Content:

BG – Biogeosciences

BG1.2 – Nitrogen cycling in terrestrial and aquatic ecosystems: microbiological processes, gas fluxes, modelling,atmospheric impacts and global change feedbacks

EGU2020-1795 | Displays | BG1.2

Differential nitrogen isotope variation of tree-rings in two coniferous forests under climate change, Japan

Maximo Larry Lopez Caceres, Satoru Tanabe, Filippo Santini, Jordi Voltas, Felix Seidel, and Toshiro Yamanaka

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.

EGU2020-7760 | Displays | BG1.2 | Highlight

Three-year dynamics of N2O fluxes from soil, stem and canopy in a hemiboreal forest: Impacts of floods and droughts

Ülo Mander, Thomas Schindler, Kateřina Macháčová, Alisa Krasnova, Jordi Escuer-Gatius, Martin Maddison, Jaan Pärn, Gert Veber, Dmitrii Krasnov, and Kaido Soosaar

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.

Moss-associated nitrogen (N) fixation provides a substantial but heterogeneous input of new N to nutrient limited ecosystems at high latitudes. The presence of “hot spots”, defined as a rate of N fixation greater than three standard errors over the mean rate, can further increase the difficulty of scaling N inputs to plant communities or ecosystems. We used 15N2 incubations to quantify the fixation rates associated with 34 moss species from 24 sites ranging from 60 to 68 degrees N in Alaska, USA. The total moss-associated fixation rates ranged from 0.08 to 4.4 kg N ha-1yr-1, with an average of 1.1 kg N ha-1yr-1, based on abundance-weighted averages of all mosses summed for each site. Five of the 24 sampled sites were hot spots of N fixation. We hypothesized that host moss diversity would be correlated with higher N fixation rates, since different mosses often have distinct microbial assemblages and higher microbial diversity has been linked with higher N fixation rates in other ecosystems. However, we found no significant correlation between either moss taxonomic richness or Simpson’s D and N fixation rates (p=0.102, R2=0.01 and p=0.522, R2=0.02, respectively). What we found instead was that certain high-fixing species, most importantly Tomentypnum nitens, were present in almost all hot spots. The relevance of moss taxonomic identity in driving N fixation rates was repeatedly observed in our survey, where both machine learning and mixed model approaches found that moss family was a significant predictor of associated fixation rates across ecosystems in Alaska. Taken together, these results indicate the importance of moss identity in driving hot spots and illustrate that host taxonomy may be a useful tool in generating more accurate large-scale assessments of associated N inputs in these vulnerable and valuable ecosystems.

How to cite: Stuart, J. and Mack, M.: “Hot spots” in high-latitude moss-associated N fixation: What drives locally high fixation rates? , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5983, https://doi.org/10.5194/egusphere-egu2020-5983, 2020.

EGU2020-11857 | Displays | BG1.2

The fixed nitrogen sensitivity of biological nitrogen fixation in salt marshes sediments from the northeastern United States

Romain Darnajoux, Rei Zhang, Katja Luxem, and Xinning Zhang

Biological nitrogen fixation, the main input of fixed N into ecosystems, converts inert N2 gas into bioavailable ammonium in an energetically costly reaction catalyzed by the prokaryotic metalloenzyme nitrogenase.  The high ATP and reductant requirements of N2 fixation explain why this process is highly regulated in diazotrophs, with the presence of ammonium inhibiting nitrogenase expression and activity. Yet, several reports of N2 fixation in ammonium- and nitrate-rich (10 to 300 µM) benthic environments challenge our understanding of a key environmental sensitivity of N2 fixation. Field studies point to heterotrophic sulfate reducers as the likely diazotrophs in these benthic settings, but the fixed N sensitivity of sulfate-reducing diazotrophs is not well understood due to a dearth of culture studies. Additionally, assays of N2 fixation in incubations rarely involve parallel measurements of dissolved inorganic nitrogen, possibly leading to experimental bias in favor of detecting activity under ammonium-replete initial conditions.

