact with soils. Here, as proof of concept, we developed a thread-based, microfluidic sensor platform. We utilized traditional polymer membrane-based ion-selective electrodes (ISEs) for potassium, nitrate, ammonium and pH were drop-casted directly on top of a miniaturized, 3D-printed holder. Electrical contact is established via graphite-based contacts link to the electrochemical signal reader via electrical wires. The sensor platform was enhanced by the addition of five 30 cm long textile threads connected to an absorption pad on the opposite side. This is the key innovation as these threads mimic the roots and via capillary action wick the moisture from the soil to the sensing area. The entire sensor platform contained 4 ISEs for each chemical species and one reference electrode and was encased into a 3D printed housing. The device is placed next to the soil that is going to be analysed inserting the threads in the soil sampling area.

Preliminary results show that thread-based sensor system is reproducible and consistently provides a near-Nernstian sensitivity of 55±5 and 50±3 for potassium, -58±1 and -63±2 for nitrate, and 60±1 and 60±12 (mV/decade) for ammonium between 2.8x10^-6 and 1.3x10^-2 M without (directly in solution) and with textile threads respectively. Analysis of soil samples with different soil moisture content (100%, 75%, 50% and 40%) using our low cost device gave a correlation coefficient of R² = 0.91 for potassium and R² = 0.92 for ammonium when compared to the values measured using traditional methods such as inductively coupled plasma optical emission spectroscopy (ICP-OES) and flow injection analysis (FIA), respectively. The promising performance of this low-cost device is encouraging towards its use as an extended network to measure soil ion concentration at high temporal and spatial resolution.

How to cite: Saiz, E., Guo, Y., Ullah, S., Sonkusale, S., and Radu, A.: Low-cost in-field determination of soil ion concentration using a portable 3D printed device based on ion-selective electrodes and textile threads, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5324, https://doi.org/10.5194/egusphere-egu23-5324, 2023.

Excess nitrogen has caused environmental issues by polluting the air and water. Many different processes help remove nitrogen compounds from contaminated soils and waters, and the presence of oxygen is one of the most decisive factors. Denitrification in anaerobic conditions is considered the main removal processes of excessive nitrogen, although lately discovered anaerobic ammonium oxidation (ANAMMOX) and dissimilatory nitrate reduction to ammonium (DNRA) may also have an important role in nitrogen elimination of different systems. To a lesser extent, also nitrification can contribute to nitrogen elimination in watery systems. All previously pointed out removal mechanisms occur in the constructed wetlands and could even be enhanced with the bio-electrochemical systems (BES). BES exploit the ability of the electroactive microorganisms to reduce the oxides of nitrogen.

We analyzed various articles treating nitrate (NO₃) polluted water in BES and normalized their NO₃ removal efficiencies to a common unit (mg liter⁻¹ day⁻¹). We analyzed the effect of various factors such as electrode materials, working mode, type of inoculum, number of chambers, systems’ capacity and the microbial community structure on the NO₃ removal efficiencies. The highest removal efficiencies were displayed by granular carbon and carbon cloth used as cathode and anode material, respectively. The electrode materials and operational parameters, such as working mode and number of chambers, were deemed important by the random forest classification algorithm. Continuous mode of operation, denitrifying microbes as inoculum type, and two chamber systems have displayed optimum NO₃ removal efficiencies. Feature selection using random forest classification showed the type of inoculum and capacity of the BES were unimportant factors. Proteobacteria and Firmicute were the prominent phyla observed in BES treating NO₃ polluted water. Besides the denitrification (abundance of narG, nirS, nirK, nosZI, and nosZII genes) process in BES, there is evidence of electrochemical support for anaerobic ammonium oxidation (ANAMMOX) (abundance of hzsB or ANAMMOX specific 16S rRNA gene) and dissimilatory NO₃ reduction to ammonium (DNRA) (abundance of nrfA gene) processes. The results of this work aid in understanding the prevalent processes in the BES and help to build efficient BES for optimum NO₃ removal.

How to cite: Gadegaonkar, S. S., Mander, Ü., and Espenberg, M.: Microbial and environmental factors affecting nitrate removal in bio-electrochemical systems (BES), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5440, https://doi.org/10.5194/egusphere-egu23-5440, 2023.

Denitrification in agricultural crop production is one of the main sources of gaseous N₂O and N₂ losses to the environment. To successfully develop mitigation strategies, it is crucial to understand N₂O production pathways, but also to quantify all other gaseous N losses, especially N₂ emissions. Therefore, this project aimed (1) to identify the main drivers of denitrification during plant growth and in the post-harvest period, (2) to quantify denitrification derived N₂O and N₂ losses during the cropping season, and (3) to assess the interactions between plant litter quality, initial litter degradation, and formation of hotspots of N₂O and N₂ production. We conducted experiments on the laboratory, greenhouse, and field plot scale using the ¹⁵N gas flux method and HeO₂ atmosphere to directly measure N₂O and N₂ losses and to determine the fraction of denitrification derived N losses. We worked with soils, crops, temperature and moisture conditions that are typical for our central German humid-temperate climate.

Plant growth affected all controlling factors of denitrification, especially soil moisture, NO₃⁻ and C_org availability. Crop species differed in their growing patterns and N uptake throughout the growing season controlling both N and C availability in soil. Accordingly, N₂O and N₂ emission patterns differed between crop species. Overall, emissions were highest when plant N uptake was low, i.e., during early growth stages and ripening, and after harvest. On the field scale, soil moisture and temperature were major controls of N₂O+N₂ losses.

In a climate chamber study under controlled temperature conditions, N₂O and N₂ fluxes mainly derived from denitrification of labeled ¹⁵NO₃⁻ in anoxic microsites, while nitrification simultaneously occurred in more oxic parts of the soil, potentially contributing to formation of unlabeled N₂O. Increasing soil moisture with irrigation increased denitrification rates in anoxic hotspots, which corresponded with increasing N₂O and especially N₂ fluxes. At the same time, it restricted nitrification and thus decreased the share of nitrification-dependent processes contributing to N₂O formation.

Incorporation of plant litter increased CO₂, N₂O, and N₂ losses irrespective of litter quality, soil moisture or soil type/SOM content. We found that under O₂ limiting conditions (70 % WFPS), the fraction of easily degradable C controlled the magnitude of N₂O and N₂ losses after litter incorporation. Under moderate soil moisture (50-60 % WFPS), interactions between litter degradation and SOM turnover affected the time course and processes contributing to N₂O formation. Overall, our high-resolution gas flux measurements showed that N₂O+N₂ emissions from harvest residues can contribute significantly to the total N loss. 

How to cite: Rummel, P. S., Well, R., Pausch, J., Englert, P., Matson, A., Beule, L., Floßmann, S., Eckei, J., Pfeiffer, B., and Dittert, K.: Crop plant effects on denitrification – what have we learned in six years DASIM project?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5615, https://doi.org/10.5194/egusphere-egu23-5615, 2023.

Abstract

    Under the predicted climate change scenarios, heavy precipitation could result in prolonged flooding (PF) and flooding-drying (FD) of soils in agriculture. The influence of PF and FD on soil greenhouse gas fluxes and nitrogen (N) dynamics of arable and grassland soils, which are the dominant land use types in UK soil, is still unclear. Two months of soil incubation experiments were conducted to find out the impact of PF and FD on soil nitrogen dynamics and greenhouse gas fluxes from arable and grassland soil. The result showed the developed ion selective electrodes (ISE) sensor was working to measure NH₄⁺ in the first 5 days of real-life application under both grassland and arable soil. There were less N₂O-N emissions in grassland and arable soil when soil moisture was higher than 100% water-holding capacity (WHC). Arable soil had more N₂O-N emissions when soil moisture was higher than 100% WHC compared to grassland soil due to a low pH. Grassland soil had more N₂O-N emissions when soil moisture was lower than 100% WHC compare to arable soil due to a high carbon and nitrogen source. When soil moisture was greater than 100% WHC, the available NO₃^--N in the soil controlled N₂O-N emissions of grassland more effectively. The N₂O-N emissions of grassland soil were more controlled by soil stable NH₄⁺-N and NO₃^--N when soil moisture was lower than 100% WHC. The emissions of N₂O-N and CO₂-C were increased with the time of FD. FD significantly increased N₂O-N, CO₂-C, and CH₄-C emissions in grassland soil compared to arable soil by 0.93, 2.15, and 37.29 times, respectively. Converting arable land use to grassland could increase the greenhouse gas (GHG) emissions under climate change (heavy rain). Further research needs to be done to find out how to reduce the GHG emissions under climate change after transfer arable to grassland.

How to cite: Guo, Y., Saiz, E., Radu, A., and Ullah, S.: Prolonged Flooding followed by drying increase greenhouse gas emissions differently from soils under grassland and arable land uses, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5834, https://doi.org/10.5194/egusphere-egu23-5834, 2023.

The flux of nitrous oxide (N₂O) from the soil to the atmosphere is an important contributor to the global greenhouse effect. Spatial variation in the distribution of factors that drive N₂O producing processes often creates hotspots within soil that are difficult to quantify and model, and this is particularly the case after manure amendment. In the stagnant soil matrix, solute diffusion is crucial in supplying the nitrate (NO₃^-)to nearby zones, i.e., hotspots, to maintain a locally high NO₃^- reduction. To provide detailed insight into the spatiotemporal variability of nitrogen (N) transformations around N₂O hotspots, we propose a multi-species, reactive transport model containing kinetic reactions of soil respiration, nitrification, nitrifier denitrification, and denitrification, built on a system of partial differential equations. The model was used to simulate the amount of N₂O, dinitrogen (N₂) and carbon dioxide (CO₂) emitted from a 10 cm soil profile with time, and concentration profiles of crucial intermediates. The measured N₂O and N₂ fluxes correlate well with the model simulations, with a simulated stratification of growing nitrifying and denitrify activities in and around the manure hotspot which is consistent with previous incubation experiments. N₂O evolution was sensitive to the initial setup of oxygen (O₂) availability, and anaerobic condition was maintained in the saturated manure zone throughout the simulation period, demonstrating the necessity of simulating the heterogeneity within soil in N₂O models. Simulation experiments will be conducted to assess the effects of solute diffusion on N transformations. We anticipate that diffusive NO₃^- transport to be crucial to facilitate the coupled nitrification-denitrification around the manure zone. Neglecting such a process in process models may make it difficult to reflect the rapid turnover of nitrogen pool around organic hotspots and underestimate N₂O emissions. The model and its parameters allows for new detailed insight into N₂O formation processes in heterogeneous environments.

How to cite: Zhang, J., Kolstad, E. L., Zhang, W., Jansson, P.-E., Cronin, I. V., and Petersen, S. O.: Modeling coupled nitrification-denitrification in manure-amended soil, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6382, https://doi.org/10.5194/egusphere-egu23-6382, 2023.

The urine patch from livestock creates an active hotspot of soil nitrogen (N) cycling due to the intrinsically high N and carbon (C) loading rates. These N hotspots frequently result in N losses to the atmosphere or leaching from soil. N losses vary due to climate conditions, soil conditions, and management practices. However, we do not fully understand how these factors influence N cycling and nitrous oxide (N₂O) emissions from urine patches. Intensive lowland grazing systems on mineral soils have been relatively well studied in this context, however, other grazing systems such as extensive upland systems on organic soils have been much less studied.

To investigate the effect of soil type on N cycling and N₂O emissions in the urine patch, soil was collected from pastures in an altitudinal gradient, from an improved lowland mineral soil with coastal influence to unimproved organic soil under acid grassland.  Depending on the position along the gradient, the soils change in properties such as pH, bulk density, organic matter content, cation exchange capacity and nutrient availability. Soil was collected for a laboratory incubation study from four sites including two lowland sites (Cambisol and Cambisol with coastal influence) and two upland sites (Podzol and Histosol). Soils were sieved and divided into four replicates of each treatment. Sheep urine from Welsh Mountain ewes was applied at an equivalent loading rate of 150 kg N ha^-1 to half of the soil and the remaining half received the equivalent volume of water as a control. All the treatments were held at 70% water-filled pore space to optimise both moisture conditions for nitrification and denitrification to occur. Over 100 days, greenhouse gas emissions were monitored along with soil pore water nitrate and ammonium concentrations.

Soil type had an overall significant effect on N₂O emissions with the highest cumulative emissions during this period being from the Podzol and the lowest cumulative emissions being from the Histosol. The two lowland sites showed no significant differences. There was a delay in nitrification in the Podzol, with the majority of the N₂O being emitted a month after urine application. The Histosol showed no evidence of nitrification as there was no build-up of nitrate concentrations over the experiment. This was probably due to differences in soil pH in the soils. There were no differences in carbon dioxide or methane emissions from the four soils, but there was a spike in methane flux on the Podzol which corresponded with increases in N₂O fluxes from this soil type.

This experiment has shown that certain upland soils have the potential to produce N₂O emissions and cycle N under optimal conditions, although this is at a much slower rate than the lowland sites. Results from this incubation study helps improve our understanding of how soil properties in organic soils affect N cycling and contribute to knowledge gaps on the sustainability of upland grazing systems.

How to cite: Hunt, D., Cardenas, L., Jones, D., and Chadwick, D.: The production of N2O from sheep urine patches is influenced by soil properties., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6652, https://doi.org/10.5194/egusphere-egu23-6652, 2023.

Soil microbial processes in drylands are limited by multiple abiotic factors, the most important being water and macronutrients (nitrogen (N) and phosphorus (P)). Understanding of relative importance of different abiotic factors for soil microbial processes is important because drylands are important regulators of global carbon (C) cycle and there is close connection between water, N, and C cycles. To assess how soil activity is affected by removing multiple nutrient limitations and manipulating water availability we conducted a short-term, multifactorial field experiment. We manipulated water, N, and P availability by application of the nutrients and water in the field. We evaluated how soil respiration, nitrous oxide, and nitric oxide emissions responded to increasing water, N and P availability individually and interactively in the Negev Desert. We hypothesized that neither water nor nutrient addition alone will enhance the activity of desert soils. On the other hand, removing multiple limitations will accelerate soil nutrient cycling. Further we hypothesized that acceleration of soil nutrient cycling will be reflected in high soil emissions of N₂O, NO, and CO₂ as proxies for the N cycle and respiration, respectively. We found that increasing water availability in desert soils significantly accelerated soil respiration rates but not the N cycle. Nitrogen availability affected soil NO production but not soil respiration. Soil emissions of N₂O were unaffected by neither water nor nutrients additions. Phosphorus additions had no effect on soil microbial activity either alone or synergistically together with N and water.

How to cite: Gelfand, I. and Osei-Yeboah, M.: Contrasting effects of increase in water and nutrients availability on soil respiration and soil nitric and nitrous oxide emissions in desert., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7971, https://doi.org/10.5194/egusphere-egu23-7971, 2023.

Flood regimes in large river systems such, as the Mississippi River, are inherently stochastic meaning that floodplain wetlands experience varying hydrostatic pressures of groundwater upwelling (exfiltration) and infiltration from overland flooding. Distinctions in water delivery can drastically alter the oxygen levels and groundwater delivery into wetland sediments where anaerobic microbes remove nitrates through denitrification. Our findings bound conditions for modeling denitrification rates across oxic flood waters versus exfiltration by anoxic groundwaters. Four-by-four factorial laboratory incubation treatments included oxic versus anoxic waters (degassed with helium) introduced by exfiltration or infiltration (Figs. 1A, 1B).

Sediments collected in triplicate from four floodplain wetlands located along Dogtooth Bend segment of the Mississippi River near the Ohio River confluence were incubated with river water. Sediments were incubated at 29 ^oC for 96 h. Nitrogen gas production was measured by membrane inlet mass spectrometry (MIMS). Inflow and outflow waters were analyzed for nitrate, ammonia, phosphate, and dissolved organic carbon while sediments were characterized for their physical traits. In contrast to most studies, that estimate denitrification relative to surface area in incubations only (i.e. address conditions of surface flooding), we also present our findings relative to sediment volumes (i.e. evaluate denitrification rates from exfiltration of groundwater). Regression analyses compared denitrification from surface area versus volume calculations (R² values > 0.89); consequently providing an excellent tool for converting estimates from surface area alone to varying sediment saturation for more rigorous assessments of subsurface interactions.

Average denitrification rates relative to sediment volume were significantly higher in anoxic-deep-injection cores (“AD cores”; 23.83 + 1.94 N mg/m³/d) compared to anoxic-surface-delivery cores (“AS cores”; 19.98 + 1 N mg/m³/d), that also exceeded oxic-deep-injection cores (“OD cores"; 14.96 + 1.78 N mg/m³/d) and oxic-surface-delivery cores (“OS cores”; 10.23 + 1.04 N mg/m³/d). Thus, average denitrification followed an anoxic-injection hierarchy of AD > AS > OD > OS (p-values < 0.003), which was maintained for denitrification relative to surface area. Regarding site-specific distinctions, for sandy sites this hierarchy persisted, and each treatment differed significantly. Sites with clayey sediments had very-low permeability regardless of injection type; thus only oxic versus anoxic treatments differed significantly irrespective of water delivery. By contrast sites with loamy sediments, injection type significantly influenced denitrification rates while neither oxic nor anoxic water treatments differed. An AICc model showed that phosphate, ammonia, temperature variation, dissolved oxygen, and sand content explained 33% (p-value < 0.05) of the variation in denitrification rates across all cores and treatments.

Our findings highlight the greater insights provided from cross-comparison incubation designs to better inform landscape-scale models of denitrification rates across floodplain wetlands depending on the magnitude and duration of flooding.

How to cite: Samberg, S. S., Brooks, M. L., Hamilton-Brehm, S. D., Krienert, J. M., and Remo, J. W. F.: Cross-Comparisons of Sediment Incubation Methods to Bound Stochastic Influences on Denitrification of Natural Waters from Mississippi River Floodplain Wetlands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8168, https://doi.org/10.5194/egusphere-egu23-8168, 2023.

Agricultural land-use makes up around 38% of the total global land surface. Farming activities are a major source of greenhouse gas emissions (carbon dioxide, methane and nitrous oxide) worldwide. Nitrous oxide (N₂O) emissions from agricultural land are an important contributor to the overall greenhouse gas budget. The high spatial and temporal variation of N₂O emissions in agricultural lands makes it more challenging and important to quantify the actual emissions. Denmark’s glacial landscape is characterized by a high abundance of topographic depressions. These are typically flooded for 1-3 months per year, mainly during late winter and spring season. As these depressions are frequent in agricultural areas, their soils are exposed to an increased nitrate availability due to regular fertilization. The combination of high-water saturation and high nitrate availability results in distinct landscape denitrification and thus N₂O emission “hotspots”.

The reduction of N₂O to N₂ by N₂O reductase can be an important mechanism to mitigate N₂O emissions. The N₂O reductase is both Cu and pH sensitive. Studies have showed Cu-modified organic fertilizer have the potential to enhance the reduction from N₂O to N₂, and therefore decrease N₂O emissions from fields.

In this study, we aimed to elucidate if Cu addition alters the emission of N₂O from upland and depression soils in a different way. Therefore, we conducted an incubation experiment with both upland and depression soils, testing how different levels of Cu addition and two different water levels affect the emission of N₂O. In order to differentiate the N₂O production pathways (nitrification or denitrification), we applied ¹⁵N tracer in the form of ¹⁵NH₄¹⁵NO₃ or ¹⁴NH₄¹⁵NO₃. We also added ¹³C labelled maize residues to be able to trace the consumption of fresh substrate in the course of denitrification as affected by different Cu and water levels.

Interestingly, although the soils were homogenized and incubated at the same water availability, we demonstrated a clearly higher N₂O emission from the depression soils compared to the upland soils. In general, we were able to demonstrate that Cu addition clearly reduces the level of N₂O emissions from upland soils, which is clearly more pronounced at higher soil water levels.

How to cite: Liu, Y., Poultney, D. M.-N., Wichern, F., Ambus, P., and Müller, C. W.: Low vs. upland - copper addition regulates denitrification in cropland soils from N2O emissions hotspots in Denmark, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8878, https://doi.org/10.5194/egusphere-egu23-8878, 2023.

The COVID-19 global pandemic has significantly affected air quality due to changes in human behavior. Gaseous nitrous acid (HONO) is a significant precursor of the hydroxyl radicals (OH), powerfully influencing atmospheric oxidization capacity and air quality. However, the impacts on the sources and sinks of HONO during COVID-19 are not well understood. Here, we observed the concentrations of HONO, nitric oxide (NO), and nitrogen dioxide (NO₂) in the suburb of Shanghai during May 2020 (P1), August 2020 (P2), and April 2021 (P3) to analyze seasonal variations of HONO chemistry and also clarify how different pandemic phases influence HONO sources and sinks. The average concentration of HONO during P1, P2 and P3 showed an increasing trend (0.292 ± 0.0078、0.358 ± 0.0115, and 0.415 ± 0.0115 ppb, respectively), with direct emission from vehicles was the most essential source of the nocturnal HONO concentration (38.14%, 47.52%, and 50.95%, respectively), followed by heterogeneous conversion of NO₂. The daytime HONO sources presented noticeable discrepancy among three study periods. In spring, homogeneous reaction was the primary HONO source with a mean production rate of 0.2 ppb h⁻¹, while there was almost no unknown source (P_unknown). In summer, however, the average production rate of homogeneous reaction decreased to 0.15 ppb h⁻¹, while P_unknown was up to 58% of the whole HONO production, demonstrating some strongly enhanced source(s) in the summer season. By comparing HONO budgets between different pandemic phases, the contributions of vertical and horizontal transport doubled from P1 to P3, with the average production rates increasing from 0.03 to 0.06 ppb h⁻¹. Our results also showed that the strict lockdown measures reduced the unknown sources of HONO (P1), and correspondingly, as Shanghai implemented regular epidemic prevention and control measures, the relatively high rate of P_unknown was observed during P3, making up 35% of the whole HONO production. What is more, through the strong correlation with J(HNO₃) (r = 0.9) and J(NO₂) (r = 0.89), it can be argued that the photolysis of nitric acid and photo-enhanced heterogeneous conversion may be a vital production pathway. The HONO photolysis was the major loss pathway, occupying approximately 85% of HONO loss during all campaigns. During noontime, the average photolysis loss rate was 1.07、2.40 and 1.86 ppb h⁻¹, accounting for up to 96% of the HONO sinks. Dry deposition was the second important loss pathway, especially in the morning and before sunset. This study indicates remarkable seasonal variations of HONO and the effects of COVID-19, and has significant implications on controlling measures of air pollutants in megacity.

How to cite: Wang, Y. and Wu, D.: Sources and sinks of atmospheric nitrous acid (HONO) in the megacity of Shanghai during COVID-19, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11088, https://doi.org/10.5194/egusphere-egu23-11088, 2023.

Reactive nitrogen from anthropogenic inputs such as fertilizers and its changes in the transport and fate in the environment as a consequence of changes in land management may alter the nitrogen balance of a catchment and thus its concentrations in water bodies. This can be enhanced by increased wet and dry deposition of nitrogen from anthropogenic activities. In the Mau Forest Complex in Kenya, the annual export of nitrogen from a catchment dominated by smallholder agriculture was reported to be almost double those from the native forest. Fertilization and livestock management are assumed to have contributed to this shift, but no empirical evidence is available to support this. Furthermore, the contribution of the nitrogen wet deposition through rainfall and throughfall to the nitrogen balance has not been quantified yet. This study aims at determining the contribution of nitrogen wet deposition and anthropogenic inputs to the nitrogen balance of a 27 km² headwater catchment characterized by smallholder farming in the Mau Forest Complex. Rainfall and throughfall samples were collected from precipitation collectors in 10 different locations within 24 hours after 11 rainfall events in the span of 9 weeks. Anthropogenic inputs were estimated from a household survey (n=185). 

Median and Interquartile range (IQR) concentrations of total dissolved nitrogen (TDN) were slightly higher in rainfall i.e. 0.7 (0.4–0.9) mg N L⁻¹ than in throughfall i.e. 0.6 (0.4–0.8) mg N L⁻¹, resulting in median wet deposition of 0.04 (0.02–0.06) kg N ha⁻¹ from rainfall and 0.03 (0.01–0.06) kg N ha⁻¹ from throughfall per sampled rainfall event (4.7 mm; 2.5–8.1 mm). Extrapolated to the full year, this leads to an estimated nitrogen input from wet deposition of 11.7 (9.5-12.5) kg N ha⁻¹ yr⁻¹ from rainfall and 6.4 (5.7-9.6) kg N ha⁻¹ yr⁻¹ from throughfall, although this estimate does not consider seasonal changes in TDN concentrations in rain- and throughfall. Median inputs of nitrogen from inorganic fertilizer was 25 (15.2–40.2) kg N ha⁻¹ yr⁻¹, whereas annual inputs from livestock were 76 (49-125) kg N ha^-1 yr⁻¹.

Reactive nitrogen inputs from farming and livestock are higher than the estimated wet deposition and could therefore significantly impact the catchment nitrogen balance. It follows therefore that a continual and increase use of nitrogen inputs from manures and fertilization with inorganic fertilizers, as well as further forest cover loss for agricultural expansion may lead to future elevated levels of nitrogen in the environment, leading to risks of progressive enrichment of water bodies and further nitrogen imbalances. To keep these in check, appropriate manure management strategies, fertilizer application and control of forest conversion cannot be overemphasized.

How to cite: Kasebele, M., Jacobs, S., and Breuer, L.: Inputs of reactive nitrogen from wet deposition and fertilization in a tropical montane catchment characterised by smallholder farming., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11325, https://doi.org/10.5194/egusphere-egu23-11325, 2023.

