Tree-ring δ¹⁵N provide long-term reliable information of soil available nitrogen, especially under increasing atmospheric N deposition upon forested ecosystems. In this study tree-ring δ¹⁵N values of Larix kaempferi and Cryptomeria japonica were measured for five trees each from a heavy snowfall region in north-eastern Japan, respectively. Larch and cedar tree-ring δ¹⁵N showed a range of -1.2 to 3.8 ‰ and -1.6 to 1.6 ‰, respectively. Larch trees showed a stable increase in δ¹⁵N values, while cedar trees showed a steady decreasing trend for the period 1970-2017. However, the divergence in the two tree series started in the early 1990’s. Both tree stands are exposed to the same atmospheric N deposition, therefore in principle both should have been affected equally. Similarly, an increase or a decrease in the δ¹⁵N value of the soil available N cannot be the reason since tree-rings values showed contrasting trends, unless this difference exists in each forest stand, however this seems unlikely. Another possibility could be the canopy uptake of depleted N from the atmosphere in cedar as the N demand increases could be responsible for cedar tree-ring δ¹⁵N temporal decrease but it does not explain the increase observed in larch. We speculate that low N demand and the increase in root biomass as tree grows could have decreased ¹⁵N discrimination by the EM fungi. The most plausible explanation for the contrasting results is that fractionation by the mycorrhiza fungi (Ecto and Arbuscular, respectively) during N root uptake was lower in larch (3.2 ‰) than in cedar (4.7 ‰) trees, which was related to the lower N demand as tree-ring wood %N was in average 0.06 and 0.10, respectively.

How to cite: Lopez Caceres, M. L., Tanabe, S., Santini, F., Voltas, J., Seidel, F., and Yamanaka, T.: Differential nitrogen isotope variation of tree-rings in two coniferous forests under climate change, Japan, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1795, https://doi.org/10.5194/egusphere-egu2020-1795, 2020.

Anthropogenic activities have notably disturbed the natural carbon and nitrogen cycle since the industry revolution. The consequential results include a warmer climate and enhanced nitrogen deposition on forest ecosystems. Covering one-third of the landmass, forests possess vital ecosystem functions such as N retention and the resulting C sequestration. However, the ongoing changes in climate and nitrogen deposition could potentially alter these important processes. Therefore, measures need to be taken to assess the distribution of deposited N in warming forest ecosystems. Here, we use ¹⁵N tracer method to investigate the short-term (2 weeks, 1 month and 3 months) fate of deposited N in a temperate forest, and by taking advantage of the in situ infrared heating, we also attempt to explore the effect of warming ( 2 °C ) on deposited N in forest ecosystems. The results showed that deposited N was largely retained by litter in all treatments (38%-57%) and mineral soil layers contained the least nitrogen. Total ¹⁵N recovery of different ecosystem compartments between warmed and control treatments showed distinct pattern, recovery in warming treatment increased from 72% to 97% after 1 month while the respect recovery of control treatment gradually decreased with time. In the top mineral soil layer (0-10cm), control treatments had higher recovery than warming treatment, suggesting warming may hinder deposited N from forging downwards, however, higher δ¹⁵N value in top mineral soil layer suggesting enhanced microbial activities maybe in action. Little leaching loss of deposited N both in warm and control was observed. Difference in deposited N fate between warming and control could deepen our understanding of how global warming influence forest ecosystem processes, particularly the N cycle.

Key words: Soil warming; ¹⁵N tracer; N deposition; N retention and redistribution; Global warming; Temperate forest

How to cite: Duan, Y. and Fang, Y.: Short-term fate of atmospherically deposited nitrogen in temperate forest under warming, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19227, https://doi.org/10.5194/egusphere-egu2020-19227, 2020.

Forests are important regulators of carbon dioxide fluxes, whereas overall greenhouse gas (GHG) budgets, in particular, nitrous oxide (N₂O), are still largely unknown. No studies on ecosystem-level N₂O budgets (soil and tree stem fluxes with eddy covariance (EC) measurements above the canopy) are found. Only a few examples are available on N₂O emissions from tree stems. Nevertheless, estimation of the N₂O and the full GHG balance in different forest ecosystems under various environmental conditions is essential to understand their impact on climate.

During the period of August 2017 to December 2019, we measured the N₂O budget of a 40-yr old hemiboreal grey alder (Alnus incana) forest stand on former agricultural land in Estonia considering fluxes from the soil, tree stems and whole ecosystem. Grey alder (Alnus incana) is a fast-growing tree species typically found in riparian zones, with great potential for short-rotation forestry. Their symbiotic dinitrogen (N₂) fixation ability makes alders important for the regulation of nitrogen (N) cycle in forested areas.

We measured the N₂O budget considering fluxes from the soil surface (12 automated chambers; Picarro 2508), tree stems (60 manual sampling campaigns from 12 model trees with chambers at 0.1, 0.8 and 1.7 m; gas chromatographic analysis in lab) and whole ecosystem (EC technique: Aerodyne TILDAS). Simultaneously, soil water level, temperature and moisture were measured automatically, and composite soil samples were taken for physico-chemical analysis. Potential N₂ flux in intact soil cores was measured in the lab using the He-O incubation method.

Average N₂O fluxes from the soil and tree stems varied from 1.2 to 3.0 and 0.01 to 0.03 kg N₂O-N ha^–1 yr^–1, respectively, being the highest during the wet periods, peaking during the freezing-thawing, and being the lowest in dry periods. The average annual potential N₂ flux in the soil was 140 kg N₂ ha^–1 yr^–1 which made the average N₂:N₂O-N ratio in the soil about 60. According to the EC measurements, the forest was a net annual source of N₂O (3.4 kg N₂O ha^–1). Thus, the main gaseous nitrogen flux in this forest was N₂ emission. Our carbon (C) budget showed that the forest was a significant net annual C sink.

Results of our long-term study underline the high N and C buffering capacity of riparian alder forests. For better understanding of C and nutrient budgets of riparian forests, we need long-term, high-frequency measurements of N₂O fluxes from the soil and tree stems in combination with ecosystem-level EC measurements. The identification of microorganisms and biogeochemical pathways associated with N₂O production and consumption is another future challenge.

How to cite: Mander, Ü., Schindler, T., Macháčová, K., Krasnova, A., Escuer-Gatius, J., Maddison, M., Pärn, J., Veber, G., Krasnov, D., and Soosaar, K.: Three-year dynamics of N2O fluxes from soil, stem and canopy in a hemiboreal forest: Impacts of floods and droughts, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7760, https://doi.org/10.5194/egusphere-egu2020-7760, 2020.

Biological nitrogen fixation (BNF) is a key contributor to sustaining the terrestrial carbon cycle, providing nitrogen input that plants require. This is particularly salient for projections of carbon uptake under increased atmospheric carbon dioxide concentrations, which may allow for so-called ‘carbon dioxide fertilisation’ if other plant requirements, such as nitrogen, do not prevent increases in productivity. The amount, processes, and global distribution of BNF is highly disputed and consequently land surface models represent it in varying ways. Looking at the latest generation of CMIP6 earth system models with terrestrial nitrogen cycles, we consider their performance with regard to BNF. We assess models against a new comprehensive meta-analysis of BNF field measurements that gives a global range and site-specific values. We find that compared to the wide range of upscaled observations, the models still have a larger range, with under and overestimates.

How to cite: Davies-Barnard, T., Meyerholt, J., Zaehle, S., Friedlingstein, P., Brovkin, V., Fan, Y., Fisher, R., Jones, C., Lee, H., Peano, D., Smith, B., Wårlind, D., Wiltshire, A., and Ziehn, T.: Terrestrial Biological Nitrogen Fixation in CMIP6 Models, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1951, https://doi.org/10.5194/egusphere-egu2020-1951, 2020.

Nitrogen deposition into arid ecosystems is increasingly shaping biogeochemical dynamics worldwide. We propose a framework to investigate the role of pulsed soil N emission as a mechanism that relays the influences of atmospheric anthropogenic N deposition to areas that otherwise would be minimally affected. We use nutrient spiraling theory, developed in lotic ecosystems, to quantify how regeneration of N by soils influences N deposition downwind of an urban plume. Our hierarchical framework of landscape functioning thereby connects ecosystem processes occurring from microbial (<1cm and hours) to regional (>100km and inter-annual) scales through reciprocal interactions among soils and microbes, pollution sources, and the atmosphere. We use southern California, USA as a case study for evaluation where we test the terrestrial nitrogen spiraling framework using a combination of field experiments, isotopic measurements, theoretical models, and atmospheric transport and chemistry model outputs. Initial results from field wetting experiments, isotope measurements and contrasting modeling approaches all support a spiraling framework and the increasing importance of soil regeneration of nitrogen to deposition farther from the urban source. Soil microbiome communities associated with nitrogen cycling vary both spatially across the deposition gradient and temporally in response to wetting events. From these results we derive terrestrial spiraling metrics that can identify consequences of both soil and anthropogenic inputs to regional nitrogen cycling. New landscape frameworks for evaluating the role of transport and transformations on N cycling can help understand and predict spatial variation in ecosystems connected across multiple scales.

How to cite: Jenerette, D., Krichels, A., Piper, S., Greene, A., Botthoff, J., Shulman, H., Aronson, E., Homyak, P., Sickman, J., and Wang, J.: Pulses of Biogenic Nitrogen Cycling Lead to Atmospheric-Based Nutrient Spiraling in Southern California, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21311, https://doi.org/10.5194/egusphere-egu2020-21311, 2020.

Restoring degraded peat soils to wetlands can be an attractive and efficient measure with many benefits including carbon sequestration, water quality improvement, food and habitat for wildlife, flood control, and opportunities for recreation. Agricultural lands which are restored to wetlands will start rebuild soils and reverse land subsidence. Using eddy covariance towers in four wetlands that were restored in 1997, 2010, 2013 and 2016 in the Sacramento-San Joaquin Delta in California, we saw high carbon sequestration potentials and peat accumulation. Since soil restoration takes place gradually, it is important to specify the critical turning-points in the process of improving soil microbial community structure and nitrogen cycling. In August 2018, soil samples from four wetlands with different restoration ages in the Delta were collected for chemical and microbial analyses. The bacterial and archaeal 16S rRNA genes and functional genes involved in nitrogen cycling (nirS, nirK, nosZ-I, nosZ-II, bacterial and archaeal amoA, nifH, nrfA, and ANAMMOX-specific genes) in soils were determined using a quantitative PCR method. Soil chemical parameters such as C%, N%, Al, Mn, Fe and two different organic and inorganic P pools were analysed as well. Preliminary results indicate significant dissimilarities in the abundance of soil bacterial and archaeal communities, as well as nirS, nirK, nosZ, nifH, nrfA and archaeal amoA gene-possessing microbial communities in different wetlands. Data analysis showed several statistically significant relationships between target gene parameters and soil chemical parameters that were different when comparing the sites with the restoration age. It is clear, that the complexity of the relationships increases as the wetland gets older. For example, in younger wetlands the availability of C and N plays a crucial role in gene abundances while in the oldest wetland, the most important chemical parameters were different phosphorus forms. This might indicate that more than 20 years of C and N accumulation has led to the availability of phosphorus for N transformation now to be the main limiting factor. Another important finding was that the design criteria can also determine how the wetland acts in terms of nitrogen gas emissions. For example, one of the wetlands was designed with more varied bathymetry that includes many open channels and a fluctuating water table. We saw that the nifH gene-possessing microbes that are responsible for molecular N fixing are highly abundant in open water areas while at the same time this wetland has also the highest abundance of nir genes that control N₂O production by denitrifiers. Our study demonstrates that the design of the wetland can have a significant impact on N-transforming processes, but most importantly at some age, restored wetlands become more similar to natural wetlands.

How to cite: Kasak, K., Anthony, T., Valach, A., Hemes, K., Kill, K., Silver, W., Mander, Ü., Szutu, D., Verfaillie, J., and Baldocchi, D.: Variability of nitrogen-cycle microbial communities determined by the age of restored wetlands , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12965, https://doi.org/10.5194/egusphere-egu2020-12965, 2020.

Stable isotope measurements of nitrogen and oxygen in nitrogen-containing molecules provide important constraints on the sources, sinks and pools of these molecules in the environment. Anammox is one of two known biological processes for converting fixed nitrogen to N₂, and through its consumption of ammonium and nitrite and production of nitrate, it impacts the supply of a wide variety of fixed N molecules. Nevertheless, the isotope fractionations associated with the various anammox-associated redox reactions remain poorly constrained. We have measured the isotope effects of anammox in microbial communities enriched for the purpose of nitrogen removal from wastewater by anammox. In this system, we can replicate the ecological complexity exhibited in environmental settings, while also performing controlled experiments. We find that under a variety of conditions, the nitrogen isotope effect for the anaerobic oxidation of ammonium in this system (NH₄⁺ to N₂) is between 19‰ and 32‰, that for the reduction of nitrite (NO₂^– to N₂) is between 7‰ and 18‰, and that for the production of nitrate (NO₂^– to NO₃^–) is between -16‰ and -43‰. We propose that these ranges reflect both (1) a mixture of signals from different anammox-performing species and (2) variation of the isotope effect associated with the anammox process within a given microbial community under different conditions. We seek to understand further what factors control this variability to better interpret stable isotope measurements of N-bearing molecules in environmental settings.

How to cite: Magyar, P., Hausherr, D., Niederdorfer, R., Wei, J., Mohn, J., Bürgmann, H., Joss, A., and Lehmann, M.: The imprint of anammox on the stable isotope compositions of nitrogen-bearing molecules, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15588, https://doi.org/10.5194/egusphere-egu2020-15588, 2020.

Nitrite (NO₂^-) is a crucial compound in the complex N soil cycle. As an intermediate of nearly all N transformations its isotopic signature may provide precious information on the active pathways and processes. NO₂^- analyses have been already applied in ¹⁵N tracing studies increasing their interpretation perspectives. Natural abundance NO₂^- isotope studies in soils were so far not applied and this study aims at testing if such analyses are useful in tracing the soil N cycle.  

We conducted laboratory soil incubations with parallel natural abundance and ¹⁵N treatments accompanied by analyses of soil N compounds (NO₃^-, NO₂^-, NH₄⁺) and released N gases (N₂O and N₂). Water content was varied during the experiment from 55 to 86% water-filled pore space. NO₂^- was immediately extracted and analysed with the denitrifier method for selective nitrite reduction with Stenotrophomonas nitritireducens.

NO₂^- content varied in the wide range from 0.6 to 6.6 μmol kg^-1 soil, whereas NO₃^- content was one order higher and quite stable from 1.3 to 1.7 mmol kg^-1 soil. Similarly, the δ¹⁵N(NO₂^-) varied largely from -16.7 to +8.8‰, whereas δ¹⁵N(NO₃^-) was very stable from 3.5 to 5.9‰. The δ¹⁵N(NO₂^-) was correlated with NO₂^- content. Applying Keeling plot the isotopic signature for the NO₂^- input of -11.7‰ was determined. When related to δ¹⁵N(NO₃^-) this gives the ε(NO₂^-/ NO₃^-) of -16.2‰, which is within the literature data for NO₃^- to NO₂^- reduction step of denitrification.

The parallel ¹⁵N treatment was used to provide interpretation for the natural abundance isotope nitrite dynamics. We observed a sudden drop in ¹⁵N abundance in NO₂^- (a¹⁵N(NO₂^-)) after water addition to the soil from 14.7 to 3.2 at%, whereas  ¹⁵N abundance in NO₃^- (a¹⁵N_NO₃^-) showed only slight decrease from 14.2 to 13.1 at%. This indicates an incorporation of another source of unlabelled NO₂^- for the wet part of the experiment. In natural abundance isotopes this change was also reflected in higher Δ¹⁵N(NO₂^-/ NO₃^-); for the wet part of the experiment it was even positive with +1.6‰, whereas for the dry part it was lower with -5.9‰. This additional nitrite source is most probably oxidation of organic N, which will be clarified by further studies, including detailed analysis with the ¹⁵N Ntrace model.

The observed changes in nitrite isotope characteristics were not reflected in N₂O. Whereas a¹⁵N(NO₂^-) droped to 3.2 at%, for a¹⁵N(N₂O) still 13.6 at% were found. The pool derived N₂O fraction calculated with the ¹⁵N gas flux method showed that the entire N₂O originated from NO₃^- in the wet part of the experiment. This shows that NO₂^- pools originating from different pathways must be isolated and not the entire NO₂^- pool undergoes further reduction to N₂O.

Natural abundance nitrite isotope studies may provide a new important tool in constraining the N soil cycling.

How to cite: Lewicka-Szczebak, D. and Well, R.: Nitrite isotope characteristics in 15N-labelled and non-labelled agricultural soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3692, https://doi.org/10.5194/egusphere-egu2020-3692, 2020.

The controlling factors of biotic denitrification in soil as a source of the greenhouse gas nitrous oxide (N₂O) and of dinitrogen (N₂) are still not fully understood due to the challenges in observing processes that co-occur in soil at microscopic scales and the difficulty to measure N₂ fluxes. N₂O production and reduction depend on the extent of anoxic conditions in soil, which in turn are a function of O₂ supply through diffusion and O₂ demand by soil respiration in the presence of an alternative electron acceptor (e.g. nitrate).

This study aimed to explore microscopic drivers that control total denitrification, i.e. N₂O and (N₂O+N₂) fluxes. To provoke different levels of oxygen supply and demand, repacked soils from two locations in Germany were incubated in a full factorial design with soil organic matter (1.2 and 4.5 %), aggregate size (2-4 and 4-8mm) and water saturation (70%, 83% and 95% WHC) as factors. The sieved soils were repacked and incubated at constant temperature and moisture and gas emissions (CO₂ and N₂O) were monitored with gas chromatography. The ¹⁵N tracer application was used to estimate the N₂O reduction to N₂. The internal soil structure and air distribution was measured with X-ray computed tomography (X-ray CT).

The interplay of anaerobic soil volume fraction (ansvf) as an abiotic proxy of oxygen supply and CO₂ emission as a biotic proxy of oxygen demand resulted in 81% and 84% explained variability in N₂O and (N₂O+N₂) emissions, respectively. These high values dropped to 5-30% when only ansvf or CO₂ was considered indicating strong interaction effects. The extent of N₂O reduction in combination with ansvf and CO₂ even increased the explained variability for N₂O fluxes to 83%. Average O₂ concentration measured by microsensors was a very poor predictor due to the extreme variability in O₂ at short scales in combination with the small footprint of the micro sensors probing only 0.2% of the entire soil volume. The substitution of predictors by independent, readily available proxies for O₂ supply (diffusivity based on air content) and O₂ demand (SOM) leads to a reduction in predictive power.