To help reconcile the environmental results, we investigate the ammonium sensitivity of N2 fixation using the acetylene reduction assay and 15N2 tracer methods in i) the model sulfate-reducing diazotroph, Desulfovibrio vulgaris str. Hildenborough (DvH), ii) four enrichment cultures from salt marsh sediments of New Jersey, and iii) slurry incubations of sediments collected from three northeastern salt marshes. In all instances, we found that ammonium strongly inhibits biological nitrogen fixation, with nitrogenase activity only detectable when ammonium concentration is below a threshold of 10 µM (slurry incubation) or 2 µM (pure cultures, enrichments). Amendment of ammonium quickly inhibits nitrogen fixation and nitrogenase activity only resumes  once ammonium is depleted to the threshold level. Ammonium additions to actively fixing samples show complete inhibition of N2 fixation within several hours post-addition. 

Our measurements of the ammonium sensitivity of benthic N2 fixation are consistent with the traditional understanding of nitrogen fixer metabolism and with early findings of Postgate et al. (1984) demonstrating that N2 fixation by the sulfate reducer Desulfovibrio gigas is inhibited by ammonium levels that exceed 10 µM. These results help clarify a long-standing paradox in benthic nitrogen cycling. We suggest that prior observations of N2 fixation at elevated ammonium levels could reflect methodological artifacts due to very fast depletion of ammonium during activity assays, legacy N2 fixation activity associated with incomplete inhibition by ammonium, or spatial heterogeneity. Further work to standardize fixed N sensitivity assays could help with cross-study comparisons and with clarifying inconsistencies in our understanding of how environmental fixed nitrogen levels control nitrogen fixation.

How to cite: Darnajoux, R., Zhang, R., Luxem, K., and Zhang, X.: The fixed nitrogen sensitivity of biological nitrogen fixation in salt marshes sediments from the northeastern United States, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11857, https://doi.org/10.5194/egusphere-egu2020-11857, 2020.

EGU2020-1951 | Displays | BG1.2

Terrestrial Biological Nitrogen Fixation in CMIP6 Models

Taraka Davies-Barnard, Johannes Meyerholt, Sönke Zaehle, Pierre Friedlingstein, Victor Brovkin, Yuanchao Fan, Rosie Fisher, Chris Jones, Hanna Lee, Daniele Peano, Benjamin Smith, David Wårlind, Andy Wiltshire, and Tilo Ziehn

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.

EGU2020-21311 | Displays | BG1.2

Pulses of Biogenic Nitrogen Cycling Lead to Atmospheric-Based Nutrient Spiraling in Southern California

Darrel Jenerette, Alex Krichels, Stephanie Piper, Aral Greene, Jon Botthoff, Hannah Shulman, Emma Aronson, Peter Homyak, James Sickman, and Jun Wang

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.

EGU2020-4954 | Displays | BG1.2

Does it pay off to link functional gene expression to denitrification rates via modelling?

Anna Störiko, Holger Pagel, and Olaf Cirpka

The abundances of functional genes and transcripts have provided new insights into microbially mediated biogeochemical processes and might improve quantitative predictions of turnover rates.
However, the relationship between reaction rates and the gene and transcript abundances may not be a simple correlation.
Most mechanistic reaction models cannot predict molecular-biological data, and it is unclear how they can be informed by such data.

We developed a mechanistic model that considers transcript abundances of denitrification genes, enzyme concentrations, biomass, and solute concentrations as state variables that are interrelated by ordinary differential equations, and thus mechanistically links molecular-biological data to reaction rates.
Important features of transcript dynamics can be reproduced with the transcript-based model.

We calibrated the model using data from a batch experiment with a denitrifying organism at the onset of anoxia.
We explored the relationship between transcript abundances and reaction rates by analyzing the model results.
The transcript abundances reacted very quickly to substrate concentrations so that we could simplify the model by assuming a quasi steady state of the transcripts.