North China Plain (NCP) is a region in China, with highly intensive food production and a hotspot of nitrogen (N) losses to the environment. Region-specific N management is, therefore, required to effectively reduce agricultural N losses. For this it is important to identify the N flows and environmental targets in the food chain (including crop production, animal production, food processing, and human consumption) at the county scale. We developed an integrated assessment N framework. It combines a food chain approach with an air quality model and groundwater model. We apply this method to quantify the relative contributions from parts of the food chain to N losses. We identify environmental targets to air and water in Quzhou, a typical agricultural county in the NCP. We found that N losses to the environment from the food chain were ~11 kt  in Quzhou in 2017. Approximately 80% of this amount is from crop and animal production, which is primarily caused by the low N use efficiency in crop production (28%) and animal production (18%). Ammonia (NH₃) emissions to air (4.1 kt N) and N leaching (2.1 kt N), and direct discharges of manure to water (1.9 kt N) are the main contributors to the N losses in Quzhou. To meet the environmental targets for air quality (PM_2.5) and groundwater quality, the NH₃ emissions and N leaching need to be reduced by 55%, and 21-50%, respectively. Our findings indicate that better nutrient management is urgently needed to reduce agricultural N losses and to support Agriculture Green Development in NCP.

How to cite: Meng, F., Wang, M., Ronda, R., Strokal, M., Kroeze, C., Ma, L., Xu, W., and Zhang, F.: Nitrogen losses from food production in the North China Plain compared to environmental targets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12416, https://doi.org/10.5194/egusphere-egu23-12416, 2023.

Nitrous Oxide (N₂O) emissions in Soil and Water Assessment Tool (SWAT) is heavily dependent on soil temperature and moisture. However, SWAT has been known to highly under-estimate soil temperature which limits movement of water and nutrients throughout the soil profile and does not replicate freeze-thaw cycles which is of paramount importance in the N₂O emissions. Thus, we integrated modules developed by individual researchers pertaining to energy balanced snow melt, rain-on-snow, energy balanced soil temperature and N₂O emission into a single SWAT model and termed in SWAT Cold Climate N₂O (SWAT-CCN2O). SWAT-CCN2O was then tested for flows, sediments, soil temperature and N2O emission simulation in a representative watershed in Ontario, Canada, the Speed River basin. Compared with the unaltered SWAT model, SWAT-CCN2O was able to significantly capture the pre-spring snowmelt induced flows. A more realistic simulation of soil temperature (soil temperatures did not go below -4^oC) and a satisfactory simulation of sediments and N₂O emissions were observed in the basin, which highlights the potential to use SWAT-CCN2O for streamflow and N₂O simulation in cold climatic catchments. This version of SWAT is made publicly available for further improvements and applications in similar watersheds.

How to cite: Daggupati, P., Ghimere, U., and Biswas, A.: Advancing the realistic simulations of N2O emissions in cold climate watersheds using Soil and Water Assessment Tool, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13010, https://doi.org/10.5194/egusphere-egu23-13010, 2023.

Prediction of liquid organic fertilizer effects by biogeochemical models on denitrification and associated N₂O and N₂ fluxes in soils is inappropriate, because previous studies mostly excluded N₂, and the calibration of the models without N₂ data is inaccurate. Besides, the models mostly homogenize the substrate content of the applied manure with the corresponding substrate pools of the soil, without the consideration of the effects of the liquid manure induced hot-spots in the soil. Therefore, the main goal of the MOFANE Project was to develop a new approach dealing with hot spot effects in manure amended soils. A simple and static model approach (Sommer et al., 2004) was improved and developed for a dynamic model to consider the effect of the manure induced hot-spots in the soils. It contemplates the effect of the application technique of the liquid manure (surface or injected), the ammonium and labile organic carbon content of the manure, the water content and the structure of the soil to calculate the NH₃ loss, the N mineralization and O₂ consumption of the degradable organic content, the nitrification and the denitrification in the manure-soil hot-spot region. The substrate exchange and flow are calculated based on the water potential difference between the liquid manure and soil. A laboratory experiment was conducted to provide proper input and output data for the model testing.  A sandy (Grosz et al., 2022) and a loamy arable soil were investigated in 10 days laboratory incubations. The temperature was constant 15^oC and the water-filled pore space (WFPS) were constant 40% and 60%. The soils were amended with and without artificial slurry in three manure treatments (control, surface-applied, injected). N₂O and CO₂ fluxes were quantified by gas chromatography. N₂ and source-specific N₂O flux was quantified by isotope-ratio mass spectrometry. The results of laboratory experiments will be used for testing the model accuracy. 

Grosz, B., Kemmann, B., Burkart, S., Petersen, S. O., and Well, R.: Understanding the Impact of Liquid Organic Fertilisation and Associated Application Techniques on N₂, N₂O and CO₂ Fluxes from Agricultural Soils, Agriculture, 12, 692, https://doi.org/10.3390/agriculture12050692, 2022.

Sommer, S. G., Petersen, S. O., and Møller, H. B.: Algorithms for calculating methane and nitrous oxide emissions from manure management, Nutrient Cycling in Agroecosystems, 69, 143–154, https://doi.org/10.1023/B:FRES.0000029678.25083.fa, 2004.

How to cite: Grosz, B., Dechow, R., and Well, R.: Modeling hot-spot of N2 and N2O production in agricultural soils as introduced by liquid organic fertilization, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13162, https://doi.org/10.5194/egusphere-egu23-13162, 2023.

Over the last 80 years, intensive agriculture has had numerous consequences globally. In particular, it has led to a loss of soil organic carbon (SOC) and a decline in soil fertility, resulting in higher nitrogen (N) fertilizer application. Excess of fertilizer has driven the emissions of N₂O, a greenhouse gas (GHG) 298 times more potent in inducing global warming than CO₂. Under the UK target of net zero emissions by 2050 and considering the recent increase in fertilizer price, conservation agriculture appears a viable solution to sustain food production whilst reducing global warming. Along with species diversification and reduction (or absence) of tillage, a permanent soil organic cover is the third pillar of conservation agriculture. In particular, “leys” consist in temporary pastures planted in between crops or to restore exhausted soils. These leys are planted with a mix of N fixing plants, which have a unique symbiotic relationship with soil bacteria collectively called “Rhizobia” that transform atmospheric N₂ into organic nitrogen. The mineralization of this organic nitrogen is expected to reduce dependence on N fertilizer. In contrast with the traditional grass/clover mix, herbal leys have recently gained popularity amongst UK farmers. They consist in a more complex mixture of grasses, legumes and herbs, bringing a range of benefits to forage, livestock health and soil fertility.

Here we report a year’s worth of measurement of soil mineral N and SOC contents, N mineralization potential, in situ measurement of denitrification (which transforms N fertilizer into N₂O and N₂) and total GHG emissions (CO₂, N₂O, CH₄) from a 4-year-old herbal ley in comparison with an arable field. We measured denitrification with our newly developed method (see Micucci et al., 2022) and GHG with conventional GHG chambers. First results show that during the early growing season (April to June), total N₂O emissions measured from GHG chambers were 10 to 60 times higher in the arable field than in the herbal ley, due to N fertilizer application. Similarly, a high loss of this N fertilizer was observed during April in the form of denitrified N₂.

Micucci, G., Sgouridis, F., Krause, S., Lynch, I., McNamara, N. P., Dos Santos Pereira, G., Roos, F., and Ullah, S. (2022). Towards enhanced sensitivity of the 15N Gas Flux method for quantifying denitrification in soil, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-585, https://doi.org/10.5194/egusphere-egu22-585

How to cite: Micucci, G., Sgouridis, F., Krause, S., Lynch, I., McNamara, N. P., Dos Santos Pereira, G., Roos, F., and Ullah, S.: In situ measurement of denitrification (N2 and N2O) and greenhouse gas emissions (CO2, N2O, CH4) in conservation agriculture, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13402, https://doi.org/10.5194/egusphere-egu23-13402, 2023.

Quantifying greenhouse gas emissions has been a priority for climate scientists for decades. As a result, the spatial and temporal dynamics of emissions have been widely studied, but to date, we still do not fully understand the main drivers of the variation in patterns. The aim of our research is to quantify the spatio-temporal variability of these greenhouse gases under various nutrient supply conditions and different tillage practices (plow or cultivator) on sandy-clay and loam soils.

Our measurements took place near Kartal on loam soil and near Gödöllő on sandy-clay soil, in Central Hungary, in 2022 on winter wheat. CO₂ and N₂O fluxes are analyzed with Li-cor gas analyzers (LI-870 CO₂/H₂O Analyzer and LI-7820 N₂O/H₂O Trace Gas Analyzer) connected to the 8200-01S Smart Chamber. We can track both modest changes brought on by natural factors (precipitation, temperature variations) and the impact of more significant artificial factors (fertilization, type of tillage) on the N₂O and CO₂ flux using these rather sensitive devices. In Kartal, 24, and in Gödöllő 40 KG-PVC rings with a diameter of 20 cm were placed in the study areas and measured on a weekly basis. In Kartal half of the collars received fertilizer, and the other half was covered during the application. In Gödöllő, 8 different treatments can be distinguished, resulting from a combination of 3 different fertilizer doses (0kg/ha, 75kg/ha, and 150kg/ha), 2 tillage methods (plow and cultivator), and soil conditioners. The collars protrude 4 cm from the soil and the inner soil surface has been cleared of vegetation. The gas exchange between soil and air is measured for 3 minutes on each collar, while simultaneously measuring soil moisture, temperature, and vegetation cover (LAI) near the collars. Soil samples were taken monthly to a depth of 15 cm, and 50 cm from the collars.

Based on our observation, in the case of N₂O emission, there are significant differences between the two study areas. On average N₂O emissions in Gödöllő were higher than in Kartal. Cumulative N₂O emissions were significantly higher in areas receiving higher doses of fertilizer. For 150kg/ha, the highest value was 42 g N m², while for 0kg/ha and 75kg/ha, lower values of around 16-20 g N m² were observed. With average emissions of 420–500 g C m², there are no discernible variations in cumulative CO₂ emission across treatments. However, the temporal variation of both GHG emissions shows differences due to the persistent drought in summer. During the rainy season, spring and autumn, a more intense N₂O and CO₂ flux were observed due to soil respiration.

How to cite: Mészáros, Á., Magyar, B., Omoding, N., Balogh, J., Fóti, S., Pintér, K., Percze, A., De Luca, G., and Nagy, Z.: Effect of various fertilizer doses on soil N2O and CO2 emissions in cropland soils in Hungary, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14663, https://doi.org/10.5194/egusphere-egu23-14663, 2023.

Different microbial species are capable of producing N₂O through multiple pathways, and these can coexist within short distances due to different microenvironmental conditions in the heterogeneous soil structure. Denitrification in soil occurs predominantly in microbial hotspots where denitrifiers use nitrate as an alternative electron acceptor. Soil water content has a profound influence on denitrification because it determines the diffusion lengths of oxygen through air- and water-filled pores, as well as the diffusion of denitrification products from the source in the soil to the atmosphere. Predicting N₂O emissions resulting from denitrification, however, is notoriously difficult without quantifying microscale hotspots.

In this experiment we evaluated results from an incubation experiment with undisturbed cores from two different soils having contrasting structures (cropland vs. meadow) at three different water contents. In addition to high-resolution gas chromatography, ¹⁵N-labeled nitrate solution allowed information on denitrification and its product ratios to be gained through IRMS measurements at selected time points. On the other hand, 7 needle-type optodes per core in combination with image analysis of images derived by X-ray tomography are used to quantify small scale diffusion distances and hotspots around POM. Last, a previous experiment, with the same but sieved soil and without particulate organic matter (POM), is used as a comparison to further investigate the influence local structure heterogeneity and POM on denitrification.

First results indicate that the reduction of diffusion pathways during sieving in the arable soil resulted in significantly lower emissions after sieving compared to the structured soil, while N₂O+N₂ emissions in the meadow soil were only slightly affected by sieving. For the first time, we were able to generate 3D images of O₂ saturation by combining image-derived diffusion length information with the measured O₂ concentrations. These allowed to explain high variabilities of N₂O+N₂ emissions from the field structured cores.

How to cite: Lucas, M., Rohe, L., Vogel, H.-J., Well, R., and Schlüter, S.: Microscale oxygen distribution to predict denitrification in structured soil, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14831, https://doi.org/10.5194/egusphere-egu23-14831, 2023.

Sugarcane is typically produced under conditions that are known to stimulate soil denitrification, i.e. high fertiliser inputs in combination with high levels of crop residue (trash) retention and a warm and humid climate, and high levels of fertiliser N losses from intensive sugarcane systems have been reported. However, there is still insufficient reliable data on N₂ losses from sugarcane soils based on field measurements since it is inherently challenging to measure N₂ emissions against the high atmospheric N₂ background. This study investigated the effect of cane trash removal and the use of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N₂ and N₂O emissions on a commercial sugarcane farm in sub-tropical Australia using the ¹⁵N gas flux method. Substantial gaseous N losses were observed under current management practice where cane trash retention and N fertiliser application (145 kg N ha^-1 as urea) resulted in elevated losses of N₂O and N₂ from a subsurface N fertiliser band, with more than 50% of these gaseous N losses emitted as N₂O. Cane trash retention increased the magnitude of N₂O and N₂ emissions reflecting overlapping effects of increased soil water content and labile C supply from residues, but had no effect on the N₂O/(N₂+N₂O) ratio. The NI DMPP was extremely effective in reducing overall N₂O and N₂ losses and also promoted complete denitrification of N₂O to environmentally benign N₂, with only 4% of total N₂O and N₂ losses emitted as N₂O. This shows that DMPP might be especially effective in reducing N₂O emissions from banded fertiliser were localized zones of high NO₃^- concentration around the fertiliser band are created that are particularly vulnerable to denitrification. Consequently, the use of DMPP in sugarcane systems with banded fertiliser does not only offer environmental benefits by reducing N₂O emissions but also substantially reduces overall denitrification losses, providing an effective strategy to improve NUE and reduce N₂O emissions for the Australian sugarcane industry.

How to cite: Scheer, C., Friedl, J., Warner, D., Rowlings, D., Wang, W., and Grace, P.: Effect of residue management and nitrification inhibitor on N2O and N2 emissions from an intensive sugarcane cropping system in sub-tropical Australia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15598, https://doi.org/10.5194/egusphere-egu23-15598, 2023.

Specific nitrification inhibitors (NIs) have been widely used to disentangle the contribution of ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB) as well as nitrite oxidizers to the nitrification process in specific environments. However, if these previously reported NIs can also be used to evaluate the activity of the newly discovered complete ammonia oxidizers (comammox) Nitrospira, remains understudied. Here we evaluated various NIs for their impact and specificity regarding inhibition of comammox Nitrospira in batch cultures of pure and mixed strains of AOA, AOB and comammox. Using these batch cultures, we observed that chlorate could specifically inhibit the ammonia oxidation and nitrite oxidation activity of comammox Nitrospira, while it had no effect on the tested AOA and AOB strains. This inhibitory effect of chlorate on comammox Nitrospira was subsequently confirmed based on ¹³CO₂-DNA-stable isotope probing (¹³C-DNA-SIP) analysis. Furthermore, by applying a set of specific NIs, the nitrification and nitrous oxide (N₂O) production rates of comammox Nitrospira in coastal wetlands were estimated as 17.45 ng N g^-1 h^-1(26.9 % of the total rate) and 0.0083 µmol^-1 L h^-1 (28.5%). Altogether, we identified and applied an effective and specific inhibitor of comammox Nitrospira, which allowed quantifying comammox activity in wetlands of the Yangtze Estuary, shedding new light on the ecological roles of comammox bacteria in coastal wetland environments.

How to cite: Han, P. and Sun, D.: Comammox Nitrospira contributed nitrification and N2O production activity in coastal wetland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17035, https://doi.org/10.5194/egusphere-egu23-17035, 2023.

Tropical forests in southern China have been suffering high level of acid rain in recent decades, which may alter soil phosphorus (P) supply capacity and thus affect ecosystem productivity. We conducted a 10-yr field experiment of simulated acid rain (SAR) to examine how acidification impacts seasonal changes of soil P fractions in a tropical forest with highly-acidic soils in south China. The results showed that SAR significantly reduced soil P bioavailability, with increased occluded P pool but reduced the other more labile P pools in the dry season. The decreased soil P bioavailability was primarily related to the repressed P desorption capacity and enhanced P sorption during soil acidification, which regulated by acid-activated soil iron/aluminum minerals and soil organic matter. However, in the wet season, SAR did not change microbial P, soluble P and labile organic P pools. Different from the decline of microbial abundance in the dry season, SAR increased ectomycorrhizal fungi and its ratio to arbuscular mycorrhiza fungi in the wet season, which significantly stimulated phosphomonoesterase activities and likely promoted the dissolution of occluded P. Our results suggest that, even in already highly-acidic soils, the acidification-induced P limitation could be alleviated by stimulating ectomycorrhizal fungi and phosphomonoesterase activities. The differential responses and microbial controls of seasonal soil P transformation revealed here should be implemented into ecosystem biogeochemical model for predicting plant productivity under future acid deposition scenarios.

How to cite: Hu, Y., Chen, J., and Deng, Q.: Mycorrhizal fungi alleviate acidification-induced phosphorus limitation: Evidence from a decade-long field experiment of simulated acid deposition in a tropical forest in south China, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2919, https://doi.org/10.5194/egusphere-egu23-2919, 2023.

How to cite: Davies, J., Janes-Bassett, V., Blackwell, M., Burgess, A., Davies, J., and Haygarth, P.: Can we account for the “missing” phosphorus in simulated low phosphorus agricultural systems?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3112, https://doi.org/10.5194/egusphere-egu23-3112, 2023.

Eutrophication of agricultural catchment streams remains a global problem despite increasingly stringent regulations. Long term, sustained release of bioavailable phosphorus (P) from legacy P stored in fluvial sediments may impact downstream water quality, hence greater understanding is required regarding P speciation dynamics and potential release mechanisms from fluvial sediments to the water column.

This study examined the dynamic P fractions, speciation and bioavailability of suspended fluvial sediments from two geologically contrasting agricultural catchment streams (Ballyboughal (BB) and Tintern Abbey (TTA)) using a combination of complimentary techniques including sequential chemical  fractionations (SCF), Dual Culture Diffusion Apparatus mesocosm experiments (DCDA), X-ray fluorescence spectroscopy (XRF) and X-ray Absorption Near-edge Structure (XANES) spectroscopy. Results from the SCF of fluvial suspended sediments pre- and post DCDA microcosm experiment’s revealed that loosely bound P (P_H2O), exchangeable P against OH^– ions (P_NaOH), and organic P (P_Org) are the major P fraction contributors to the bioavailable P fraction which would promote algal growth. Other P fractions including acid-soluble P principally associated with calcium phosphate compounds (P_HCl) and ferric bound P (P_CBD) showed relatively lower mineralisation to bioavailable P. Significantly, P K-edge XANES spectra enabled identification of seasonal and spatial P speciation dynamics and the existence of major P fractions including Fe-P and Ca-P associated mineral phases along with organic P compounds. Additionally, SCF, XRF and Ca K-edge XANES show contrasting Ca associated phases between both catchments, with calcite dominant in the BB sediments and Ca humic-complexes predominant in the TTA sediments. Contrasting Ca-P fraction transformation mechanisms of the two catchments are indicated by P redistributions in SCF and the reduction of elemental Ca amounts from XRF analysis. Calcium (Ca) K-edge XANES shows the BB catchment has a large amount of calcite while TTA was shown to contain organic Ca compounds, likely in the form of Ca-humic-complexes. This study provides a conjunctive method for future studies and validation of P speciation and bioavailability assessment associated with fluvial suspended sediments from agricultural catchments streams. The results contribute to future catchment scale sedimentary fluvial P modelling and enhanced catchment management strategies to improved water quality.

How to cite: O'Connell, D., Zhang, Q., Ferreira, D., Sandstrom, S., Goodhue, R., Gill, L., and Hu, Y.: Phosphorus Bioavailability and Speciation dynamics within fluvial suspended sediments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7187, https://doi.org/10.5194/egusphere-egu23-7187, 2023.

The evolution of land plants in terrestrial environments brought about one of the most dramatic shifts in the history of the Earth system — the birth of modern soils — and likely stimulated massive changes in marine biogeochemistry and climate. In particular, multiple marine mass extinctions characterized by widespread anoxia, including the Late Devonian mass extinction around 375 million years ago (Ma), may have been linked to terrestrial nutrient release driven by newly-rooted landscapes. Here, we use recently generated constraints from Earth’s lacustrine rock record as variable inputs in an Earth system model of the coupled C-N-P-O₂-S biogeochemical cycles in order to evaluate whether recorded changes to phosphorus fluxes would be adequate to sustain Devonian marine biogeochemical perturbations and extinction dynamics. Results show that globally scaled riverine phosphorus export during the Late Devonian mass extinction generates widespread marine anoxia and produces carbon isotope, temperature, oxygen, and carbon dioxide perturbations generally consistent with the geologic record. Similar results for a competing extinction mechanism, large scale volcanism, suggest the Late Devonian mass extinction was likely multifaceted with both land plants and volcanism as contributing factors.

How to cite: Filippelli, G., Smart, M., Gilhooly, W., Ozaki, K., Reinhard, C., Whiteside, J., and Marshall, J.: Land plant evolution and volcanism led to the Late Devonian mass extinction, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7734, https://doi.org/10.5194/egusphere-egu23-7734, 2023.

Agriculture can be a significant contributor of nutrients, such as phosphorus (P) and nitrogen (N) to surface water, increasing the risk of eutrophication. Soil frost and freeze-thaw (FT) cycles impact both the transport of nutrients through changes in the hydrologic regime of the field and the mobility/availability of nutrients through changes in the biogeochemistry of the field.  With a changing climate, changes in the frequency and duration of FT cycles are expected in regions of higher latitudes and altitudes. However, there is a knowledge gap related to the response of nutrient leaching with changing FT patterns in a changing climate.

The aim of this study was to investigate the impact of soil freezing and thawing on nutrient leaching (N, P) from an agricultural field in northern Sweden for the period 1989-2021. The FT dynamics were modelled in terms of a soil temperature profile using an explicit soil moisture and energy-based process model – the COUP, at an hourly time step. Long term environmental monitoring data of surface and drainage runoff, combined with soil temperature and soil moisture data were used for model calibration and validation. Finally, the modelled FT dynamics and measured nutrient concentrations and runoff were statistically related to each other.

Our preliminary findings confirm the importance of soil frost occurrence for the separation of surface runoff and drainage. However, no clear relationship between soil FT dynamics and nutrient loads (or concentrations) in surface or drainage water could be observed. This suggests that changes in the hydrological regime through freezing and thawing are most important for the amount and export pathways of nitrogen and phosphorous as compared to alternative mechanisms of nutrient mobilisation.

How to cite: Lackner, A., Klöffel, T., and Barron, J.: The impact of changing freeze-thaw dynamics under recent climatic changes on nutrient leaching in a Swedish agricultural field, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12271, https://doi.org/10.5194/egusphere-egu23-12271, 2023.

Human activities have contributed to significant disruptions of the phosphorus (P) cycle on Earth’s surface.  Yet, there is little information about when and how humans started to influence the global P cycle in the past. In this study, we reconstruct lake-wide P burial rates during the Holocene based on sediment-P data of 108 lakes across the globe. The results indicate the first distinct increases in lake P burial rates after the mid-late Holocene (at around 4000 years before present BP) at global scales and in Europe. Yet, different land-use histories have caused different timings of the first increases in lake P records in other regions, with ~2000 BP in China and ~550 BP in North America. We further show that global lake P-sequestration rate from ~4000 BP to 1850 Common Era (CE) has doubled compared with that in the period before 4000 BP. Since 1850 CE, the value increased ~six-fold compared with the period before 4000 BP. These findings indicate that anthropogenic activities have been affecting the global P cycle over a pre-industrial background for millennia.

How to cite: Tu, L., Moyle, M., Boyle, J., Zander, P., Huang, T., Meng, L., Huang, C., Grosjean, M., and Zhou, X.: Human-caused increases in phosphorus burials in global lake sediments during the Holocene, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12467, https://doi.org/10.5194/egusphere-egu23-12467, 2023.

In 2019 the EU Marie Sklodowska-Curie Training Network P-TRAP has been launched and is now approaching its end. The project has been targeting the diffuse flux of phosphate (P) into surface waters, i.e. the problems of understanding and controlling environmental P fluxes. P-TRAP has been aiming to develop new methods and approaches to trap P in drained agricultural areas and in the sediments of eutrophic lakes. The P-TRAP technologies have in common that they rely on the naturally strong connection between the biogeochemical cycling of P and iron (Fe). Trapping of P involved the application of Fe-containing by-products from drinking water treatment. P-TRAP aspired the ideas of a circular economy and aimed at recovering the retained P in agricultural systems and to convert it into valuable products for agricultural applications. In order to direct and support the development of the technologies, process-orientated investigations on the behaviour of P during the transformation of Fe minerals have been conducted. The poster will highlight some results from the project and will present conclusions, which can be drawn based on the current achievements.

How to cite: Behrends, T. and Walter, S.: P-TRAP – Reducing diffuse phosphorus input to surface waters, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13516, https://doi.org/10.5194/egusphere-egu23-13516, 2023.