To our knowledge this is the first study analyzing total denitrification in combination with X-ray CT image analysis, which opens up new perspectives to estimate denitrification in soil and also contribute to improving models of N₂O fluxes and fertiliser loss at all scales and can help to develop mitigation strategies for N₂O fluxes and improve N use efficiency.

How to cite: Rohe, L., Schlüter, S., Apelt, B., Vogel, H.-J., and Well, R.: Oxygen supply and demand as controls of denitrification at the microscale in repacked soil , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5257, https://doi.org/10.5194/egusphere-egu2020-5257, 2020.

Eutrophication of aquatic ecosystems provoked by excess nitrogen (N) concentration is still a major concern worldwide with severe consequences such as hypoxia, biodiversity loss, and degradation of drinking water quality. To face these challenges, a novel N mitigation measure has emerged in the last decades consisting of biofilters made of woodchips. Drainage water from agricultural areas infiltrate through a layer of woodchips before it discharges to an aquatic recipient such as a ditch or a stream. The goal with this technique is to provide optimal conditions for denitrification i.e. an easy degradable carbon source (the woodchips) and an anaerobic environment. There is, however, some concerns regarding the emissions of the greenhouse gas nitrous oxide (N₂O) which can be a by-product of denitrification.

Here, we present results on N removal and N₂O emissions from 9 biofilters differing in age (1–8 years) and representing a total of 18 years of monitoring. The biofilters were all located in agricultural catchments in Denmark (temperate climate conditions). Nitrogen removal in the biofilters was estimated using a mass balance approach measuring N species dissolved in the water (total N, nitrate, nitrite, ammonium) using time proportional automated samplers placed at inlet and outlet of the biofilters. Nitrous oxide emissions were measured every third week both as gaseous form at the surface of the biofilters (closed chamber technique and gas chromatography) and in dissolved form in the water phase at inlet and outlet of the biofilters (headspace technique and gas chromatography). We take advantage of this unique dataset to identify the factors enabling to maximize N removal while minimizing N₂O emissions. Furthermore, we make a first assessment of the potential impact of the increasing number of biofilters on N₂O emissions in agricultural landscapes.

How to cite: Audet, J., Zak, D., and Hoffmann, C. C.: Nitrogen removal and nitrous oxide emissions in woodchips biofilters treating agricultural drainage waters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3318, https://doi.org/10.5194/egusphere-egu2020-3318, 2020.

Gaseous nitrous acid (HONO) and nitric oxide (NO) play a significant role in atmospheric chemistry through the contribution to the hydroxyl radical (OH) and influencing atmospheric oxidization capacity. Soil HONO emissions are considered as a major source of atmospheric HONO. However, soil HONO emissions and their contribution to air quality are rarely quantified. In this study, HONO and NO emissions from cropland, forest, urban green land, and grassland soils in Shanghai were measured by a dynamic chamber system under controlled laboratory conditions. HONO and NO emissions at the optimal water content (10 - 40% of water holding capacity) were highest from forest soil (50.3 ± 30.1 and 70.4 ± 43.9 ng m^-2 s^-1; average ± standard error, respectively), following by cropland soil (48.6 ± 17.4 and 55.8 ± 23.1 ng m^-2 s^-1, respectively), urban green land soil (44.2 ± 9.5 and 39.3 ± 13.3ng m^-2 s^-1, respectively), and grassland soil (27.7 ± 15.6 and 18.4 ± 6.9 ng m^-2 s^-1, respectively). Correlation analysis showed that soil HONO and NO emissions were significantly related with nitrate, total nitrogen, and total carbon (P < 0.01). The total soil emissions of HONO and NO in Shanghai were estimated based on “wetting-drying method”, and then upscaling to China and global. Results showed that global NO emissions from natural and fertilized soils were ~ 4.5 and 2.6 Tg N yr^-1, respectively, which are comparable with the results from IPCC report (2013). The estimated global HONO emissions from natural and fertilized soils were ~ 3.3 and 2.7 Tg N yr^-1, respectively, while those were 0.12 and 0.35 Tg N yr^-1 for China, and 0.01 and 0.33 Gg N yr^-1 for Shanghai, respectively.

The impact of soil HONO emissions on atmospheric oxidation capacity and O₃ concentrations in Shanghai were evaluated using the WRF-Chem model in March of 2016. Daytime HONO concentrations were increased by 0.036 ± 0.015 ppb after considering soil HONO emissions during typical wetting-drying days, and the contribution of HONO photolysis to OH radicals enhanced from 0.095 ppb h^-1 to 0.22 ppb h^-1 and was ~ 2 times the contribution of O₃ photolysis (0.1 ppb h^-1), leading to 0.5 - 1.0 ppb enhancement of 8h-O₃. The sensitivity test showed that O₃ enhancement caused by soil HONO emissions were larger (1.0-1.5 ppb) under low NO_x (cutting down 50%) conditions compared with the current conditions, implies that the importance of soil HONO emissions could be even larger in future considering the on-going NO_x reducing management in China.

How to cite: Wang, M., Zhang, J., An, J., Zhou, F., Zhang, X., Wang, R., Deng, L., Hou, L., Liu, M., and Wu, D.: Emissions of nitrous acid (HONO) and nitric oxide (NO) from soils and its impact on air quality in Shanghai, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-397, https://doi.org/10.5194/egusphere-egu2020-397, 2020.

Climate change has gained extensive international attention due to the impacts on the regional agriculture and water supply. According to IPCC, the global mean temperature will increase by 0.3-0.8 centigrade. Greenhouse gases such as CO₂, CH₄, and N₂O will concentrate and global mean temperature are projected to be increasing. This study separately examines the Greenhouse gases effect arise from different tillage type (dry land and paddy crop) in Wujiang river basin using DeNitrification - DeComposition (DNDC) model. The simulations indicate that, the atmospheric CO₂ and CH₄ concentration increases with the paddy crop plants. Although between two irrigation periods, the field drying event can decrease the CH₄ production effectively. In addition, the paddy soils in this region tend to increase the effect of carbon source resulted from the flooding irrigation. Especially in the first flood irrigation period, the N₂O increases to the maximum value. By contrast, in crop land under rotation of rape and Maize, the effect of carbon sink induced from CO₂ fertilization could generally offset the effect of carbon source. Meanwhile, the effect of carbon sink increased resulted by the plant grows. Thus, the production of CO₂ is always negative. There is no CH₄ production in crop land under rotation of rape and Maize. By contrast, with fertilization input, the N₂O production increases from 0.05 kg C/kg to 0.5kg N/ha/day. The SOC from the top soils (0-10 cm) to bottom (40-50 cm) decreases from 0.021 kg C/kg to 0.014 kg C/kg in either dry land and paddy soils of the Wujiang River region from 1991 to 1994, respectively. These results suggest that SOC storage in paddy and dry land of this region is steady. For the dry land crop (rotation of rape and Maize), the N₂O increased with the fertilization. But for the paddy soils, the irrigation time is the key point period for greenhouse gases production and the variation of carbon and nitrogen in soil. As a representative of paddy crop and dry land crop (rotation of rape and Maize) in western China, the insights gained from the Wujiang River basin may be potentially transferable to other similar agricultural practices in other part of China.

How to cite: wu, X.: The Effect of Cultivation on the Greenhouse Gases Emissions in wujiang river Basin, Yangtze River, China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2345, https://doi.org/10.5194/egusphere-egu2020-2345, 2020.

Nitrogen is the primary limiting nutrient in high latitude ecosystems. Biological nitrogen fixation (BNF) by microorganisms associated with cryptogamic covers, such as cyanolichens and bryophytes, is an important source of new reactive nitrogen in pristine, high-latitude ecosystems. BNF is catalyzed by the enzyme nitrogenase, for which three isoforms have been described; the canonical molybdenum (Mo) nitrogenase which requires Mo in its active site and two alternative nitrogenases, the vanadium and iron-only nitrogenases. The low availability of Mo on land has been shown to limit BNF in many ecosystems from the tropical forest to the arctic tundra. Alternative nitrogenases have been suggested as viable alternatives to cope with Mo limitation of BNF, however, field data supporting this long-standing hypothesis have been lacking.

Here, we elucidated the contribution of the vanadium nitrogenase to BNF by cyanolichens across a 600 km latitudinal transect in eastern Canadian boreal forests. We report a widespread activity of the vanadium nitrogenase which contributed between 15 to 50% of total BNF rates on all sites. Vanadium nitrogenase contribution to BNF was more robust in the northern part of the transect. Vanadium nitrogenase contribution to BNF also changed during the growing season, with a three-fold increase between the early (May) and late (September) growing season. By including the contribution of the vanadium nitrogenase to BNF, estimates of new N input by cyanolichens increase by up to 30%, a significant change in these low N input ecosystems. Finally, we found that Mo availability was the primary driver for the contribution of the vanadium nitrogenase to BNF with a Mo threshold of ~ 250 ng.g_lichen^-1 for the onset of vanadium based BNF.

This study on N₂-fixing cyanolichens provides extensive field evidence, at an ecosystem scale, that vanadium-based nitrogenase greatly contributes to BNF when Mo availability is limited. The results showcase the resilience of BNF to micronutrient limitation and reveal a strong link between the biogeochemical cycle of macro- and micronutrients in terrestrial ecosystems. Given widespread findings of Mo limitation of BNF in terrestrial ecosystems, additional consideration of vanadium-based BNF is required in experimental and modeling studies of terrestrial biogeochemistry.

How to cite: Bellenger, J.-P., Darnajoux, R., Magain, N., Renaudin, M., Lutzoni, F., and Zhang, X.: Ecosystem scale evidence for the contribution of vanadium-based nitrogenase to biological nitrogen fixation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10069, https://doi.org/10.5194/egusphere-egu2020-10069, 2020.

Elevated atmospheric carbon dioxide concentrations are stimulating photosynthesis and carbon sequestration. However, the extent of photosynthetic stimulation in forests under future climates is highly uncertain given that nutrient limitation in soils may constrain the CO₂ fertilization effect. The Birmingham Institute of Forest Research (BIFoR), University of Birmingham established the only global mature temperate deciduous forests Free Air Carbon Dioxide Enrichment (FACE) experiment to study the response of forests to future climates. Fumigation of the forest with ~550 ppm CO₂ started in 2017 and will continue until at least 2026. Soil nutrients cycling including nitrogen transformation in response to elevated atmospheric CO₂ (eCO₂) fumigation is currently investigated to determine the role of nutrient availability in carbon capture by forests. In this paper, we show preliminary results of the response of asymbiotic biological nitrogen fixation (BNF) in soils and epiphytic bryophytes at BIFoR-FACE following a year of eCO₂ fumigation. It is hypothesized that the demand for available nitrogen by trees will increase under eCO₂ and that competition of roots and soil microbes for available nitrogen will enhance asymbiotic BNF to at least meet microbial metabolic nitrogen demands in the long run. Surface soils (0-5 cm) and epiphytic feather moss (Hypnum cupressiforme) growing on oak tree stems in the FACE site were  collected during the second year of eCO₂ fumigation for the quantification of BNF activity using the ¹⁵N₂ assimilation methods (Saiz et al. 2019). Samples were incubated in 50 mL serum bottles under in situ conditions, followed by the analysis of soil and tissue samples for ¹⁵N signature on an Isotope Ratio Mass Spectrometer for the quantification of BNF activity.

The BNF activity under eCO₂ were 369% higher than in soils under ambient atmospheric CO₂. BNF rates associated with feather mosses (Hypnum cupressiforme) did not differ between the eCO₂ and control plots; however, rates under eCO₂ on average were 60% lower than in the control plots. Unlike soils, the moisture of feather mosses correlated significantly (R² = 51%) with BNF activity. Among nutrients in soil with implications for BNF activity, the concentrations of Mg, K, Co and Ni were significantly lower in soils under eCO₂ than in the control plots, while in feather moss tissues no differences were observed.  Our preliminary results show that eCO₂ fumigation primed asymbiotic BNF activity in soils. An enhancement of BNF together with the observation of a relatively low nutrient content under eCO₂ points to important changes in nitrogen cycling processes in the early years of CO₂ fumigation. Further detailed studies are underway to fully disentangle controls on nitrogen availability to trees under future climates.

Reference

Saiz, E, Sgouridis, F, Drifjhout, F & Ullah, S. 2019. Biological nitrogen fixation in peatlands: comparison between acetylene reduction assay and ¹⁵N₂ assimilation methods. Soil Biol. Biochem:131:157-165

How to cite: Ullah, S., Saiz Val, E., Sgouridis, F., and Drijfhout, F.: Early response of biological nitrogen fixation in a mature oak dominated forest to elevated atmospheric CO2 fumigation at BIFoR-FACE , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8678, https://doi.org/10.5194/egusphere-egu2020-8678, 2020.

N₂O and N₂ Emissions from soil in terrestrial ecosystems is a crucial component of the global nitrogen (N) cycle. The response of these two gases emissions from forest soil to temperature change and its underlying mechanisms are essential for predicting N cycle to global warming. Despite the warming-induced effects on soil N cycle is considered to be positive in general, our understanding of temperature sensitivity (Q₁₀) of N₂O and N₂ emissions is rather limited. We quantified the Q₁₀ of N₂O and N₂ emissions in forest soils and explored their major driving factors by conducting an incubation experiment using ¹⁵N tracer (Na¹⁵NO₃) with soil samples from nineteen forest sites from temperate to tropical zones. The environmental conditions largely varied: mean annual temperature (MAT) ranging from -5.4 to 21.5^oC and mean annual precipitation (MAP) ranging from 300 to 2449 mm. The soil pH varied between 3.62 to 6.38. We incubated soil samples under an anaerobic condition with temperature from 5 to 35^oC with an interval of 5^oC for 12 or 24 hours, respectively. Soil temperature strongly affected the production of N₂O and N₂. N₂O and N₂ production rates showed a positive exponential relation with incubate time and temperature for all forest soils. Our results showed that the Q₁₀ values ranged from 1.31 to 2.98 for N₂O emission and 1.69 to 3.83 for N₂ emission, indicating a generally positive feedback of N₂O and N₂ production to warming. Higher Q₁₀ values for N₂ than N₂O implies that N₂ emission is more sensitive to temperature increase. The N₂O/(N₂O+N₂) decreased with increasing temperature in fifteen of nineteen forest soils, suggesting that warming accelerates N₂ emission. Strong spatial variation in Q₁₀ were also observed, with tropical forest soils exhibiting high Q₁₀ values and relatively low Q₁₀ in temperate forest soils. This variation is attributed to the inherent differences in N biogeochemical cycling behavior between the microbial communities among sites. Despite soil temperature primarily controls the N₂O and N₂ emissions, we  explored the effects of other factors such as pH, C/N, DOC and related functional genes. In addition, we partitioned N₂O and N₂ emissions to different microbial processes (e.g., denitrification, co-denitrification and anammox). The results indicated that denitrification was the main pathway of N₂O and N₂ production under anaerobic environment and the contribution increased as temperature rise.

Key words: Temperature sensitivity, N₂O, N₂, Forest soil, Nitrogen cycle, Global warming, Denitrification

How to cite: Yu, H., Fang, Y., and Kang, R.: Response of N2O and N2 Emissions in Forest Soils to Temperature Change across China , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12706, https://doi.org/10.5194/egusphere-egu2020-12706, 2020.

The effects of intermittent drying of normally saturated organic systems such as peatlands, swamps, or wetlands has not been reported quite as often as those of wetting and drying cycles of normally dry soils. We report here the effects of weekly drying and rewetting events on saturated woodchips used as denitrification bed. We used denitrification rates and gas effluxes as indicators of the response of normally saturated organic substrate to intermittent aerobic conditions. We used replicated eight upflow columns in the lab fed with nitrated water, and undergoing variable duration of intermittent aerobic conditions (none, 2, 8, and 24 hours) over a 400d experiment.  We used high-frequency sensors to measure in- and outflow nitrate and DOC concentrations on a 2-hour basis, from which we calculated denitrification rates. We also measured the CO2 and N2O effluxes in the headspace on an hourly basis. The results show a burst of respiration activity during drying events and for several days after rewetting. Isotopic data suggest that respiration was bacterial denitrification. Intermittent aerobic conditions seem to provide the conditions conducive to the generation of more and better quality DOC, which microbes use during subsequent saturated conditions. Our results suggest that intermittent aerobic conditions may have lasting impacts on microbial respiration in wetlands.

How to cite: Birgand, F., Maxwell, B., Thomas, A., Schipper, L., Williams, D., Christianson, L., Tian, S., Helmers, M., Chescheir, C., and Youssef, M.: Effects of drying and rewetting cycles on denitrification and greenhouse gas emissions in normally saturated organic substrate, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22205, https://doi.org/10.5194/egusphere-egu2020-22205, 2020.

Biochar additions may mitigate N₂O emissions from soil. The mechanisms underpinning the mitigation of emissions remain to be elucidated. A series of incubation experiments were performed to investigate the effects of biochar on N₂O production and reduction in columns with a low-fertility or high-fertility soil, with or without the injection of N₂O in the subsoil and with and without glucose (to stimulate denitrification). Biochar was added to the calcareous soils in 0 and 1% (w/w) amounts and moisture was maintained at 70% water-filled pore space (WFPS) over the incubation period. The results revealed that biochar reduced the emissions of soil-produced N₂O by 37−47% and those of injected N₂O by 23−44%. The addition of glucose solution strongly increased N₂O emissions, while biochar reduced total N₂O emissions by as much as 64−81% and those of injected N₂O alone by 29−51%. Differences between the low-fertility and high-fertility soils in the apparent N₂O emission mitigation by biochar were relatively small, but tended to be larger for the low-fertility soil. The results suggest that biochar addition can suppress the production of N₂O in soil and simultaneously stimulate the reduction of N₂O to N₂. Further studies are needed to elucidate the regulatory effects of biochar in soil.

How to cite: Dong, W., Walkiewicz, A., He, C., Bieganowski, A., and Hu, C.: The effect of boichar on the emission of N2O from a calcareous soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6628, https://doi.org/10.5194/egusphere-egu2020-6628, 2020.