We compared our model to a classical Monod-type formulation, which was as good at simulating the concentrations of nitrogen species as the transcript-based model, but it cannot make use of any molecular-biological data.
Our results, thus, suggest that enzyme kinetics (substrate limitation, inhibition) control denitrification rates more strongly than the dynamics of gene expression.

How to cite: Störiko, A., Pagel, H., and Cirpka, O.: Does it pay off to link functional gene expression to denitrification rates via modelling?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-4954, https://doi.org/10.5194/egusphere-egu2020-4954, 2020.

EGU2020-12965 | Displays | BG1.2

Variability of nitrogen-cycle microbial communities determined by the age of restored wetlands

Kuno Kasak, Tyler Anthony, Alex Valach, Kyle Hemes, Keit Kill, Whendee Silver, Ülo Mander, Daphne Szutu, Joseph Verfaillie, and Dennis Baldocchi

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.

The anaerobic ammonium oxidation (anammox) process converts ammonium to dinitrogen gas (N2) using nitrite as an electron acceptor under anaerobic conditions, which plays an important role in global nitrogen cycle. Anammox has been extensively investigated at different spatial scales. However, most previous studies have focused on the impacts of environmental factors on anammox bacterial community composition, whereas the influence of spatial factors, such as geographical distance, remains unclear. Here, we took sediment and water samples from two large-scale river in China: the Yangtze River. High-throughput biomolecule analysis was performed to explore the spatial patterns of anammox bacterial community and their response to environmental factors, spatial factors, community interchange and anammox bacterial traits. Additionally, 15N tracer analyses has been performed to estimated anammox activity and its contribution to N2 production (ra), and factors shaping its occurrence. Main conclusions are draw as follows: 
(1) The Three Gorges Dam (TGD) induced sediment coarsening could enhance anammox role as an important N-sink and decrease anammox bacterial alpha diversity. Anammox is ubiquitous in sediment of the Yangtze River, with high bacterial abundance (1.0×105 to 2.90×108 copies g-1 dry sediment), and activity (0.003-6.67 nmol N g-1 h-1), accounting for 3.5-82.8% of total N2 production (ra). Our results showed that the ra at the post-dam site was steeper than that before the dam, whereas the alpha diversity of anammox bacteria showing an opposite trend. Further analysis showed that hydraulic erosion leads to sediment coarsening and loss of organic matter downstream of the dam, which ultimately leads to the enhancement of the ra and the decrease of anammox bacterial alpha diversity. TGD induced sediment coarsening would extend downstream nearly to the river mouth in the coming decades, which would inevitably enhance the importance of anammox in nitrogen loss and alter anammox bacterial community in the Yangtze River for a long time.
(2) A significant distance-decay relationship was observed for anammox bacterial community similarity in the Yangtze River, which was significantly influenced by geographical distance rather than local environmental factors. This implied that niche-independent dispersal limitation plays an important role in shaping anammox community assembly. Furthermore, the slope of the distance-decay curve was much higher than previously reported for whole bacteria, which indicating the species turnover rate of anammox bacteria (z-value = 0.35) was significantly higher than that of the whole bacteria (approximately 0.008-0.05). Anammox bacteria harbor stronger adsorption ability and film-forming ability than other bacteria. As such, anammox bacterial harbor lower dispersal potential, and ultimately exhibited a higher species turnover rate than whole bacteria.
 This study investigated the geographical patterns and the driving mechanisms of anammox bacterial community in large-scale riverine ecosystems, and estimated the key shaping factors of anammox activity and its contribution to total N2 production. The results or conclusions of this study are of scientific significance for further revealing the community assembly and geographical patterns of anammox bacteria on a global scale, as well as the theoretical system of nitrogen cycle.

How to cite: Liu, S. and Chen, L.: Key shaping factors of anammox bacterial geographical distribution and function in riverine ecosystems, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-6367, https://doi.org/10.5194/egusphere-egu2020-6367, 2020.