Globally, surface water quality and ecosystem functioning are challenged by anthropogenic P inputs. While sterner legislation has led to lower external P loading, internal loading fed by legacy P accumulated in the sediment has become the controlling factor of surface water P concentrations in many European freshwater systems. Fe amendment is a treatment method to control internal P loading, but is not always successful on the long term. In Lake Terra Nova, a polymictic shallow peat lake in the Netherlands, treatment with FeCl₃ only led to a temporary decrease in sedimentary P release. Two years after treatment seasonal peaks in surface water P concentrations started to appear and have been increasing in intensity for the past 8 years. Depth-resolved solid phase analysis by sequential Fe and P extractions was combined with bulk X-ray absorption spectroscopy (XAS) at the Fe K-edge and high-resolution micro-X-ray fluorescence spectrometry (µ-XRF) and µ-XAS. At spots with distinctively high Fe contents, pyrite and silicate-bound Fe are identified by microscopic and spectroscopic analyses. The spectroscopic data, however, also point to a finely dispersed Fe species in the sediment matrix which most likely corresponds to Fe complexed by OM in the surface sediment. The correlation of the distribution of P and Fe suggests that P is bound to these Fe-OM complexes. This interpretation is supported by the sequential extraction results which showed that the Fe treatment induced a shift in the dominant P pool from Ca-bound P to Fe- and OM-bound P. Overall, the results indicate that FeCl₃ application caused a change in sediment P dynamics towards a highly redox sensitive system in which P bound to Fe-OM is released to the surface water during seasonally low bottom water oxygen concentrations. The results of this study therefore indicate that FeCl₃ may not be the ideal additive for the remediation of internal P loading in peaty water bodies due to the high affinity of Fe to OM.

How to cite: Münch, M., van Kaam, R., As, K., Peiffer, S., ter Heerdt, G., and Voegelin, A.: Fe solid phase chemistry and its effect on P retention in the sediment of a eutrophic peat lake 10 years after Fe amendment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13631, https://doi.org/10.5194/egusphere-egu23-13631, 2023.

Phosphorus (P) is an essential element for all life on Earth. Understanding P cycling is in the context of global change crucial both for modelling of global biogeochemical cycles and for agricultural productivity. Recently, concerns about the future of P fertilizer supply have prompted much research on soil P and method development. ³¹P Nuclear Magnetic Resonance (NMR) Spectroscopy has been used to analyse speciation of inorganic and of organic P species (Po), using in alkaline soil extracts¹. The region containing signals from phosphomonoesters is particularly important because these compounds are considered biologically active, but there are still significant problems to be resolved particularly for this region of P NMR spectra, including: 1. Poor signal resolution often makes quantification of Po species in this region very challenging. 2. It is unclear if observed signals are due to free P species, or originate from P compounds bound to high-molecular weight soil matter. 3. The question needs to be addressed how signals observed in alkaline extracts relate to P species that were originally present in the soil. Here we present two approaches to address these problems:

In a study of a 5000-year soil chronosequence in Northern Sweden², we found that humus P composition barely changed, although time since fire varied up to 5000 years. We will present a new method to back-calculate original Po speciation from the observed composition. Results of this method indicate absence of “recalcitrant” Po species, and instead indicate that most Po was originally present as biologically active P metabolites, probably present in live soil organisms. We will discuss implication of these findings for P biogeochemistry.

Second, we studied a diverse group of soils to address how the poorly resolved phosphomonoester region should best be analysed. Deconvolution techniques are required to handle the overlap, but a better understanding of the nature of the signals is required for reliable quantification. Based on combined analysis of 1D ³¹P NMR, 2D ¹H-³¹P NMR and ³¹P linewidth measurements, we present a strategy for quantification of phosphomonoester species, as next step in linking observed Po speciation to P bioavailability.

(1) Cade-Menun BJ, Preston CM (1996) A comparison of soil extraction procedures for 31P NMR spectroscopy. Soil Sci 161:770–785

(2) Andrea G. Vincent, Jürgen Schleucher, Reiner Giesler, David A. Wardle (2022) Soil phosphorus forms show only minor changes across a 5000‑year‑old boreal wildfire chronosequence. Biogeochemistry (2022) 159:15–32  https://doi.org/10.1007/s10533-022-00910-2

(3) Vestergren J, Vincent AG, Jansson M et al (2012) High-resolution characterization of organic phosphorus in soil extracts using 2D 1H–31P NMR correlation spectroscopy. Environ Sci Technol 46:3950–3956. https:// doi. org/ 10. 1021/ es204016h

How to cite: Schleucher, J., Haddad, L., Paneque, M., Wardle, D., Vincent, A., and Giesler, R.: Speciation of soil organic phosphorus: Steps from NMR spectra to bioavailability, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16011, https://doi.org/10.5194/egusphere-egu23-16011, 2023.

The Atacama Desert is a temperate desert restricted by the Pacific Ocean and the Andeans, which is an ideal place to study the biogeochemical phosphate-water dynamics in the conditions with extreme limited water and biomass. We hypothesized that phosphate pools and oxygen signature change along with the increasing distance to the coast and thus aridity. The surface soils (0-10 cm) were sampled along the transect with distance to coast in Paposo region (~25°S) which is located in the Coastal Cordillera nearby the Pacific Ocean from 2.3 to 22.9 km, including 9 altitude sites (600 m, 900 m, 880 m, 920 m, 1000 m, 1200 m, 1450 m, 1700 m, 2110 m). Each site involved 3 samples surrounding the plant with a distance of 0-10 cm and other 3 samples far from the plant with 1 m. The Ca-bound P (HCl-extracted P followed the Hedley sequential P fractionation) accumulated along the increasing distance to coast within 37.9 km and could be described by a mono-exponential regression mode. However, an initial declining trend was detected for phosphate ¹⁸O of HCl-P_i and it reached a steady-state condition beyond 10 km from the coastline, which was the maximum distance that advective fog could penetrate inland. Only the nearest site at 2.3 km (600 m.a.s.l) to coast showed an isotope value within the range of full isotopic equilibrium with biologically cycled phosphate. Furthermore, the effects of the present plant distribution on surface soil Hedley P stocks and phosphate ¹⁸O signatures were very limited. We concluded that both P stocks and phosphate ¹⁸O signatures followed primarily the aridity gradient but phosphate ¹⁸O signatures could work as a tracer for long-term climate conditions.

How to cite: Sun, X., Amelung, W., Tamburini, F., Klumpp, E., Morchen, R., and Bol, R.: Phosphate pools and oxygen signature in the hyper-arid Atacama Desert, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16254, https://doi.org/10.5194/egusphere-egu23-16254, 2023.

The oxidation of dissolved Fe(II) upon exfiltration of anoxic groundwaters into oxic surface waters leads to precipitation of poorly crystalline Fe(III)-solids that strongly bind phosphate (PO₄) and thereby can attenuate eutrophication. Fresh Fe(III)-precipitates may transform into more crystalline phases over time, which may lead to the release of initially co-precipitated PO₄. The formation and transformation of Fe(III)-precipitates in natural waters is strongly affected by other solutes (Ca, Mg, PO₄, silicic acid (SiO₄)) that interfere with Fe(III) precipitation and transformation, and thereby also affect PO₄ binding. Furthermore, in Ca-containing waters, the repartitioning of PO₄ released from Fe(III)-precipitates into Ca-carbonates or –phosphates, could limit PO₄ release.

For better understanding the fate of PO₄ in aquatic environments, there is a need for a mechanistic understanding of coupled Fe(III)- and Ca-precipitate formation and transformation processes induced by groundwater exfiltration, and their effects on PO₄ sequestration. In this laboratory study, we examined the effects of Ca, Mg, and SiO₄ on the formation and transformation of Fe(III)- and Ca-precipitates in bicarbonate-buffered aqueous solutions upon Fe(III)-precipitate formation by Fe (II) oxidation in the presence of PO₄, over aging periods up to 100 d. Changes in precipitate structures were probed with spectroscopic and microscopic techniques and linked to changes in the retention or release of PO₄ over time.

The results show that especially Ca and SiO₄ contribute to effective PO₄ retention via multiple interdependent processes, and thereby strongly attenuate PO₄ release over extended periods of time.

REFERENCES

Senn, A.-C.; Kaegi, R.; Hug, S. J.; Hering, J. G.; Mangold, S.; Voegelin, A., Composition and structure of Fe(III)-precipitates formed by Fe(II) oxidation in near-neutral water: Interdependent effects of phosphate, silicate and Ca. Geochim. Cosmochim. Acta 2015, 162, 220–246.

Senn, A.-C.; Kaegi, R.; Hug, S. J.; Hering, J. G.; Mangold, S.; Voegelin, A., Effect of aging on the structure and phosphate retention of Fe(III)-precipitates formed by Fe(II) oxidation in water. Geochim. Cosmochim. Acta 2017, 202, 341–360.

How to cite: Nenonen, V., Kaegi, R., Hug, S. J., Mangold, S., Göttlicher, J., Winkel, L. H. E., and Voegelin, A.: Formation and aging of Fe(III) and Ca precipitates in exfiltrating anoxic groundwater and effects on phosphate retention, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17064, https://doi.org/10.5194/egusphere-egu23-17064, 2023.

The build-up of soil phosphorus (P) in agricultural soils exceeding crop requirements can lead to diffuse P losses that could impair surface water quality. Therefore, adequate spatial information is required to develop viable tools and recommendations for sustainable P management at the local scale. Here, we present a database of nearly 8.000 samples, collected over a 12-year period in four meso-scale (~10 km²) agricultural catchments in Ireland. The agricultural area of each catchment is divided into sampling units (up to 2 ha) and soil samples are repeatedly taken from each sampling unit every 4 years. Four soil sampling campaigns were carried out to date. The results were analysed in the context of soil test P values (Morgan’s P) and classified according to the P index system as defined in the Ireland’s Nitrates Action Programme.

Overall, levels of soil test P did not show substantial changes, with the exception of the most recent sampling campaign. However, when the collected data are considered in a spatial context and accompanied with soil data and land use information, they reveal a more complex story. Notable differences in soil P trends are observed at the individual catchments scale and impacted by land use, agricultural management intensity and some soil properties across and within the catchments. Similarly to the overall soil test P trends, the total area under P index 4 soils (above optimal) decreased in the period preceding the most recent sampling campaign. The most notable decreases in P index 4 soils are found in tillage and drystock fields, but also in the catchment dominated by highly stocked dairy farms availing of a nitrate derogation.

Recent increases in soil test P and consequently areas under P index 4 may not be linked to increased organic or mineral P inputs, but rather come as a result of an overall increase in soil pH from increased lime application observed over the most recent period, which had an impact on the extractable Morgan’s P content. On-farm redistribution of fertilizer P inputs to soils with lower P index status has the potential to increase P use efficiency and decrease P loss risk to surface water.

How to cite: Zurovec, O., Hawtree, D., Leach, S., and Lynch, B.: Impact of agricultural land use and management on available soil phosphorus content in agricultural catchments of Ireland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17071, https://doi.org/10.5194/egusphere-egu23-17071, 2023.

Vivianite (Fe₃(PO₄)₂·8H₂O) has been reported to form as a secondary mineralization product during the microbial reduction of phosphate-containing Fe(III) minerals [1 – 3]. The phosphate-rich nature of vivianite makes it a suitable sink for phosphorus, which is a scarce and irreplaceable resource, and a major contributor to eutrophication in surface water bodies. There is, therefore, interest in synthesizing vivianite by Fe(III) reducing bacteria such as Geobacter sulfurreducens and Shewanella putrefaciens, to treat phosphate-rich waters, recovering the phosphate for re-use in agriculture. In this study, factors including the presence and absence of phosphate and electron shuttle, the buffer system, pH, microbial load, and the type of Fe(III)-reducing bacteria that influence the formation of vivianite under laboratory batch systems have been investigated. The rate of Fe(II) production, and its interaction with the residual Fe(III) and other oxyanions (e.g., PO₄^3-, CO₃^2-) was found to be the main driving factor for secondary mineral formation. Magnetite was formed in treatments with zero phosphates whereas vivianite and green rust were formed in treatments containing phosphate. The rate and extent of Fe(III) bioreduction were higher in Shewanella putrefaciens than in Geobacter sulfurreducens. Vivianite and green rust were both identified as the dominant endpoints in treatments with Geobacter sulfurreducens and Shewanella putrefaciens.

[1] Fredrickson, Zachara, Kennedy, Dong, Onstott, Hinman, & Li (1998). Geochimica et Cosmochimica Acta 62, 3239-3257.

[2] O’Loughlin, Boyanov, Gorski, Scherer, & Kemner (2021). Minerals 11, 149

[3] Zachara, Kukkadapu, Fredrickson, Gorby, & Smith (2002). Geomicrobiology Journal 19, 179–207. 

How to cite: Eshun, L., Coker, V., Shaw, S., and Lloyd, J.: Strategies for optimizing the scalable microbial synthesis of vivianite, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17121, https://doi.org/10.5194/egusphere-egu23-17121, 2023.

Internal phosphorus (P) loading from sediments is an important component of total P supply to the water column of many eutrophic lakes.  A long-standing paradigm states that the magnitude of internal loading through diffusion of P is limited in the presence of iron (Fe) oxides at the sediment-water-interface, due to efficient sorption and co-precipitation of P with oxide minerals. Iron-rich sediments underlying oxic water columns in shallow lake areas are thus expected to retain, rather than release P. However, recent statistical investigations have suggested that oxic epilimnetic areas of stratifying lakes may be responsible for a significant fraction of the internal P loading in these systems [1], implying a "leaky" seal of Fe oxides even under oxic conditions. Here we study the mechanisms of internal P loading in two Fe-rich eutrophic lakes in southern Finland through geochemical analysis of porewaters, over one annual cycle at five study sites per lake. Diffusive flux calculations using Fick's Law, and upscaling to whole-lake areal estimates, confirm that shallow (approx. <10 m) areas dominate internal P loading even during stratified conditions in summer. Furthermore, the highest instantaneous fluxes of the study were observed in shallow sites in late summer. The results suggest in shallow eutrophic settings with a high organic matter flux to sediments and elevated summer temperatures, remineralization reactions at the sediment-water interface regenerate P efficiently enough to escape capture by Fe oxides, even under sediment molar Fe/P ratios >20.     

[1] Tammeorg, O., Möls, T., Niemistö, J., Holmroos, H., & Horppila, J. (2017). The actual role of oxygen deficit in the linkage of the water quality and benthic phosphorus release: potential implications for lake restoration. Science of the Total Environment, 599, 732-738.

How to cite: Jilbert, T., Zhao, S., and Hermans, M.: The paradox of internal phosphorus loading from oxic areas of iron-rich eutrophic boreal lakes: insights from porewater geochemistry, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17179, https://doi.org/10.5194/egusphere-egu23-17179, 2023.

The presence of high levels of phosphorus (P) in surface waters can negatively impact the functioning of ecosystems and water quality. Despite efforts to decrease P concentrations, the accumulation of P reservoirs in sediment from past high external inputs still poses a problem. This legacy P can contribute to internal P loading, which has been shown to extent eutrophication in many freshwater systems. To effectively restore these systems, it is important to understand the geochemical processes that control the fixation and release of P in the sediment. While it is known that under anoxic conditions, P can be stored in the form of the mineral vivianite, it is not well understood if the vivianite reservoir can also act as a source of P. In a field study, mixed sediment from Lake Arendsee, Germany that naturally contained vivianite was placed in the sediment floor of the same lake, in both sulfate reduction depths and below (0-45cm). After three months, the sediment was retrieved and analyzed to investigate the effect of sulfide production on the vivianite pool. Sequential extraction and XRD analysis of the sediment solid phase showed that at shallower depths where sulfide concentrations were higher, there was a significant reduction of the vivianite reservoir and a decrease of P bound to Fe relative to S bound Fe forms. This suggests that P bound in vivianite can act as a P source in sulfidic sediment. Further research is needed to determine the extent of this phenomenon in lakes with increased sulfide production.

How to cite: van Kuppevelt, H. and Hupfer, M.: Effect of increased sulfate reduction on the stability of authigenic vivianite in lake sediment, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17209, https://doi.org/10.5194/egusphere-egu23-17209, 2023.

Tropical rainforests invest in their root systems to store soil moisture from water-rich periods for use in water-scarce periods. An inadequate root-zone soil moisture storage predisposes or forces these forest ecosystems to transition to a savanna-like state, devoid of their native structure and functions. Yet changes in soil moisture storage and its influence on the rainforest ecosystems under future climate change remain uncertain. Using a mass-balance-based (empirical) understanding of root zone storage capacity, we assess the future state of the rainforests and the forest-savanna transition risk in South America and Africa. For this, we analyse the hydroclimatic estimates of 33 Earth System Models under four different shared socioeconomic pathway scenarios (i.e., SSP1-2.6, SSP2-4.5, SSP3-7.0 and SSP5-8.5). We find that by the end of the 21^st century, nearly one-third of the total forest area will be influenced by climate change. Furthermore, beyond 1.5-2⁰C warming, ecosystem recovery reduces gradually, whereas the forest-savanna transition risk increases several folds. For Amazon, this risk can grow by about 1.5-6 times compared to its immediate lower warming scenario, whereas for Congo, this risk growth is not substantial (0.7-1.65 times). The insight from this study underscores the urgent need to limit global surface temperatures below the Paris agreement.

How to cite: Singh, C., van der Ent, R., Fetzer, I., and Wang-Erlandsson, L.: Global warming beyond 1.5–2⁰C multiplies the rainforests' tipping risk, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-95, https://doi.org/10.5194/egusphere-egu23-95, 2023.

Abstract

Growing attention has been paid to the significance of microbial metabolism for soil carbon (C) and nutrient cycle as well as their feedback effects on global warming. The estimated annual release of carbon dioxide from soil microbial respiration is 60 petagrams, and because aged native soil organic matter (SOM) has higher temperature sensitivity, the anticipated warming is expected to speed up its C release. Warming might increase litter and root exudate C inputs to hasten the decomposition of older SOM through priming effects. Microorganisms, however, have a rapid rate of growth and turnover and the new SOC formation from labile C inputs may be able to partly counteract the C losses through primed SOM decomposition. We are examining how temperature and the availability of C and nutrients affect the size and direction of priming effects. We conducted an incubation experiment on intact soil cores collected from altitudes ranging from 1500 to 3050 m a.s.l, and that were part of the Kosñipata gradient in the Peruvian Amazon. We incubated the soils for seven months, at two different temperatures to evaluate the impact of temperature, on the magnitude of priming effect caused by added ¹³C-labeled glucose, which was used as a model compound for labile root derived C inputs. At the end of the incubation, we determined the amount of ¹³C integrated into the microbial biomass and amino sugars, as well as the ¹³C remaining in bulk SOM.

Keywords 

Soil organic carbon, Priming effect, Soil respiration, Microbial residues, Elevational (altitudinal) gradient, Amazon

How to cite: Martin Vivanco, A. K., Sietiö, O.-M., Seppänen, A., Glaser, B., Uhlgren, O., Mganga, K., Kalu, S., Nottingham, A., and Karhu, K.: Is priming influenced more by in situ or incubation temperatures? Evidence from a 1500 m elevation gradient in the Amazon, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-357, https://doi.org/10.5194/egusphere-egu23-357, 2023.

How are carbon dioxide assimilation by photosynthesis and (shallow) cumulus clouds connected? What is the local interaction between rainforest evapotranspiration and cloud formation modulated by incoming regional air masses? These interrelated questions were the main drivers of the experimental campaign CloudRoots-Amazonia22 that took place at the ATTO/Campina supersites in the pristine Amazon rainforest during August 2022 (dry season). CloudRoots-Amazonia22 collected observational data to derive relationships between leaf level processes to canopy scales and connected them to the diurnal evolution of the clear to cloudy atmospheric boundary layer. At leaf level, first results indicate a diurnal asymmetry of the leaf conductance with maximum openings before midday. These observations are related to radiative energy fluxes to study the partitioning into sensible and latent heating and of plant-soil carbon dioxide exchnages. By coupling measurements of carbon and water stable isotopologues by fast laser instruments to turbulence measurements we aim to quantify flux variations related to the radiation fluctuations driven by clouds. These observations are integrated with 75 soundings of state variables and greenhouse gas profiles taken by flights below, through and above the cloud layers. We investigate what controls the transition from shallow to deep convection and the causality between the surface-cloud shear and the moisture transport at the interface between the different atmospheric layers. The observational analysis is completed with conceptual modelling and systematic large-eddy simulation experiments, which include dynamic vegetation models to advance our understanding of the diurnal energy, water and carbon cycles over the Amazon rainforest.

How to cite: Vila-Guerau de Arellano, J. and Hartogensis, O. and the CloudRoots and collaborators from Brasil and Germany: CloudRoots-Amazonia22: Integrating clouds with photosynthesis by crossing scales, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1307, https://doi.org/10.5194/egusphere-egu23-1307, 2023.

Isoprene emissions are a key component in biosphere-atmosphere interactions, and the most significant global source is the Amazon rainforest. However, intra- and inter-annual variations in biological and environmental factors that regulate isoprene emission from Amazonia are not well understood and, thereby, poorly represented in models. Here, with datasets covering several years of measurements at the Amazon Tall Tower Observatory (ATTO) in central Amazonia, Brazil, we (1) quantified canopy profiles of isoprene mixing ratios across seasons of normal and anomalous years and related them to the main drivers of isoprene emission – solar radiation, temperature, and leaf phenology; (2) evaluated the effect of leaf age on the magnitude of the isoprene emission factor (Es) from different tree species and scaled up to canopy with intra- and inter-annual leaf age distribution derived by a phenocam; and (3) adapted the leaf age algorithm from MEGAN with observed changes in Es across leaf ages. Our results showed that the variability in isoprene mixing ratios was higher between seasons (max. during the dry-to-wet transition seasons) than between years, with values from the extreme 2015 El-niño year not significantly higher than in normal years. In addition, model runs considering in-situ observations of canopy Es and the modification on the leaf age algorithm with leaf-level observations of Es presented considerable improvements in the simulated isoprene flux. This shows that MEGAN estimates of isoprene emission can be improved when biological processes are mechanistically incorporated into the model.  

How to cite: Gomes Alves, E., Aquino Santana, R., Quaresma Dias-Junior, C., Botía, S., Taylor, T., Yáñez-Serrano, A. M., Kesselmeier, J., Lembo Silveira de Assis, P. I., Martins, G., de Souza, R., Duvoisin Junior, S., Guenther, A., Gu, D., Tsokankunku, A., Sörgel, M., Nelson, B., Pinto, D., Komiya, S., Weber, B., and Martins Rosa, D. and the Cybelli Barbosa: Intra- and inter-annual changes in isoprene emission from central Amazonia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4410, https://doi.org/10.5194/egusphere-egu23-4410, 2023.

The contribution of vegetation to the South American carbon balance is critical for understanding the regional dynamics in net carbon exchange. Of particular interest is the role of the Amazon region as a sink or source of carbon to the atmosphere. Recent evidence indicate a weakening of the Amazon carbon sink, and when taking fires into account, the region represents a source of carbon to the atmosphere. In this study we use a regional atmospheric inversion system together with data from the Amazon Tall Tower Observatory (ATTO) and airborne profiles of CO₂, to constrain the Net Biome Exchange (NBE) in tropical South America. At the domain-wide scale we find that the atmospheric observations can constrain 64% of the land mass, with uncertainty reductions in most of the Amazon region, and the adjacent Cerrado and Caatinga biomes. Furthermore, we provide a sub-regional-specific analysis showing the effect of assimilating the Amazon Tall Tower Observatory CO₂ time series on the mean seasonal cycle of NBE for four areas within the Amazon, the Cerrado and the Caatinga. An emerging sink-source gradient between the Amazon region (sink) and the integrated effect of the Cerrado and Caatinga (source) is found, but the source is located in the boundaries and outside the eastern border of the legal Amazon. Optimized NBE estimates at regional and subregional scales are shown and the importance of the continuous measurements at ATTO is highlighted. Finally, we indicate the areas with a limited data constraint in our system and conclude that the observational network has to be further expanded for reducing the remaining uncertainty in top-down inverse approaches for this region.

How to cite: Botía, S., Munassar, S., Koch, T., Abdi, A. H., Basso, L. S., Komiya, S., Lavric, J., Walter, D., Gatti, L. V., Gloor, E., Miller, J., Peters, W., Rödenbeck, C., and Gerbig, C.: Top-down constraint of net carbon exchange in tropical South America, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4499, https://doi.org/10.5194/egusphere-egu23-4499, 2023.

Tropical rainforests in the Amazon play a vital role in absorbing atmospheric CO2, yet there remains a significant degree of uncertainty surrounding the process, magnitude, and potential future changes. In this study, we used outputs of Earth System Models (ESMs) to explore the impacts of dry-season precipitation changes on the terrestrial carbon cycle, with a specific focus on Gross Primary Production (GPP), which has yet to be thoroughly examined. The seasonal amplitude of GPP over the Amazon rainforests from the CMIP6 ensemble displayed significant variations among models resulting from dry-season decline, and these are much higher amplitude compared to reference data from 1981-2000. The regions with less precipitation are particularly vulnerable in the models, and this dry-season decline is anticipated to significantly intensify by the end of the 21st century due to the drying associated with global warming.

How to cite: Taguchi, T. and Ichii, K.: Analyzing the sensitivity of gross primary production to the water stress in the Amazon rainforest using CMIP6 models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6496, https://doi.org/10.5194/egusphere-egu23-6496, 2023.