Liming to increase pH of acidic soils is a common agricultural practice to optimize crop yields, which also modulates greenhouse gas emissions from soils. In particular, soil pH has been identified as a primary regulator of denitrification pathways with enhanced ratio of nitrous oxide (N₂O) to dinitrogen (N₂) emissions (i.e., enhanced N₂O/N₂ ratio) at lower soil pH. Therefore liming could represent a potential management option to mitigate soil N₂O emissions. However, changes in soil pH have pervasive effects on general microbial activity and on soil properties, including transformations of carbon (C) and bioavailability of phosphorus (P), with a feedback on microbial processes. Thus, the eventual net effects of liming on microbially derived N₂O emissions may be complex. The aim of this study was to discern the interaction between liming (soil pH), and availability of C and P in regulating N₂O emissions from acidic fertilized agroecosystems. Using coarse sandy soils from a long-term liming field experiment, N₂O/N₂ ratios from denitrifying enzyme activity was shown to be strongly affected by liming, i.e., with gradually decreasing ratios at increasing soil pH. Although liming acidic soil (pH, 3.6) to almost neutral (pH, 6.4) favored the reduction of N₂O to N₂, it also enhanced the overall denitrification rate, which eventually resulted in the highest N₂O emission from moderately limed treatments (pH, 4.7). Interactions between P availability and denitrification (and N₂O emission) occurred, where P addition generally increased cumulative N₂O emissions with strongest effect at the moderately limed soil. Mechanistic hypotheses for this effect are discussed. Overall, our results suggest that a critical liming rate should be pursued which may lead to substantial mitigation of N₂O emissions from acidic arable soil.

How to cite: Liang, Z., Abalos, D., and Elsgaard, L.: Interactions between liming and availability of C and P regulate nitrogen transformations and denitrifying potential in an acidic arable soil, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3890, https://doi.org/10.5194/egusphere-egu2020-3890, 2020.

Denitrification usually takes place under anoxic conditions and over short periods of time and depends on readily available nitrate and carbon sources. Variations in CO₂ and N₂O emissions from soils amended with plant residues have mainly been explained by differences in their decomposability. Another factor rarely considered so far is water-extractable organic matter (WEOM) released into soil during residue decomposition. Here, we examined the potential effect of plant residues on denitrification with special emphasis on WEOM. A range of fresh and leached plant residues was characterized by elemental analyses, ¹³C-NMR spectroscopy, and extraction with ultrapure water. The obtained solutions were analyzed for the concentration of organic carbon (OC), organic nitrogen (ON), and by UV-VIS spectroscopy. To test the potential denitrification induced by plant residues or three different OM solutions, these carbon sources were added to soil suspensions and incubated for 24 hours at 20 °C in the dark under anoxic conditions; KNO₃ was added to ensure unlimited nitrate supply. Evolving N₂O and CO₂ were analyzed by gas chromatography and acetylene inhibition was used to determine denitrification and its product ratio. The production of all gases as well as the molar N₂O+N₂-N/CO₂-C ratio was directly related to the water-extractable OC (WEOC) content of the plant residues and the WEOC increased with carboxylic/carbonyl C and decreasing OC/ON ratios of the plant residues. Incubation of OM solutions revealed that the molar N₂O+N₂-N/CO₂-C ratio and share of N₂O are influenced by the WEOM’s chemical composition. In conclusion, the effect of plant residues on potential denitrification is governed by their composition and the related production of WEOM.

How to cite: Surey, R., Schimpf, C. M., Sauheitl, L., Mueller, C. W., Rummel, P. S., Dittert, K., Kaiser, K., Böttcher, J., and Mikutta, R.: Denitrification induced by plant residues is driven by water-soluble organic carbon, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2760, https://doi.org/10.5194/egusphere-egu2020-2760, 2020.

Controlling soil N cycling to mitigate N-oxide emissions and optimize N use efficiency is an important aspect of agricultural soil management. Numerous denitrification models exist that can inform management decisions, but these are limited by the lack of soil N2 flux measurements to validate the model estimates. Measurements of soil denitrification - including both N₂O and N₂ fluxes - are challenging, however, due to methodological limitations for the measurement of N₂ and the spatial/temporal heterogeneity of denitrification in soils.

We used laboratory incubations of re-packed soil cores, combined with both soil flushing and stable isotope techniques, to measure denitrification in two agricultural soils, as part of the DFG-research unit “Denitrification in Agricultural Soils: Integrated Control and Modelling at Various Scales (DASIM)”. The laboratory incubations used an automated mesocosm system, with regular measurements of both N₂O and N₂, to assess the response of soil denitrification to a variety of control factors. Control factors simulated typical scenarios that might occur in the field, including different amounts/types of plant residue, and changes in moisture, temperature, NO₃^- and oxygen concentration. Both natural abundance and ¹⁵N labeling of the soil mineral N pool were used to assess denitrification pathways.

Here we contrast the results of the incubation data from a sandy Podzol and silt-loam Luvisol. These data will be used to calibrate newly developed DASIM models as well as denitrification sub-modules of existing biogeochemical models. They will also inform the next steps of this work, which will extend the laboratory incubation technique to measure denitrification in undisturbed field soils.

How to cite: Matson, A., Burkart, S., Grosz, B., Köster, J. R., Merl, S., and Well, R.: Response of soil N2 and N2O fluxes to denitrification control factors in two agricultural soils , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15158, https://doi.org/10.5194/egusphere-egu2020-15158, 2020.

Living roots and arbuscular mycorrhiza fungi (AMF) are widespread in most terrestrial ecosystems and play an important role in ecosystem nitrogen (N) cycling. However, the influence of living roots and AMF on soil N₂O emissions remains poorly understood. In this study, we conducted a pot experiment with ryegrass (Lolium perenne) growing in a greenhouse for three months with three factors: root and AMF presence (None or unplanted, Root or with roots, and Root+AMF or with roots colonized by AMF), two N addition levels (N0 and N1 with 0 and 50 mg N kg^-1 soil) and two P addition levels (P0 and P1, with 0 and 20 mg P kg^-1 soil).

Our results showed that N addition didn’t have significant effect on N₂O emission, however, we detected significant effects of Root and Root+AMF, particularly under P addition. Though the colonization of AMF didn’t significantly influence N₂O emission, the presence of roots (Root and AMF+Root treatments) deceased N₂O emission by 58%-67% compared with the None treatment. P addition increased (+134%) N₂O emission from unplanted soil but decreased (74%-98%) N₂O emission under planted soil regardless of AMF colonization. Moreover, there were no significant relationship between N₂O emission and soil pH, NH₄⁺-N and net N mineralization. The lower N₂O emission from rooted treatments were mainly due to the lower soil NO₃^--N (and MBN) content which might be immobilized by plant biomass, while the higher N₂O emission from unplanted soil under P addition was attributed to increased soil available (r=0.760, P<0.01) and total (r=0.654, P<0.01) phosphorus content. We conclude that root presence and P addition played an important role in regulating N₂O emission from P-limited soils.

How to cite: Shen, Y., Xu, T., and Zhu, B.: The effects of living roots and arbuscular mycorrhiza fungi (AMF) on soil N2O emissions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6822, https://doi.org/10.5194/egusphere-egu2020-6822, 2020.

Nitrous oxide (N₂O) is a potent greenhouse gas associated with nitrogen fertiliser inputs to agricultural production systems. Minimising N₂O emissions is important to improving the efficiency and sustainability of grassland agriculture. Multispecies grassland swards composed of plants from different functional groups (grasses, legumes, herbs) have been considered as a management strategy to achieve this goal. Numerous soil nitrogen transformation pathways can lead to the production of N₂O emissions. These transformation pathways are regulated by soil microbial communities and the environmental conditions and management practices that impact on them. Much research has been carried out on N cycling and N₂O emissions from predominantly grass monoculture systems. However, there is a lot yet to understand about how agricultural grasslands with diverse plant communities influence soil N cycling and N₂O emissions. A lysimeter experiment was set up as a completely randomised block design and carried out over a full year to investigate N₂O production, and nitrogen cycling associated with four sward types. The swards four swards were: perennial ryegrass (PRG, Lolium perenne); PRG and low white clover (PRG + LWC, Trifolium repens); PRG and high white clover (PRG + HWC); PRG, WC and ribwort plantain (PRG + WC + PLAN, Plantago lanceolata) managed at 250, 90, 0, and 45 kg N ha^-1yr^-1, respectively. Fertiliser N was applied by syringe as urea in splits at suitable timings to meet grass growth demands. N₂O fluxes were measured using a static chamber technique and additional samples were taken after the final flux sample to measure the associated N₂O isotopomers using a novel Cavity Ring Down Spectroscopy technique. Leachate volumes were measured on a weekly basis and composite monthly samples were used to determine the total amount of N leached from each treatment over the full year. Herbage was harvested on a monthly basis to measure DM yield (kg DM ha^-1), total N (%) and N yield (kg N ha^-1).This work reports on the N₂O emissions and N leaching associated with the four sward treatments and related these N losses to the treatments DM yields and N uptake as an estimation of the efficiency of these differing grassland management strategies. N₂O isotopomer measurements were used to indicate N transformation pathways driving N loss over the growing season particularly around periods of peak N₂O emissions.

How to cite: Bracken, C., Lanigan, G., Richards, K., Tracy, S., Müller, C., and Murphy, P.: Analysis of N2O emissions and isotopomers to understand nitrogen cycling associated with multispecies grassland swards at a lysimeter scale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9218, https://doi.org/10.5194/egusphere-egu2020-9218, 2020.

Growing plants affect soil moisture, mineral N and organic C (C_org) availability in soil and may thus play an important role in regulating denitrification. The availability of the main substrates for denitrification (C_org and NO₃^-) is controlled by root activity and higher denitrification activity in rhizosphere soils has been reported. We hypothesized that (I) plant N uptake governs NO₃^- availability for denitrification leading to increased N₂O and N₂ emissions, when plant N uptake is low due to smaller root system or root senescence. (II) Denitrification is stimulated by higher C_org availability from root exudation or decaying roots increasing total gaseous N emissions while decreasing their N₂O/(N₂O+N₂) ratios.

We tested these assumptions in a double labeling pot experiment with maize (Zea mays L.) grown under three N fertilization levels S / M / L (no / moderate / high N fertilization) and with cup plant (Silphium perfoliatum L., moderate N fertilization). After 6 weeks, all plants were labeled with 0.1 g N kg^-1 (Ca(¹⁵NO₃)₂, 60 at%), and the ¹⁵N tracer method was applied to estimate plant N uptake, N₂O and N₂ emissions. To link denitrification with available C in the rhizosphere, ¹³CO₂ pulse labeling (5 g Na₂¹³CO₃, 99 at%) was used to trace C translocation from shoots to roots and its release by roots into the soil. CO₂ evolving from soil was trapped in NaOH for δ¹³C analyses, and gas samples were taken for analysis of N₂O and N₂ from the headspace above the soil surface every 12 h.

Although pots were irrigated, changing soil moisture through differences in plant water uptake was the main factor controlling daily N₂O+N₂ fluxes, cumulative N emissions, and N₂O production pathways. In addition, total N₂O+N₂ emissions were negatively correlated with plant N uptake and positively with soil N concentrations. Recently assimilated C released by roots (¹³C) was positively correlated with root dry matter, but we could not detect any relationship with cumulative N emissions. We anticipate that higher C_org availability in pots with large root systems did not lead to higher denitrification rates as NO₃^- was limited due to plant uptake. In conclusion, plant growth controlled water and NO₃^- uptake and, subsequently, formation of anaerobic hotspots for denitrification.

How to cite: Rummel, P. S., Well, R., Pfeiffer, B., Dittert, K., Floßmann, S., and Pausch, J.: NO3- uptake and C exudation – do plant roots stimulate or inhibit denitrification?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19445, https://doi.org/10.5194/egusphere-egu2020-19445, 2020.

Sufficient nitrogen fertilisation is essential for obtaining the crop yields required to feed the growing population. Moreover, nitrogen applied to fields is often lost to a number of processes including denitrification, surface run-off and leaching. These processes can damage the local ecology and contaminate water supplies. Additionally, nitrogen lost as ammonia gas and the large energy input required to synthesize ammonia are both large contributors to global greenhouse gas emissions. Choosing fertilisation strategies to optimise the proportion of nitrogen taken up by crops (nitrogen use efficiency) can reduce the production of ammonia and the pollution of water supplies.

We developed a mathematical model that describes the movement of water and multiple nitrogen species in soil at the field scale over a growing season. The model was then used to assess the nitrogen use efficiency of varying fertilisation strategies. We consider the effects of a number of biological, chemical, and physical processes including: root growth, root uptake, the transformation of nitrogen between different nitrogen species, and the effect of soil water movement on nitrogen transport. The resulting model is comprised of a coupled system of partial and ordinary differential equations that describe the mathematical interplay between nitrogen transport, water movement, and root uptake, which were solved numerically using a finite element approach. Numerical experiments were conducted to determine how nitrogen uptake efficiency was affected by different fertilisation strategies. We examine numerous cases by varying the quantity of fertiliser applied to the soil and the fertiliser application times.

The numerical experiments suggest that, under uniform rainfall rates, the optimal fertilisation times (within the bounds of typical times found in agriculture) can result in 25% more nitrogen uptake than the worst strategies. However, there were large time periods, 28 days for the first application and 10 days for the second, which resulted in close-to-optimal nitrogen use efficiency. The results of this study, in addition to crop health and past and predicted rainfall, could be taken into consideration by farmers while choosing fertilisation times to optimise nitrogen uptake efficiency.

How to cite: McKay Fletcher, D., Ruiz, S., Duncan, S., Chadwick, D., Jone, D., and Roose, T.: Optimising Fertilisation Strategy for Nitrogen Uptake Efficiency, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8609, https://doi.org/10.5194/egusphere-egu2020-8609, 2020.

Denitrification in unsaturated soils is widely assumed to be a result a result of the formation of so-called hot spots. However, this is a hypothesis, which is hard to test experimentally. Furthermore a better understanding of the microscale dynamics might be very helpful to derive better models at the macroscale.

Experiments have been conducted, where artificial aggregates from sintered glas have been inocculated with microorganisms and been placed in environments with different oxygen availabilities. Very high-resolution simulations are conducted to reproduce the dynamic of the generation of nitric and nitrous oxide based on a model of microbial growth parametrised with experimental data from batch experiments. The simulations allow a detailed analysis of the local and temporal dynamics of denitrification inside the aggregates.

How to cite: Ippisch, O., Zawallich, J., Dörsch, P., Schlüter, S., Horn, M. A., and Vogel, H.-J.: Understanding the Dynamics of Denitrification with high-resolution Simulations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19467, https://doi.org/10.5194/egusphere-egu2020-19467, 2020.

Nitrogen (N) fertilization is an essential agronomic practice, which increases crop yields and improves soil fertility. Globally, more than 110 x 10⁹ kg of chemical N fertilizers are applied each year with urea-N being one of the most affordable options. Upon urea hydrolysis, any portion not assimilated by crops is either volatilized as NH₃ or microbially nitrified (i.e., NH₄⁺ oxidized) to leachable NO₃^- and NO₂^-. Nitrification inhibitors (NI) are increasingly co-applied as a sustainable agricultural practice and block the process of nitrification, resulting in a temporal increase of NH₄⁺ in the soils. Several studies have documented the effectiveness of NIs in retaining soil NH₄⁺ and increasing crop yields, but less is known about the effects of NIs on the fate of urea–N and the overall impact of NIs on the soil microbial community.

In a 60 day soil mesocosm experiment, we investigated the effects of Nitrapyrin (NI; 2-chloro-6-(trichloromethyl)pyridine) co-applied with a selection of urea-based fertilizers: urea (U); U with urease inhibitors (U+UI); methylene-urea (MU); and zeolite-coated urea (ZU), on a typical Mediterranean soil under ambient summer conditions. We showed that NI applied with urea fertilizers resulted in a slower decay of extractable NH₄⁺ with a concurrent increase in NH₃ volatilization. Integrated measures of soil NH₄⁺ were 1.5 to 3.3-fold greater when NI was applied. At the same time, there was a 10 to 60% reduction in integrated measures of NO₃^- and NO₂^- when NI was applied with the tested fertilizer types, except MU fertilizer where the integrated measures of NO₃^- and NO₂^- doubled. Upon urea hydrolysis, the released NH₄⁺ was transformed to NO₃^- and NO₂^-, which subsequently decreased in concentration following a typical nitrification - denitrification pathway in the absence of plants. Soil N₂O emissions from urea fertilizers were reduced by 40% with UI, 50% with NI, and 66% with NI + UI.

Interestingly, 15 days after the application of NI, there was a decrease in bacterial abundance (eub genes; qPCR) in all fertilized treatments. NI dramatically reduced the abundance of ammonia-oxidizing microbes (amoA genes) and there were fewer bacteria associated with denitrification genes (nirK, nirS, nosZ) when NI was applied. 

At the end of the experiment, there was no significant difference in total N among all fertilized soils. Total N was in excess when compared to the control, and it was a considerable N pool potentially immobilized in microbial biomass in the absence of crops.

In conclusion, the use of NI doubled NH₄⁺ retention in the soil and decreased soil N₂O emission by 50%, through negatively affecting ammonia oxidizing and denitrifying microbes and subsequently reducing soil available NO₃^- and NO₂^-. The application of NIs should be carefully planned and synchronized (timing) with crop growth to reduce subsequent N transformations and N loss to the environment.

Keywords: urea, zeolite, methylene-urea, nitrification inhibitor, nitrapyrin, calcareous soil, soil nitrogen

How to cite: Giannopoulos, G., Elsgaard, L., Zanakis, G., B. Franklin, R., L. Brown, B., and Barbayannis, N.: Effects of the nitrification inhibitor nitrapyrin on urea-based fertilizers in a Mediterranean calcareous soil: N dynamics and microbial functional genes., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1763, https://doi.org/10.5194/egusphere-egu2020-1763, 2020.

Sources of N₂O (nitrous oxide) are multiple in the biosphere, but the only known process consuming N₂O is the microbial reduction of N₂O to dinitrogen (N₂), which has traditionally been attributed to denitrifying bacteria and archaea. Recently, N₂O reductase genes (nosZ) clearly phylogenetically differentiated from “typical” NosZ (Clade I) were shown to be more abundant in many soil ecosystems than “typical” nosZ genes, suggesting that our understanding of the role of nosZ in controlling soil N₂O emissions was incomplete. This more abundant group of nosZ genes was designated as “atypical NosZ” or Clade II.  Here, by synthesizing a meta-data of the 631 peer-reviewed papers published on NosZ in the six years since NosZ Clade II was first reported in the literature, we found that only 10% of studies evaluated Clade II NosZ and an additional 7% of papers merely mentioned Clade II NosZ showing little awareness of this novel gene. In addition, disciplinary silos also contribute to the slow spread of awareness about Clade II nosZ. A lack of consensus on the terminology used to refer to Clade I versus Clade II nosZ (more than 17 terminologies) may contribute to confusion about the two clades. Finally, we proposed several recommendations to accelerate progress in understanding the roles of Clade I versus Clade II N₂O reducers in controlling soil N₂O emissions.