EGU2020-15588 | Displays | BG1.2

The imprint of anammox on the stable isotope compositions of nitrogen-bearing molecules

Paul Magyar, Damian Hausherr, Robert Niederdorfer, Jing Wei, Joachim Mohn, Helmut Bürgmann, Adriano Joss, and Moritz Lehmann

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.

EGU2020-3692 | Displays | BG1.2

Nitrite isotope characteristics in 15N-labelled and non-labelled agricultural soil

Dominika Lewicka-Szczebak and Reinhard Well

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.

EGU2020-5257 | Displays | BG1.2

Oxygen supply and demand as controls of denitrification at the microscale in repacked soil

Lena Rohe, Steffen Schlüter, Bernd Apelt, Hans-Jörg Vogel, and Reinhard Well

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.

EGU2020-3318 | Displays | BG1.2 | Highlight

Nitrogen removal and nitrous oxide emissions in woodchips biofilters treating agricultural drainage waters

Joachim Audet, Dominik Zak, and Carl Christian Hoffmann

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.

EGU2020-5396 | Displays | BG1.2

Validation of satellite-constrained ammonia using a CTM and ground and satellite measurements

Nikolaos Evangeliou, Yves Balkanski, Sabine Eckhardt, Didier Hauglustaine, Anne Cozic, and Andreas Stohl

Ammonia (NH3) has received a lot of attention nowadays due to its major implications for the population and the environment. Global sources of ammonia include wild animals, ammonia-containing water areas, traffic, sewage systems, humans, biomass burning (mainly from dung fires and domestic coal combustion), volcanic eruptions and agriculture. In the present study, we used 10 years (2008–2017) of satellite measurements of ammonia retrieved from the Infrared Atmospheric Sounding Interferometer (IASI) to calculate surface emissions. In contrast to other methods, we first used a sophisticated Inverse Distance Weighting (IDW) interpolation algorithm to define a grid of column-integrated ammonia concentrations globally. In a hypothetical box model, emissions are given as a function of the mass of ammonia in each atmospheric box (in molecules cm-3) divided by the lifetime of ammonia in the box (in seconds) based on all the potential removal processes that affect atmospheric ammonia. Instead of considering the lifetime of ammonia as a constant value, such as in the relevant literature, we used calculated gridded lifetimes from a Chemistry Transport Model (CTM). The estimated emissions were then imported in a CTM and were simulated for the same 10–year period. To verify the improvement of the calculated emissions of ammonia, we evaluated the modelled surface concentrations against ground–based measurements from different monitoring stations. The same comparison was performed for the most recent state–of–the–art emission dataset for ammonia.

How to cite: Evangeliou, N., Balkanski, Y., Eckhardt, S., Hauglustaine, D., Cozic, A., and Stohl, A.: Validation of satellite-constrained ammonia using a CTM and ground and satellite measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-5396, https://doi.org/10.5194/egusphere-egu2020-5396, 2020.

EGU2020-397 | Displays | BG1.2

Emissions of nitrous acid (HONO) and nitric oxide (NO) from soils and its impact on air quality in Shanghai

Mengdi Wang, Jingwei Zhang, Junling An, Feng Zhou, Xiuying Zhang, Ruhai Wang, Lingling Deng, Lijun Hou, Min Liu, and Dianming Wu

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 NOx (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 NOx 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.

EGU2020-10069 | Displays | BG1.2

Ecosystem scale evidence for the contribution of vanadium-based nitrogenase to biological nitrogen fixation

Jean-Philippe Bellenger, Romain Darnajoux, Nicolas Magain, Marie Renaudin, Francois Lutzoni, and Xinning Zhang

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.glichen-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.

EGU2020-8678 | Displays | BG1.2

Early response of biological nitrogen fixation in a mature oak dominated forest to elevated atmospheric CO2 fumigation at BIFoR-FACE

Sami Ullah, Ernesto Saiz Val, Fotis Sgouridis, and Falko Drijfhout

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.