Amazonian forest productivity is related to gradients in climate and soil fertility, and impacted by extreme climate events such as drought. However, interactions between soil fertility and drought in influencing regional and interannual variations in tree diameter growth are still poorly explored. To fill this gap, we used radiocarbon measurements to evaluate the variation in tree growth rates over the past decades for 30 individual trees from an important hyperdominant species, Eschweilera coriacea (Lecythidaceae). Trees were sampled from six sites in the state of Amazonas, Brazil, spanning a range of soil properties and climate. Using a linear mixed model, we show that temporal variations in mean annual diameter increment for a specific time period reflects interactions between soil fertility and SPEI drought index (Standardized Precipitation and Evapotranspiration Index). Overall differences between sites in mean tree growth, wood density and biomass production primarily reflected soil fertility, while temporal variations in growth response to drought also strongly dependence on soil fertility. Whereas drought strongly limited tree growth in fertile environments, its impact on tree growth was attenuated in poorer soils. Our results suggest that the growth response of trees to drought is strongly dependent on soil conditions, a facet of Amazon forest productivity that is still underexplored. As the Eschweilera coriacea is a hyperdominant species in the Amazon and is ranked second for highest biomass production in the basin, the pattern of tree growth in response to soil-climate interactions influences the carbon balance of the entire Amazon basin. This result has a large potential to improve predictions of how tropical tree growth affect the global carbon cycle in the face of climate change.

How to cite: Durgante, F., Higuchi, N., Ohashi, S., Householder, J. E., Wittmann, F., and Trumbore, S. and the collaborators: Soil fertility and drought stress episodes explain the variations in diameter growth of the hyperdominant Amazon tree species Eschweilera coriaceae, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9165, https://doi.org/10.5194/egusphere-egu23-9165, 2023.

For tropical forests, such as the Amazon Forest, the turbulence intensity at the forest-atmosphere interface is high since in this region there is strong convective activity during the day and the aerodynamic roughness of the forest canopy is high. Heat and other scalar properties are exchanged between the flow and the canopy. Understanding these exchange mechanisms is essential for a variety of applications in various fields of science. Furthermore, it is known that the Amazon region has a strong influence on the transport of heat and water vapor to regions located at higher latitudes and plays an important role in the carbon cycle. Measurements carried out in micrometeorological towers are crucial for the correct quantifications of the turbulent fluxes. However, the use of micrometeorological towers in the Amazon is recent. High frequency measurements (eg Eddy covariance systems) in the Amazon rainforest were usually performed at a single point, often above the forest canopy. The first analyses from the fast response data clearly showed the existence of what is now known as the roughness sublayer (RSL). In these works, it was speculated that the surface boundary layer, was higher up. Within Amazonian RSL, important discoveries have already been made, for example: (i) the Monin-Obuhkov similarity functions are not the most appropriate for estimating turbulent fluxes in the region immediately above the forest canopy. (ii) The Amazonian nocturnal boundary layer is often populated by submeso phenomena, which create episodes of intermittent turbulence and increase the complexity of exchange processes between the forest and the atmosphere during the night. (iii) Above the Amazonian RSL, it was possible to verify that there is no evidence of a classic inertial layer. Since July 2021, the ATTO (Amazon Tall Tower Observatory) tower has been performing continuous measurements, carried out by nineteen 3D-sonic installed from 5 m (inside the forest canopy) to 316 m (above the RSL). Therefore, in this work we will show the profiles of different turbulent fluxes measured since mid-2021 under different stability conditions and at different periods of the year (dry and rainy season). These new measurement profiles, with high vertical resolution, are unique and they will allow us to understand the turbulent exchange processes in regions of the Amazon planetary boundary layer that have not been previously explored.

How to cite: Dias-Junior, C. Q., Dias, N., Acevedo, O., Mortarini, L., Brondani, D., Oliveira, P., Araújo, A., Oliveira, L., Ferreira, R., Acosta, R., Takeshi, B., and Quesada, C. A.: Turbulent Fluxes Within and Above the Amazon Roughness Sublayer, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10412, https://doi.org/10.5194/egusphere-egu23-10412, 2023.

The ATTO (Amazon Tall Tower Observatory) tower is a 325m tall tower located in the middle of the pristine Amazon rainforest. Since 2022, continuous greenhouse gas concentrations at different heights (4m, 42m, 81m, 150m, 273m, 321m) are monitored by use of a Spectronus FTIR-spectrometer, measuring CO2, CH4, CO, N2O and del13CO2 hourly, compliant to WMO/GAW standards. This unique measurement system is the first set up which measures greenhouse gases continuously until 325m above a tropical rainforest, which fill an important gap in the global continous observation network. The measurements can be used for regional and global modelling, and can be used for biosphere-atmosphere exchange flux estimates. In this presentation, we will show the main observations of the first year of data collection, and will present the typical daily cycles observed for the different gases at different heights.

How to cite: van Asperen, H., Komiya, S., Jones, S., Botia, S., Lavric, J., Warneke, T., Griffith, D., and Trumbore, S.: Unique Tall Tower Greenhouse Gas Measurements in the Amazon Rainforest: observed patterns and daily cycles, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10522, https://doi.org/10.5194/egusphere-egu23-10522, 2023.

The recent development and improvement of commercially available laser-based spectrometers have expanded onsite continuous water vapor (H₂O) stable isotope composition (e.g. δ¹⁸O, δ¹⁷O and δ²H) measurements in a variety of sites across the world in the last decade. However, we still lack continuous observations in the Amazon basin region, a region that significantly influences atmospheric and hydrological cycles on local to global scales.

The Amazon Tall Tower Observatory (ATTO) site is located in well-preserved central Amazon upland rainforest. In August 2022, a commercial cavity-ring down (CRDS) analyzer (L2140-i model, Picarro, Inc., USA) was installed to continuously measure water vapor isotope compositions at four levels (79, 38, 24, and 4 m above ground) of the 80 m walk-up tower. Also, deuterium excess (hereinafter called d-excess; d-excess = δ²H–8δ¹⁸O) was assessed to trace processes that contribute to diel variation in atmospheric moisture inside and above canopy.

During the dry season, d-excess generally decreased during the nighttime, reaching minimum values at 6 am to 8 am local time (LT), followed by an increase to maximum values at 12 pm to 4 pm. The diel d-excess variation indicates that atmospheric entrainment occurred in the early morning and evapotranspiration was a dominant moisture source in the afternoon. Further results will be analyzed and discussed in the presentation.  

How to cite: Komiya, S., Jones, S., van Asperen, H., Lavric, J., Adnew, G., Moonen, R., Botia, S., Quaresma Dias-Júnior, C., Acosta Gotuzzo, R., Rodrigues Ferreira, R., Kondo, F., and Trumbore, S.: Continuous water vapor isotope measurements at the Amazon Tall Tower Observatory site during a dry season: Insights into diel atmospheric moisture sources, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10954, https://doi.org/10.5194/egusphere-egu23-10954, 2023.

Amazonia contains the most extensive tropical forests on Earth, but the role of the region as a carbon appears to be declining. Increasing deforestation, fire and climate change-associated increases in drought, threaten to push forests past a tipping point. However, forests are complex, exhibiting drought responses indicative of both resilience (photosynthetic “greening”) and vulnerability (browning and tree mortality) that are difficult to explain by climate variation alone. Still needed is a framework for understanding and predicting how different regions will respond to different kinds of future drought. Here, we combine remotely-sensed photosynthetic vegetation indices (enhanced vegetation index, EVI, corrected for sun-sensor geometry; and solar-induced chlorophyll fluorescence, SIF) with ground-based tree demography to test recent ecological hypotheses about forest drought resilience and vulnerability for different forest ecotypes across the basin, defined by their water-table depth, soil fertility and vegetation characteristics. In high-fertility southern Amazonia, drought response was importantly structured by water-table depth, with resilient greening in shallow-water-table-forests (where greater water availability heightened responsiveness to excess sunlight) contrasting with vulnerability (“browning” and excess tree mortality) over deeper water tables. Notably, shallow-water-table-forest resilience weakened as droughts lengthened. By contrast, low-fertility northern Amazonia, with slower-growing but drought-hardy trees (or tall trees, with deep-rooted water access), supported more drought-resilient forests independent of water-table depth. This work reveals a new biogeography of forest drought response that provides a framework for conservation decisions and improved prediction of heterogeneous forest responses to future climate changes, but warns that longer/more frequent droughts undermine these multiple ecohydrological strategies of Amazon forest resilience.

How to cite: Chen, S., Stark, S., Nobre, A., Cuartas, L., Amore, D., Restrepo-Coupe, N., Smith, M., Chitra-Tarak, R., Ko, H., Nelson, B., and Saleska, S.: Regional ecotypes structure biogeography of Amazon forest drought resilience and vulnerability, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11005, https://doi.org/10.5194/egusphere-egu23-11005, 2023.

Soil nutrient availability is a key constraint on tropical forest growth. On highly weathered soils, intact forests' carbon-nutrient cycles have developed over pedogenic time scales, leading to tight nutrient cycling of some depleted elements, such as phosphorus. Ecosystem nutrient recycling and plant nutrient limitation are predominant in lowland Amazonia, controlling the forests' response to disturbance and climate change. Deforestation, biomass removal, and fire lead to the loss of carbon and nutrients previously stored in vegetation, potentially enforcing nutrient limitation and reducing carbon storage in regrowing forests.   

Here, we employ the process-based terrestrial biosphere model QUINCY (Thum et al., 2019), coupled with the microbial-explicit soil model JSM (Yu et al., 2020) to simulate carbon and nutrient cycling rates at intact Amazonian forest sites, which span a natural gradient of 30 to 727 mg phosphorus g dry soil^-1, and from 2 to 81% clay. The model QUINCY-JSM accounts for dynamic plant carbon investment in growth and nutrient acquisition, and microbial-explicit growth, turnover, and nutrient cycling. We confront the ecosystems with historical changes in atmospheric CO₂ and climate, and simulate an experimental harvest of the entire forest stand to assess the consequences of that nutrient loss on the regrowing forest stand. Simulations of the Amazon forest sites are in good agreement with forest census data on vegetation carbon dynamics. Biologically-driven nutrient mineralization represents the main source of nutrients for plants, with negligible contribution of inorganic nutrient cycling in highly weathered sites. After experimental deforestation, we find that the inorganic nutrient supply is insufficient and restricts forest growth, leading to lower vegetation biomass equilibrium after deforestation. Our simulations suggest that forest degradation may occur through biomass removal in tropical forests.

Thum, T., Caldararu, S., Engel, J., Kern, M., Pallandt, M., Schnur, R., et al. (2019). A new model of the coupled carbon, nitrogen, and phosphorus cycles in the terrestrial biosphere (QUINCY v1.0; revision 1996). Geoscientific Model Development, 12(11), 4781–4802. https://doi.org/10.5194/gmd-12-4781-2019

Yu, L., Ahrens, B., Wutzler, T., Schrumpf, M., & Zaehle, S. (2020). Jena Soil Model (JSM v1.0; Revision 1934): A microbial soil organic carbon model integrated with nitrogen and phosphorus processes. Geoscientific Model Development, 13(2), 783–803. https://doi.org/10.5194/gmd-13-783-2020

How to cite: Fleischer, K., Yu, L., Fuchslueger, L., Quesada, C. A., and Zaehle, S.: Modelling soil phosphorus cycle feedbacks in old-growth and regrowing tropical forests in Amazonia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11140, https://doi.org/10.5194/egusphere-egu23-11140, 2023.

The study of forest fragmentation, the break-up of forests into smaller patches, has become increasingly important due to increases in human-induced forest clearance, with 12 million hectares of forest being lost per year and 32% of this loss being tropical. There is substantial evidence showing that edge effects can alter the ecology structure and vertical profile of remaining forests, even hundreds of meters from the forest edge.  However, implementing empirical experiments (for example in the framework of the Biological Dynamics of Forest Fragments Project (BDFFP)) to understand the effects of fragmentation on forest structural traits can be logistically and scientifically challenging and limited to smaller areas.  The use of forest models may help overcome these limitations, as they are able to quickly reproduce long-term data, as well as simulate a broad range of geographical conditions. This study aimed to reproduce the vertical distribution of plants in Amazonian forests affected by fragmentation using the forest model FORMIND. To achieve this, we optimized parameters driving plant demography and mortality, as well as their response to edge effects. FORMIND is an individual and process-based gap model suited for species rich vegetation communities, with the option of a fragmentation module. We modified processes and parameters in FORMIND to mimic the dynamics observed in the BDFFP experiment. Forest structural traits extracted from the FORMIND model output were compared with those obtained from terrestrial laser scans of the BDFFP fragments. The resulting simulations demonstrated that, after 40 years of edge effects, the optimized model was able to reproduce similar results to those observed using the terrestrial LiDAR system. Total plant area index (PAI), and PAI at varying height intervals (PAI 0-10m, PAI 10-20m, PAI 20-30m), showed consistent responses from edge effects, thus resulting in an adequate vertical plant distribution. Results demonstrate that, forest models such as FORMIND have strong potential to study the mechanisms and the impact of environmental changes on forests. Models can also expand the possibilities of in-situ studies, which are limited in time and space, when calibrated carefully with suitable in-situ data, here delivered by terrestrial LiDAR.

How to cite: Downie, E., Fischer, R., Knapp, N., Ghizoni Santos, E., Fassnacht, F., Camargo, J. L., Andrade, A., and Maeda, E.: Creating virtual forests to understand fragmentation in tropical ecosystems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11315, https://doi.org/10.5194/egusphere-egu23-11315, 2023.

Atmospheric CO₂ concentrations are still rising due to land-use change and fossil fuel burning, and have unambiguously influenced Earth’s climate system and terrestrial ecosystems. 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. For these reasons, current global climate simulations consistently predict that 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 also report on baseline measurements at the AmazonFACE site and show the progress on model development with regard to phosphorus uptake strategies.

How to cite: Anja, R. and David, L. and the AmazonFACE Team: AmazonFACE: A Free Air CO2 Enrichment Experiment in the Amazon rainforest is ready to launch, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11338, https://doi.org/10.5194/egusphere-egu23-11338, 2023.

The spatial representativeness of anemometric tower measurements and the underlying hypothesis of horizontal homogeneity of the atmospheric flows have long being questioned in the literature. Further, forest are rarely situated on uniform and flat terrain in which the horizontally homogeneity of turbulence holds. The orography around the Amazon Tall Tower Observatory (ATTO) site makes no exception. The measurement site is located on a narrow plateau SW-NE oriented, surrounded by lower hills. It is then natural to investigate the spatial variability of the turbulent field around the ATTO and the INSTANT towers to understand the role played by gentle topography. The Parallelized Large-Eddy Simulation Model (PALM) is used to simulate the atmospheric flow over the Amazon Forest and to investigate the effect of topography on the Atmospheric flow within and above the roughness sublayer. The real topography of the ATTO site is considered, while a horizontally homogeneous leaf area density (LAD) profile is assumed for the canopy over the whole area. Hence, the flow variability can be totally ascribed to spatial orography gradients. The influence of orography is assessed comparing the profiles of the turbulent kinetic energy components and fluxes evaluate over flat terrain and over the real topography at different position on the horizontal plane. The dependence of the orography influence on the wind direction is investigated considering two different wind directions.

How to cite: de Oliveira, R., Brondani, D., Mortarini, L., Giostra, U., Alves, E., Quesada, C. A., and Dias-Junior, C. Q.: Topography influence on turbulent profiles over the ATTO site, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14926, https://doi.org/10.5194/egusphere-egu23-14926, 2023.

 Atmospheric aerosol particles are essential for the formation of clouds and precipitation, thereby impacting
the global energy budget and the water cycle. However, particle production in pristine environments like the
Amazon rainforests are not yet well understood. New particle formation can occur in the outflow of high
convective clouds and be transported downward (top-down) or they may form and grow from oxidized
biogenic volatile organic compounds at low altitudes before entering the largescale vertical circulation
(bottom-up). In this study, we examine a comprehensive measurement dataset of aerosols, trace gases,
and meteorological parameters to examine new particle formation and growth in the Amazon rainforest.
The results reveal that rain events are important not only for the downdraft of particles from aloft but
also for the injection of ozone into the forest canopy. While near-ground particle enhancements by
downdrafts were modest, .another less frequent but more efficient process acted to increase sub-40 nm
particle concentrations nearly one hour after the maximum precipitation. This phenomenon occurs due to
downdrafts of ozone-rich air entering the canopy containing reactive organic species and initiating particle
production. Particularly on days when the previous night has a high ozone concentration, these particles
grow in the early morning to form cloud condensation nuclei in the early afternoon 

How to cite: Toledo Machado, L. A. and the Gabriela R. Unfer, Christopher Pohlker , Jonathan Williams, Harder Hartwig, Meinrat O. Andreae, Paulo Artaxo, Yafang Cheng, Joachim Curtius, Marco A. Franco, Micael A. Cecchini, Achim Edtbauer, Bruna Holanda, Leslie A. Kremper, Bruno B. Meller, Eva Pfanne: Rainfall-Particle Feedback in the Amazon Forest, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16898, https://doi.org/10.5194/egusphere-egu23-16898, 2023.

Aerosol particles impact health, ecosystems, and climate, especially when in high concentrations in urban environments. Wet deposition is one of the most critical limiting mechanisms of particulate matter in the atmosphere.  This mechanism captures particles inside clouds (rain-out) or below the cloud due to precipitation (washout). In the Amazon basin, the physical mechanisms and scavenging rates remain unknown in many regions. Several studies over the last decades have empirically ascertained the impact of wet deposition to develop local atmospheric models or to estimate the contribution of its effects. Here, we analyzed some of the physical and chemical properties of aerosols: nucleation mode (NU, 10-30 nm), Aitken (30-100 nm), accumulation mode (AC, 100-430 nm), total particle number (10-430 nm), Black Carbon equivalent (BCe), and chemical properties, such as organic aerosols (OA), sulfate (SO₄²⁻) and nitrate (NO₃⁻). We obtained the data set from the Intensive Observation Periods (IOPs) of the GoAmazon2014 experiment, Iranduba-AM (T2 sampling site), ~ 9 km NE of Manaus city. We conducted three analyzes from these data: (I) daily cycles on dry and rainy days; (II) scavenging rates (TS), i.e., the difference in the concentration of aerosol one hour before and the first hour of rainfall events, generally, during local thunderstorms or Mesoscale Convective Systems - MCS; and (III) scavenging coefficients (λ). We verified significant statistics decreases at both NU and AIT modes, as well SO₄²⁻ and NO₃⁻. In TS analysis, we observed a similar decline (NU: -21%, AIT: -17%, AC: -22%), contributing to an overall removal of up to -13% (on average). The soluble fractions were removed easily (OA: -21%, SO₄²⁻: -16%, and NO₃⁻: -16%) compared to insoluble fractions (BCe: -11%). In λ analysis, a substantial decrease in all size classes (NU: 2.0 × 10⁻⁴ s⁻¹, AIT: 7.8 × 10⁻⁴ s⁻¹, AC: 1.3 × 10⁻⁴ s⁻¹, CN: 5.4 × 10⁻⁴ s⁻¹) was also observed, with unexpected prominence to the AIT. We've attributed this result to introducing aerosol particles of 10-50 nm by deep convection, which may counteract the washout. Measurements of cloud properties might help confirm this hypothesis. Our preliminary findings are helpful for the local modeling of pollutant dynamics and provide evidence that wet deposition substantially removes sub-micron particles in the Amazon region. The wet deposition rates for other storms and clouds in the atmosphere, however, remain unknown.

How to cite: Cirino, G., Matheus, M., Barbosa, H., Schumacher, C., Funk, A., Brito, J., Rizzo, L., Palácios, R., Silva, S., Imbiriba, B., Lavric, J., Martin, S., and Artaxo, P.: Wet deposition of sub-micron aerosol particles in an urban area of the Amazon central, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16945, https://doi.org/10.5194/egusphere-egu23-16945, 2023.

Losses in above- and belowground biodiversity are linked to changes in land use practices and immediately affect processes in the upper soil horizons. Theoretically, these superficial changes are reversible unless a tipping point on an ecosystem level was crossed. This safety net of functional redundancy facilitates the return of vital soil functions and processes to the initial state. Little is known about how deep these changes have reached into the subsoil over time, because early warning indicators of a tipping point being about to be crossed are still sparse. This is especially important for the tropics, as soils are typically intensively weathered and nutrient depleted, therefore, plants relying largely on nutrients from below. Net nitrous oxide (N₂O) emission rates from the soil surface have proved to be valid proxies for detecting the crossing of tipping points in soil biogeochemistry. Here, we advanced this approach by looking deeply into the soil and reveal that potential greenhouse gas (GHG) production and consumption are useful proxies to estimate how deep the loss of aboveground biodiversity has already impacted soil microbial processes. We performed incubation experiments on forest and pasture soils stemming from shallow as well as 1 m deep profiles from the Peruvian Amazon Basin to determine the production and consumption potential of the GHGs at different water holding capacities. We expected pasture soils to have lost direct carbon(C)-related connections to deeper soil horizons. In forests, roots with different and greater depths also connect deeper soil layers. Therefore, in greater depth, carbon dioxide (CO₂) production declined faster under pastures than under forests because C limitations are reached sooner. In the surface, grasses are well known for their input of C and increased CO₂ production. Since old pastures are limited in nitrogen (N), almost no N₂O should be produced, possibly increasing the potential to take up N₂O. However, denitrification is a heterotrophic process also dependent on available C, therefore, the potentials of N₂O production and consumption in deeper forest soils were larger with increasing water holding capacity. These findings could indicate that losses in aboveground biodiversity due to forest conversion can have profound impacts on soil microbial processes, extending also to deeper soil layers while altering the connection of the subsoil to the top.

How to cite: Kilian Salas, S., Andrino, A., Díaz García, E., Boy, D., Horn, M. A., Boy, J., Guggenberger, G., and Jungkunst, H. F.: Forest conversion cuts off biogeochemical connections of the subsoil to the top, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17108, https://doi.org/10.5194/egusphere-egu23-17108, 2023.

Deforestation in the Amazon basin has the potential to affect regional atmospheric circulations, possibly causing changes in the moisture transport by altering the regional Hadley and Walker cells (Zhang et al.1996). Previous studies that modelled the atmosphere under different extreme deforestation scenarios have shown that deforestation in the Amazon basin could increase the length and frequency of dry seasons in the Southern Amazon, while an increase of rain is expected in the Northern Amazon (e.g. Espinoza et al., 2019; Ruiz-Vasquez et al., 2020). Beyond climate models, it is also possible to trace the effect of past deforestation on the atmosphere using a Lagrangian transport model applied on atmospheric reanalysis data. Using the FLEXPART global simulations on the ERA-5 ECMWF reanalysis dataset (1959-2022), we are able to track air parcels through time and space, making it possible to locate the origin of moisture and latent heat, and quantify how global atmospheric circulation is affected by air transport from deforested areas.

How to cite: Bakels, L., Bucci, S., and Stohl, A.: Effects of deforestation events on atmospheric dynamics using Lagrangian reanalysis data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17534, https://doi.org/10.5194/egusphere-egu23-17534, 2023.

Africa contributes significantly to the global greenhouse gases (GHG) budget through extensive land use change that is driven by rapid population growth and low human development status. As part of the REgional Carbon Cycle Assessment and Processes Phase 2 (RECCAP2) project, we developed a comprehensive GHG budget for the period 2009-2019 for Africa. We considered bottom-up process-based models, data-driven remotely sensed products, and national greenhouse gas inventories in comparison with top-down atmospheric inversions, accounting also for lateral fluxes. We incorporated emission estimates derived from novel methodologies for termites, herbivores, and fire, which are of particular importance in Africa. We further constrained global biomass change products with high-quality local observation data. During the RECCAP2 period, Africa remains a net sink for carbon. Emissions from land cover change represents the largest contribution to the African budget. However, land cover change emissions in the drier savanna regions were largely offset by increased vegetation growth in the wet tropics. Additionally, fire emissions decreased as suggested by strong reductions in burned area. Burning of fuelwood has however increased. As expected, an upward trend in anthropogenic fossil fuel emissions was evident, ascribed to an increasing demand for energy by a growing and developing population. For all the component fluxes, uncertainty and interannual variability is large, which highlights the need for increased efforts to address Africa-specific data gaps. However, for RECCAP2, we have improved our overall understanding of many of the important components of the African GHG budget that will help to inform climate policy and action.

How to cite: Ernst, Y. and Archibald, S. and the RECCAP2 Africa team: The African greenhouse gases budget: flux trends and uncertainties for the 2009-2019 period, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-606, https://doi.org/10.5194/egusphere-egu23-606, 2023.

Inland waters are important sources of the greenhouse gasses (GHGs) carbon dioxide (CO₂), methane (CH₄) and nitrous oxide (N₂O) to the atmosphere. While a growing number of global estimates of inland water GHG emissions exists, the integration of inland waters into regional GHG budgets is often hampered by the lack of adequate geo-spatial datasets. Moreover, existing estimates diverge substantially, in part due to persisting uncertainties related to the size and distribution of effective inland water surface areas.  In the framework of the 2^nd phase of the REgional Carbon Cycle Assessment and Processes (RECCAP-2) initiative, we synthesize existing estimates of GHG emissions from streams, rivers, lakes and reservoirs, and homogenize them with regard to underlying global maps of inland water surface areas and the effects of seasonal ice cover. We then produce estimates of inland water GHG emissions for 10 extensive land regions that are used for the regional land budgets of RECCAP2. According to our synthesis, global inland waters emit 5.6 (3.5-9.1) Pg CO₂ yr^-1, 101 (83-135) Tg CH₄ yr^-1 and 326 (254-592) Gg N₂O yr^-1. South American rivers contribute about one third of global inland water CO₂ emissions. North-American and Russian lakes contribute together one third of global inland water CH₄ emissions. Finally, North America alone contributes one fourth of global inland water N₂O emissions.