How to cite: Shan, J., Ooi, S., Sanford, R. A., Chee-Sanford, J., Löffler, F., Konstantinidis, K., and Yang, W. H.: Advancing our understanding of novel nitrous oxide reducers, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20866, https://doi.org/10.5194/egusphere-egu2020-20866, 2020.

Using reclaimed water as a resource for landscape water replenishment may alleviate the major problems of water resource shortages and water environment pollution. However, the safety of the water and the risk of eutrophication remain doubted by the public. Our study aimed to reveal the difference between natural water and reclaimed water and to discuss the rationality of reclaimed water replenishment from the perspective of microorganisms. We analyzed the microbial community structures in natural water, reclaimed water and natural biofilms and the community succession was clarified along the ecological niches, water resources, liquidity and time using 16S rRNA gene amplicon sequencing. Primary biofilms without the original community were added to study the formation of microbial community structures under reclaimed water acclimation. The results showed that the difference caused by ecological niches was more than those caused by the liquidity of water and different water resources. No significant difference was found in the microbial diversity and community structure caused by the addition of reclaimed water. Based on the microbial analysis, reclaimed water replenishment is a feasible solution that can be used for supplying river water. Innovatively, we introduced the study of biofilms and determined that the monitoring of biofilms or sediments closely related to water was also important for the early warning of water bloom, providing a unique perspective for the management of eutrophication.

How to cite: Li, J., Sun, Y., Wang, X., Yin, M., and Xu, S.: Formation and succession of microbial community structure in different ecological niches under reclaimed water acclimation, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12613, https://doi.org/10.5194/egusphere-egu2020-12613, 2020.

Freshwater microalgae isolates from a UK headwater catchment (collected in 2017) were tested for their growth and media nitrogen speciation changes when presented with low molecular weight dissolved organic nitrogen compounds. The location has input from livestock run off increasing organic matter in stream. Experimental treatments and initial isolation took place in controlled culture cabinets kept at 15°C, with a 16:8 light:dark cycle and light c.a. 50 µmol m^-2 s^-1. Treatments included separately presented urea and glutamate, alongside negative (no N or P sources) and positive controls (nitrate or ammonium). Nitrogen addition treatments were provided with the same phosphorus source, trace minerals, trace metals and took place for two weeks. Different species isolated from the location showed optimal growth on different organic nitrogen sources. Organic nitrogen compounds caused growth at least comparable to inorganic sources. Cell growth was best on dissolved organic nitrogen compounds for some species. This relatively quick cycling of organic nitrogen compounds in river systems to photosynthetic growth has implications for ecosystem heath and capacity to mitigate organic nitrogen inputs. Anthropogenic activity that increases organic nitrogen may favour certain species compositions, altering downstream ecosystem functions such as algal bloom formation and dominant microalgae species. Further work will use stable isotope investigation of potential uptake mechanisms and wider work is required on understanding how the ecosystem may respond to organic nitrogen changes. 

How to cite: Bayliss, C. E., Johnes, P., Evershed, R. P., Sanchez-Baracaldo, P., and Maberly, S. C.: Responses to dissolved organic nitrogen compounds by recently isolated freshwater microalgae species, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5713, https://doi.org/10.5194/egusphere-egu2020-5713, 2020.

Magnetic-nanoparticle mediated isolation (MMI) is a new method for isolating active functional microbes from complex microorganisms without substrate labeling. In this study, the composition and properties of the magnetic nanoparticles （MNPs）were characterized by a number of techniques. And then the MNPs were added to activated sludge rich in ammonia nitrogen-degrading bacteria after long-term stable treatment,  another set of experiments plus urea was set as the only carbon source in the system. Compared with the group without MNPs, degradation experiment results showed that the ammonia nitrogen degradation ability of a group of MNPs was slightly improved. The high-throughput sequencing results showed that the addition of MNPs did not change the microbial community structure of activated sludge under long-term stable conditions, and that the addition of urea as a nitrogen source significantly changed the microbial community structure. RDA analysis results also showed that Comamonadaceae_unclassified and Thiobacillus absolutely dominated in situ ammonia degradation, and the change in dominant genera showed the same trend as the degradation rate of ammonia nitrogen. It has also proved that the complex flora after adding magnetic nanoparticles is more adaptable to newly introduced pollutants, using MMI to study pollutant-degrading microorganisms under in-situ conditions has a broad application prospect.

How to cite: Yin, M., Sun, Y., Zheng, D., Wang, L., Zhao, X., and Li, J.: Separating and characterizing functional nitrogen degraders via magnetic-nanoparticle mediated isolation technology in high concentration of ammonia nitrogen wastewater treatment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12833, https://doi.org/10.5194/egusphere-egu2020-12833, 2020.

The membrane rotary energy-yielding ATPases represent the cornerstone of cellular bioenergetics for all three domains of life. The archaeal ATPases (A-type ATPases) are functionally similar to the eukaryotic and bacterial F-type ATPases that catalyze ATP synthesis using a PMF. However, they are structurally more similar to the vacuolar-type (V-type) ATPases of eukaryotes and some bacteria that function as proton pumps driven by ATP hydrolysis. Significant variation in subunit composition, structure, and mechanism of the archaeal ATPases is thought to confer adaptive advantage in the variety of extreme environments that archaea inhabit.

The ammonia-oxidizing archaea are recognized to exert primary control of nitrification in the marine environment, are major contributors to soil nitrification, and have a habitat range extending from geothermal systems, to acidic soils and the oceanic abyss. The basis for their remarkable adaptive radiation is obscured by a relatively simple metabolism – autotrophic growth using ammonia for energy and nitrogen. In this study, we find that their adaptation to acidic habitats and the extreme pressures of the hadal zone of the ocean at depths below 6000 meters is correlated with horizontal transfer of a variant of the energy-yielding ATPase (atp) operon. Whereas the ATPase genealogy of neutrophilic soil and upper ocean pelagic AOA is congruent with their organismal genealogy inferred from concatenated conserved proteins, a common clade of V-type ATPases unites phylogenetically disparate clades of acidophilic and piezophilic species.

A function of the so-acquired V-ATPases in pumping excessive cytoplasmic protons at low pH is consistent with its increased expression by acid-tolerant AOA with decreasing pH. Consistently, heterologous expression of the thaumarchaeotal V-ATPase significantly increased the growth rate of E.coli at low pH. Additional support for adaptive significance derives from our observation that horizontal transfer is also associated with the adaptive radiation of Micrarchaeota, Parvarchaeota and Marsarchaeota into acidic environments. Their ATPases are affiliated with the acidophilic lineage ATPases of Thermoplasmatales and phylogenetically divergent from the corresponding species tree.

Another notable finding is that single hadopelagic AOA species contain both A- and V-type ATPases, suggesting that extensive horizontal transfer of atp operons is a highly active and ongoing process within AOA. The presence of an additional V-type ATPase in hadopelagic AOA may provide fitness advantages in the deep ocean with elevated hydrostatic pressure, as the proposed function of V-ATPase in pumping excessive cytoplasmic protons at high pressure may serve to maintain the cytosolic pH homeostasis in marine AOA.

Taken together, our study provides the first clear evidence of a significant role of horizontal transfer of atp operon in the adaptive radiation of AOA, one of the most successful organisms on Earth, and other archaeal species, spanning the TACK and DPANN superphyla as well as Euryarchaeota phylum.

How to cite: Wang, B. and Qin, W.: Archaea as Global Explorers: Let`s Exchange ATPase and Occupy More Extreme Habitats!, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20953, https://doi.org/10.5194/egusphere-egu2020-20953, 2020.

Bulk sedimentary nitrogen isotopes (δ¹⁵N) have been used as an accurate redox proxy in well-preserved sedimentary systems, however, fewer studies of N-isotope have been performed in lacustrine shales.  In this paper, we report the first δ¹⁵N data from the Chang 7 Shale from a core drilled in the Ordos Basin. Bulk δ¹⁵N values are significantly higher in Zone A (the Chang 7₃ and the lower part of the Chang 7₂ submembers, average = 9.4 ± 1.3‰) than in Zone B (the upper part of the Chang 7₂ and the Chang 7₁ submembers, average = 5.4 ± 1.5‰). Given the lithological characteristics and previous geochemical measurements, we suggest that sediments within Zone A of the Chang 7 Shale were mainly deposited under suboxic bottom water conditions, whereas Zone B sediments show evidence of deposition under oxic deep water regimes. Additionally, organic carbon isotopes (δ¹³C_org) and total nitrogen (TN) values were measured to characterize any processes that might control alteration of the bulk δ¹⁵N signal, including changes in organic matter source and post-depositional processes. Our results show that there is no significant difference in the organic carbon isotopes (δ¹³C_org) and total nitrogen (TN) values between the two zones. In conclusion, we suggest that the difference in δ¹⁵N values through the Chang 7 Shale primarily reflects differences in the depositional redox conditions and δ¹⁵N values of shale can provide important details regarding the depositional history of unconventional resource plays.

How to cite: Chen, R. and Liu, G.: Evaluating nitrogen isotopes as proxies for depositional redox conditions in shales: A case study from the Chang 7 Shale in the Ordos basin, North China., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1814, https://doi.org/10.5194/egusphere-egu2020-1814, 2020.

The definition of natural background concentration levels (NBLs) of geogenic trace metals in groundwater is a challenging issue, particularly in areas where anthropogenic activities are also present. The estimation of NBLs, in combination with environmental quality standards, in such areas is particularly important for the establishment of relevant groundwater threshold values. Over 100 groundwater samples were collected and analysed from four Cr(VI) impacted, alluvial groundwater bodies of central Greece during two consecutive hydrologic years. A common feature of the examined aquifers is the presence of weathered ultramafic rock material in the alluvial sediments. Most sampled boreholes (79 %) are used for irrigation, whereas 21 % of them are used for domestic drinking water supply. Hexavalent Cr concentrations in groundwater, ranging from below detection limit to 430 μg/L, have been attributed to both geogenic and anthropogenic factors. The scope of the present study is to estimate the NBL of Cr(VI) by using a classical statistical approach and a deterministic preselection method and test the comparability of results. In the statistical approach the distribution of samples versus Cr(VI) concentrations has been explored by using probability plots. In this way, the concentration variations within the examined groundwater bodies can be studied and the presence of sub-populations becomes evident by breaks in the slope. In the instance of the preselection method, the concentrations of a set of additional analyzed parameters in ground water, including major water ions and nitrate as well as dissolved oxygen, have been taken into account in order to categorize the samples into two groups of low and high anthropogenic influence, respectively. The comparability of the results derived by the two approaches are discussed in the context of EU Water Framework Directive.

How to cite: Argyraki, A., Pyrgaki, K., Kelepertzis, E., Botsou, F., and Megremi, I.: Estimation of natural background level of Cr(VI) in ultramafic rock related alluvial aquifers of central Greece: Comparison of results by statistical and deterministic preselection method approaches, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11699, https://doi.org/10.5194/egusphere-egu2020-11699, 2020.

Soil pollution is a worldwide concern and several countries are established guidelines. In the case of Chile, the very diverse soils characteristics along the country made difficult to set guidelines to acceptable levels of potentially toxic elements (PTEs) in soils. However, due to several reasons such as anthropogenic contamination, and increment of erosion rates there is urgency in to establish guidelines values to this parameters. In Chile, the most of abandoned mining wastes are located in the northern part which could negatively have impacted the ecosystem and human health. Thus, in absence of guidelines to PTEs in soils, the use of regional geochemical baseline (GBL) as a reference values could be a first approach to preliminary determine pollution levels of PTEs in soils. The objective of this study was to use the calculated GBL values to determine the influence of mining activities on the levels of PTEs in soils and to determine the spatial distribution maps of PTEs. A regional mapping of soils was conducted in northern part of Chile during 2017-2018 and the pH, electrical conductivity, redox potential and concentration of PTEs was determined. A systematic sampling in a 20,000 square-kilometer area was conducted and 467 rural top and sub soil samples were taken to determine their physical and chemical composition. The content of PTEs was determined by ICP-OES. The GBL values were estimated following the upper-whisker limit method. The pH, electrical conductivity, and redox potential of soils were 4.9-9.5, 10.5-56,000 mS/cm, and 89.7-348.3 mV, respectively. The median concentration of Mn (695.9 mgkg^-1) was the highest followed by V (148.4 mgkg^-1), Ni (75.2 mgkg^-1), Zn (59.7 mgkg^-1), Cu (59.0 mgkg^-1), Sb (34.0 mgkg^-1), As (18.3 mgkg^-1), Cr (17.9 mgkg^-1), Sn (17.5 mgkg^-1), Pb (14.6 mgkg^-1), Co (13.0 mgkg^-1), Cd (12.9 mgkg^-1), Hg (3.6 mgkg^-1), and Mo (3.3 mgkg-1). The GBL for Cu, Zn, V, As, Mo, and Sb were higher than the reported average for world soils. The spatial distribution maps of Cu, Pb, Zn, Cr, As and V were used to determine pollution levels. Statistical correlation models showed the influence of either abandoned mining sites or active mining operation on the pollution levels of PTEs in the surrounding soils. The geochemical baseline values could contribute for government decision-makers to choose the best available remediation technologies for the impacted area.

How to cite: Reyes, A. and Delgado, J.: Spatial distribution maps of Cu, Pb, Zn, Cr, As and V in rural soils in northern part of Chile: The use of geochemical baseline values as an index in environmental assessment., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12342, https://doi.org/10.5194/egusphere-egu2020-12342, 2020.

Mining is an important pillar of economic growth of many African countries. However, problems arising from this activity pose serious challenges, which most of these countries have difficulties to address properly because of poor environmental governance as highlighted in the Africa Mining Vision. Many African countries also lack a precise inventory and assessment of environmental impacts of abandoned and derelict mines. As a consequence, there is an urgent need to evaluate the true extent of the detrimental effects of metal and metalloid pollutants and their impact on human and animal health, as well as on ecosystems. Between 2013 and 2017 and thanks to a Partnership Programme between UNESCO and the Swedish International Development Cooperation Agency (Sida), a network of over 100 Earth scientists from 29 Africa assessed the impacts of mining activities in sub-Saharan Africa. The project intended to provide crucial scientific knowledge that will contribute to understanding the factors that control cycling of pollutants from mine sites (abandoned or active) to soils, water and vegetation and the impact on the food chain. We anticipate that the results of the project will be used to improve the environmental norms in individual countries in Sub-Saharan Africa and the efficiency of governments in addressing the challenges related to the adverse effects of mining activities. The preliminary results of the project have recently been published as a Special Issue in the Journal of Geochemical Exploration. During the presentation, we intend to highlight few examples where mining activities alone or in interaction geological background are contributing to threat the ecosystem and health of neighbouring communities. We will also draw the lessons learnt from the implementation of this continental-scale project.

How to cite: S. Félix, T.: Highlights on a UNESCO/Sida project to assess the environmental and health challenges of mining activities in Sub-Saharan Africa, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18709, https://doi.org/10.5194/egusphere-egu2020-18709, 2020.

Uranium is a trace metal yielding an average concentration in the Earth’s crust of about 2 to 4 mg/kg, and it occurs naturally in low levels in rock, soil, and water. Although widely known for its radioactive properties, at low levels dissolved uranium is more harmful by its chemical toxicity. The World Health Organisation (WHO) recommends a maximum concentration of 30 µg/l uranium in tap water, as well as a tolerable daily intake limit of 0.6 µg/kg body weight. Since 2011, tap water in Germany must not exceed uranium concentrations of 10 µg/l.

The uranium budget of the groundwater in Lower Saxony comprises mainly of geogenic input through water-rock interaction along the hydrological cycle and within the respective hydrogeological units, and possibly through century-old mining activities, and more recently the use of uranium bearing mineral fertilisers in farming. While the vast majority of uranium concentrations are significantly below 10 µg/l with many values below detection limit, some detached areas display elevated uranium with one confined maximum concentration of 124 µg/l. In order to determine uranium background values, statistical analyses accounted for hydrogeological units of the aquifer, land use, and well depths. Anomalous peak concentrations are unlikely to be a result of variations in geogenic background values alone and require further investigations. A possible rise of uranium concentrations caused by a downward shifting redox front, as proposed in other regions in Northern Germany, is yet to be identified in Lower Saxony.

How to cite: Stumpf, R., Budziak, D., Deus, N., and Elbracht, J.: Spatial anomalies of uranium background levels in groundwater of Lower Saxony, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21458, https://doi.org/10.5194/egusphere-egu2020-21458, 2020.

The aeration zone beneath topographic groundwater recharge areas, comprising variably water-saturated soil, regolith and bedrock is a typically large but hardly explored compartment of the Critical Zone. Fluid and matter exchange within the deep hillslope aeration zone, the dynamics of its diverse microbial dwellers and their contribution for subsurface matter cycling and groundwater quality are widely unknown. In the Hainich Critical Zone Exploratory (Collaborative Research Center AquaDiva, Küsel et al., 2016), we accessed the aeration zone and groundwater resources in fractured limestone-mudstone alternations by exploratory drillings and hillslope monitoring wells. Multi-year groundwater sampling, environmental monitoring, drill core and petrological analyses revealed a multi-storey architecture of the aeration zone, covering perched water bodies and multi-directional flow phenomena (Lehmann and Totsche 2020). In a ~50 m deep well that underwent pronounced seasonal head fluctuation up to 25 m of oligotrophic groundwater, we incubated bedrock fragments that mimicked large fracture habitats and monitored the dynamic environmental conditions in the fractured mixed carbonate-/siliciclastic alternations as well. During groundwater-saturated colonization, successional exposure to seasonal de-saturation and re-saturation, we analyzed the bacterial and archaeal 16S rRNA diversity and found a diverse bacterial, and less diverse archaeal community, both including persistent genera that withstood the harsh environmental changes. In accordance with mature fracture-surfaces (drill cores), the colonized rock fragments were dominated by Gammaproteobacteria. General compositional differences to communities within the phreatic zone (i.e. groundwater and rock matrices), and shallow sources in soil, suggest a distinct subsurface microbiome that is hardly represented by ecological surveys that utilize groundwater or rock samples.