The global inland water emissions sum up to a global warming potential (GWP) of an equivalent emission of 13.6 (10.0-20.3) and 8.3 (5.8-12.7) Pg CO₂ yr^-1 at a 20- and 100-year horizon, respectively. At 100-year horizon, the contribution of CO₂ dominates the GWP of global inland water GHG emissions, with rivers being the largest emitters. At the 20-year horizon, on the contrary, lakes and rivers are equally important emitters, and the contributions of CH₄ to the GWP of inland water GHG emissions even exceed those of CO₂. Contributions of N₂O to the GWP appear to be less significant at both time horizons. Normalized to the area of the RECCAP-2 land regions, South America and South East Asia show the highest inland water emission rates in terms of GWP, dominated by riverine CO₂ emissions.

How to cite: Lauerwald, R., Allen, G. H., Deemer, B. R., Liu, S., Maavara, T., Raymond, P., Alcott, L., Bastviken, D., Hastie, A., Holgerson, M. A., Johnson, M. S., Lehner, B., Lin, P., Marzadri, A., Ran, L., Tian, H., Yang, X., Yao, Y., and Regnier, P.: Synthesis, homogenisation and regionalisation of inland water greenhouse gas budget estimates for the RECCAP2 initiative, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1333, https://doi.org/10.5194/egusphere-egu23-1333, 2023.

As one of the most sensitive regions to climate change on the Earth's surface, the Qinghai-Tibet Plateau is experiencing lasting warming, which has been evidenced to enhance surface carbon uptake but also could lead to carbon emission due to accelerated permafrost degradation and ecosystem respiration. Due to the difficulties of limited observations and imperfect modeling techniques, whether the Qinghai-Tibet Plateau is a carbon sink or source has been an ongoing debate. The recent satellite XCO₂ Observations could provide some useful constraints on the carbon budget in this region.  Here, based on the recent OCO-2 XCO₂ observations and the inversion results from the OCO-2 v10 MIP, we estimated the net biome carbon fluxes for the Qinghai-Tibet Plateau. Our results suggest that this region has become a carbon source (around -0.10 PgC/year) already, which is supported by an upscaling estimate with intensified eddy covariance flux measurements over China. Meanwhile, we found this carbon source signal is not detected by either in-situ CO₂ inversions or terrestrial biosphere model simulations. Currently, although some studies based on flux measurements report this region is a carbon sink and even keeps increasing recently, many others hold opposite viewpoints about it. Our result provides an important piece of evidence supporting that the Qinghai-Tibet Plateau becomes a carbon source, albeit additional evidence is needed, especially from in-situ CO₂ observations and aerial CO₂ observations (e.g., by aircraft, unmanned aerial vehicle, and AirCore). In principle, atmospheric CO₂ measurements could provide a more complete picture of the carbon budget in this region compared to discrete and limited eddy flux measurements. In the future, enhanced in-situ and aerial CO₂ observations are expected to disentangle the puzzle of this carbon budget issue in this region.

How to cite: He, W., Jiang, F., Ju, W., Wang, H., Nguyen, N. T., and Chen, J. M.: The Qinghai-Tibet Plateau may have already shifted to carbon source: Evidence from OCO-2 satellite XCO2 observations, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1609, https://doi.org/10.5194/egusphere-egu23-1609, 2023.

Global net biome production (NBP), or net land carbon uptake, has been repeatedly shown to increase during recent decades. However, whether the temporal variability and autocorrelation of NBP has changed during this period remains elusive. Answering this question is particularly relevant given that an increase in both could indicate destabilising C sinks and potentially lead to abrupt changes. We investigated the trends and controls of net land C uptake and its temporal variability and autocorrelation, from 1981 to 2018, using two atmospheric inversion models, the amplitude of the seasonal cycle of atmospheric CO₂ derived from nine monitoring stations distributed across the Pacific Ocean, and 12 dynamic global vegetation models. Spatially, we found that plant biodiversity presented a convex parabolic relationship with NBP and its temporal variability at the global scale while nitrogen deposition generally increased annual NBP. We also found that annual NBP and its interdecadal temporal variability globally increased, but temporal autocorrelation decreased. Regions characterized by increasingly variable NBP were usually with warmer and with increasingly variable temperatures, and lower and weaker trends in NBP compared to those where NBP variability did not increase, where NBP became stronger. Annual temperature increase and its increasing temporal variability were the most important drivers of declining NBP and increasingly its variability. Our results show that increasing regional NBP variability can be mostly attributed to climate change.

How to cite: Fernández-Martínez, M., Peñuelas, J., Chevallier, F., Ciais, P., Obersteiner, M., Rödenbeck, C., Sardans, J., Vicca, S., Yang, H., Sitch, S., Friedlingstein, P., Arora, V. K., Goll, D., Jain, A. K., Lombardozzi, D. L., and McGuire, P. C.: Is destabilisation risk increasing in land carbon sinks?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2813, https://doi.org/10.5194/egusphere-egu23-2813, 2023.

The Amazon is the largest continuous tropical forest in the world and plays a key role in the global carbon cycle. Human-induced disturbances (e.g., deforestation and wildfires) in combination with climate change have impacted its carbon cycling. However, uncertainties remain on the magnitude of carbon fluxes associated with human-induced disturbances and the old-growth forest sink, and thus the net land carbon balance of the Amazon. Here we synthesize state-of-the-art estimates of the land carbon flux components in the Amazon. To quantify the human-disturbance fluxes from deforestation, land use and land cover changes and degradation, we use a set of bookkeeping models. The annual intact sink was quantified using a set of 16 Dynamic Global Vegetation Models (DGVMs). We then combine the carbon flux estimates from disturbances with the intact sink estimates to provide a bottom-up estimate of the net land carbon flux and compare them alongside top-down estimates from atmospheric model inversions. Between 2010 and 2018, the net land carbon flux in the Brazilian Amazon estimated with the bottom-up approach was -59 (±160) Tg C yr^-1 and +36 (±125) Tg C yr^-1 with the top-down approach. Despite disagreeing on the sign of the flux, this analysis suggests that the Brazilian Amazon was on average near carbon neutral over the 2010-2018 period, given the large uncertainties underlying both methods. The net land carbon fluxes for the years 2019 and 2020 based on the bottom-up approach were larger than for 2010-2018. This is likely primarily due to direct emissions related to an increase in deforestation although it may possibly be partly caused by a weakening of the forest carbon sink, both in response to deforestation and a warming climate. Spatially, both methodologies agree that the south-eastern Amazon was a net carbon source over the whole study period. These results have important implications for the mitigation potential of Brazilian ecosystems within the goals of the Paris Agreement. 

How to cite: Rosan, T. M., Sitch, S., O’Sullivan, M., Wilson, C., Basso, L. S., Fawcett, D., Heinrich, V. A., Souza, J. G., von Randow, C., Mercado, L. M., Gloor, E., Gatti, L., Friedlingstein, P., Wiltshire, A., Pongratz, J., Schwingshackl, C., and Aragão, L. E. O. C. and the TRENDY-v11 Team: The contemporary Amazon Forest carbon budget, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3228, https://doi.org/10.5194/egusphere-egu23-3228, 2023.

Timely, fine-grained gridded carbon emission datasets are particularly important for global climate change research. Often, fine-grained datasets are challenging to visualize over the globe, and clear visualization tools are also needed. Therefore, we present a near-real-time global gridded daily CO₂ emissions dataset (GRACED). GRACED provides gridded CO₂ emissions at a 0.1° × 0.1° spatial resolution and 1-day temporal resolution from cement production and fossil fuel combustion over seven sectors, including power, industry, residential consumption, ground transportation, domestic aviation, international aviation, and international shipping. GRACED is prepared from the near-real-time daily national CO₂ emissions estimates (Carbon Monitor), multi-source spatial activity data and satellite NO₂ data for time variations of those spatial activity data. Here, we examined the spatial patterns of sectoral CO₂ emission changes from January 1, 2019, to December 31, 2021. In 2021, most regions showed rapid rebounds in carbon emissions compared with 2020, reflecting the continuing challenges to accelerate climate mitigation in the post-COVID era. GRACED provides the most timely and more refined overview than any other previously published datasets, which enables more accurate and timely identification of when and where fossil CO₂ emissions have rebounded and decreased as the world recovers from COVID-19 and witnesses contrasted efforts to decarbonize energy systems. Uncertainty analysis of GRACED gives a grid-level two-sigma uncertainty of value of ±19.9%, indicating the reliability of GRACED was not sacrificed for the sake of higher spatiotemporal resolution that GRACED provides. In addition, we also examined the distribution of emission in a grid-wise perspective for major emission datasets, and compared it with GRACED. The similarity in emission distribution was observed in GRACED and other datasets. One of the advantages of our dataset is that it provides worldwide near-real-time monitoring of CO₂ emissions with different fine spatial scales at the sub-national level, such as cities, thus enhancing our comprehension of spatial and temporal changes in CO₂ emissions and anthropogenic activities. With the continued extension of GRACED time series, we present crucial daily-level input to analyze CO₂ emission changes in the post-COVID era, which will ultimately facilitate and aid in designing more localized and adaptive management policies for the purpose of climate change mitigation in the post-COVID era.

How to cite: Dou, X., Liu, Z., Ciais, P., Hong, J., Chevallier, F., Wang, Y., Yan, F., Davis, S. J., Crippa, M., Janssens-Maenhout, G., Guizzardi, D., Solazzo, E., Song, X., Huo, D., Ke, P., Wang, H., and Deng, Z.: Near-real-time global gridded daily CO2 emissions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3303, https://doi.org/10.5194/egusphere-egu23-3303, 2023.

Determining the temperature dependence of wetland CH₄ and CO₂ emissions is critical for predicting the impacts of climate change on greenhouse gas (GHGs) emissions in wetland ecosystems. However, the spatial variation for temperature dependence of wetland CH₄ and CO₂ emissions is poorly understood, especially at the global scale. Here, we investigate the temperature dependencies of wetland CH₄ and CO₂ emissions across large-scale climatic gradients using 56,271 daily paired observations of ecosystem-level CH₄ and CO₂ emissions in 45 widely distributed wetlands from the FLUXNET-CH₄ database. The temperature dependencies of CH₄ and CO₂ emissions show contrasting spatial patterns across globally geographic climate gradients. Specifically, the temperature dependence of CH₄ emissions  increased with increasing mean annual temperature (MAT), but the opposite was true for that of CO₂ emissions. The ratio of CH₄ to CO₂ emissions was positively dependent on temperature when only MAT and mean annual precipitation were greater than 4.7 °C and 483 mm, respectively. Our results imply that the relative contribution of CH₄ to total GHG emissions increases with ambient temperature increases in a warmer and wetter climate region and could act as a positive feedback mechanism in the future. 

How to cite: Chen, H. and Zhou, X.: Contrasting patterns in the temperature dependence of wetland CH4 and CO2 emissions across globally geographic climate gradients, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4684, https://doi.org/10.5194/egusphere-egu23-4684, 2023.

India is primarily concerned with comprehending regional carbon source-sink response in tandem with changes in atmospheric carbon dioxide (CO₂) concentrations or human-caused anthropogenic emissions. Atmosphere CO₂ is the most significant greenhouse gas contributing to climate change and global warming. To develop a countrywide mitigation policy, it is therefore critical to identify underlying source-sink locations and their mechanisms at various temporal scales and regional levels. To better understand the variability of CO₂ and its relationship with the climate variables requires long-term observations. Recent advancements in high-resolution satellite measurements provide a viable opportunity to examine CO₂ variability at a regional level. In this work, we presented the long-term variations and growth rates of the Greenhouse Gas Observing Satellite (GOSAT) and Orbiting Carbon Observatory-2 (OCO-2) satellite retrieved column-averaged dry-air mole fraction of CO₂ (XCO₂ ) and the relationship of XCO₂ growth rate with ENSO and climate parameters (temperature, precipitation, soil moisture, and NDVI) over India for the period 2010 to 2021. Results revealed an increase of 2.54 (2.43) ppm/yr of XCO₂ in GOSAT (OCO-2) retrievals during overlapping measurement period (2015-2021). In addition, a wavelet analysis shows an increase in XCO₂ every year for GOSAT; however, OCO-2 decreases and increases in XCO₂ every 5-6 months. This is attributable to high resolutions measurements of OCO-2 favouring better capture of source (high XCO₂)-sink (low XCO₂) signal than GOSAT. The Principal Component Analysis (PCA) analysis on XCO₂ anomalies showed EOF-1 contributed mainly by the south and southeast of India. Further analysis demonstrated that the trend and seasonal cycle of XCO₂ regulates the variability. The XCO₂ growth rates strongly correlate with ENSO and NDVI (clear during major ENSO events), whereas precipitation and temperature show a weak correlation. Further, lag correlation analysis reveals that ENSO and climate parameters precede the GOSAT XCO₂ growth rates, with soil moisture, NDVI, and ENSO having a good correlation with 8,4 and 3 months of leads, respectively.

How to cite: Das, C. and Kunchala, R. K.: Understanding long-term carbon dioxide (CO2) variability and its link with ENSO and climate parameters over India using satellite retrievals, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4738, https://doi.org/10.5194/egusphere-egu23-4738, 2023.

Despite the urgent need for reduction of greenhouse gas concentrations, their emissions remain at high levels worldwide. Atmospheric inverse modelling allows to quantify these emissions by leveraging observations of greenhouse gas mole fractions and chemistry-transport models. However, this technique largely relies on models with an imperfect representation of transport and chemical processes and the resulting errors propagate to emission estimates. Atmospheric scientists can improve their models by comparing simulated processes against available observational data.

One efficient, although challenging, way of acquiring such validation data is to perform a tracer release experiment. It consists of releasing one or multiple decaying tracers into the atmosphere at one or multiple locations in the world, and then observe their time-evolving mixing ratios to understand transport pathways, mixing and decay rates. To the best of our knowledge, tracer release experiments have only been performed at local or regional scales to study transport processes, but never at the global scale. A global tracer release experiment could generate invaluable data against which to compare model outputs. However, modelers must be able to disentangle transport and chemical processes from the data, which requires that the experiment be carefully designed. Subject to this requirement being met, it could help to better quantify and even reduce 1) transport errors by investigating inter- and intra-hemispheric transport and 2) chemistry errors by constraining OH tropospheric concentrations. These data could also help to create a benchmarking methodology to highlight the strengths and weaknesses of the regional and global models that are currently used to quantify greenhouse gas emissions.

Here, we present design considerations for such a global tracer release experiment based on simulations with the 3-D chemistry-transport model ICON-ART. Our first results indicate that releasing several hundred tons of two tracers with different lifetimes as pulses could be sufficient to obtain a good estimate of OH concentrations along the parcel trajectories. This method could be applied at different locations in order to sample a large part of the world and at different times, e.g., to account for seasonal variations in OH concentrations. However, we also show that many parameters influence the results and therefore we enumerate the benefits but also the limits of such an experiment.

How to cite: Thanwerdas, J., Brunner, D., and Henne, S.: A global tracer release experiment to help estimate OH tropospheric concentrations and benchmark chemistry-transport models, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5420, https://doi.org/10.5194/egusphere-egu23-5420, 2023.

The number of in-situ CO₂ measurements in the Southern Hemisphere is very limited. This leads to large 
uncertainties in estimates of regional carbon fluxes by in-situ based inverse models. Satellite-based CO₂ 
measurements, on the other hand, are available in the Southern Hemisphere with a dense spatial 
coverage. By evaluating these, the regional carbon cycle can be studied in more detail and the results of 
carbon cycle models can be validated against the satellite data.

Here, we present a comparison of atmospheric CO₂ data provided by the Greenhouse gases Observing 
SATellite (GOSAT) and in-situ based inverse models for South America from 2009 to 2019. The seasonal 
cycle of atmospheric CO₂ concentrations measured by the GOSAT satellite shows differences in both,
amplitude and timing, compared to in-situ based atmospheric inversions. To determine the reason for
these discrepancies, we use the TM5-4DVar atmospheric inversion model assimilating GOSAT satellite 
data to obtain GOSAT based land-surface fluxes. This allows us to identify sub-regions responsible for the 
differences. In order to gain a deeper understanding of the underlying processes, we also analyse various 
climate parameters, fire emission data, and vegetation proxies (for example Solar Induced Fluorescence, 
SIF). By doing so, we aim at improving our understanding of the mechanisms that influence the seasonal 
carbon cycle in South America.

How to cite: Artelt, L., Metz, E.-M., Vardag, S., Basu, S., and Butz, A.: The seasonal cycle of atmospheric CO2 in South America over the last ten years seen by GOSAT, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6152, https://doi.org/10.5194/egusphere-egu23-6152, 2023.

Fires in the tropics are linked to both climate and land-use change. While in the Amazon, deforestation-related fires decreased following a substantial reduction in deforestation activities until 2012, there have been recent upturns in deforestation and forest fires. Furthermore, earth system models predict a further increase in the intensity of dry seasons in this region in the 21st century. Therefore, carbon emissions from drought-induced forest fires can counteract further pledged deforestation reductions in the following decades, yet they are only partially accounted for in national carbon emission estimates. Improved assessments of fire impacts, including the carbon fluxes arising from post-fire mortality and regrowth, are therefore highly important. 
Combining a range of available satellite products enables spatially specific fire emissions estimations. We developed a remote sensing based approach where biomass maps, observed forest loss, burned area and active fire data are combined to generate updated fuel load and emission estimates. In addition, space-for-time methods are employed to derive estimates of post-fire mortality as a function of pre-fire biomass. This high-resolution model guarantees an improved separation of fire types, and we can report emissions associated with deforestation, forest degradation and savanna fires for the entire Amazon basin and the Brazilian Cerrado at monthly intervals. 
Results show that over 2015-2020 fires cause annual gross emissions of ~300 Tg C over the Amazon and Cerrado. While instantaneous emissions from forest fires are small, the fire-induced mortality and subsequent decomposition cause legacy fluxes which are closer to deforestation fire emissions in magnitude, highlighting their importance. Recent upturns in deforestation fire emissions were observed, including in conservation areas established before 2004. There is overall good agreement with previous instantaneous fire emission estimates from other approaches (GFED4s, GFED 500 m) while remaining disagreements highlight areas of uncertainties, such as combustion completeness values, which could benefit from additional field measurements and spatial modelling supported by EO products.
Outputs from this work can further be used to improve regional greenhouse gas budgets and inform emission reduction and mitigation efforts.

How to cite: Fawcett, D., Ng, L., Tai, A., Yan, X., Rosan, T., Silva Junior, C., Bastos, A., Ciais, P., Albergel, C., Aragão, L., and Sitch, S.: Carbon fluxes from different fire types in the Amazon and Cerrado biomes quantified using Earth-observation based modelling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6173, https://doi.org/10.5194/egusphere-egu23-6173, 2023.

Increasing extreme events and drastic shifts in the variability, intensity and frequency of droughts, heavy precipitation and frost are predicted to accompany further climate change. It is most likely that an increasing occurrence of such events will be accompanied by soil feedback of GHG emissions, particularly of nitrous oxide (N₂O) known to be an extremely sensitive GHG. The increase in extreme events can lead to an increased occurrence of short-term emission pulses, referred to as ‘hot moments’, which can contribute significantly to the total annual N₂O emission balance.
To account for this potential feedback to the climate system, biogeochemical models driven by climate projections of multi-model ensembles (CPM) can be used to generate scenarios observing future trends in N₂O emission behavior.
Most commonly, the CPM average is used as climate input in biogeochemical models. While averaging CPM’s may provide the best overall comparison with real mean climate change, it poses the risk of ‘averaging out’ expected extreme events, thereby biasing soil-atmosphere feedbacks and future N₂O emission trends! 

We follow the hypothesis, that for nitrogen-saturated soils as common in industrialized countries, the annual N₂O emissions simulated by the averaged CPM differ from the average annual N₂O emissions simulated by the individual CPM’s, as hot moment inducing extreme climate events are averaged as well.

For our biogeochemical model simulations, we used weather data from ten selected individual climate-projections based on the multi-model ensemble of the EURO-CORDEX initiative. To focus on the effects of climate and to exclude possible biases, remaining input parameters were unified, i.e., homogeneous soil horizons and a single crop rotation were assumed. In addition, each simulation period was initialised with the same parameters to exclude possible changes in fluxes resulting from soil carbon and nitrogen cycling.

First results with CANDY and LDNDC seem to support our hypothesis, showing that annual N₂O emissions simulated with the averaged CPM differ clearly from those resulting from the output mean of the individual CPM’s.

This emphasises to consider using the averaged output based on individual CPM’s rather than relying solely on averaged CPM’s for predicting future N₂O emission trends.

How to cite: Hey, L., F. Jungkunst, H., and H. E. Meurer, K.: A potential bias using averaged climate projection multi model ensembles when forecasting nitrous oxide emissions from soils under climate change, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8208, https://doi.org/10.5194/egusphere-egu23-8208, 2023.

Methane (CH₄) levels in the atmosphere increased by 15.1 ± 0.4 ppb in 2020, the highest annual increase from 1984 to 2020, despite a likely decrease in anthropogenic CH₄ emissions during COVID-19 confinements. Here, we used bottom-up and top-down methods to quantify the changes in different sources of CH₄, and in its atmospheric sink due to the hydroxyl radical (OH) in 2020 compared to 2019. Bottom-up methods showed that, globally, total anthropogenic emissions slightly decreased by ~1.2 Tg CH₄ yr^-1, fire emissions were lower than in 2019 by ~6.5 Tg CH₄ yr^-1, and wetland emissions increased by 6.0 ± 2.3 Tg CH₄ yr^-1. In addition to higher wetland emissions in 2020 than 2019 from bottom-up, we found a decrease of 1.6–1.8% in tropospheric OH concentration relative to 2019, mainly due to lower anthropogenic NO_x emissions and associated lower free tropospheric ozone during the confinements. Based on atmospheric CH₄ observations from the surface network, and considering the decrease in OH, using top-down inversions, we infer that global net emissions increased by 6.9 ± 2.1 Tg CH₄ yr^-1 in 2020 relative to 2019, while the global CH₄ removal from reaction with OH in the atmosphere decreased in 2020 by 7.5 ± 0.8 Tg CH₄ yr^-1. Therefore, we attribute the positive growth rate anomaly of atmospheric CH₄ in 2020 relative to 2019 to lower OH sink (53 ± 10%) and higher natural emissions (47 ± 16%), mostly from wetlands. Warmer and wetter climate conditions in the Northern Hemisphere promoted wetland emissions, but fires decreased in the Southern Hemisphere, compared to the previous year. Our study highlights that northern microbial emissions of CH₄ are highly sensitive to a warmer and wetter climate and could act as a positive feedback in the future. Our study also hints that the global CH₄ pledge must be implemented by taking into account NO_x emissions trend, whose reduction lengthens the lifetime of atmospheric CH₄.

How to cite: Peng, S., Lin, X., Thompson, R., Xi, Y., Liu, G., Lan, X., Hauglustaine, D., Poulter, B., Ramonet, M., Saumois, M., Yin, Y., Zhang, Z., Zheng, B., and Ciais, P.: Why atmospheric methane surged in 2020?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8372, https://doi.org/10.5194/egusphere-egu23-8372, 2023.

Wildfires are an integral part of boreal forest dynamics. Understanding the carbon loss/recovery associated with fires is crucial to assess the stability of these slow-growing forests.  Yet, the carbon balance from fires and post-fire forest recovery remain uncertain at the biome scale due to the lack of spatial details about rates of forest regrowth. Here, we quantify carbon losses from fire emissions and gains from post-fire regrowth using high spatial-resolution satellite data and a bookkeeping model. We combined a 35-year long record of burned area from the Landsat satellites since 1985 with local biomass-age regrowth curves derived from high-resolution satellite-based above ground biomass (AGB) datasets. We found that forests in Eurasia tend to recover faster and reach higher biomass levels than those in North America. Young forests recovering from post-1985 wildfires produced a carbon sink of 652±200 TgC during the period 1985 to 2020. The additional recovery of older secondary forests that burned before 1985 further adds a cumulative sink of 1659±346 TgC. Comparatively, old-growth forests that did not burn accumulated 930±233 TgC during the period 1985-2020. This result shows 71% of the contemporary carbon sink in AGB is contributed by recovery from fires. After accounting for fire emissions each year and for the slow decay of coarse woody debris after burning, the net AGB carbon sink in boreal forests is 2108±234 TgC during 1985-2020. This study provides the first spatially explicit aboveground observation-based carbon budget of boreal forests and provides insights on the key factors that will control its future evolution.

How to cite: Xu, Y., Ciais, P., Li, W., Saatchi, S., Santoro, M., Cescatti, A., Shchepashchenko, D., He, G., Guido, C., He, J., Fan, L., Brandt, M., Fensholt, R., Wigneron, J.-P., Kay, H., Sitch, S., Bastos, A., Bowing, S., Ritter, F., and Fayad, I.: Biomass recovery after fires dominates the carbon sink of boreal forests over the last three decades, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-9695, https://doi.org/10.5194/egusphere-egu23-9695, 2023.

As a contribution to the Regional Carbon Cycle Assessment and Processes phase 2 (RECCAP2) project, we present synthesized estimates of the Arctic Ocean CO₂ uptake and their uncertainties from state-of-the-art surface ocean pCO₂-observation products, global and regional ocean biogeochemical models and atmospheric inversions. For the period of 1985−2018, the Arctic Ocean represents a net sink of CO₂ of 103 ± 19 TgC yr⁻¹ in the pCO₂ products and 92 ± 30 TgC yr⁻¹ in the ocean biogeochemical models. While the long-term mean CO₂ uptake in the Arctic Ocean is primarily caused by steady-state fluxes of natural carbon, it is enhanced 28% by the atmospheric CO₂ increase and 15% by climate change. Moreover, the climate effect in the Arctic Ocean has become more important in recent years. The CO₂ uptake peaks in late summer and early autumn, and is low in winter because the sea ice cover inhibits sea-air fluxes. The annual mean of CO₂ uptake increased due to the decreasing sea ice concentration both in the pCO₂ products and the ocean biogeochemical models. Both, the mean CO₂ uptake and the trend, is substantially weaker in the atmospheric inversions. Uncertainty across all estimates is large especially in the estimated surface ocean pCO₂ values in the East Siberian Sea and the Laptev Sea, due to scarcity of observations and missing processes in models, such as land-sea fluxes and sediment dynamics.