References:

Küsel, K., Totsche, K. U., Trumbore, S. E., Lehmann, R., Steinhäuser, C., Herrmann, M. (2016). How deep can surface signals be traced in the critical zone? Merging biodiversity with biogeochemistry research in a central German Muschelkalk landscape. Frontiers in Earth Science 4 (32). https://doi.org/10.3389/feart.2016.00032

Lehmann, R., Totsche, K. U. (2020). Multi-directional flow dynamics shape groundwater quality in sloping bedrock strata. Journal of Hydrology 580. https://doi.org/10.1016/j.jhydrol.2019.124291

How to cite: Lehmann, R., Lazar, C. S., Küsel, K., and Totsche, K. U.: Exploring the hydrogeological functioning and microbial habitats of the deep hillslope aeration zone in limestone-mudrock alternations, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18437, https://doi.org/10.5194/egusphere-egu2020-18437, 2020.

Despite the high relevance of karstic aquifers as drinking water reservoirs, nitrate pollution of groundwater is posing an increasing threat on a global scale. Under anoxic conditions, nitrate can be converted to N₂ by denitrification or anaerobic ammonia oxidation (anammox) and thus be removed from the system. However, in the presence of oxygen, nitrification may continue in the groundwater, supported by the activity of ammonia oxidizing bacteria (AOB), archaea (AOA), and the recently discovered complete ammonia oxidizers (comammox bacteria). We aimed to disentangle different sources and sinks of nitrate and key microbial players involved in nitrogen transformation processes in oligotrophic limestone aquifers of the Hainich Critical Zone Exploratory (CZE; Germany). Assessment of process rates using ¹⁵N-labeling techniques revealed a variance of nitrification rates by two orders of magnitude across six oxic groundwater wells. Surprisingly, wells with nitrate concentrations higher than 300 µmol L⁻¹ showed only very low nitrification activity of less than 2 nmol NO₃⁻ L⁻¹ d⁻¹, pointing to surface inputs rather than in situ production. In turn, maximum nitrification activity of 127 nmol NO₃⁻ L⁻¹ d⁻¹ coincided with a consistently large fraction of comammox bacteria of more than 70% in the groundwater nitrifier community. Estimated per cell activities of ammonia oxidation suggested that a contribution from comammox was needed to sufficiently explain the observed nitrification rates. Anaerobic ammonia oxidation (anammox) and denitrification as potential nitrate or nitrite sinks varied within a smaller range of 1 to 5 nmol N₂ L⁻¹ d⁻¹ across anoxic wells and were dominated by anammox, most likely linked to a low availability of organic carbon and suitable inorganic electron donors for chemolithoautotrophic denitrification. Differences in activities agreed well with 100 times higher transcriptional activity of hzsA genes involved in anammox compared to nirS genes involved in denitrification. Our findings provide strong evidence for nitrification supported by comammox bacteria in oligotrophic groundwater and for anammox as the dominating N removing process.

How to cite: Herrmann, M., Krüger, M., Thamdrup, B., and Küsel, K.: Nitrate sources and sinks in oligotrophic groundwater, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14556, https://doi.org/10.5194/egusphere-egu2020-14556, 2020.

Human activity has more than doubled reactive nitrogen delivery to Earth’s ecosystems. In the past several decades, efforts have been made to reduce agricultural inputs of nitrogen, but the decrease of the nitrate concentration in rivers is also controlled by natural processes, especially by flow and denitrification in the aquifer. Yet, with current knowledge, it remains difficult to characterize transit times and groundwater denitrification rates at scales relevant for mitigation actions (catchment scale to regional scale).

Data directly obtained in piezometers generally display large variabilities without any obvious correlation to any landscape, geological or geomorphological characteristics. Here we propose an alternative method based on in-stream measurements to get a representative view of the role of the aquifer in the temporary storage and degradation of nitrates. We performed spatially-distributed measurements in low-order streams within a 35 km2 agricultural catchment underlain by a crystalline, fractured bedrock aquifer. Measurements were performed during low-flow. Stream discharge and radon activity were used to determine the groundwater discharge into the streams. Silica was used as an age-tracer [1]. Nitrate concentrations and isotopic ratios allowed to characterize the denitrification in the aquifer.

Results show that in-stream measurements provide a representative view of transport and denitrification in the aquifer. They highlight that the scale of homogenization is larger than the studied catchment, and reveal an unexpected correlation between the mean residence time and the characteristic denitrification time. This allows to hypothesize a common control on residence time and denitrification in the aquifer, that could be exercised by the depth of the weathered zone. Unraveling such a correlation could be a first step towards a global characterization of aquifer processes through geophysical imagery methods.

[1] Marcais, J., et al. 2018. Dating groundwater with dissolved silica and CFC concentrations in crystalline aquifers. STOTEN.

How to cite: Vautier, C., Petton, C., Abhervé, R., Pinay, G., Lavermann, A., and de Dreuzy, J.-R.: Characterizing denitrification in the aquifer and transit times based on spatially-distributed measurements in streams, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18141, https://doi.org/10.5194/egusphere-egu2020-18141, 2020.

In the last few decades, the degradation of water quality and resulting regulations, such as the European Water Framework Directive, the United States Clean Water Act, and the New Zealand Resource Management Act 1991 have promoted water quality monitoring in terms of parameter richness, spatial density and high temporal resolution. Long-term catchment observatories have been strengthened to gain insight into hydrological and biogeochemical processes. New technologies have been developed and deployed to collect more in situ water quality data at higher frequencies. Thus, water quality monitoring around the world has produced a large amount of data from research catchments but also from national monitoring networks. Despite these efforts, water quality data are highly heterogeneous in terms of targeted parameters, measurement methods, sampling frequencies. Also, accessibility to water samples differ from each hydrological compartment (stream, groundwater, soil water and precipitation). Among water quality time-series, higher sampling frequencies are available for stream water where monitoring is relatively easy to carry out generating a high amount of data. However, groundwater data are rare since monitoring and access is relatively difficult. Also, the aim of monitoring network evolved with time. In fact, networks are usually established for a specific purpose which is changing with time and the questions the network is trying to answer? This raise the issue of spatial and temporal flexibility- multi purpose network and the use of network to support model development which could be seen as a “theoretical” monitoring network.

The objective of this talk is to present a review of methods used for analysing temporal water quality signals and models outputs, based on a panel of examples from few but densely monitored environmental research observatories. Such infrastructures also give an insight into critical zone (CZ) research that help to build a transdisciplinary community to identify the main knowledge gaps in CZ processes and behaviour.

How to cite: Thomas, Z., Fovet, O., Zhang, Q., Rajanayaka, C., Zammit, C., and Gascuel-Odoux, C.: Main knowledge gaps in critical zone processes and behaviour: Extracting information from water quality time-series data and models outputs, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11400, https://doi.org/10.5194/egusphere-egu2020-11400, 2020.

Weathering processes in clay environments are of major importance because they participate to regulate elemental cycling and mass transfer in the critical zone with major implications for carbon and nitrogen cycling.

In that aim, we measured 1) dissolved CO₂, alkanes, O₂ and N₂ concentrations in clay pore waters by rock degassing, 2) soil gas flux and concentrations, and 3) δ¹³C of CO₂ and alkanes in two contrasted tectonic contexts.

The first context is the marine Jurassic black marls in the French Alps, characterized by deep burial, high erosion rates and dominant physical weathering processes. These marls are well-known for their occurrences of natural methane gas seeps. In this area, we carried out rock degassing on outcropping weathered claystone in complement of soil flux measurements to constrain the implication of weathering processes on the natural gas releases. These measurements are also tested as a new component of environmental baseline assessment in the field of unconventional hydrocarbons.

The second context is the marine Cretaceous Tégulines Clay of the north-eastern part of the Paris Basin, characterized by low burial, low erosion rates, and dominant chemical weathering processes. In this area, we carried out rock degassing on soil and weathered claystone accessible by deep boreholes, in order to define the depth of the critical zone and major reactions controlling the weathering profile.

Oxygen and nitrogen concentrations are the record of the atmospheric diffusion through the formations. Some values are higher than the gas solubility, which could be attributed to rock desaturation and air bubbles, and clay sorption (only for nitrogen).

Weathering processes induce a significant CO₂ increase and a large range of δ¹³C_CO2, providing evidence of two major CO₂ sources: CO₂ internally controlled by carbonates and organic-derived CO₂ of internal and external origins. In Alpine black marls, field observations suggest a low depth affected by weathering, due to intense erosion. In Tégulines Clay, the CO₂ increase provides evidence of a ~ 20 m-thick critical zone. The lowest δ¹³C_CO2 indicates that the highest reactive zone (organic matter degradation, calcite dissolution and pyrite oxidation) is ~10 m deep, in agreement with the depth of the root network.

Nature and amounts of alkanes are contrasted in the two contexts. In deep burial environment, alkanes are abundant, in particular, in the “ fontaines ardentes” gas seeps in the French Alps. Composition of hydrocarbon gas and δ¹³C of methane strongly suggest a thermogenic origin. Outcropping black marls contain methane, suggesting oxidation of higher alkanes. That assumption is supported by δ¹³C_CO2 of soil close to δ¹³C of alkanes. In low burial environment, small amounts of methane are present that rapidly disappear with weathering. Some methane concentrations could be attributed to diffusion of external methane formed by degradation of organic matter under reducing conditions in soil.

Overall those results suggest that dissolved gas and their isotopic signature are good markers of weathering processes in the critical zone.

This research was funded by the EU H2020 Programme (grant 764531 - SECURe), ANDRA-BRGM projects.

How to cite: Lerouge, C., Blessing, M., Debure, M., Gal, F., Kloppmann, W., and Robinet, J.-C.: Dissolved gas (CO2, alkanes, O2, N2) in critical zone developed on claystone, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11430, https://doi.org/10.5194/egusphere-egu2020-11430, 2020.

In the treatment of raw domestic wastewaters in vertical flow constructed wetlands (VFCW), a sludge layer is formed at the surface of the first-stage filters by the retention of wastewater’s suspended solids. The deposits constituting this layer is now known to accumulate and degrade a large variety of contaminants during regular conditions of operation. The potential release of the contaminants from the sludge deposits under disturbed conditions or during off-site sludge reuse is therefore a major concern. This study investigated the influence of organic colloids on the mobilization of major and trace elements bound to VFCW surface sludge deposits.   

Although the role of organic and/or mineral colloidal carrier phases in the transport of elements in natural systems has been extensively studied, little is known in contrast on the production of colloidal carrier phases from anthropic materials and media such as the sludge deposits considered here.

The acid/base neutralizing capacity (environmental assessment procedure ANC/BNC) (CEN/TS 14429) was carried out to assess the release at different pHs. Samples of sludge deposits were contacted with solutions in a wide pH range and the suspensions filtered through 0.45 µm acetate cellulose filters were subsequently analyzed. In addition, the suspensions were also treated by ultrafiltration using successively membranes of decreasing pore size (30 kDa, 10 kDa and 3 kDa). The leached organic molecules were thereby divided into three groups: (i) large colloids (30 kDa-0.45 µm), (ii) small colloids (10 kDa-3 kDa) and (iii) truly dissolved fraction (< 3 kda). The permeates were analyzed for major and trace elements and organic particles. UV-vis spectra were also recorded to evaluate organic matter aromaticity.  

Results showed that the molecular weight of the organic matter released was pH-dependent. Under very acidic conditions, the release of dissolved and poorly aromatic organic matter was mostly observed. At natural pH, close to neutrality, the sludge deposits released mostly large organic colloids. At higher pHs, the release of larger organic colloids was observed associated with an increase in the aromaticity of organic molecules.

The major and trace mineral elements released were found in the different fractions analyzed, depending on  their affinity with the organic colloidal carrier phases described previously. A first group of elements (As, P, B, V, Na, K) were mostly found in solution, and therefore poorly affected by colloidal transport regardless of pH conditions.  A second group (Co, Cu, Ni, Cd, Zn) was found to be relatively uniformly distributed in the fractions associated with the large and small colloids as well as in the dissolved fraction. A third group (Cr, Ba, Mn, Ca, Li, Mg, Sr) was mostly associated to large organic and/or mineral colloids.  

The results obtained in this study are a contribution to a better description of colloidal production and the release of associated elements and contaminants from VFCW sludge deposits. This is a key issue in the assessment of environmental risks related to the operation of the treatment plants or the reuse of the sludge material.

How to cite: Banc, C., Gautier, M., Denise, B., Maria, L.-T., Rémi, M., and Rémy, G.: Influence of pH on the formation of organic and mineral colloïds and the associated release of various elements from surface sludge deposits of vertical flow constructed wetlands., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17490, https://doi.org/10.5194/egusphere-egu2020-17490, 2020.

Climate change threatens to exacerbate existing problems in urban areas arising from the urban heat island. Furthermore, expansion of urban areas and rising urban populations will increase the numbers of people exposed to hazards in these vulnerable areas. We therefore urgently need study of these environments and in-depth assessment of potential climate adaptation measures.

We present a study of heat wave impacts across the urban landscape of Vienna for different future development pathways and for both present and future climatic conditions. We have created two different urban development scenarios that estimate potential urban sprawl and optimized development concerning future building construction in Vienna and have built a digital representation of each within the Town Energy Balance (TEB) urban surface model. In addition, we select two heat waves of similar frequency of return representative for present and future conditions (following the RCP8.5 scenario) of the mid 21^st century and use the Weather Research and Forecasting Model (WRF) to simulate both heat wave events. We then couple the two representations urban Vienna in TEB with the WRF heat wave simulations to estimate air temperature, surface temperatures and human thermal comfort during the heat waves. We then identify and apply a set of adaptation measures within TEB to try to identify potential solutions to the problems associated with the urban heat island.

Global and regional climate change under the RCP8.5 scenario causes the future heat wave to be more severe showing an increase of daily maximum air temperature in Vienna by 7 K; the daily minimum air temperature will increase by 2-4 K. We find that changes caused by urban growth or densification mainly affect air temperature and human thermal comfort local to where new urbanisation takes place and does not occur significantly in the existing central districts.

Exploring adaptation solutions, we find that a combination of near zero-energy standards and increasing albedo of building materials on the city scale accomplishes a maximum reduction of urban canyon temperature of 0.9 K for the minima and 0.2 K for the maxima. Local scale changes of different adaption measures show that insulation of buildings alone increases the maximum wall surface temperatures by more than 10 K or the maximum mean radiant temperature (MRT) in the canyon by 5 K.  Therefore, additional adaptation to reduce MRT within the urban canyons like tree shade are needed to complement the proposed measures.

This study concludes that the rising air temperatures expected by climate change puts an unprecedented heat burden on Viennese inhabitants, which cannot easily be reduced by measures concerning buildings within the city itself. Additionally, measures such as planting trees to provide shade, regional water sensitive planning and global reduction of greenhouse gas emissions in order to reduce temperature extremes are required.

We are now actively seeking to apply this set of tools to a wider set of cases in order to try to find effective solutions to projected warming resulting from climate change in urban areas.

How to cite: Hamer, P., Trimmel, H., Weihs, P., Faroux, S., Formayer, H., Hasel, K., Laiminghofer, J., Leidinger, D., Masson, V., Nadeem, I., Oswald, S., Revesz, M., and Schoetter, R.: Can climate adaptation solutions fix the urban heat island? An assessment of the thermal conditions during heat waves in Vienna impacted by climate change and urban development scenarios for the mid-21st-century , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8668, https://doi.org/10.5194/egusphere-egu2020-8668, 2020.

Chemical weathering strongly impacts the evolution of the Critical Zone and the climate system. The large number of factors affecting weathering rates, however, makes it difficult to interpret measurements across different climatic and geologic settings. Here, we use the π theorem of dimensional analysis to develop a theoretical framework for global datasets of chemical weathering rates. The analysis reveals the dominant role of wetness on the chemical depletion of parent materials and provides a functional relationship to estimate the chemical depletion fraction from readily available climatic variables. Based on this finding, we calculate the spatial distribution of chemical depletion fraction and identify the areas where weathering rates are limited by the supply of fresh minerals or by water availability, and the areas where they are susceptible to future shifts in wetness.

How to cite: Calabrese, S. and Porporato, A.: Hydroclimatic control on global weathering regimes, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11645, https://doi.org/10.5194/egusphere-egu2020-11645, 2020.

The present study seeks to evaluate the application of the ²³⁸U-²³⁴U-²³⁰Th radioactive disequilibrium methodology for the determination of the regolith production rates in thick weathering profiles marked by long histories, encountered under various climate regimes, but still very little studied by these techniques. For this purpose, ²³⁸U-²³⁴U-²³⁰Th disequilibria have been analyzed in a ≈ 11 m-deep profile developed on a granitic bedrock in south China (Longnan, Jiangxi Province) under a subtropical climate. The results demonstrate that in such deep weathering profiles the determination of weathering rates from the analysis of U-series nuclides in bulk rock samples cannot be recovered by applying in one step to the entire alteration profile the modeling approach classically used to interpret the U-series nuclides, i.e. the “gain and loss” model. The modeling has to be made on subsections of relatively small size (<1 or 2 meters of thickness), so that the model assumptions can be met, especially the constancy of the mobility parameters along the weathering zone. The results also confirm that the upper part of the weathering profiles marked by the vegetation/biological influences and responding to the short-term climate variations is not well adapted for applying the U-series nuclides methodology for recovering regolith production rates. Based on the data, regolith production rates were estimated independently on four different zones of the profile. Similar values of ~2m/Ma have been obtained whatever the level, suggesting that such a profile of more than 5 million years would be formed at a relatively stable long-term production rate (averaged over several thousand years). This slow production rate of 2 m/Ma can be reconciled with the previously published in situ ¹⁰Be data from the same profile, when assuming non steady-state erosion of the upper part of the profile. Slow denudation rates similar to the U-series derived production rates of 2 m/Ma can thus be obtained with a minimum exposure time of 40 ky, and an inherited component of 20-25*10⁴ at/g originating from the exhumed deeper part of the profile. Altogether the data demonstrate that the combined analysis of U-series and cosmogenic nuclides, which has the potential to become a relevant approach to constrain the dynamics of continental surfaces, requires (a) dense and deep sampling for both nuclides studies, and (b) also to consider more systematically the polyphased and variable history of erosion of the continental surface during the Quaternary. These results have implications for the interpretation of long-term accumulation of ¹⁰Be at depth and ¹⁰Be data variations in granitic alteration profiles.

How to cite: Jia, G., Chabaux, F., van der Woerd, J., Pelt, E., di Chiara, R., Ackerer, J., Zhao, Z.-Q., Yang, Y., Xu, S., and Liu, C.-Q.: Regolith production rates from 238U-234U-230Th disequilibrium in a deep granitic weathering profile (Longnan, SE China), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11100, https://doi.org/10.5194/egusphere-egu2020-11100, 2020.