How to cite: Yasunaka, S., Manizza, M., Terhaar, J., Olsen, A., Yamaguchi, R., Landschützer, P., Watanabe, E., Carroll, D., Adiwira, H., Müller, J., and Hauck, J.: An assessment of sea-air CO2 flux in the Arctic Ocean from 1985 to 2018, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10462, https://doi.org/10.5194/egusphere-egu23-10462, 2023.

An increasing trend is observed in the frequency of climate extremes. Drought is a widely observed extreme event that has a significant influence on the terrestrial ecosystem functioning and carbon balance. Interannual variability in the Indian summer monsoon (ISM) rainfall, an important meteorological phenomenon providing 90 percent of the country’s annual precipitation, also significantly influences the vegetation carbon processes and carbon balance. Identifying the changes in vegetation greenness and terrestrial carbon fluxes to droughts and variability in ISM is essential for planning mitigation strategies and policy making. The main objective of this study is to identify the impact of drought and ISM variability in terrestrial biosphere carbon processes and their impact on the national carbon budget. Here we attempt a comprehensive study using different meteorological datasets available and CO​2 flux data prescribed from inversion, process-based, and LUE-based models to quantify the impact of extreme events and monsoonal variability on the ecosystem behavior and, thereby, on the atmosphere-biosphere  CO​2 exchange fluxes over the Indian region while considering prominent vegetation classes. We also use the inference from the satellite-derived  Solar Induced Fluorescence (SIF) and eddy covariance flux observations over the region. Preliminary results will be presented and discussed. 

How to cite: Ravi P, A. and K Pillai, D.: Assessing the impact of climate extremes and Indian summer monsoon variability on terrestrial biosphere carbon fluxes over Indian region using satellite observations and modeling., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10881, https://doi.org/10.5194/egusphere-egu23-10881, 2023.

Here we present a synthesis of surface ocean pCO₂ and air-sea CO₂ flux seasonality for a modern climatology and      their decadal trends between the 1980s and 2010s, as part of the REgional Carbon Cycle Assessment and Processes Phase 2 (RECCAP2) project. Working with both surface ocean pCO₂-observation products (pCO₂ products) and global ocean biogeochemistry models (GOBMs), our main findings are: (i) Over biome scales, both pCO₂ products and GOBMs confirm increases in the seasonal amplitude of pCO₂ and integrated CO₂ fluxes between 1985-1989 and 2014-2018. (ii) For the 2014-2018 climatology, GOBMs exhibit a systematic bias with too-weak biologically-driven seasonal variability in surface dissolved inorganic carbon (DIC), such that the pCO₂ seasonal cycle in subtropical biomes is spuriously large and both the amplitude and phase of seasonal pCO₂ variations diverge from those in the pCO₂ products in subpolar and circumpolar biomes. (iii) Decadal increases in pCO₂ seasonal cycle amplitude in subtropical biomes are attributed to being largely driven by reducing CO₂ buffering capacity and increasing sensitivity to temperature due to increasing anthropogenic carbon (C_ant) content insurface waters for both the pCO₂ products and GOBMs. In subpolar and circumpolar biomes, the seasonality change for GOBMs is dominated by C_ant invasion, whereas for pCO₂ products modulations of the climate state are equally important. (iv) Considered together, the subtropical biomes exhibit decadal increases in CO₂ flux seasonality that are larger during winter than summer, consistent with the mechanism described by Fassbender et al. (2022) and potentially promoting a negative feedback in the climate system by increasing the CO₂ uptake in winter, by virtue of surface winds being stronger in winter than summer. (v) Large ensemble simulations with ESMs were applied to confirm the validity of biomes as aggregation domains for identifying forced signals. Despite compromises to DIC seasonality impacting pCO₂ seasonality, the chosen biome-scale is appropriate for representing the decadal rate of increase of pCO₂ seasonality for both GOBMs  and pCO₂ products.

How to cite: Rodgers, K. and the RECCAP2 coauthors: seasonal variabiltiy in surface ocean carbon cycle: Seasonal variabiltiy of the surface ocean carbon cycle: a global synthesis, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10894, https://doi.org/10.5194/egusphere-egu23-10894, 2023.

Climate change mitigation requires – besides greenhouse gas emission reductions – actions to increase carbon sinks and storages in terrestrial ecosystems. However, quantification of sources and sinks of carbon depends on reliable estimates of the net ecosystem exchange of carbon dioxide (CO₂). This also involves the eddy covariance technique (EC), a key method to directly measure the CO₂ fluxes between ecosystems and the atmosphere. Various methods have been used to impute, or gap-fill, missing EC data and previous comparisons have shown that the accuracy of the best-performing methods, e.g. the widely-used marginal distribution sampling (MDS), is reaching the noise limit of measurements. However, knowledge on the performance of gap-filling methods is lacking from northern ecosystems.

By analyzing an extensive global data set, we show that MDS causes significant carbon balance errors for northern ecosystems. MDS systematically overestimates the carbon dioxide (CO₂) emissions of carbon sources and underestimates the CO₂ sequestration of carbon sinks. We discuss reasons for the errors and show how a machine learning method called extreme gradient boosting or a modified version of MDS can be used to minimize the northern site bias.

How to cite: Vekuri, H., Tuovinen, J.-P., Kulmala, L., Papale, D., Kolari, P., Aurela, M., Liski, J., Laurila, T., and Lohila, A.: A new gap-filling method to avoid systematic bias in carbon balance estimates in northern ecosystems, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11163, https://doi.org/10.5194/egusphere-egu23-11163, 2023.

Methane (CH₄) has a relatively long tropospheric lifetime and is consequently a well-mixed greenhouse gas. CH₄, released by several
types of human activity and natural processes, is one important driver of climate change. The global mean concentration of CH₄ has
increased by 156% between the beginning of the industrial revolution around 1750 and 2019, reaching roughly 1866 ppb in 2019 (IPCC).
The time dependence of this increase is not well understood. For example, it is not entirely clear why CH₄ growth rates reached record 
high values in 2020 and 2021. Furthermore, the number of published growth rates (annual methane increases) is limited and includes data
from NOAA and the Copernicus Climate Change Service. Hence the rate of increase of CH₄ calculated from independent data sources are
valuable for cross-verification and in furthering our understanding of the methane cycle.
The TROPOMI instrument onboard the Sentinel-5P satellite provides daily CH₄ data with a spatial resolution of roughly 7x7 km²
and global coverage. We analyze the TROPOMI CH₄ data with the goal of determining robust values of the annual methane increases (AMI)
for both global and zonally resolved data. For this we utilize a dynamic linear model approach to separate the underlying methane level,
the seasonal and short-term variations. The AMIs are defined as the difference in the underlying (i.e. fitted) methane level between
the first and last day of a year. In this contribution, we present first results for global and zonal TROPOMI AMIs for the years 2019-2022.
We compare the resulting global TROPOMI AMIs with data from NOAA and Copernicus and discuss the distribution of zonal AMIs for the given years.

How to cite: Hachmeister, J., Schneising, O., Buchwitz, M., Burrows, J. P., Notholt, J., and Buschmann, M.: Recent methane trends derived from S5P/TROPOMI data, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11303, https://doi.org/10.5194/egusphere-egu23-11303, 2023.

In Australia, increasing temperatures and prolonged drought periods lead to an intensification of wildfires. In particular, severe fires are expected to occur more frequently in Southeast Australia’s eucalyptus forests leading to strongly enhanced CO₂ emissions and preventing the renewed uptake of the released CO₂ by vegetation. However, current fire emission estimates presented by conventional fire emission databases show significant discrepancies in their emission estimates of extreme fire events like the Australian fire season 2019/2020.

Here, we investigate the fire emissions released during the Australian summer 2019/2020 based on total column measurements of CO₂ and CO using the Lagrangian Particle Dispersion Model FLEXPART. We calculate footprints and backward trajectories of trace gases to inversely retrieve carbon emission estimates. In a first case study we focus on TCCON total column measurements of CO and CO₂ taken in Wollongong located close to the hot-spot of eucalyptus fires. As the measurements show a significant enhancement of all mentioned tracers during the fire event, FLEXPART is used to calculate emission estimates for southeast Australia. Furthermore, we retrieve emission factors between the trace gases. Our results are compared to the conventional databases like GFED, GFAS and FINN and emission estimates published by other studies.

How to cite: Dillerup, I., Lüken-Winkels, C., Metz, E.-M., Vardag, S., Deutscher, N., Griffith, D., and Butz, A.: Fire emission estimates for Australian extreme fire season 2019/2020 using FLEXPART , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12203, https://doi.org/10.5194/egusphere-egu23-12203, 2023.

The growth rate of atmospheric CO₂ mole fractions can be measured with high accuracy, but there are still large uncertainties in our ability to separate anthropogenic and natural sources and sinks. One major source of uncertainty is the net flux of carbon from the biosphere to the atmosphere, or Net Ecosystem Exchange (NEE). There are two major approaches to quantifying NEE; top-down approaches that typically use atmospheric inversions, and bottom-up estimates using process-based or data-driven terrestrial biosphere models, upscaled to the regional or global scale. Both approaches have known limitations. A system that harmonizes these approaches, providing a high-quality estimate of the spatial distribution of NEE, and an accurate integral of NEE at regional and global scales, would improve our ability to model the full carbon budget. With other component fluxes, a harmonized product could help improve our monitoring of regional and national greenhouse gas budgets, and thus verify the trajectory towards CO₂ emission goals.

This study builds upon our previous work that connected the bottom-up eddy-covariance model to top-down estimates of regional NEE from atmospheric inversions using fixed regional linear oper-ators. That work demonstrated that top-down estimates of atmospheric CO₂ provide an important additional constraint to a data-driven bottom up model. The use of top-down constraints improved the regional and global upscaling of NEE, leveraging the strengths of the two different approaches. However, the previous work had a simplified computational link between the top-down and bottom-up fluxes of NEE, and did not access the very large volume of atmospheric observations of atmospheric CO₂. Here, we replace the regional atmospheric inversion estimates of NEE with direct observations of the atmospheric mole fractions of CO₂. The fixed regional linear operators are replaced by estimating the near-field sources of an observation using an atmospheric transport model. For training, the bottom-up model is run for the source locations. We apply this technique to observations from to tropical, extra-tropical and boreal tall-tower sites over different meteorological conditions where we infer NEE from the observed atmospheric mole fraction, corrected for CO₂ background and non-biogenic CO₂ fluxes. This inference is combined in the objective function with tower-level inferences, and directly used to update the bottom-up model. The model can ‘see’ more varied inputs in the dynamic footprints, and the size of our pool of training data is increased. The new process improves our ability to accurately infer the regional and global distribution of NEE by directly learning across spatial scales, using diverse observations of CO₂.

How to cite: Upton, S., Peters, W., Reichstein, M., Botia, S., Gans, F., Kraft, B., and Bastos, A.: Constraining land surface CO2 fluxes by ecosystem and atmospheric observations using atmospheric transport, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12424, https://doi.org/10.5194/egusphere-egu23-12424, 2023.

Keeping global warming in line with the Paris Agreement requires rapid reductions in CO₂ emissions. Tracking these reductions demands a thorough bookkeeping of natural and anthropogenic carbon fluxes. The second REgional Carbon Cycle Assessment and Processes (RECCAP2) activity of the Global Carbon Project aims to accurately assess land and ocean CO₂ sources and sinks through the efforts of hundreds of scientists around the globe. 

For the ocean component, regional budgets are developed for the global ocean and five large regions for the period 1980-2018. In addition, four ‘special focus’ themes, namely the biological carbon pump, the seasonal cycle, the coastal ocean and model evaluation are addressed. We use state-of-the-art ocean models and observation-based datasets to provide robust estimates of regional CO₂ budgets and constrain their uncertainties. Here, we will provide an overview of RECCAP2 activities, and showcase key results focusing on mean ocean carbon fluxes, and their trends and variability.

How to cite: Hauck, J., Gruber, N., Ishii, M., and Müller, J. D. and the RECCAP2 ocean chapter leads: Constraining regional and global ocean carbon fluxes in RECCAP2, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12786, https://doi.org/10.5194/egusphere-egu23-12786, 2023.

Tropical ecosystems play an important role in regulating the global carbon balance. Existing studies have extensively analyzed the carbon dynamics of tropical forests, the largest terrestrial component of the global carbon budget, showing a likely neutral contribution of tropical forests to the global carbon cycle. However, high-resolution dynamics of aboveground carbon (AGC) change of the whole tropical terrestrial ecosystem and its processes remain rarely investigated. In this study, we first used low-frequency L-band passive microwave observations to derive wall-to-wall maps of annual AGC stocks over the tropics at 25-km spatial resolution. Using high-resolution satellite observations of land-cover change and biomass maps and random forest models, we separated the AGC stock into various ecosystems, including forest, shrub, and short-vegetation (grass and crop), and attributed the change to different degradation processes such as fires and deforestation at 100-m resolution. Our preliminary results show that total AGC stocks in tropical ecosystems increased by  +2.25 [+1.19,+3.29] PgC (the range represents the minimum and maximums of the multiple estimates) from 2010 to 2020. The coast of Brazilian Mata Atlantica, Central African Republic, and east Tanzania are the hotspots of net increase, while the Arc of Deforestation in the Amazon basin and the Congo Basin show substantial net losses. Gross losses from non-fire deforestation and fire totaled -1.62 [-1.38,-1.86] PgC yr^-1. We also observed strong recovery in African burned regions, possibly due to post-fire regrowth and additional recovery resulting from declining fires in the region. Our results highlight the importance of explicit temporal and spatial mapping of tropical carbon dynamics at high resolution, which can help us better understand the role of tropical terrestrial ecosystems in the global carbon cycle.

How to cite: Feng, Y., Ciais, P., Xu, Y., Wigneron, J.-P., Li, X., and Fan, L.: High-resolution quantification of aboveground carbon change over the tropics, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12963, https://doi.org/10.5194/egusphere-egu23-12963, 2023.

The dynamic and thermohaline characteristics of the Atlantic Ocean linked to the Atlantic Meridional Overturning Circulation (AMOC) give it a specific role in the accumulation of heat and CO₂, either of natural or anthropogenic origin (Cant), from the surface layer to the deep waters, significantly mitigating the impacts of anthropogenic climate change. Here, we evaluate the annual mean, long-term trends, seasonal cycle and interannual variability of net sea-air CO₂ fluxes (FCO₂) between 1985 and 2018 based on observation products (pCO₂-products) and global ocean biogeochemical models (GOBMs) for the Atlantic from 30ºS to the Nordic Seas (~79ºN) and the Mediterranean. The mean contemporary FCO₂ (sum of anthropogenic and natural components) is estimated to be 0.362 ± 0.067 and 0.47 ± 0.15 Pg C yr^-1 using pCO₂-products and GOBMs, respectively. The GOBMs show consistent growth trends in CO₂ uptake with rates similar to the atmospheric CO₂ growth, however trends obtained from CO₂-products show a sharp increase from the pre-2000 period to the post-2000 period. There is overall agreement between pCO₂-products and GOBMs results for mean values, seasonal cycle and interannual variability in all biomes, except for the North Atlantic subpolar biome, where pCO₂-products show lower mean values, larger trends, and a different seasonal cycle than GOBMs. The GOBMs and pCO₂-products show very concordant values in equatorial and subtropical regions, where CO₂ variability is strongly determined by temperature. For the period 1994-2007, GOBMs show concordant values in annual Cant storage rate with carbonate marine system observations (Gruber et al., 2019) with values of 0.506 ± 0.106 Pg C yr^-1 vs 0.673 ± 0.066 Pg C yr^-1, respectively. The Cant storage rate agreement between GOBMs and observations are also registered in the different biomes, although in both permanently stratified subtropical in North and South Atlantic biomes, the storage rates in GOBMs show a larger spread with their mean values 30 and 40% lower than those estimated from observations. In general, the Atlantic accumulates more Cant than that inferred from the cumulative FCO₂ changes, partly due to a significant lateral Cant transport from the Southern Ocean (about 30%).

How to cite: Perez, F. F., Gehlen, M., Tjiputra, J., Olsen, A., Becker, M., Lopez-Mozos, M., Müller, J. D., Goris, N., and Hauck, J.: An assessment of CO2 storage and sea-air fluxes for the Atlantic Ocean and Mediterranean Sea between 1985 and 2018 , EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13759, https://doi.org/10.5194/egusphere-egu23-13759, 2023.

Land-based mitigation is essential in reducing carbon emissions. Yet, the attribution of land carbon fluxes to their sinks and sources remains highly uncertain, in particular for the forest-rich but data-poor region of Eastern Europe. Here we integrate various data sources (from top-down and bottom-up modelling, earth observation, inventories) to show that Eastern Europe accounted for an annual aboveground biomass (AGB) carbon sink of ~0.49 GtC in 2010‑2019, or about 75% of the entire European carbon uptake. However, we find that the land-based carbon sink is declining. This declining trend is mainly driven by changes in land use and land management, but also by increasing natural disturbances due to ongoing climate change. Despite the high overall importance of environmental factors such as soil moisture, nitrogen and CO₂ for enhancing the land-based carbon sink, we find indicators of a saturation effect of the regrowth in abandoned former agricultural areas, combined with an increase in wood harvest, particularly in European Russia. Our results contribute to a better understanding of the regional carbon budget of Eastern Europe and its trend. This study sheds light on land use and management as drivers of the land-based carbon sink and their role for climate mitigation.

How to cite: Winkler, K., Yang, H., Ganzenmüller, R., Fuchs, R., Ceccherini, G., Duveiller, G., Grassi, G., Pongratz, J., Bastos, A., Shvidenko, A., Araza, A., Herold, M., and Ciais, P.: Impacts of land use and environmental change on the Eastern European land carbon sink, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13792, https://doi.org/10.5194/egusphere-egu23-13792, 2023.

The global atmospheric CH₄ growth rate stagnated between 2000 and 2007, and has continued to grow since 2007. This renewed CH₄ rise has been analysed with respect to a 2007 onward decline in  δ¹³C(CH₄), indicating changes in the relative contribution of CH₄ sources. However, this is still subject to debate and a variety of hypotheses have been put forward. In our work, we present numerical sensitivity simulations that investigate the impact of different inventories of methane emission fluxes on the globally averaged δ¹³C(CH₄) signature. We apply the state-of-the-art global chemistry-climate model EMAC and use a simplified approach to simulate methane loss. We include methane isotopologues and take the kinetic isotope effects in physical and chemical processes into account. We further consider regional differences in the isotopic signatures of individual emission source categories, such as, for example, the differences between signatures of tropical and boreal wetlands emissions. Based on recent emission inventories and isotopic source signatures from the literature, our chemistry climate model reproduces the actual atmospheric methane and δ¹³C(CH₄) distribution adequately. We show that our setup is suitable to constrain the individual influence of different CH₄ sources on the global average δ¹³C(CH₄). We further present an approach to optimize the global methane level with respect to station measurements probing for a strategy to include the isotopic information into such an optimization process.

How to cite: Nickl, A.-L., Winterstein, F., and Jöckel, P.: Numerical simulation of the atmospheric CH4 increase and the corresponding decrease of δ13C(CH4) after 2007, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14171, https://doi.org/10.5194/egusphere-egu23-14171, 2023.

Accurate national carbon budget assessments allow nations to evaluate their progress in cutting carbon emissions and therefore be aligned with the Paris Climate Agreement goals. To support the initiative of The REgional Carbon Cycle Assessment and Processes (RECCAP-2), we built a synthesis of the Australasia (Australia and New Zealand) terrestrial carbon budget for 2010-2019 based on top-down and bottom-up approaches. Major carbon flux components in the bottom-up budget (e.g., net primary productivity and heterotrophic respiration) were simulated by CABLE model, Biome-BGC model and Cewn simulations. In addition, this budget include carbon flux components from the land-ocean aquatic continuum, such as inland waters, estuaries, blue carbon ecosystems, and continental shelves and carbon fluxes embodied in trade (export and import) of crops, woods, livestock and fossil fuel. We reconciled Australia and New Zealand bottom-up budgets separately with fluxes derived from regional and global OCO-2, GOSAT flux inversions, as well as fluxes obtained from in-situ measurement only (CarbonWatchNZ). We found that annual mean budgets for Australia agree relatively well (within the uncertainty range) with regional and global top-down GOSAT and OCO-2 flux estimates. New Zealand's annual bottom-up carbon budget also agrees relatively well with fluxes derived from CarbonWatchNZ inversion and GOSAT but disagrees with global flux estimates from OCO-2.

How to cite: Villalobos, Y., Canadell, P., Briggs, P., Harman, I., Keller, E. D., Bukosa, B., Mikaloff-Fletcher, S. E., Smith, B., Kirschbaum, M. UF., Giltrap, D., Liang, L., Lauerwald, R., Rosentreter, J., Maavara, T., Resplandy, L., Rayner, P. J., Schöemann, E., and Basu, S.: A comprehensive synthesis of anthropogenic and natural sources and sinks of Australasia carbon budget (2010-2019), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15006, https://doi.org/10.5194/egusphere-egu23-15006, 2023.

Around 31% of carbon dioxide derived from human activities (C_anth) has been absorbed by the ocean (DeVries, 2014; Gruber et al., 2019; Sabine et al., 2004). This accumulation helps to mitigate atmospheric carbon dioxide (CO₂), but in turn leads to severe consequences on marine systems (IGBP, IOC, SCOR, 2013). Both components of CO₂, i.e. anthropogenic and natural, present high variability and uncertainties difficult to observe and quantify. In particular, the C_anth signal represents a small fraction of the total dissolved inorganic carbon pool (C_T) and it is not directly distinguishable from the natural component, resulting in the emergence of back-calculation techniques (Brewer 1978; Chen and Millero, 1979) to derive it indirectly. Over the years, back-calculation techniques have undergone remarkable improvements (Gruber et al., 1996; Sabine et al., 2004; Touratier et al., 2004, 2007; Vázquez-Rodríguez et al., 2009a, 2009b, 2012), resulting in different methods for estimating C_anth that, despite providing helpful and advanced results, show various biases and limitations. Here, we present a new approach for estimating C_anth that relies on a back-calculation methodology, purely based on carbon data, and provides results that show good agreement with previous global C_anth climatologies. Our approach mainly differs from previous methodologies by pioneering using the transport matrix output from a data‐assimilating ocean circulation inverse model (TMI: Total Matrix Intercomparison; Gebbie and Huybers, 2010) to obtain preformed properties, instead of the historical use of Optimum Multiparameter analysis (OMP). This improvement prevents from the need to use (sub)surface-property linear regressions to estimate preformed alkalinity or air-sea CO₂ disequilibrium, and allows introducing different corrections for denitrification and, as a novelty, oxygen disequilibrium.

How to cite: López-Mozos, M., Pérez, F. F., Carracedo, L. I., Gebbie, G., and Velo, A.: A new approach for estimating anthropogenic carbon relying on an observational back-calculation method, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15146, https://doi.org/10.5194/egusphere-egu23-15146, 2023.

The oceanic uptake and release of carbon dioxide (CO₂) play a critical role in global carbon cycle since oceans can act both as sink and source of CO₂ which vary spatially and temporally. The ocean primary productivity has significant effects on the CO₂ flux, as it consumes the dissolved CO₂ at the sea surface for the photosynthetic carbon production, reducing the surface carbon content, while higher production rates at surface layers cause higher respiration rates in the subsurface layers, thereby increasing the sea water CO₂ partial pressures (pCO₂) in these layers. Northern Indian Ocean is found to be a perennial source of CO₂ and also one of the most productive regions of Indian Ocean, however, while the western sub basin acts as an annual source, the eastern counterpart is a seasonal sink, especially during the monsoon and winter seasons. The major factors contributing to its high productivity is the summer and winter blooms caused by the wind-driven upwelling and winter cooling as well as convective mixing. The present study attempts to understand the relation between the CO₂ fluxes and primary productivity in the western and eastern sub basins of the northern Indian Ocean. The study divides the Sea in to North, West, East and Central parts based on the productivity and analyses the spatial and temporal variation of the CO₂ exchange between the sea and atmosphere in connection with the primary production. Satellite as well as climatological data were used to derive the monthly CO₂ fluxes and ocean primary productivity. Both sub basins exhibited high rates of productivity during the monsoon and winter seasons; high monsoon and winter CO₂ outfluxes were observed over the western sub basin in the northern waters towards the coast, while the eastern basin was found to have strong influxes in both the seasons over the northern waters. Towards the open ocean part, both fluxes and productivity showed decreasing trends in the western basin, whereas, the eastern sub basin showed an increasing trend of CO₂ outflux over the open ocean waters in the south. Surface stratification and limited nutrient availability have resulted in the low productivity rates during the pre- and post-monsoon seasons in both basins, while the absence of the surface mixing resulting from the stratification along with photosynthetic consumption lowered the fluxes. The primary production was observed to have a significant influence over the western basin fluxes while the fluxes over the eastern basin were primarily affected by the physical forcing i.e., the thermohaline stratification.

How to cite: Krishna, L., Bharti, R., and Mahanta, C.: Significance of biological forcing on the spatio-temporal variability of carbon dioxide fluxes over the Northern Indian Ocean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15166, https://doi.org/10.5194/egusphere-egu23-15166, 2023.

This contribution presents a new view of the global carbon cycle which accounts for the land-to-ocean transport of carbon through inland waters, estuaries, tidal wetlands and continental shelf waters—the ‘land-to-ocean aquatic continuum’ (LOAC). We highlight how biogeochemical and ecological processes from land-to-ocean have been perturbed by human interventions, including atmospheric composition change, climate change and land-use change. The extend to which these anthropogenic perturbations have altered regional and global CO₂ budgets and trends along the LOAC are also presented and the knowledge gaps that are key to reduce uncertainties in future assessments of LOAC fluxes are identified. Finally, broader implications regarding the quantification of the terrestrial and open ocean sinks of anthropogenic carbon are briefly discussed 

How to cite: Regnier, P., Resplandy, L., Rosentreter, J., Najjar, R., and Ciais, P.: The land-to-ocean loops of the global carbon cycle: How much do we know about long-term trends and drivers of changes in CO2 fluxes ?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16001, https://doi.org/10.5194/egusphere-egu23-16001, 2023.

The use of δ²H as well as δ¹³C methane isotope measurements will help improve regional and global source apportionment and understanding of reasons for methane’s continued and accelerating growth. However more data on regional variability in isotopic signatures of the main sources is required as well as regular measurements of both isotopes in methane in background air.

Field campaigns across Canada in June 2022 and to northern Finland and Norway in August 2022 were carried out to collect air samples for methane δ¹³C and δ²H isotopic characterisation from boreal wetlands.

In Finland and Norway a road campaign with continuous measurements of methane mole fraction was carried out from Södankyla, Finland to Aidejavri, Norway, with a generally decreasing gradient in methane from south to north and this has been compared with land cover maps. Air samples for isotopic analysis were collected at Södankyla, Kaamanen and Lompolojänkkä fens in Finland and Aidejavri and Suossjavri degrading palsa mires in Norway. In Canada δ²H and δ¹³C isotopic signatures were determined in methane emitted by wetlands in northern Ontario including at Fraserdale, and northern Saskatchewan (East Trout Lake).

Overall the mean signatures of emissions from the boreal samples collected were -67‰ for δ¹³C and -320‰ for δ²H, but there was significant local variability when sampling air close to ground level. Aircraft campaigns would be a better way of identifying the integrated isotopic signature of regional wetland emissions (as demonstrated previously for δ¹³C signatures across northern European wetlands). Weekly sampling for methane δ¹³C and δ²H was started at Pallas Sammaltunturi in northern Finland in August 2022. These data will be used to identify the regional source signature of emissions.

How to cite: Fisher, R., Woolley Maisch, C., Lowry, D., France, J., Rockmann, T., van der Veen, C., Fowler, C. M. R., and Nisbet, E. G.: Measurement of the isotopic signature of boreal wetland methane emissions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16482, https://doi.org/10.5194/egusphere-egu23-16482, 2023.

The RECCAP2 global ocean project provides an assessment of the mean, trends, and variability of the global ocean carbon sink for the period 1985-2018. The analysis is based on a comprehensive assessment of models and observation-based products, including global ocean biogeochemical models (GOBMs), pCO₂ observation-based air-sea CO₂ flux products, ocean data assimilation models, and DIC-observation based products. We find that the mean ocean CO₂ sink from 1985-2018 is -1.7±0.3 PgC yr^-1 as diagnosed by pCO₂-observation based air-sea CO₂ flux products. The dominant component of the global air-sea CO₂ flux is the oceanic uptake of anthropogenic CO₂, which is estimated at between -2.0 to -2.6 PgC yr^-1 using a range of GOBMs, assimilation models and DIC-based products. The second largest component of the global air-sea CO₂ flux is the outgassing of terrestrially-derived CO₂, which is estimated at 0.65±0.3 PgC yr^-1 but is not yet fully resolved by RECCAP2 models. The trend in the global air-sea CO₂ flux from 1985-2018 ranges from -0.26 PgC yr^-1 decade^-1 in the GOBMs to -0.39 PgC yr^-1 decade^-1 in the pCO₂ products. Over the 2001-2018 period, when the pCO₂-based estimates benefit from improved data coverage, they predict a strengthening trend in the ocean carbon sink of -0.63 PgC yr^-1 decade^-1. This is driven primarily by the trend in anthropogenic carbon uptake of -0.41 PgC yr^-1 decade^-1, and secondarily by a climate-forced trend of -0.28 PgC yr^-1 decade^-1. This climate-forced strengthening of the ocean carbon sink since 2001 is not diagnosed in the GOBMs, and the reasons for this trend remain unclear. We find that the interannual to decadal variability of the global carbon sink is mainly driven by climate variability, with the climate-driven variability exceeding the CO₂-forced variability by 2-3 times. GOBMs suggest that the climate-driven variability is about 4-8% of the global mean carbon sink, while the climate-driven variability is about 9-14% of the global mean flux in the observation-based pCO₂ products. In all, the RECCAP2 analysis provides a state-of-the-art summary of our current knowledge of the ocean carbon sink, and the mechanisms driving its magnitude, trends, and variability over time.

How to cite: DeVries, T., Yamamoto, K., and Wanninkhof, R. and the RECCAP2 Global Ocean Team: Magnitude, trends, and variability of the global ocean carbon sink from 1985-2018, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16842, https://doi.org/10.5194/egusphere-egu23-16842, 2023.

Understanding climate change and possible solutions to recent increases in concentrations of major GHG concentrations dependent upon quantifying the emission inventory of these gases. The objective of this study, which is part of the Regional Carbon Cycle Assessment and Processes-2 (RECCAP2) project, is to estimate the country-specific GHGs budget (sources and sinks) for the South Asia (SA) region for the 2010s. The region comprises seven countries: Afghanistan, Bangladesh, Bhutan, India, Nepal, Pakistan, and Sri Lanka. Each country in the region is experiencing rapid changes due to the continuous development of agriculture, deforestation, reforestation, afforestation, and the increased demand for land for people to live in. In this study, we synthesize top-down (TD) and bottom-up (BU) model results and ground-based and other data sets to estimate the GHG emissions for carbon dioxide (CO2), methane (CH4), and nitrous oxide (N2O) due to anthropogenic and natural biospheric activities. Major contributing factors include net biome productivity, fossil fuel emissions, inland waters, and wetland and wet/dry soils. Our study shows that the SA region was the net source of atmospheric CO2 for the 2010s. BU estimates for CO2, CH4, and N2O emissions were 1974, 1047, and 715 Tg CO2eq, and TD estimates were 2010, 1247, and 799 Tg CO2 eq. The total GHG emission for the region based on BP and TD were 3736 and 4056 Tg CO2 eq. Among SA countries, India was the most significant contributor to the total GHG emission.

How to cite: Jain, A., Anand, J., Chandra, N., and Patra, P.: Greenhouse gas budget for South Asia region, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-16920, https://doi.org/10.5194/egusphere-egu23-16920, 2023.

Cool temperatures, vigorous overturning circulation, and high biological productivity make the Southern Ocean a key region for the air-sea CO₂ exchanges. It is also the main gateway for anthropogenic CO₂ into the ocean owing to the upwelling of old water masses with low anthropogenic CO₂ concentration, and the transport of the newly equilibrated surface waters into the ocean interior. Here we present results from the Southern Ocean chapter of RECCAP2, which is the Global Carbon Project’s second systematic study on Regional Carbon Cycle Assessment and Processes. We analyse Southern Ocean contemporary carbon fluxes and anthropogenic carbon accumulation in 1985-2018 from a wide range of global ocean biogeochemical models (GOBMs), surface ocean pCO₂-based data products (pCO_2-products), and data-assimilated models, with the aim of identifying patterns of regional and temporal variability, model limitations and future challenges. Our results highlight agreement of GOBMs and pCO₂-products on the mean Southern Ocean contemporary CO₂ uptake (0.75 ± 0.28 PgC yr^-1 and 0.74 ± 0.07 PgC yr^-1 respectively). Compared with RECCAP1 (where the database of model- and observation-based estimates was significantly smaller), the new estimates suggest a weaker sink, possibly due to better representation of winter outgassing. Strong discrepancies exist between GOBMs and pCO₂-products in seasonality and trend estimates between 1985-2018. The pCO₂-products show the presence of a stagnation in uptake through the 1990’s followed by a rapid increase in uptake, while GOBMs show consistent uptake throughout the 1985-2018 period. On a regional level, the subtropical seasonally stratified (STSS) biome has the largest air-sea CO₂ flux with uptake of CO₂ peaking in winter, whereas the ice (ICE) biome is characterised by a generally small magnitude of fluxes into and out of the ocean and a pronounced seasonal cycle with the largest ocean uptake of CO₂ in summer. Connecting these two, the subpolar seasonally stratified (SPSS) biome has intermediate flux magnitude, with GOBMs showing spread in the strength of winter outgassing and difficulties in simulating the strongest CO₂ uptake in summer. The biases in GOBMs originate mainly from the non-thermal component of air-sea CO₂ flux, and in particular from the difficulty in simulating the competing effects of circulation and biology on carbon draw-down in summer. Our analysis reveals a distinct zonal asymmetry (secondary to the latitudinal gradient) between the Atlantic, Pacific and Indian sectors. The zonal asymmetry is observed in the mean uptake and amplitude of the seasonal cycle rather than the phasing of the seasonal cycle. GOBMs show a 20% spread and an overall underestimate of their simulated anthropogenic carbon accumulation, pointing to insufficient water mass formation and interior ventilation. These first results confirm the global relevance of the Southern Ocean carbon sink and highlight the strong regional and interannual variability of the Southern Ocean carbon uptake in connection to physical and biogeochemical processes. 

How to cite: Patara, L., Hauck, J., and Gregor, L. and the RECCAP2 Southern Ocean team: RECCAP2 – Southern Ocean carbon fluxes and storage, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17328, https://doi.org/10.5194/egusphere-egu23-17328, 2023.

High latitude regions are increasingly affected by climate change, where large stocks of carbon sequestered in permafrost are at risk of being released. Monitoring this change is therefore vital for our understanding of  the Arctic and global climate, but adverse conditions and the heterogeneity of Arctic landscapes make it exceptionally challenging to gain a comprehensive observational view of the carbon cycle. In this work we explore the growth of the high latitude eddy covariance (EC) network, and evaluate ways to improve its design both from a spatial and temporal aspect to better monitor this vital region. We utilise the relative extrapolation index (EI) metric, a method to assess upscaling errors as a factor of a location's distance in predictor variable space to the EC network. Our EC site survey, last updated in 2022, identified 213 site locations in the Arctic, of which 124 are currently active. Of these active sites, 79% intend to remain active for 5 years or longer, although on average these sites only have 3.1 years of funding. We investigated the effect of limited site activity periods on the network, and found that if sites only stayed active for a maximum of 36 month (3 full years) or 18 month (3 full summers), the network’s mean EI would increase by 27.3 and 24.5 percentage points, respectively. This deterioration in network data coverage is similar to setting the network back to 2012 and 2008, i.e. a time when fewer sites by far were active. In addition, we investigated the effect of long time series of data, and the optimal configuration of the network in depth versus breadth. For the former, our results show that even for time series that are already long, adding more data years still contributes to increasing network performance overall. For the latter, we find that with total site-months remaining constant, many sites with fewer site-months results in a lower EI than a few sites with many site-months. Summarising, our findings demonstrate that a top-down network management should ideally combine long-term monitoring sites with observations that are rotated between multiple observation sites, to capture both long-term trends and spatial heterogeneity in exchange flux rates. 

How to cite: Pallandt, M., Jung, M., and Goeckede, M.: Temporal factors in the high latitude eddy covariance network design, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-391, https://doi.org/10.5194/egusphere-egu23-391, 2023.

Groundwater is one of the largest continental carbon reservoirs and tightly linked to globally significant carbon fluxes such as uptake on land, evasion from inland waters and delivery to oceans. Despite emerging evidence that these fluxes are sensitive to environmental changes, long-term trends in groundwater carbon dynamics remain widely unknown. Here I show that dissolved inorganic carbon and carbon dioxide concentrations in groundwater have increased on average by 29% and 48%, respectively, across Sweden (55−68°N) during 1980−2020. I attribute these changes mainly to a partial recovery from historic atmospheric sulfate deposition and associated shifts in weathering pathways in acid-sensitive bedrock, but also to enhanced soil respiration as a likely consequence of climate and land use changes. The results highlight previously neglected significant long-term and large-scale dynamics in groundwater carbon cycling and have implications for the pathways and time scales through which carbon is cycled through the land - inland water - ocean continuum. The observed dynamics should be included in carbon cycle models for accurate evaluations and predictions of the effects of environmental changes on regional and global carbon fluxes.

How to cite: Klaus, M.: Rising carbon dioxide concentrations in Swedish groundwater during 1980−2020, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1265, https://doi.org/10.5194/egusphere-egu23-1265, 2023.

In this study, CO₂ and CH₄ fluxes were measured in the tundra ecosystem in order to evaluate the potential future sensitivity of the carbon cycle to climate change using chamber systems and eddy covariance methods during summer in 2019 and 2022 in Canada. The study site is located on dry tundra with ponds in high-arctic near Cambridge Bay, Nunavut, Canada (69°7'47.7"N, 105°3'35.3"W). The vegetation cover around the site is mainly covered with dwarf-shrubs, graminoids, and lichens. CO₂ and CH₄ fluxes were examined to understand the mechanism of the carbon cycle over the tundra ecosystems with the pond. From chamber methods, the variability of net CO₂ exchange was more sensitive to grass of wet condition than vegetation of dry condition and the variability and magnitude of CH₄ emission near the pond was larger than that of dry condition. The emission CO₂ and CH₄ fluxes were examined positive relationship at almost bare soil of wet condition and negative relationship at various vegetation at dry condition. Net ecosystem exchange, ecosystem respiration, and gross primary production were measured or calculated using the both methods to investigate the influence of the ecosystem with ponds in the tundra carbon cycle. This study was supported by a National Research Foundation of Korea grant from the Korean government (MSIP) (NRF-2021M1A5A1065679 and NRF-2021R1I1A1A01053870).  

How to cite: Chae, N., Hwang, H., Choi, T., and Lee, B. Y.: Carbon dioxide and methane fluxes measurement for tundra ecosystem with ponds in High Arctic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1744, https://doi.org/10.5194/egusphere-egu23-1744, 2023.

Wetlands play an important role in the carbon balance of the Arctic. All wetland types are characterized by an individual combination of hydrological conditions, soils, vegetation cover, etc. These characteristics influence their feedback with current and future climate conditions, and therefore also their greenhouse gas exchange processes. While most climate models distinguish only one or two types of wetlands, biogeographical approaches define at least ten types of wetlands in the Arctic.

Improving the representation of wetland ecology in carbon upscaling studies in the Arctic requires finding the balance between the diversity of wetlands, including their variability in responses to climate forcing, and the information that is commonly available to represent them in modelling frameworks. On the one hand, a larger number of classes allows a more precise description of the conditions and characteristics of the fluxes within each class. On the other hand, more classes also mean less information per class, and thus more gaps that need to be interpolated.

To support the development of a refined classification scheme, we first built a database on Arctic wetland characteristics, including measured carbon pools and fluxes, based on the available information from published studies. Our database covers the period 1988 – 2019, with observations for all seasons available. Most data was taken from flux chamber studies, since this technique allows to resolve the highly heterogeneous mosaic of landcover, environmental conditions, vegetation and consequently GHG fluxes that characterize large fractions of the Arctic. For all plots, general (coordinates, time of measurements, etc.), physical (pH, vegetation composition, water table, etc.) site characteristics and CH₄ and CO₂ fluxes were collected. However, for some of these parameters, data coverage turned out to be too sparse to complete analyses. For example, permafrost depth, pH, and water table level cover only 45, 15 and 34% of all available plots. To improve this situation, remotely-sensed data was included, allowing to equally cover all measurement points, albeit often with less accuracy.

Based on statistical processing using agglomerative hierarchical cluster analysis, we divided all observations into wetland categories based on their CO₂ and CH₄ flux signatures and the response to dominant environmental factors. We present the most successful classifications for different total numbers of classes, allowing to base the choice of scheme on the information that is available for a specific modelling study.

How to cite: Ivanova, K. and Goeckede, M.: Optimization of a classification scheme for Arctic wetlands to support carbon and energy flux upscaling, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-1905, https://doi.org/10.5194/egusphere-egu23-1905, 2023.

Wildfire is the most important disturbance agent in boreal forests. These disturbances play a major role in the boreal forest carbon cycle. They lead to direct CO₂ and CH₄ emissions during the active fire phase and to long-lasting post-fire impacts on net CO₂ and CH₄ fluxes through changes in forest structure and in microclimatic conditions. For example, a forest’s ability to minimise differences between land surface and air temperature can preserve permafrost and can lower soil temperatures and thus soil respiration. Fire and post-fire succession are linked to diverse changes in ecosystem function and structure shaping land-atmosphere interactions and, thus, forest microclimate for decades after the disturbance event. However, the mechanisms behind changes in boreal forest microclimate remain uncertain hampering our understanding of carbon cycle impacts of wildfires. Here, we analyse surface energy balance observations from 17 eddy covariance flux tower sites across fire disturbance chronosequences in the North American boreal biome to identify the main drivers of post-fire changes in land surface-air temperature gradients. We use 102 years of observations to quantify winter and summer changes in important ecosystem properties such as evaporative fraction, aerodynamic conductance, and albedo following stand-replacing fire disturbances. Then, we link changes in ecosystem properties to decadal changes in surface-air temperature gradients.

We find that the summer daytime surface-air temperature gradient increases after the fire disturbance indicating reduced ability to cool the land surface during the warm summer months. However, in the winter, the daytime temperature gradient becomes smaller. Decreased aerodynamic conductance contributes mainly to the post-fire surface heating in the summer while increasing albedo mainly explains winter cooling. Evaporative fraction increases initially in the first few decades after the post-fire disturbance. However, during drought years, the evaporative fraction declines rapidly. Our results provide important insights into fire impacts on microclimatic conditions and ground thermal regimes in boreal forests and highlight the reduced capacity of post-fire forests to reduce land surface temperatures during heatwave events. The findings have the potential to contribute to a better mechanistic understanding of post-fire permafrost thaw and soil respiration changes.

How to cite: Helbig, M. and Daw, L.: Boreal forests on fire - Decadal wildfire impacts on boreal forest microclimate, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3533, https://doi.org/10.5194/egusphere-egu23-3533, 2023.

The Arctic is warming at a faster rate than the rest of the planet due to climate change. The warmer temperatures are causing, among other effects, the permafrost to thaw. When ice-rich permafrost thaws, thermokarst features form due to subsidence of the ground surface and the creation of dynamic depressions, basins, and lakes. As a result, the hydrological cycle in these latitudes is intensifying, causing an increase of nutrients and organic carbon in surface waters. Such impacts on freshwaters affect microbial community composition, and thus, these systems are good sentinels to study processes in primary ecological succession related to ecosystem processes such as productivity and greenhouse gas (GHG) emissions. This study aims to improve the current understanding of microbial processes leading to release of GHG in thermokarst lakes. To that end, we sampled a total of 12 thermokarst basins in August 2022 along a latitudinal gradient (67ºN - 69ºN) in the Northwestern Territories (Canada). The basins were selected so that half were in the taiga biome and half in the tundra biome. In addition, based on satellite images and in-field observations, half of the lakes sampled were in expansion and the other half were undergoing drainage. Water samples were collected for the analysis of GHGs (CH_4, CO₂, N₂O), major ions, dissolved nutrients (organic C, δ¹³C-DOC, organic and inorganic -N) and microbial community composition (16S rRNA gene metabarcoding). We used Ar-corrected gas saturation of each GHG as a proxy of net metabolic changes. Our first results show that both expanding and shrinking lakes were strongly oversaturated in CH₄ andCO₂, slightly saturated in N₂O, and slightly undersaturated in O₂, pointing out higher respiration activity than primary production. Microbial mineralization of organic matter was used as a proxy for GHG production. We found higher concentrations of dissolved organic C in shrinking lakes compared to expanding ones. Following the latitudinal gradient (i.e. biomes), higher temperatures were found in lakes sampled in the taiga compared to those located in tundra, together with deeper permafrost table depths. In surface waters, pH values and dissolved O₂ concentrations were significantly higher in tundra lakes compared to taiga lakes, probably as a result of lateral DOM fluxes in more productive ecosystems (i.e. boreal forests). Differences between microbial communities in both biomes are therefore expected, which we will verify once the ongoing sequencing analyses are available. Our study advances the current knowledge of GHG dynamics in thermokarst lakes and helps to predict future effects of climate change impacts in northern latitudes.

How to cite: Valiente, N., Grau, O., Martin, V., Janssens, I., Van de Putte, I., Dörsch, P., Schmidt, H., and Richter, A.: Greenhouse gas dynamics across a latitudinal gradient of thermokarst lakes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4338, https://doi.org/10.5194/egusphere-egu23-4338, 2023.

In the context of global climate change, permafrost thaw in northern high-latitude territories is becoming a major concern due to the vast amount of organic carbon that is stored within this region. To accurately predict the feedback between Arctic permafrost carbon pools and future climate change, detailed insight into current carbon cycle processes and their environmental controls is imperative. A highly valuable data source for this purpose are continuous observations of turbulent exchange fluxes of carbon (e.g. CO₂ and CH₄ fluxes) and energy (e.g. fluxes of sensible and latent heat) with the eddy-covariance technique, in combination with the monitoring of environmental parameters such as e.g. air or soil temperature and moisture, radiation,  atmospheric turbulence, water table levels, precipitation, and snow depth.

In this study, we evaluate the effect of drainage on vertical carbon fluxes and environmental parameters within a Northeast Siberian wet tundra permafrost ecosystem. Our experiment includes two co-located eddy-covariance sites, one reflecting disturbed conditions affected by a drainage system which was built in 2004, and the other as an undisturbed control site. Both towers were identically outfitted with eddy covariance instruments mounted on 5 m tall towers on the floodplain of the Kolyma River near Chersky (68.75 º N, 161.33º E) in Northeast Siberia, Russia. The dataset analyzed here covers the period from July 2013 to December 2021, including continuous coverage throughout the winter seasons. We present a statistical analysis of the long-term trends in the environmental parameters and surface-atmosphere exchange fluxes at both sites. In addition, we relate the carbon and heat fluxes at both sites in the spectral and temporal domain to the inter-annual variability in climate conditions, which include extremes in both summer (temperature, precipitation) and winter (snow cover) conditions. Finally, we show the annual carbon budget of both sites, with a specific focus on the long-term impact of the drainage on carbon cycle process.

How to cite: Bolek, A., Schlutow, M., El-Madany, T., Kolle, O., Heimann, M., and Goeckede, M.: Impact of the Long-Term Drainage on the Eddy-Covariance Fluxes in Northern High Latitude Permafrost Regions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5011, https://doi.org/10.5194/egusphere-egu23-5011, 2023.

Gas hydrates are known to be an enormous potential energy resource that are accumulated worldwide, especially in the polar regions, and yet the estimates for this resource remain uncertain. In the Arctic region, methane emissions into the atmosphere are a substantial factor in global warming that poses a great danger to the environment. Previously, several studies have been conducted to estimate the gas hydrates in the Arctic to ease such problems despite the need for more data compared to conventional reserves. In the western continental margin of the Chukchi Plateau, the sea mound morphologies were first discovered, and gas hydrate samples were obtained via gravity coring during the first expedition in 2016. In the following expedition in 2018, an intensive gas hydrate exploration including the single-channel seismic survey was conducted in the area of mound morphologies and identified the local bottom simulating reflectors. Consequently, an extensive multichannel seismic survey was conducted in 2019 to investigate the geophysical characteristics of widely distributed gas hydrates in the western continental margin of the Chukchi Plateau. The objective of this study is to estimate the potential volume of gas hydrate resources in the Chukchi Plateau based on the geophysical data. From this study, the distribution of bottom-simulating reflectors and local gas hydrate saturations were derived from the geophysical data. The gas hydrate saturation model in this study area was constructed using the kriging method with few geological assumptions. Then, the total volume of gas hydrates in the western continental margin of the Chukchi Plateau was proposed. The results of this study will provide basic information on the estimates of gas hydrates in the western continental margin of the Chukchi Plateau and contribute to assessing the size of the associated volume of methane emissions due to global warming.

How to cite: Choi, Y., Kang, S.-G., Choi, Y., and Hong, J. K.: Estimation of potential gas hydrate resources based on the geophysical data in the western continental margin of the Chukchi Plateau, the Arctic Ocean, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5019, https://doi.org/10.5194/egusphere-egu23-5019, 2023.