Lithium (Li) contents and isotopes were studied in the Dommel catchment, a small riverine system in northern Belgium and the southern part of the Netherlands discharging into the Meuse River downstream of Eindhoven. This covered surface and groundwaters developed onto sand and gravel in the catchment. The integrated investigation aimed at evaluating the potential of Li isotopes as effective tracers of anthropogenic activities in addition to efficiently trace water/rock interaction processes within a sandy environment. The d⁷Li values and Li concentrations were measured following standard chemical purification of Li using the cationic exchange resin protocol in a clean lab. Lithium-isotope compositions were measured with a Neptune MC-ICP-MS and Li concentrations by ICP-MS.

Dissolved lithium concentrations in the Dommel catchment span one order of magnitude ranging from 1.55 to 39.20 µg/L, with a mean concentration of 6.58 µg/L higher than the worldwide riverine average of 1.9 µg/L. The dissolved d⁷Li displays a large range of variation from +5.4‰ to +27.8‰. Part of the catchment can be impacted by smelter effluents with Li concentrations in the range 91 – 526 µg/L (mean value 288.36 µg/L) and a d⁷Li of around +25.6‰ and then dilution along the flowpath of the river basin.

To go further into the interpretation of the dataset in terms of using Li isotopes as a probe of anthropogenic activities, we first applied an atmospheric-input correction to waters both for Li concentration and d⁷Li as rainfall constitutes an important fraction of dissolved elements in the Dommel waters (8 to 100% of Li in waters is derived from atmosphere). Secondly, we determined and quantified the anthropogenic influence using δ⁷Li and mixing equations in the impacted parts of the catchment.

How to cite: Negrel, P., Millot, R., and Petelet-Giraud, E.: Lithium isotopes as a probe of anthropogenic activities: Dommel River, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20385, https://doi.org/10.5194/egusphere-egu2020-20385, 2020.

By 2017, the book "Soils within cities" (Levin et al., 2017) is moving away from the pedologist's description of urban soils to a broader understanding of urban soils, including the functions and the services they provide. This approach, which complements the naturalistic description of the soil, corresponds to the approach derived from the millennium ecosystems assessment (Morel et al., 2015; Walter et al., 2015). It is considered to be relatively anthropocentric and thus favours the integration of the soil in the urban socio-ecosystem.

Considering the soil by both its pedogenesis and functioning in ecosystems induces taking into account the dynamics of this system, but raises, with regard to the literature on urban soils, the existing lack to qualify and quantify the processes of genesis and evolution, especially in relation to ongoing climate change (Baveye et al., 2016). On the other hand, the description of soil ecosystem services (regulation, provisioning, cultural services) immediately reveals the interdependence of soil biophysicochemical processes with those occurring in the hydrosphere, the atmosphere and the biosphere (Adhikari and Hartemink, 2016). In this respect, the soil plays an interface role, but is deeply disturbed in urban areas.

The objective of the communication will be to review the status of urban soil in the "urban critical zone" concept. Through methodologies and results from projects implemented in French major cities that have enabled the development of databases, we will review the classification of these atypical soils and the changes in their properties and functions. Through the definition of the services they provide, we will propose a more integrated vision of this compartment of the urban ecosystem, by specifying the forcing caused by its interface position, but also the opportunities of improvement foreseen by the development of solutions for revegetation and de-sealing. We will see how the timeframe of soil evolution in urban zones can influence the data collection of soil parameters and mapping.

How to cite: Bechet, B., Beaudet, L., Branchu, P., Cannavo, P., Delolme, C., Jean-Soro, L., Lebeau, T., Le Guern, C., Marseille, F., and Schwartz, C.: Soils in the urban critical zone - Analyse of anthropogenic pressures and current proposals to preserve soil functions and ecosystem services, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12113, https://doi.org/10.5194/egusphere-egu2020-12113, 2020.

One significant effect of urbanization is the modification of environmental conditions, with potential effects on the functioning of urban ecosystems and on their ability to perform functions and to provide service. This is due to both the multiple changes of surfaces and soils, and to an increased human pressure. These changes have indeed major negative impacts on natural resources such as air, water, soil, and biodiversity they host, and may affect locally the human thermal comfort, in addition to the climate change. A better understanding of the physical and biogeochemical processes leading to these changes is then crucial in order to propose and to optimize the mitigation and adaptation strategies. Following the recent efforts in the development of Critical Zones Observatories (CZOs), a new research initiative will regroup well-monitored and well-characterized urban field sites all over the French national territory within a National Observation Service called Observil. This observatory aims to address a multidisciplinary approach of urban environments, through a smart definition of appropriate variables and indicators required to better describe the physical and geochemical processes involved in the quality and the dynamic of the soil-surface-atmosphere compartments in cities. To do that, a common Spatial Information System dedicated to the creation of a structured observation database is under construction, in order to regroup the data from a large network bringing together 9 French cities under very contrasted environmental conditions (urban morphology, geology, climate). The main scientific questions addressed by this observation network project will be presented, along with a description of the the selected variables measured on the different sites.

How to cite: Rodriguez, F., Nabucet, J., Kouadio, J., Bechet, B., Blond, N., Bozonnet, E., Chebbo, G., David, D., Guernouti, S., Houet, T., Keravec, P., Lebeau, T., Lipeme-Kouyi, G., Masson, V., Puissant, A., Richard, Y., Schwartz, C., and Thomas, Z.: Observil - A French network project of urban critical zone observatories, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14486, https://doi.org/10.5194/egusphere-egu2020-14486, 2020.

Arctic tundra is currently undergoing significant changes induced by the effects of a rapid temperature rise, that in the Arctic is about twice as fast as in the rest of the world. The response of the system composed by the permafrost active layer, soil and vegetation is especially relevant. In fact, it is still unclear whether the system will turn from a carbon sink to a carbon source, owing to the interplay of two opposite phenomena: the increasing time span of the growing season, favouring Net Ecosystem Production (NEP), and the increasing soil temperatures, favouring degradation of organic matter through heterotrophic respiration (HR) and then creating a positive climate feedback. In this work, we analyse soil-vegetation-atmosphere CO₂ flux data of a field campaign conducted in the Bayelva river basin, Spitzbergen, in the Svalbard Archipelago (NO) during summer 2019, measured by a portable accumulation chamber. We use a “Critical Zone” perspective, considering the multiple interactions between biotic and abiotic components. We measured the Net Ecosystem Exchange (NEE) and Ecosystem Respiration (ER) along a slope gradient at different degrees of soil humidity and active layer depths, relating flux data to climate and environmental parameters, soil physical-chemical parameters and vegetation type. The statistical empirical relationships between variables are analysed to identify the main drivers of carbon exchanges. An empirical data-driven model is built to describe the coupled dynamics of soil, vegetation, water and atmosphere that contributes to budgeting the carbon cycle in the Arctic Critical Zone. A comparison of the carbon fluxes obtained with the accumulation chamber method and an Eddy Covariance tower located in the same area is also addressed.

How to cite: Giamberini, M., Baneschi, I., Lelli, M., Magnani, M., Raco, B., and Provenzale, A.: A Critical Zone Approach to Carbon Fluxes in the Arctic Tundra, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2956, https://doi.org/10.5194/egusphere-egu2020-2956, 2020.

Increasing drought event is one of the major threats to yield stability and crop production. However, the precise quantification of crop response to such extreme weather is still in lack. Unlike the deterministic researches of drought effects, we propose an insightful probabilistic perspective to quantify drought impacts on maize yield across China. The county-specific combination of annual maize yield anomaly and standardized precipitation evapotranspiration index (SPEI) across its growing season during 1981-2010 was utilized to build a copula-based probabilistic diagram, for the purpose to predict yield loss risk under different drought types. The results reveal that, when compared with the expected long-term yield, the reduction of maize yield and its uncertainty was in line with the drought severity across the growth season, with yield reduced by -5.14%, -8.05% and -3.94% under moderately dry, severely dry, and extremely dry, respectively. Despite the spatial pattern of SPEI existed varying timescales in determining yield anomaly across different counties, the number of counties where maize experienced drought with a response time starts from June and July accounted for 55.28% of counties across China, and that drought with one month duration occupied 50.29%. A considerable gap in the likelihood of maize yield reduction was detected under drought and under non-drought conditions, which further confirmed the negative impacts of drought on maize yield. Moreover, the conditional estimation revealed that the semi-arid region was more susceptible to the drought-induced yield loss risk of maize in comparison to other regions. The probability of yield loss for maize amplified according to the drought severity along with the significant differences (P < 0.05) among the extreme, severely and moderately drought conditions across all of these sub-regions. Our results highlight the improving knowledge of drought on crop yield anomaly and consequent adaptation was essential for the decision making in coping with extreme weather in agricultural production.

How to cite: Liu, S. and Wu, W.: The occurrence of drought amplified yield loss risk for maize production in China, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4130, https://doi.org/10.5194/egusphere-egu2020-4130, 2020.

Shrub is the main vegetation type for vegetation restoration in the Loess Plateau, which plays an important role in the regional ecosystem restoration. Study on the relationships between vegetation and soil water of typical shrub ecosystems are significant for the restoration and reconstruction of ecosystems in the Loess Plateau. Three typical shrub (Hippophae rhamnoides Linn., Spiraea pubescens Turcz., and Caragana korshinskii Kom.) ecosystems were chosen in the Loess Plateau. Field experiments were conducted to investigate the factors that influencing the processes of rainfall interception and root uptake of typical shrubs. S-Biome-BGC model was established based on the Biome-BGC model by developing the rainfall interception and soil water movement sub-models. The model was calibrated and verified using field data. The calibrated S-Biome-BGC model was used to simulate the characteristics of leaf area index (LAI), net primary productivity (NPP), soil water content and the interactions among them for the shrub ecosystems along the precipitation gradients in the Loess Plateau, respectively. The results showed that the predictions of the S-Biome-BGC model for soil water content and LAI of typical shrub ecosystems in Loess Plateau were significantly more accurate than that of Biome-BGC model. The simulated RMSE of soil water content decreased from 0.040~0.130 cm³ cm^-3 to 0.026~0.035 cm³ cm^-3, and the simulated RMSE of LAI decreased from 0.37~0.70 m² m^-2 to 0.35~0.37 m² m^-2. Therefore, the S-Biome-BGC model can reflect the interaction between plant growth and soil water content in the shrub ecosystems of the Loess Plateau. The S-Biome-BGC model simulation for LAI, NPP and soil water content of the three typical shrubs were significantly different along the precipitation gradients, and increased with annual precipitation together. However, different LAI, NPP and soil water correlations were found under different precipitation gradients. LAI and NPP have significant positive correlations with soil water content in the areas where the annual precipitation is above 460~500 mm that could afford the shrubs growth. The results of the study provide a re-vegetation threshold to guide future re-vegetation activities in the Loess Plateau.

How to cite: Zhang, Y., Li, X., Li, W., Fang, W., and Shi, F.: Coupling model of ecohydrology and simulation of typical shrub ecosystems on the Loess Plateau, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4423, https://doi.org/10.5194/egusphere-egu2020-4423, 2020.

To estimate the energy amount needed to heat indoor living and public spaces, the heating degree day (HDD) parameter is applied. This is the most common climatic indicator of energy consumption for the building heating, which is calculated for a certain period of the year by summing the absolute deviations of the average daily ambient temperature from the selected base temperature. However, human biometeorological sensitivity is based not only on the ambient temperature, but on a combination of temperature, humidity, and wind speed.

We have conducted a comparative analysis of the climatic and biometeorological characteristics of the regions including the largest Russian cities. For the effective ambient temperature range of 17.2 to 21.7⁰C (comfort zone), we have calculated changes in the comfort zone for Moscow, St. Petersburg, Krasnodar, Novosibirsk, and Vladivostok according to data from 1959 to the present. Despite all climate differences between regions with selected cities, allowance for wind speed leads to a decrease in the number of days with temperature within the comfort zone.

This study supported by Russian Science Foundation (project No 16-17-00114).

How to cite: Belova, I., Krivenok, L., and Dokukin, S.: Energy demand estimates in large Russian cities and its biometeorological characteristics , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8931, https://doi.org/10.5194/egusphere-egu2020-8931, 2020.

Since the founding of New China, especially since the reform and opening up, China has experienced the fastest economic development and the most profound population migration in history. The large-scale migration of China's rural population and labor force is particularly evident. China's rural population accounts for 40.42% in 2019. China's rural population is large, and urban-rural and regional differences are also large. Due to the current data and information limitations and the characteristics of China's national conditions, there are very few related studies on China's overall rural population.

Fine-scale population distribution data at the fine scale play an essential role in numerous fields, for example urban planning and management, and disaster assessment and developing population differentiation policies. The rapid technological development of remote sensing (RS) and geographical information system (GIS) in recent decades has benefited many fine resolution population spatialization studies. However, most of the existing population spatialization methods have been studied at the regional or urban scale, and few studies have been conducted on the unit population in rural areas. In view of the fact that existing demographic data cannot meet the actual needs of analysis, management and scientific research in terms of spatial precision, a new population distribution estimation method combining nighttime lighting and residential building attributes is proposed in our study. In view of this, studying the spatial distribution of the population in rural areas is used as the purpose of this article. Based on the night light data, natural city boundaries are determined. A rural area delineation method based on Head-to-Tail segmentation classification combined with administrative village verification is proposed, which provides a feasible method for large-scale automatic extraction of rural area boundaries. Coupled with POI (Points of Interest) data, based on elevation, slope, night light images, and land cover, the population spatialization model of the random forest is developed and improved based on the weight of the house properties and light intensity. Finally, a high-precision population distribution dataset is obtained, which is closer to the actual population distribution. The research results show that based on the proposed population spatialization model, street demographic values can be fitted better, and the basis for more accurate population estimation is laid. It provides a reference for data fusion and is of great significance for rural area development planning.

How to cite: Dong, C.: Research on Improvement of Rural area Population Spatial Distribution Model Based on Random Forests, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13129, https://doi.org/10.5194/egusphere-egu2020-13129, 2020.

Adaptation to global changes and promotion of cities resilience requires the development of integrated approaches to take into account the urban critical area as a whole. The major challenge is to assess this integrated approach evolving the main actors taking part on critical zone management. One way to do so might be the development of a network of actors and scientists committed to the long-term evolution of practices and having a common strategy for territories use. The poster presents a case study aiming to implement an integrated water management strategy in urban development based on the organization of a network of territory actors and scientists. The methodology here presented was built to focus on three main questions: what specific problems does integrated water management reveal for the various stakeholders? What are their usual opportunities of exchange and information? And which organization allows them to solve their problems, while taking into account the pre-existing networks on water management?. To answer these questions, we conducted comprehensive interviews with water and development stakeholders and representatives of networking organization.

Our results highlights the need of collaborative development of urban projects between planners and water managers: each of them is confronted with a diversity of concerns related to several factors, such as

• their position as a stakeholder in the intentional management of water or in the effective management of water;
• the scope of responsibilities of local communities in the management of wastewater, stormwater, drinking water, biodiversity ;
• the specific regional characteristics (coastal territories, morphologies of urban area).

Moreover, the results show that the existing networks address partially some of the questions: the study highlights in particular the lack of dialogue and knowledge transfer between water management actors and urban development actors, resulting in the design of urban projects that are not adapted to the new standards of urban management (e.g. stormwater). In addition, research projects are emerging in relation to big cities issues, but are sometimes in competition with each other. Also, the dissemination of results remains reserved for cities already endowed with significant engineering capacities.

Improvements in the networking is required to promote integrated urban water management, we come up with three organizational scenarios including objective analysis of existing networks of the main actors. The implementation of an integrated approach to hydrological systems linked to energy efficiency in urban areas requires taking into account the critical zone as a whole.

How to cite: Diaz, M., Thomas, Z., Prenveille, A., and Floch, N.: A case study aiming to promote cities resilience based on urban critical zone management as a whole, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22557, https://doi.org/10.5194/egusphere-egu2020-22557, 2020.

The level of urban residential land has a great relationship with the composition of urban residential land and the urban residential area of human settlements. Urban residential land includes residential land, road land, ancillary facilities and public green land. Geographical information monitoring land cover/land use includes cultivated land, garden land, forest land, grassland, housing construction area, roads, structures, artificial digging land, desert and bare land, and water. The Land cover/land use data and resident population spatialization data based on maps of housing construction areas are this article’s data sources. This article chose urban residential land types and per capita residential land area as an evaluation index system, establish the relationship between residential land indicators and geographical information monitoring indicators, calculate the area of various residential land areas and per capita land area, and follow the "Urban Residential Area Planning and Design Standards", a statistical analysis of the land use of residents in the five-, ten-, and fifteen-minute living quarters. Select a test area from each of the megacities, megacities, large cities, medium cities, and small cities, and use the statistical results to determine the level of urban residential land Perform a comparative evaluation.

How to cite: fengguang, K.: Analysis of the level of urban residential land based on land cover/land use, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12929, https://doi.org/10.5194/egusphere-egu2020-12929, 2020.

Anthropogenic activities such as heavy industries produced, among others, airborne pollutants, which are deposited inside the attic of houses like dust material for decades.  Study of attic dust can be an efficient media to better understand long-term airborne dust contamination and distribution in urban areas.  Ózd (OZD) and Salgótarján (STN) are two former industrial cities in the northeastern part of Hungary and separated by 40 km.  Both cities have exposed contaminants for different time periods and sources such as coal mining, local coal fired power plant, iron/steelworks and glass factories, transportation, etc.

For this study, 40 attic dust samples from STN and 49 attic dust samples from OZD were collected in houses with attics intact for at least 30 years containing long-term industrial pollution.  The concentrations of 13 metals (Ti, V, Cr, Mn, Fe, Co, Ni Cu, Zn, Ag, Sn, Mo and W) were analyzed with ICP-MS.  Most of these elements are considered potentially toxic elements related to industrial activities.  The main aim of the present study was to compare the concentrations, enrichment factors (EFs) in both cities.  EF of each metal was calculated with the formula: EF = [M/Fe]sample/[M/Fe] background, where (M) metals concentration and Fe was used for normalization, following the suggestion in the literature [1] for industrialized cities.  However, geochemical background values for both cities were taken from STN brown-forest soil.

The median concentration (mg kg^-1) of the studied metals for the 40 attic dust samples for STN= Fe(23000), Zn(631), Mn(422), Ti(385), Cu(67.7), Cr(26.9), V(42.0), Ni(29.7), Sn(8.70), Co(7.60), Mo(5.24), W(3.26), and Ag(0.030). Likewise, median concentration (mg kg^-1) for the 49 attic dust samples for OZD= Fe(48000), Zn(1338), Mn(1249), Ti(230), Cu(104), Cr(55.9), V(42.0), Ni(28.0), Sn(16.2), Co(7.20), Mo(4.68), W(3.64), Ag(0.116).