Rapid warming is currently accelerating Arctic carbon cycling, including increased permafrost thaw and CO₂ production from soil organic matter decomposition, but also CO₂ uptake by plants. Plants can additionally stimulate soil organic matter decomposition near their roots, via the rhizosphere priming effect. In a recent modeling study, we showed that priming can accelerate Arctic soil carbon loss at a globally relevant rate, and spatial analysis pointed to large potential contributions from carbon-rich permafrost peatlands. At the same time, the high carbon content of peatlands might render them insusceptible to input of easily available organic compounds by plant roots, which is considered a key component of priming. We here investigated the susceptibility of permafrost peat soils to priming by plant compounds under aerobic conditions that resemble the dominant rooting zone. To that end, we combined a 30-week laboratory incubation of peat soils from five circum-Arctic locations, with a literature meta-analysis of priming studies of Arctic peat and mineral soils. The combined experimental and literature data showed substantially and significantly weaker priming susceptibility of peat than mineral soils. Organic carbon addition increased CO₂ production from soil organic matter in mineral, but not in peat soils. Organic nitrogen addition had a significant effect on both sample types, but that of peat was much weaker. These observations point at fundamental, mechanistic differences in the response of peat and mineral soil organic matter decomposition to changing carbon and nitrogen availability. In a new model sensitivity analysis, we show that insusceptibility of peatlands to priming would substantially reduce estimates of priming-induced carbon loss from the circum-Arctic. While our study suggests a limited effect of plant-released organic compounds on peat decomposition, it does not preclude a vegetation effect on decomposition under natural conditions. The large carbon stocks of circum-Arctic peatlands and expected changes in vegetation and drainage, call for increased efforts to quantify the combined effect of living plants on soil processes beyond carbon input.

How to cite: Wild, B., Monteux, S., Wendler, B., Hugelius, G., and Keuper, F.: Rhizosphere priming in a warming Arctic: Are peatlands insusceptible?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6128, https://doi.org/10.5194/egusphere-egu23-6128, 2023.

The warming of the Arctic and its consequences for the global climate system have become one of the strongest manifestations of human-induced climate change. Over the four decades, the Arctic has warmed three to four times faster than globally. In addition to the long-term trend in average temperatures, extreme weather events are becoming increasingly frequent causing disturbances to the Arctic terrestrial ecosystems. 

Many existing datasets primarily concentrate on seasonal precipitation and temperature at coarse spatial (10-100 km) and temporal (30-year average climatologies) resolutions forming the basis of current understanding of how Arctic ecosystems will respond to climate change. For this reason, the conventional datasets likely leave out many ecologically significant aspects of the Arctic climate relevant for biological or biogeochemical processes. For instance, snow cover duration, rain-on-snow events, or extreme wind events are known to be important variables for Arctic ecology that may not be adequately represented by the more widely used climate statistics.

Here, we introduce a new dataset of bioclimatic indices relevant for investigating the changes of Arctic terrestrial ecosystems. The dataset, called ARCLIM, consists of several climate and event-type indices for the northern high-latitude land areas. The indices are calculated from the hourly ERA5-Land reanalysis data for 1950-2021 in a spatial grid of 0.1 degree (~9 km) resolution. We provide the indices in three subsets: (1) the annual values during 1950-2021; (2) the average conditions for the 1991-2020 climatology; and (3) temporal trends over 1951-2021. 

The 72-year time series of various climate and event-type indices draws a comprehensive picture of the Arctic bioclimate variability. We hope that the ARCLIM dataset opens new research opportunities aiming to better understand the impacts of climate change in Arctic terrestrial ecosystems.

How to cite: Rantanen, M., Kämäräinen, M., Niittynen, P., Phoenix, G. K., Lenoir, J., Maclean, I., Luoto, M., and Aalto, J.: ARCLIM: bioclimatic atlas of the terrestrial Arctic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6610, https://doi.org/10.5194/egusphere-egu23-6610, 2023.

Large stores of carbon frozen in the Arctic as permafrost are under threat of thawing as temperatures in the Arctic increase at a rate four times that of the global mean. This study uses recent atmospheric data from the North Slope of Alaska and Northeast Siberia to provide the most up-to-date assessment of emissions and trends from these two major high-latitude regions.

We use two methods to quantify emissions and assess trends across different seasons: 1) Using 35 years of data from Barrow, Alaska, a wind sector method that quantifies trends in emissions by calculating concentration enhancements over background using wind direction to identify the land sector (first used in Sweeney et al., 2016), and 2) using Barrow data and recent data from three Siberian stations, an inversion method with the high-resolution atmospheric transport model NAME that quantifies both emissions and trends from these regions. We use results from these two approaches to quantify the temperature sensitivity (Q10) of soils based on correlations between surface air and ground temperatures with methane emissions.

With the inclusion of atmospheric concentration data after 2015, we now show that land emissions from the North Slope of Alaska have been increasing since 2000, reflecting a change from previous analyses, which showed no significant increase in summertime methane emissions between 1986-2014 (Sweeney et al., 2016). We find significant emissions from the late shoulder season (Autumn-Winter), which has historically been undermeasured and underrepresented in models and emissions inventories, in this region of Alaska as well as two North-eastern Siberian locations, the Taymyr Peninsula and the East Siberian Lowlands. We show that emissions during this late-season have been growing over the past two decades at a rate similar to summer-time emissions.

Our results based on long-term atmospheric data can be used to show that important change is happening in the Arctic, with an increasing emissions trend and the presence of late shoulder season emissions.

How to cite: Ward, R. H., Ganesan, A. L., Sweeney, C., Miller, J., Goeckede, M., Laurila, T., Hatakka, J., Ivakhov, V., and Makshtas, A.: Increasing methane emissions from the North Slope of Alaska since 2000 and late Autumn-Winter emissions from multiple Arctic regions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7504, https://doi.org/10.5194/egusphere-egu23-7504, 2023.

Ongoing climate change has a significant impact on marine and terrestrial polar ecosystems. The increased melting, and retreat of glaciers, as well as the permafrost thawing, intensify the transport of dissolved organic matter from land to Arctic fjords. It has been estimated that the permafrost surface layer contains as much as 1035 ± 150 Pg of organic carbon (Hugelius et al., 2014), so even a small release can significantly change the carbon loads reaching the fjords. Although there are quantitative estimations of the dissolved organic carbon (DOC) delivered from land, the fate of the soil-derived DOC in fjords remains highly unknown. It is still unclear to what extent this DOC pool is bioavailable and how fast can it be remineralized. Therefore, the following research objectives have been formulated: (1) to quantify the shares of labile, semi-labile, and refractory fractions in the soil-derived DOC, and (2) to estimate remineralization rate constants and half-life times for different bioavailable fractions of DOC. This has been done through the 180-days-lasting incubation experiments of the DOC released from soils (soil leachates) mixed with the seawater from adjacent fjord. At the beginning and after 1, 2, 3, 5, 9, 19, 29, 65, 90, and 180 days of incubation, the individual samples were collected to measure DOC concentrations. For the study site, the catchments of two rivers in Kongsfjorden (West Spitsbergen, Svalbard) - Bayelva River and Londonelva River were selected. Bayelva River is 4 km long, with a glacierised catchment area of 32 km², which is almost entirely underlain by permafrost with a seasonal active layer (Killingtveit, 2004). Londonelva River is located on Blomstradøya (small island in Kongsfjorden) and is characterized by a small (0.7 km²) de-glacierised catchment area. The results indicate that the soil leachates contain a lot of DOC (420 μmol L^-1 in the Bayelva catchment and 2730 μmol L^-1 in the Londonelva catchment), which is highly bioavailable - 61% and 66% of DOC was remineralized during the incubation experiment, respectively. This high bioavailability of terrestrial DOC indicates that its supply has the potential to play an essential role in sustaining the bacterial loop in the fjord and, through the CO₂ release, to amplify ocean acidification in the coastal zone. The obtained results contribute to a better understanding of the processes shaping the carbon cycling in the Arctic fjords (and likely in other polar regions).

How to cite: Koziorowska-Makuch, K., Bromboszcz, L., Makuch, P., Pałka, I., Winogradow, A., and Kuliński, K.: Remineralization of soil-derived dissolved organic carbon in the high Arctic fjord (Kongsfjorden), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8337, https://doi.org/10.5194/egusphere-egu23-8337, 2023.

Arctic and boreal wetlands and lakes are experiencing complex ecological changes as a result of warming. The potential for rapidly thawing permafrost to promote large increases in methane (CH₄) emissions via ground subsidence and ponding (thermokarst), and permafrost carbon mineralization is of particular concern for accelerating the permafrost carbon feedback (PCF) [Turetsky et al. 2020]. However, complex hydrological dynamics produce large uncertainties regarding the sign and magnitude of carbon loss in modeling and forecasting efforts. Determining CH₄’s current and future contributions to the PCF is challenging due to sparse observations, high spatiotemporal variability, and heterogeneous Arctic landscapes. As a result, top-down (observation-based) and bottom-up (model/inventory-based) evaluations of annual Arctic and boreal CH₄ emissions disagree by 50-200% [McGuire et al. 2012; Peltola et al. 2019]. Constraining the current budget and forecast uncertainty in future Arctic emissions will require scale-bridging approaches that reconcile fine spatiotemporal variability and regional to continental scale coverage. To this end, we compiled multiple large remote sensing datasets to study relationships between Arctic lake and thermokarst landscape morphology trends with remotely-sensed (AVIRIS-NG) CH­₄ emission hotspot detections. Preliminary analyses from a lake-and-wetland-rich 1,750 km² study area of the Yukon Kuskokwim Delta, AK, USA reveal discrete correlations between recently wetted areas and CH₄ hotspot detections. However, in an analysis of over 1,200 lakes > 1 ha, hotspots were detected in greater abundance surrounding lakes that have shrunk in area since 1999 (p < 0.05) (Fig. 2). Our preliminary results imply a complex response of CH₄ emissions surrounding dynamic permafrost environments. Ongoing analyses seek to further elucidate patterns related to waterbody size, permafrost ice and carbon contents, and relationships between terrestrial and limnetic hotspot detections. 

How to cite: Elder, C. D., Thompson, D. R., Baskaran, L., Nitze, I., Grosse, G., Hasson, N., Walter Anthony, K. M., and Miller, C. E.: The impacts of regional Arctic lake change on remotely sensed methane emission hotspots in Alaska, USA, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10051, https://doi.org/10.5194/egusphere-egu23-10051, 2023.

Methane (CH₄) is a strong greenhouse gas that accelerates climate change, yet its emissions from wetlands in general and Arctic permafrost-affected wetlands in particular remain very uncertain in the global CH₄ budget. Arctic CH₄ sources and the expected effect of permafrost thaw on these sources have gained much attention by the public, media, policy makers, and researchers during the past decade, but neither inversion nor process-based models provide clear trends in emissions and there has not been any observational evidence for increasing CH₄ emissions from Arctic permafrost ecosystems.

Here, we provide this observational evidence. 

Based on the longest record of direct Arctic CH₄ flux observations acquired since 2002 at a Siberian tundra site using the eddy covariance method, we found an increase in the early summer (June and July) CH₄ emissions by 1.9 ± 0.7 % yr^-1 since 2004 along with a strong increase in June air temperatures of 0.3 ± 0.1 °C yr^-1. Although the tundra’s maximum source strength in August has not yet changed and the overall mean annual emissions of 171.5 ± 12.3 mmol m⁻² yr⁻¹ remain in the lower half of the published range, the increase in early summer methane emissions shows that atmospheric warming has begun to affect the methane flux dynamics of permafrost-affected ecosystems in the Arctic. This is especially noteworthy, given the very thick and cold continuous permafrost in the study area compared to most other observational sites.
While the observed changes clearly happen in the early warm season, we also estimate 39 % of the annual emission to originate from the re-freezing and frozen period, highlighting the importance of the cold season for annual permafrost CH₄ emission estimates and the substantial challenges in achieving continuous data coverage in the Arctic winter.

How to cite: Sachs, T., Rößger, N., Wille, C., Boike, J., and Kutzbach, L.: Seasonal increase of methane emissions linked to warming in Siberian tundra, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10145, https://doi.org/10.5194/egusphere-egu23-10145, 2023.

Carbonyl sulfide (OCS), the most abundant atmospheric sulfur-carrying gas, can contribute to regulating Earth’s radiative balance through forming sulfate aerosols. The bryophyte-dominated tundra lying over the ice-free Antarctica is an important terrestrial carbon sink and provides colonies for sea animals, such as penguins and seals, which remains hitherto unexplored concerning OCS biogeochemistry. Here, we measured OCS fluxes from the Antarctic tundra and coupled their fluxes to soil biogeochemical properties to explore OCS production and degradation processes. The bryophyte-dominated normal upland tundra was an OCS sink at -0.97 ± 0.57 pmol m^-2 s^-1, resulting from both bryophytes and OCS-metabolizing enzymes (e.g., carbon anhydrase, nitrogenase) secreted by soil microbes, such as Acidobacteria, Verrucomicrobia, Chloroflexi, and Mortierellomycota. In comparison, tundra within sea animal colonies was an OCS source up to 1.35 ± 0.38 pmol m^-2 s^-1, due to the input of organosulfur from sea animals and the animal-induced anaerobic soil environment, which promoted simultaneous abiotic OCS production in soil, and outweighed the biogenic OCS uptake by bryophytes and soil microbes. Furthermore, sea animal colonization shaped the soil microenvironment, affecting nutrient levels, pH and moisture, which may have reduced the abundances of OCS-metabolizing microbes and thereby OCS degradation and further unveiled concurrent OCS production. Basic calculation suggested that sea animals contribute about 107 metric tons yr^-1 of OCS-S to the atmosphere. The strength of this OCS source is expected to increase in response to Antarctic warming. Overall, tundra ecosystems are important interfaces for OCS exchange and sea animals exert an impact on the sulfur cycle in coastal Antarctica.

How to cite: Zhang, W., Zhu, R., Jiao, Y., Rhew, R. C., Sun, B., Rinnan, R., and Zhou, Z.: Sea animals promote carbonyl sulfide (OCS) emissions from Antarctic tundra, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10192, https://doi.org/10.5194/egusphere-egu23-10192, 2023.

Permafrost soils store vast amounts of carbon, twice as much as the atmosphere. With climate warming occurring at a rate three to four times the global average in Arctic-boreal ecosystems this carbon is at risk of being released to the atmosphere in the form of carbon dioxide or methane (hereby, carbon fluxes) exacerbating global climate warming. However, gaps in carbon flux data in high latitude ecosystems limit our ability to understand, upscale, model, and project carbon fluxes, which in turn limit our ability to set accurate emissions reduction targets to stay within globally agreed upon temperature thresholds such as 1.5 or 2°C. To address this, we are strategically expanding the informal Arctic-boreal carbon flux network through the installation of ~10 new eddy covariance sites and supporting expanded measurements (during winter and for CH₄) at existing sites. To guide site selection decision making, we are using a representativeness analysis of the current eddy covariance network, determining the Euclidean distance in environmental data space using key carbon flux drivers at a 1 km² resolution across the Arctic-boreal region (Pallandt et al., 2022). Analyses show a lack of representation in the high Arctic, Siberia, and Eastern Canada, and representation is substantially lower when considering only sites with year-round measurement or that measure methane, limiting our ability to estimate the full impact of carbon fluxes from the Arctic-boreal region. Additional consideration is given to logistical constraints, partnerships, and modeling gaps. Work has begun including a re-installation in Churchill, MB, and upgrades for year-round and additional instrumentation for 4 towers in Alberta and the Northwest Territories and a site in Iqaluit, NU. We will further synthesize existing network data to inform the Dynamic Vegetation [Model] Dynamic Organic Soil Terrestrial Ecosystem Model (DVM-DOS-TEM) model and use machine learning approaches to upscale Arctic-boreal carbon fluxes.

How to cite: Arndt, K. and Natali, S. and the Permafrost Pathways Flux Steering Committee: Strategic expansion of the Arctic-Boreal carbon flux network, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10643, https://doi.org/10.5194/egusphere-egu23-10643, 2023.

Spatio-temporal patterns of methane (CH₄) and carbon dioxide (CO₂) release from natural sources needs to be better understood across the Arctic region. Climate change in the Arctic is occurring at a pace that may be 2 to 4 times the global average, and existing measurements derive from a limited number of field sites, and most originate during the growing season although important studies show that release continues during winter. The Mackenzie River Delta in the western Canadian Arctic holds thin and destabilizing permafrost, high organic content soils, a high proportion of wetlands, and vast natural gas occurrences at depth, all of which create high methane potential. In the present study, we conducted atmospheric CH₄ and CO₂ measurements using a mobile laboratory equipped with a greenhouse gas analyzer during the summer and winter. We also visited known aquatic and terrestrial CH₄ flux hotspots, including pingos, lakes, river channels and wetlands, where we measured concentration transects and stable carbon isotope (¹³C-CH₄) values to characterize CH₄source and spatial pattern. Source stable carbon isotope (δ¹³C-CH₄) signatures at hotspots ranged from -42 to -88 ‰ δ¹³C-CH₄. Active surface microbial production was responsible for at least 4 of the 8 hotspots investigated, indicating that microbial production may be responsible for a greater number of CH₄ hotspots than is indicated by previous studies in the region. Mobile surveys showed that shrubland, grassland and deep water were the most important ecosystems for CH₄ and CO₂ production during the wintertime and that low lying areas of the Delta had the highest atmospheric mixing ratios of CH₄.

How to cite: Wesley, D., Dallimore, S., MacLeod, R., Sachs, T., and Risk, D.: Characterization of atmospheric methane release at hotspots in the outer Mackenzie River Delta, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-10711, https://doi.org/10.5194/egusphere-egu23-10711, 2023.

High latitude peatlands are a significant source of atmospheric methane. Production, consumption and emission rates are spatially and temporally heterogeneous, resulting in a wide range of global estimates for the atmospheric budget of methane. Increasing temperatures in Arctic regions cause degradation of underlying permafrost, changing hydrology, vegetation and microbial communities, but the consequences of this for methane cycling, including stable methane isotopes, are poorly understood. We provide evidence of direct linkages between below ground methanogen communities and above ground plant communities that can be remotely sensed and used in model simulations to effectively predict methane and isotopic fluxes across the landscape. Combining remote sensing with biogeochemical modeling can be used to predict methane dynamics, including the fraction derived from hydrogenotrophic versus acetoclastic microbial methanogenesis. Applying this approach across heterogeneous discontinuous permafrost peatlands enables us to accurately predict isotopic emissions, which will help constrain the global role of Arctic methane emissions.

How to cite: Varner, R., Crill, P., Kuhn, M., Cronin, D., Palace, M., McCalley, C., Burke, S., Deng, J., Saleska, S., and Rich, V. and the A2A and EMERGE project teams: From Archaea to the atmosphere: linking above and belowground communities to scale methane and isotopic emissions across the Arctic, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11027, https://doi.org/10.5194/egusphere-egu23-11027, 2023.

Many aspects regarding biogeochemical cycles in carbon-rich permafrost ecosystems remain poorly constrained to date, resulting in a major source of uncertainty for prognostic simulations of the global greenhouse gas budget, and the associated design of effective future climate policies. Only very few studies have investigated the role of nutrients on carbon cycle processes in Northern ecosystems, and existing data is particular limited for elements beyond nitrogen (N) and phosphorus (P). Consideration of their impacts may be particularly relevant for simulating a warmer future Arctic with substantially increased thaw depths, and associated input of nutrients from currently deep-frozen permafrost pools.

For the presented study, we enhanced a high-latitude version of the terrestrial ecosystem model QUINCY, which fully couples carbon (C), nitrogen (N) and phosphorus (P) cycles in vegetation and soil, with an additional first-order factor derived from soil incubation experiments that accounts for stabilization and mobilization of soil organic matter through Calcium (Ca) and Silicon (Si). In a preparation step, based on thaw depths of CMIP6 models we first computed the pan-Arctic scale magnitude of Si and Ca susceptible to release to the active layer under different climate warming scenarios. Subsequently, considering changes in the active layer depth computed by QUINCY, we calculated historical and future changes in active layer Ca and Si contents at selected sites. Element availability and associated effects on carbon cycle processes were simulated for three Siberian permafrost observatories, Chersky, Spasskaya Pad and Chokurdakh.

For a historical time period, testing the Ca/Si relationship at the Chersky site for the carbon cycle resulted in a slightly improved agreement between model results and eddy covariance flux data, mainly linked to an increase in organic matter stabilization induced by higher Ca content in the soil. To illustrate the potential future implications of Ca and Si on the permafrost carbon cycle, we then compared a historical (2000 – 2020) against a future (2060 – 2080) period, with the simulations for the latter based on RCP 4.5 emissions. The substantial increase in active layer depth (0.5 – 0.8m) between these periods led to various changes in Ca/Si availability across our three study sites, including neutral to positive trends for Si and both increases and decreases for Ca. Since Ca dominated the net effect on carbon cycling, accordingly we observed both increases and decreases in GPP and ecosystem respiration linked to the consideration of Ca/Si effects, with mean changes in component fluxes reaching up to ±24 g m^-2 yr^-1. This implies that considering stabilization factors induced by Ca/Si, and potentially other soil minerals, could be important for a process-based reproduction of present-day permafrost carbon cycles, and projections of future scenarios.

How to cite: Göckede, M., Lacroix, F., Schaller, J., Stimmler, P., and Zaehle, S.: Process-based simulation of nutrient (N, P, Si, Ca) effects on permafrost carbon cycling under present and future climate conditions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11216, https://doi.org/10.5194/egusphere-egu23-11216, 2023.

Lakes and drained lake basins (DLB) are ubiquitous landforms in permafrost lowland regions, covering 50% to 75% of permafrost lowlands in parts of Alaska, Siberia, and Canada. Depending on the time passed since the drainage event, surface characteristics within the DLB such as surface roughness, vegetation, moisture and abundance of ponds may vary. The mosaic of vegetative and geomorphic succession within DLBs and the distinct differences between DLBs and surrounding areas can be discriminated with remote sensing and used to derive a landscape-scale classification. Previously published local and regional studies have demonstrated the importance of DLBs regarding carbon storage, greenhouse gas and nutrient fluxes, hydrology, geomorphology, and habitat availability. To help quantify these processes on a circumpolar scale and improve the representation of Arctic landscapes in large scale models, a circumpolar data set of DLBs distribution and DLB properties is needed.  Due to the inherent temporal characteristics of DLBs, such a data set also has the potential for space-for-time applications regarding landscape models. A pan-Arctic scale effort to map and further the understanding of DLBs in permafrost-regions is the outcome of work conducted within the International Permafrost Association (IPA) Action Group on DLBs, a bottom-up effort led by the scientific community that includes developing a first pan-Arctic drained lake basin data product based on multispectral remote sensing data (Landsat-8). Comprehensive mapping of DLBs areas across the circumpolar permafrost landscape and including field data into this approach will allow for future utilization of these data in pan-Arctic models, aid upscaling efforts and greatly enhance our understanding of DLBs in the context of permafrost landscapes. This will improve quantitative studies on landscape diversity, wildlife habitat, permafrost, hydrology, geotechnical conditions, high-latitude carbon cycling, and landscape vulnerability to climate change.

How to cite: Bergstedt, H., Jones, B., Bartsch, A., Farquharson, L., Wolter, J., Breen, A., Kanevsiy, M., Grosse, G., Roy-Léveillée, P., and von Baeckmann, C.: Mapping Drained Lake Basins on a circumpolar scale, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11626, https://doi.org/10.5194/egusphere-egu23-11626, 2023.

Land-terminating glaciers in Greenland and Iceland are sources of methane (CH₄) to the atmosphere^1,2,3. CH₄ is produced through microbial methanogenesis underneath the ice, transported dissolved in subglacial meltwater to the margin where the gas is emitted to the atmosphere via degassing⁴. However, sparse empirical data exist about the spatial distribution of subglacial CH₄ production and emission in other glaciated regions of the world, limiting our understanding of its regional and global importance in atmospheric carbon budgets and its possible role in the climate system.

In August 2022, we conducted fieldwork at three outlet glaciers - Dusty, Kluane and Donjek glaciers - of the St. Elias Icefields in Yukon, Canada, to investigate if these alpine glaciers are also sources of CH₄ emissions to the atmosphere. The glaciers were chosen due to the absence of proglacial lakes and the presence of meltwater upwellings at the glacier termini, which were accessed via helicopter.

In-situ extracted dissolved CH₄ and CO₂ concentrations were measured in the field with a portable greenhouse gas analyzer. Additionally, extracted gas was collected in exetainers for concentration measurements via gas chromatography and in Tedlar gas bags for stable carbon and hydrogen isotope analyses of CH₄ to decipher its origin. Further, water samples were collected for geochemical analyses. At Dusty glacier, we performed a high-intensity sampling campaign over 10 hours and continuous measurements of dissolved CH₄ concentrations with a custom-made low-cost and low-power dissolved CH₄ sensor⁵ to study changes in dissolved gas concentrations, stable isotopic signatures and water chemistry during the rising limb of the diurnal discharge curve.

In-situ measured CH₄ and CO₂ concentrations yielded significantly elevated CH₄ and depleted CO₂ levels in the meltwater of all three glaciers. Discrete gas samples confirmed dissolved CH₄ concentrations 45x, 135x and 250x above the atmospheric equilibrium concentration (3.6 nmol L^-1) in the meltwater of Dusty, Kluane and Donjek glaciers, respectively. First measurements of stable carbon and hydrogen isotope values of CH₄ showed enrichment in ¹³C, while ²H was depleted compared to atmospheric CH₄, at all sites, likely originating from a thermogenic source or caused by bacterial CH₄ oxidation. Water analyses showed an alkaline environment enriched in carbonates and DOC, in contrast to more acidic waters from glaciers in Greenland and Iceland.

These first measurements demonstrate that the subglacial meltwaters from glaciers in the St. Elias Icefields are net sources of CH₄ and net sinks of CO₂ to the atmosphere. Our findings indicate that CH₄ emissions from subglacial environments under alpine glaciers may be a more common phenomenon than previously thought, and a potential cause for remotely sensed CH₄ concentrations anomalies over glaciated regions. However, more alpine glaciers and outlets from the Greenland Ice Sheet need to be studied to evaluate this link and provide the needed ground truthing for satellite sensors in high latitudes.

1. Christiansen & Jørgensen (2018) DOI 10.1038/s41598-018-35054-7