The values of median enrichment factor (EF) revealed the following order: STN=(Ti>W>Sn>Cu>Zn>Mo>Ag>Cr>V>Ni>Mn>Co) and OZD=(W>Ti>Sn>Ag>Zn>Cu>Cr>Mo>V>Mn>Ni>Co).  The results for both cities are Ti, W, Sn, Cu, Ag, Zn with enrichment factor (EF)>5, which represent significant or very significant enrichment; Ni, Mn, Co show values of (EF)<2 indicating no enrichment- to minimal enrichment, and Cr has 2<(EF)<5 = moderate enrichment.  Note that V shows moderate enrichment in STN samples and minimal enrichment in OZD samples.  Molybdenum shows significant in STN samples and moderate enrichment in OZD samples.

The differences between OZD and STN attic dusts show the complexity of two scenarios where concentrations in OZD attic dusts are 1.5 – 4 times higher than STN ones and significant enrichment for Sn, Ag, Zn, Cu, Cr due to probably more intense steelwork activities.

Keyword: Attic dust, enrichment factor, Salgótarján, Ózd.

Reference:

[1] Luo, X. S., Xue, Y., Wang, Y. L., Cang, L., Xu, B., & Ding, J. (2015). Source identification and apportionment of heavy metals in urban soil profiles. Chemosphere, 127, 152–157. https://doi.org/10.1016/j.chemosphere.2015.01.048

How to cite: Salazar, N., Abbaszade, G., Tserendorj, D., Völgyesi, P., Zacháry, D., Szabó, K., and Szabó, C.: Study of metallic trace elements in attic dust from two former industrial cities, Salgótarján and Ózd (Hungary), EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-19992, https://doi.org/10.5194/egusphere-egu2020-19992, 2020.

Drinking water quality in agricultural rural areas remains locally a challenge even all the effort made by local authorities to restore the groundwater resources quality, especially regarding nitrates. In Plourhan, a ~2000 inhabitants, about 10 km from the sea, NW France, the drinking water is pumped in a natural spring emerging from the Brioverian basement. The nitrate concentrations exceed the 50 mg/L standard for drinking water supply, and thus needs to be diluted to be delivered to the population. Over the last 15 years, a large programme of measures was undertaken in order to reduce the NO₃ concentration, including the purchase of agricultural parcels around the spring, moving progressively from mixed farming and livestock to fallows and meadows, and thus drastically change the local land use. Despite all these efforts, nitrate concentrations only decrease very slowly and remain above the 50 mg/L standard.

In this context, the objective of this study is to better understand the transfer of nitrates at the basin scale, by studying flow paths, geochemical reactions, transit times that are key parameters to estimate the vulnerability and the recovery-time of the critical zone. In that way, a geochemical and isotopic approach is applied at the basin scale. Major elements analysis of the groundwater reflect the drained contrasted lithologies as metasediments (pelites & sandstones) and amphibolite, with a large spatial heterogeneity of the NO₃ concentrations, ranging from a few mg/L to more than 50 mg/L. Nitrogen and oxygen isotopes of nitrates (δ¹⁵N-NO₃ and δ¹⁸O-NO₃) suggest that denitrification can occur locally in some wells presenting low or intermediate  NO₃ contents, whereas other wells present high or low NO₃ concentrations without any evidence of denitrification processes. The mean residence time of groundwater is assessed through CFCs and SF6 dissolved gas measurements. Some wells preferentially in amphibolite, present water with low recharge temperature (around 6°C while the mean recharge temperature in Britany is 11-12°C) correlated with low CFCs/SF6 values indicating that some very old groundwater (last glaciation :  -19/17 k yrs) exists in the reservoir. Other ones in metasediments have modern water or a mixing between an old and a present day recharge. These results, together with structural and lithological detailed geological field mapping, help to draw up the conceptual model of the aquifer functioning regarding nitrates transfer in the critical zone.  

This work is part of the POLDIFF study that benefits from the funding of BRGM and the French Loire-Bretagne water Agency.

How to cite: Petelet-Giraud, E., Baran, N., Vergnaud, V., Lucassou, F., and Schroetter, J.-M.: Nitrate transfer in the Critical zone view through N & O isotopes of NO3 and CFC-SF6 groundwater residence time assessment, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17524, https://doi.org/10.5194/egusphere-egu2020-17524, 2020.

Utah Lake is one of the largest natural freshwater lakes in the western United States. Its watershed is 9,800 km². Utah Lake is located in Utah County which is expected to have the highest population growth in the state through 2060. Land use and water regulation has shifted the Utah Lake shoreline since the 1900s. Monitoring the land use and land cover change (LULCC) in the watershed is critical to understanding surrounding hydrology and future sustainability. In this study, we compared the Utah Lake shoreline change from 1953-2014 and classified the land cover in the Utah Lake watershed from 1985-2018. Our results show that there was a 41.45 km²  decrease in lake surface from 1953 to 2014. The shoreline around the Provo Bay and Goshen Bay has receded lake-ward considerably in 2014 compared to the 1953 shoreline, and the lost water and wetland area was equivalent to 3,851 football fields in size. Land cover change calculations indicate that from 1985 to 2018 urbanization increased by 6%, forest by 2%, and barren by 3%, whereas water and agriculture decreased by 1% and 6%, respectively. The findings from this project could be used by Utah’s legislature to implement meaningful watershed planning and management, especially in light of the state considering House Bill 272 that promotes “comprehensive restoration of Utah Lake by building an island on it.” The bill proposes an island in Utah Lake which could dramatically alter LULCC around the lake. In addition, any significant LULCC on and around the lake will modify the lake water budget, its ecosystem, and have profound consequences on Utah Lake watershed and the surrounding regions.

How to cite: Wang, W.: Assessing the Impact of ~65 years of Land Use and Land Cover Change on the Utah Lake Watershed with Remote Sensing and Spatial Modeling, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-1286, https://doi.org/10.5194/egusphere-egu2020-1286, 2020.

Soils are the largest terrestrial organic carbon pool and one of the largest terrestrial sources of CO₂ in the atmosphere. However, not all CO₂ produced in soils is released into the atmosphere, as dark CO₂ fixation has been shown to modulate CO₂ release from soils. Temperate forest soils store up to half of the soil organic carbon pool to 1m depth and are recognized as important components of the global carbon cycle, yet studies on dark CO₂ fixation in temperate forest soils are scarce. Using a well characterized Cambisol soil plot in the Hainich National Park (temperate forest), Germany, we explore dark CO₂ fixation with the aim to assess the CO₂ fixation rates, the influencing biogeochemical parameters, and the contribution of this process to temperate forest soil organic carbon (SOC).

Dark CO₂ fixation was quantified via the uptake of ¹³C-CO₂ added to microcosms containing soils sampled from three depths. Under 2% CO₂ headspace, rates of dark CO₂ fixation at soil level decreased with depth from 0.86 µg C gdw^-1d^-1 in 0 - 12 cm to 0.05 µg C gdw^-1d^-1 in 70 -100 cm, accounting for up to 1.1% of microbial biomass and up to 0.035% of soil organic carbon. However, as differences in microbial biomass abundance and community profiles with depth were found, no significant difference in the rates across depth was observed at microbial level. This suggests that microbial biomass is an important driver of dark CO₂ fixation in soils. Given a global temperate forest area of 6.9 million km² and an average soil bulk density of 1 Mg/m³ dark CO₂ fixation will potentially account for the gross sequestration of 0.31 - 0.48 GtC/yr to a depth of 1 m. Furthermore, an increase in headspace CO₂ concentration enhanced CO₂ fixation rates by up to 3.4-fold under 20% v:v CO₂ showing that dark CO₂ fixation can be substantial in soils with higher CO₂ concentrations.

To validate microbial biomass as a driver of dark CO₂ fixation in soils, we made comparisons with soil plots from the Schorfheide-Chorin exploratory forest, Germany, a temperate forest characterized by vegetation-specific bacterial community structure, higher sand content and acidic pH gradients. Under these conditions, CO₂ fixation rates at microbial level were significantly different across depth suggesting that aside microbial biomass, other abiotic factors may influence dark CO₂ fixation in these soils. Of all the tested abiotic variables, water content was the main explanatory factor for the variations in dark CO₂ fixation rates in the Schorfheide-chorin soils. Additionally, based on 16S rRNA sequencing, qPCR and PICRUSt2 analysis, only a few putative autotrophic communities were present and displayed vegetation-specific variations indicating an influence of vegetation type and input on the active community.

Our findings highlight microbial biomass, CO₂ and water content as the main drivers of dark CO₂ fixation in temperate forest soils with only a small proportion of autotrophs being present, suggesting the potential mediators of this process. We also demonstrate the significance of this process in global temperate forest SOC inputs.

How to cite: Akinyede, R., Taubert, M., Schrumpf, M., Trumbore, S., and Küsel, K.: Significance and driving forces of dark CO2 fixation for organic carbon inputs in temperate forest soils , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22447, https://doi.org/10.5194/egusphere-egu2020-22447, 2020.

A peat deposit close to Venice was monitored both in the field and in the lab (1) to investigate the hydrological response of peat soil to changing meteorological conditions in the frame of land subsidence assessment. The whole area is about 3 meters lower than the sea level and therefore subsidence is a major issue. Predictions highlighted the risk of an almost complete disappearance of the peat layer in this area during the next 50 years, due to the increased frequency of warmer periods. Unfortunately, despite the considerable impacts that are expected to affect peatland worldwide, only a few measured datasets are currently available to assess the response of a peat deposit to enhanced drying due to global warming.

The lab measurements were performed both at the pedon and at the core scale. An undisturbed peat monolith of approximately 0.7 m³ was collected, transferred to the lab, and instrumented to monitor matric potential, water content, and total weight. This undisturbed peat lysimeter allows to monitor water content variations (both through the weight monitoring and time domain reflectometry sensors), and matric potential, with drier conditions with respect to the field campaign. A complete cycle of wetting and drainage was performed, raising the water table from the bottom to the top of the sample and down again. Additional measurements of matric potential and water content were collected by testing peat cores on a suction table.

A set of water retention curves was experimentally determined. They were derived for a range of  matric potential much broader than that experienced in situ . Variations were found, with respect to the field natural conditions, in the relations between the matric potential and the volumetric water content of different horizons as a result of the initial prolonged drying. Also, the hysteresis behaviours in the lab and in the field were different, with much wider loops in the lab conditions because of extended range of potential. Hydraulic non-equilibrium between the water content and water potential could also  be a possible cause, but further modelling work is necessary to assess it. The van Genuchten parameters were obtained for both wetting and drying, for modelling purposes.

(1) Previati et al. (2019), Hydrological Processes.

How to cite: Ferraris, S., Canone, D., Gisolo, D., Putti, M., Teatini, P., and Previati, M.: Peatland hydrological behavior with global warming, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13716, https://doi.org/10.5194/egusphere-egu2020-13716, 2020.

Throughfall and stemflow are critical components of the hydrological and biogeochemical cycles of forested ecosystems, as they are the two hydrological processes responsible for the transfer of precipitation and solutes from vegetative canopies to the soil. Despite stemflow rarely accounts for >10% of the rainfall, its concentration over small areas at the base of trunks seems to affect the magnitude and timing of water inputs to the soil and biogeochemical cycling excessively.

Though substantial amount of literature on throughfall and stemflow research is available, recent reviews on eco-hydrology of forested ecosystems identified several key points of uncertainty where current knowledge is weak. These points especially address the role of canopy structure among tree species (i.e., interspecific variation) as well as within a single tree species (i.e., intraspecific variation as caused e.g. by morphology and age) for explaining the large variations in precipitation partitioning into throughfall and stemflow, the spatial variability of throughfall volume and chemistry as well as the temporal and spatial patterning of stemflow inputs to the ground. The latter two points are particular sources of uncertainty, since most sampling approaches fail to adequately identify the infiltration area of stemflow inputs at the trunk base resulting in incomplete or biased evaluations of tree species effects on rainfall partitioning.

Based on these deliberations we conducted a color tracer experiment with Brilliant Blue to identify flow patterns of stemflow water along the stem surface of two broad-leafed tree species (Fagus sylvatica and Acer pseudoplatanus) and to estimate the infiltration area at the trunk base and down to 12 cm soil depth. The trunk area was dye-stained up to 1.5 m height in advance and stemflow patterns along the trunk surface and soil infiltration zone were visually quantified following two natural rainfall events. Furthermore, we tested the relationship between color-stained zones of "high through-flow” and ecological soil characteristics such as fine root distribution and soil pH. This approach differs from common color tracer experiments, where stems are actively and homogeneously sprinkled with large amounts of color tracer solution.

We found distinct spatially restricted stemflow pathways on the tree trunks, which appeared specific for the tree individual exhibiting larger washed-off areas for beech (4441 cm²) compared to maple (1816 cm²). The infiltration area of stemflow at the trunk base was smaller than the basal area (BA) amounting to 17% (226.2 cm²) of the BA for beech and to 30% (414.4 cm²) for maple. For beech, colored areas were restricted to a maximum extension of 13 cm distance from the stem and of 30 cm for maple.

Our investigation exhibited that stemflow infiltration was spatially more concentrated at the trunk base than commonly assumed. The outcome of this study might contribute to our understanding on hydrological and biogeochemical interlinkages between the surface and subsurface of the Critical Zone.

How to cite: Michalzik, B., Tischer, A., and Lotze, R.: Identifying stemflow pathways and infiltration areas for sycamore maple (Acer pseudoplatanus) and European beech (Fagus sylvatica) by passive dye application, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9972, https://doi.org/10.5194/egusphere-egu2020-9972, 2020.

Microbial community in the vadose zone has been widely investigated. However, how microbial community varies from the vadose zone to deep-subsurface aquifer are poorly understood. In this study, 12 samples from vadose zone and three aquifer sediments were collected along a 42.5 m bore at a typical agricultural land in central China. High-throughput sequencing and multivariate statistical analysis were applied to explore the underlying distributions of bacterial, archaeal and fungal communities, and their response to environmental factors. The results showed that bacterial community changed considerably at vertical scales and essential variation occurred at the third aquifer layer. Actinobacteria (19.5%), NC10 (11.0%), Alphaproteobacteria (7.7%), Gammaproteobacteria (6.9%), and Deltaproteobacteria (6.4%) were most abundant classes in the vadose zone, where Alphaproteobacteria (22.3%), Gammaproteobacteria (20.1%), Actinobacteria (17.7%) and Bacteroidia (6.9%) enriched in the aquifer sediments. Archaeal and fungal communities were relatively more homogenous, with no significant trend as a function of depth. Process analysis further indicated that Selection dominated in bacterial community, whereas stochastic process governed archaeal and fungal communities. Moreover, environment-bacteria interaction analysis revealed that metal(loid)s (especially alkali metals) rather than physiochemical variables highly shaped the bacteria community in the vadose zone-aquifer continuum, where Bacteroidetes exhibited the strongest link to the variation of metal(loid)s. This research extends our knowledge about microbial community’s variation through the vadose zone to deep aquifer sediments in the studied area and similar agricultural areas.

How to cite: Chen, Q. and Zhong, S.: Vertical distribution of microbial communities and their response to metal(loid)s along vadose zone-aquifer sediments, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4296, https://doi.org/10.5194/egusphere-egu2020-4296, 2020.

Biogeochemical processes in the aeration zone (AZ) may severely affect the fluid flow, composition, and the amount of mobile matter. The AZ is a subsurface part of the Critical Zone (CZ) that connects the soils sensu stricto (SSS) with the aquifers. Depending on the groundwater dynamics, the fluid transiting in the AZ is not only recharged by the ascending seepage, but also by upwelling groundwater. Since the collection of fluids is a rather demanding task, fluid migration and matter transport have not been considered in CZ research so far. To address this research gap, we developed novel drain collectors and installed twenty of them within four different lithologies in the fractured carbonate AZ of the Hainich Critical Zone Exploratory (Hainich CZE) in central Germany. Drainage sampling was done on a regular monthly basis with additional event-based sampling. Size, chemical composition, and physio-chemical properties of the aqueous samples were analyzed by a range of spectroscopic, chromatographic, and microscopic techniques.

The amount of drainage water varied extremely between the locations and lithologies. We attribute this both to the foremost migration pathway operative (i.e., fractures, fluid flow regime, fracture flow, and film-flow) and to the different spatial extents of the “capture zones” that recharge the drainage collectors. For all lithologies, pH and EC were found to be independent of the lithology with rather high contents of organic carbon and showed significant differences between the hydrological summer and winter season. Significant amounts of colloids and larger suspended particles of calcite, clay minerals (Illite), and quartz were identified in almost all samples. While the general hydrochemistry seems to be controlled by the biogeochemical processes in the topsoils, we presume that the percolating water collects the mobilizable materials from exposed interfaces in the AZ. These materials are made “susceptible” to release and transport by weathering within the AZ during the periods of no flow. Additionally, upwelling groundwater may also be replenished the inventory of mobilizable materials in the AZ. Our study suggests that the AZ is not just an “inert” transition zone, but has to be considered as a biogeochemical reactor that may severely alter the seepage composition and properties, and thus the groundwater recharge.

How to cite: Eshvara Arachchige, D. and Totsche, K. U.: Mobile matter in the aeration zone of the Hainich Critical Zone Exploratory: First results from one-year monitoring by employing novel drain collectors , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20621, https://doi.org/10.5194/egusphere-egu2020-20621, 2020.

The mobile inventory in soil seepage is of fundamental importance for soil development and for functioning of subsurface ecosystem compartments. The mobile inventory may encompass inorganic, organo-mineral and organics, dissolved and colloidal, but also particulate matter and microbiota. Still unknown are the conditions and factors that trigger the release and export of seepage-contained mobile matter within soil, and its translocation through the subsurface of the critical zone. Long-term and high-resolution field studies that includes the mobile particulate inventory are essentially lacking. To overcome this knowledge gap, we established long-term soil monitoring plots in the Hainich Critical Zone Exploratory (HCZE; NW-Thuringia, central Germany). Soil seepage from 22 tension-supported lysimeters in topsoil and subsoil, covering different land use (forest, pasture, cropland) in the topographic recharge area of the HCZE, was collected and analyzed by a variety of analytical methods (physico-/chemical and spectroscopic) on a regular (biweekly) and event-scale cycle. With our study we proved that substances up to a size of 50 µm are mobile in the soils. The material spectra comprised minerals, mineral-organic particulates, diverse bioparticles and biotic detritus. Atmospheric forcing was found to be the major factor triggering the translocation of the mobile inventory. Especially episodic infiltration events during hydrological winter seasons (e.g. snow melts) with high seepage volume influences seepage hydrochemistry (e.g. pH, EC) and is important for transport of mobile matter to deeper compartments. Seasonal events cause mobilization of significant amounts of OC. On average, 21% of the total OC of the seepage was particulate (>0.45 µm). Furthermore, our results suggest that the formation environment and the geopedological setting (soil group, parent rock, land use) are controlling factors for the composition and the amount of soil-born mobile inventory. Our study provides evidence for the importance of the mobile inventory fraction >0,45 µm for soil element dynamics and budgets and highlights the role of weather events on soil and subsoil development and subsurface ecosystem functioning.

How to cite: Lehmann, K., Lehmann, R., and Totsche, K. U.: Dynamics of seepage mobile inventory in forest and agricultural soils - Results from a comparative multi-year lysimeter study, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-14451, https://doi.org/10.5194/egusphere-egu2020-14451, 2020.

We urgently need to wake up to the role that climate change will be playing in the phosphorus cycle.  The paper will attempt to address the complexities, controversies and uncertainties of estimating the effects that climate change is having on the phosphorus cycle.  Citing an example from three UK catchments, the effect of climate change on average winter phosphorus loads is predicted to increase by up to 30% by the 2050s, and these effects will only be off-set by large-scale agricultural changes (e.g. a 20–80% reduction in phosphorus inputs).  Achieving phosphorus-related quality water in diverse and productive agricultural landscapes under a changing climate is going to be a massive challenge.  It is less than a century since we started mining rock phosphate, but in the context of a 4.5-billion-year-old earth and the acceleration due to climate, we are living through a switching point for phosphorus in the earth system.

How to cite: Haygarth, P.: Time to wake up to climate change and the accelerating phosphorus cycle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10238, https://doi.org/10.5194/egusphere-egu2020-10238, 2020.

Phosphorus (P) as a key element in DNA, RNA as well as ATP and phospholipids is essential for the growth, functioning and reproduction of all life on earth. However, if fertilization with animal wastes or human excreta is not available or not organized, P fertilizers stem from nonrenewable geological P deposits, which are an increasingly limited resource. The potential threats of a global P limitation due to “peak phosphorus” have been discussed intensively in the recent past  including the socio economic as well as political consequences which will be dramatic. While a deficit in available soil P leads to a loss of agricultural yield, an excess of total P in soils triggers aquatic eutrophication, loss in biodiversity and wildlife habitat in surrounding water bodies in other regions of the world.

We calculated global soil P balances considering input from atmosphere and plant management (as sum of manure and residue input minus plant uptake) versus depletion due to soil erosion in coupling P fluxes from (Ringeval et al., 2017) with soil erosion rates from (Borrelli et al., 2017).

The world’s soils are currently being depleted in P in spite of high chemical fertilizer input. Considering the current high chemical fertilizer inputs most continents result in slightly positive P balances (e.g. net P input to soils). Exception are Africa with very low chemical fertilizer input of 1.7 kg ha^-1yr^-1 paired with high losses due to soil erosion of 2 kg ha^-1yr^-1 and Europe (the latter is the average for the geographic Europe including eastern European countries with very low chemical fertilizer input). Results indicate negative balances globally as well as for all continents (depletion between 4 and 19 kg P ha^-1yr^-1 ) if input of chemical fertilizers is neglected.

Parallel to the distribution pattern and dynamics of global soil erosion by water (Borrelli et al., 2017), P losses from soils due to water erosion are most dramatic in countries and regions with intensive agriculture and/or extreme climates (e.g., high frequencies of heavy rain storm or droughts followed by significant rain events).

References

Borrelli, P., Robinson, D.A., Fleischer, L.R., Lugato, E., Ballabio, C., Alewell, C., Meusburger, K., Modugno, S., Schütt, B., Ferro, V., Bagarello, V., Oost, K.V., Montanarella, L. and Panagos, P., 2017. An assessment of the global impact of 21st century land use change on soil erosion. Nature Communications, 8(1): 2013.

Ringeval, B., Augusto, L., Monod, H., van Apeldoorn, D., Bouwman, L., Yang, X., Achat, D.L., Chini, L.P., Van Oost, K., Guenet, B., Wang, R., Decharme, B., Nesme, T. and Pellerin, S., 2017. Phosphorus in agricultural soils: drivers of its distribution at the global scale. Global Change Biology

How to cite: Alewell, C., Borrelli, P., Ringeval, B., Ballabio, C., Robinson, D. A., and Panagos, P.: Obvious but overlooked: soil erosion neglect in the global phosphorus cycle, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9980, https://doi.org/10.5194/egusphere-egu2020-9980, 2020.

Despite the importance of phosphorus (P) as a nutrient for all life, its availability is highly constrained in terrestrial ecosystems. The availability of P to plants and microbes is regulated by abiotic processes (e.g. P sorption/desorption, precipitation/dissolution) and biological activities (microbial P immobilization/organic P mineralization). Due to the strong geochemical component of the P cycle, it can be expected that soil C, N and P cycling may differ in terms of effects of geology, climate and management. Despite advances in our understanding of physico-chemical controls on P availability, there is still little mechanistic understanding of large scale controls on soil P cycling and its relation to soil C and N cycling, due to a lack of broad scale studies using common methodologies.

Here we aimed to investigate soil physicochemical and biological factors that drive soil P cycling and may cause a (de)coupling of C, N and P processes. We therefore sampled mineral topsoils (0-10 cm, n=95) across a continental transect in Europe (Southern Spain to Northern Scandinavia), covering major geological, climatic and land use gradients. The soils derived from different land uses (cropland, grassland, forest/woodland) and bedrock types (silicate, sediment, calcareous). We analyzed a wide range of potentially relevant physico-chemical and biological properties and measured gross rates of soil N and P processes by short term (24 h) incubations of soils with ³³P and ¹⁵N following isotope pool dilution approaches.

(i) Across the whole transect land-use effects on soil P pools and processes exceeded those of geology, reflecting the accumulation of fertilizer P in soils of managed ecosystems. Cropland (and grasslands) had higher values of soil total P and soil inorganic P (Pi), available Pi (Olsen P), and gross Pi mobilization rates by abiotic and biotic processes compared to forests. Soil phosphatase activity did not vary between land-uses. Soils on silicate bedrock had significantly higher total and labile P than calcareous soils.

(ii) Climate differentially affected P pools and processes. Soil total P, dissolved organic P, and gross Pi desorption decreased with mean annual temperature (MAT; these properties were not sensitive to mean annual precipitation - MAP), while soil phosphatase activity and gross total Pi mobilization through abiotic and biotic processes increased with MAP but were insensitive to MAT. This clearly points to adverse climatic controls of biotic and abiotic soil P processes.

(iii) We found strong interlinkages between soil C, N and P pools (soil organic matter and microbial biomass) and soil enzymes (beta-glucosidase, chitinase, phosphatase) but not in related gross processes (respiration, N and P mineralization). Interestingly the slopes of C-P and N-P relations of pools and enzymes differed systematically between land-uses, indicating that land management causes a partial decoupling of P from C and N cycles, reflecting the P-richness of croplands.

How to cite: Wanek, W., Wasner, D., Püspök, J., Böckle, T., Noll, L., Zhang, S., Zheng, Q., and Hu, Y.: Continental scale climate, land-use and geological controls of soil P cycling and relations with soil C and N, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10893, https://doi.org/10.5194/egusphere-egu2020-10893, 2020.

The eutrophic lake Eichbaumsee, a ~ 1 km long and 280m wide (maximum water depth 16m) dredging lake southeast of Hamburg (Germany), has been treated for water quality improvements using various techniques (i.e. aeration plants, removal of dissolved phosphate by aluminium phosphate precipitation and by Benthophos adsorption) during the past ~ 15 years. Despite these treatments no long-term improvement of the water quality was observed and the lake water phosphate content continued to increase by e.g. ~ 350 kg phosphate per year between March 2016 and February 2019. As no creeks or rivers drain into the lake and hydrological groundwater models do not suggest any major groundwater discharge into the lake, sources of phosphate (and other nutrients) are unknown.

We investigated the phosphate fluxes from sediment pore water and groundwater into the water body of the lake. Sediment pore water was extracted from sediment cores recovered by divers in August 2018 and February 2019. Diffusive phosphate fluxes from pore water were calculated based on phosphate gradients using first Fick`s law. Stable water isotopes (δ²H, δ¹⁸O) were measured in the lake water, sediment pore water, interstitial waters in the banks surrounding the lake, the Elbe river and in three groundwater wells close to lake. Stable isotope (δ²H, δ¹⁸O) water mass balance models were used to compute water inflow/outflow to/from the lake.

Our results revealed pore-water borne phosphate fluxes between – 0.07 mg/m²/d (i.e. slight phosphate uptake by the sediments) and 2.6 mg/m²/d (i.e. phosphate release to the lake). Assuming that the measured phosphate fluxes are temporarily and spatially representative for the whole lake, about 100 kg/a to 220 kg/a of phosphate is released from sediments. This amount is slightly lower than the observed phosphate increase of the lake water. Stable isotope signatures indicate a water exchange between the aquifer and the lake water. Based on stable isotope mass balances (δ²H, δ¹⁸O) we estimate an inflow of phosphate from the aquifer to the lake between 190 kg/a and 1400 kg/a. This inflow indicates that groundwater-born phosphate is as or even more important than phosphate supply via sediment pore-water. Our study suggests that groundwater may have an important impact on lake nutrient budgets.

How to cite: Scholten, J., Förster, W., Schubert, M., Knöller, K., Classen, N., Lechelt, M., Richard, J.-H., Rohweder, U., and Zunker, I.: Phosphate supply to the eutrophic lake Eichbaumsee (Germany): Sedimentary versus groundwater sources, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4664, https://doi.org/10.5194/egusphere-egu2020-4664, 2020.

Phosphorus (P) is a development-limiting nutrient for crops, hence global food production relies on P fertilizer application. However, P mobility in soil depends on many abiotic and biological processes, most notably its chemical interactions with the soil particles. Optimizing the timing and amount of fertilization could lead to higher production efficiencies and also reduce P runoff and subsequent contamination of water bodies. Plants have developed strategies to improve P uptake by optimizing the root system architecture and exuding organic acids for enhancing P mining locally to the root tips. However, these adaptations are mainly a response to low P availability or to already immobilized P patches in soil, and little is known about the fate of P in the early stages of fertilization.

In this framework, we developed an experimental assay for investigating P release from the fertilizer pellets, and its movement through soil using non-invasive microdialysis sampling techniques and inductively coupled plasma - mass spectrometry (ICP-MS) analytical techniques. Microdialysis allowed for time resolved in-situ samplings and the small size of the probes also allows for a fine spatial resolution.

Results showed a very rapid release of the P from the fertilizer pellet (triple super phosphate, TSP), producing a high concentration pulse that lasts a few hours. P concentrations then decrease over time until reaching steady low concentrations after 6-8 days and P replenishment from the pellet was not observed after the first pulse. The experiments showed that the speed of P movement in soil is greatly influenced by soil particle size distribution, and that gravity plays an important role in promoting quick P movement in the downward direction, while diffusion can account for P observed in the upward direction. Modelling was also applied to data fitting for quantifying trends and deriving an effective P diffusion coefficient in saturated soil.

How to cite: Petroselli, C., Williams, K., Ghosh, A., Scotson, C., McKay Fletcher, D., Ruiz, S., Walker, N., Sousa Dias, T. G., and Roose, T.: Monitoring early stages of P release from fertilizer pellets to bulk soil using non-invasive sampling techniques, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8677, https://doi.org/10.5194/egusphere-egu2020-8677, 2020.

Preventing dissolved phosphorus (P) accumulation in soils and its transport to water bodies has been subject of many studies. However, despite the continuous efforts and advances, excessive P is still a concern and it is especially problematic in freshwater systems: excessive dissolved P leads to eutrophic conditions, a threat for water quality and aquatic life. P removal structures are a novel technology used in urban and rural settings to intercept dissolved P in surface and subsurface flows. P sorption materials (PSMs), active media with high affinity for dissolved P, are the core components of these structures. Once the PSMs reach service life, replacing the spent media can be costly. The objective of this research is to assess potential regeneration techniques that will extend the lifetime of Aluminum (Al)/Iron (Fe)-rich PSMs. We are proposing a regeneration involving a continuous circulation of 1M KOH aiming to restore unavailable sorption sites on the PSMs. A series of flow-through experiments was conducted alternating between P sorption (0.5 and 50 mg/L input solution) and desorption with KOH (5 or 20 pore volumes), varying residence times (0.5 min and 10 min) and number of recirculations (0, 6 and 24). We tested the treatments in 3 manufactured PSMs, Alcan, Biomax and PhosRedeem. Across two cycles of sorption-desorption, Alcan, Biomax and PhosRedeem showed an average P recovery of 81%, 79% and 7%, respectively.  The comparative investigation of the tested treatments revealed that the most effective regeneration treatment is characterized by a larger KOH volume (20 pore volumes) and no recirculation, with up to 100% reported P recovery. This research demonstrates the ability of Al/Fe-rich PSMs regeneration to contribute to a circular economy of P, as P recovery enables a more sustainable P cycle in both terrestrial and aquatic environments.

How to cite: S P C Scott, I., J Penn, C., and Huang, C. H.: Development of a regeneration technique for aluminum-rich and iron-rich phosphorus sorption materials , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4211, https://doi.org/10.5194/egusphere-egu2020-4211, 2020.

The sustainable management of phosphorus (P) includes recycling and enhancing P-use efficiency (PUE) in agriculture.  In this study, we compared plant yield and the PUE of lettuce growing with soil amendments of biosolids from three wastewater treatment plants in comparison to commercial fertilizer.  Furthermore, we used AVP1-transformed lettuce (Lactuca sativa cv. Conquistador), which is genetically improved to enhance its PUE, and compared its performance to non-transformed (wildtype, WT) lettuce in greenhouse conditions.  AVP1 lettuce produced higher yield than WT lettuce only with commercial-fertilizer treatments; the yield with biosolid treatments did not vary between the two lettuce types.  PUE did not differ between WT and AVP1 lettuce but was higher for commercial fertilizer than for biosolids.  WT lettuce had higher P content in below-ground biomass than AVP1 lettuce when both were treated with biosolids.  This suggests that capability of AVP1 lettuce to acidify the root zone may have mobilized heavy metals from biosolids and these toxins reduced the yield, P uptake, and PUE in AVP1 lettuce.  In particular, Cd and As contents were high in lettuce biomass from biosolid treatments and exceeded recommendations for human daily oral dose.

How to cite: Chan, N. I., Rittmann, B., and Elser, J.: Evaluating P sustainability using biosolids in comparison to commercial fertilizer for P-use efficient genetically transformed lettuce, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5870, https://doi.org/10.5194/egusphere-egu2020-5870, 2020.

Phosphate is known to absorb strongly to schwertmannite (Fe₈O₈(OH)₆(SO₄)·nH₂O)¹ and as such, schwertmannite has been proposed to limit phosphate in solution in acid mine drainage (AMD) environments. This in turn will limit phosphate availability to the micro-organisms that live in and propagate AMD². Here we have studied sediment samples from the Rio Tinto river in Spain collected during Europlanet field area visit to verify whether phosphate can be incorporated into sulphate-rich minerals in this river. The minerals were identified using X-ray diffraction. Our analyses show that the concentration of phosphate in the river is in the nM range. Digestion of modern sediments in nitric acid followed by inductively coupled plasma atomic emission spectroscopy (ICP-AES) analysis indicate that sites with sulphate-rich minerals are correlated with elevated phosphate concentrations. In addition, phosphate is also retained in ancient sediments that are dominated by goethite (FeO(OH)).

We have also conducted experiments to explore the competition between Fe³⁺, phosphate and sulphate ions in solution as well as the effect of this on schwertmannite nucleation. UV-Vis and Raman spectroscopy demonstrate that contact ion pairs form between Fe³⁺ and phosphate or sulphate in solution. Particularly, phosphate and sulphate compete for Fe³⁺ in solution consistent with predictions by the solution speciation modelling program PHREEQC. Our experiments also show that above a critical concentration, phosphate retards the nucleation of schwertmannite. As this critical concentration is above that found in Rio Tinto river fluids, phosphate is expected to have a limited role in schwertmannite precipitation, but, its concentration is regulated by its incorporation into schwertmannite and other sulphate-bearing phases in AMD systems.

References

¹Eskandarpour et al. 2006, Material Transactions, 1832. ²Chen et al. 2015, ISME, 1579.

How to cite: King, H. E., Bakker, S., Munnecom, G., and Gomez, F.: Regulation of dissolved phosphate through incorporation into schwertmannite , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6206, https://doi.org/10.5194/egusphere-egu2020-6206, 2020.

Phosphate (P) as an essential resource for food production is becoming scarce. Its uncontrolled loss from agricultural areas is in conflict with the principles of a circular economy. Enhanced loading of surface waters with P is the main cause for eutrophication and presents a key challenge in meeting the objectives of the EU Water Framework Directive. Understanding and controlling environmental P fluxes therefore is key to target both problems, to develop new methods and approaches to manage environmental P fluxes, and to improve surface water quality.

In March 2019 the EU Marie Sklodowska-Curie Innovative Training Network P-TRAP has been launched. P-TRAP establishes a framework of partners from multiple science and engineering disciplines. Integration of non-academic partners from various stakeholder groups into the P-TRAP consortium paves the way for direct implementation of the acquired knowledge. The project is targeting the diffuse flux of phosphate (P) into surface waters, i.e. the problems of understanding and controlling environmental P fluxes. P-TRAP aims to develop new methods and approaches to trap P in drained agricultural areas and in the sediments of eutrophic lakes. Trapping of P involves the application of iron(Fe)-containing by-products from drinking water treatment. P-TRAP aspires the ideas of a circular economy and aims at recovering the retained P in agricultural systems. Novel microbial technologies will be developed to convert P-loaded Fe-minerals into marketable fertilizers whose suitability will be evaluated. The P-TRAP technologies have in common that they rely on the naturally strong connection between P and Fe and the innovative P-TRAP strategies will be underpinned by process-orientated investigations on the behaviour of P during the transformation of Fe minerals. The latter are key in trapping and recycling of P in agricultural systems and lakes. The poster will present the structure and the planned research of the project, including a first overview of achievements of the first year.

How to cite: Walter, S. and Behrends, T. and the P-TRAP team: P-TRAP - Diffuse phosphorus input to surface waters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-7857, https://doi.org/10.5194/egusphere-egu2020-7857, 2020.