Increasing atmospheric CO2 concentrations in temperate forests may affect soil nitrogen (N) cycling processes due to the increased demand  for nitrogen availability by trees to support CO2 uptake through photosynthesis. This in turn can affect the emission of nitrous oxide (N2O) from the forest soil leading to a potential trade-off between the enhanced canopy CO2 uptake and soil N2O emission. The Birmingham Institute of Forest Research (BIFoR) established a Free-Air CO2 Enrichment (FACE) facility in a mature oak forest in Staffordshire, UK, which became operational in 2017. In April 2018 and again in May 2019, two years after the start of fumigation with 550 ppm CO2, we collected soil samples (0 – 15 cm depth) from the three elevated CO2 (eCO2) and three control plots. Soils were amended in the laboratory with 98 at % 15N-NH4+ and 15N-NO3- . Gross N mineralisation and nitrification were estimated by the isotope dilution technique, while N2O emission from nitrification (15N-NH4+ treatment) and denitrification (15N-NO3- treatment) were estimated by the 15N Gas-Flux method. Additionally, C/N ratio and δ15N and δ13C were measured in unamended eCO2 and control samples via EA-IRMS. Whilst gross N mineralisation and N2O emission were only marginally higher in eCO2 plots compared to controls after one year of fumigation, there was a significant stimulation of N cycling after the second year that led to more pronounced differences. Gross N mineralisation rates doubled in the eCO2 plots (mean: 4.09 μg N g-1 d-1, P < 0.05) compared to the control plots (mean: 2.02 μg N g-1 d-1), while a similar twofold increase was observed for gross nitrification rates (mean eCO2: 1.63 μg N g-1 d-1;  mean control: 0.70 μg N g-1 d-1, P < 0.05). N2O emission from both denitrification (mean: 0.03 ng N g-1 d-1) and nitrification (mean: 0.02 ng N g-1 d-1) were generally low but of similar magnitude and more than double than in the control plots. C/N ratio was conservative between eCO2 and control plots as a result of proportional increase of C and N contents in the eCO2 plots. The observed stimulation in N cycling was further corroborated by the significantly enriched δ15N signal (-0.66 ‰) in eCO2 plots compared to the controls (-1.38‰). Moreover, the eCO2 samples had a more depleted δ13C signal (-28.37 ‰) compared to the controls (-27.99 ‰), as a result of the additional carbon supplied through fumigation (CO2 δ13C ~ -28 ‰). Following the first year of CO2 fumigation, there were indications of soil N limitation despite the high rates of atmospheric N deposition (22 kg N ha-1 y-1). However, after only 2 years of the FACE experiment there is strong evidence of a shift in key soil N processes to sustain the enhanced nutrient demands to support enhanced canopy CO2 uptake. Further research is underway in BiFOR-FACE to elucidate whether carbon quantity and/or quality drives the stimulation of soil N cycling and what are the long-term implications of the trade-off between enhanced CO2 sequestration and a potential increase in N2O emissions.

How to cite: Sgouridis, F., Cotchim, S., and Ullah, S.: Stimulation of soil N cycling after two years of Free Air CO2 Enrichment increases nitrous oxide emissions in a temperate forest, UK., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15899, https://doi.org/10.5194/egusphere-egu2020-15899, 2020.

EGU2020-13067 | Displays | BG1.2

Fate of atmospheric nitrogen depositions in two Italian temperate mountain forests assessed by isotopic analysis

Luca Da Ros, Maurizio Ventura, Mirco Rodeghiero, Damiano Gianelle, and Giustino Tonon

Abstract. Forests ability to store carbon is strongly connected with the amount of nitrogen (N) that forest ecosystems can retain; N is indeed considered the most limiting nutrient for terrestrial ecosystem's net primary productivity. Since the industrial revolution, human activities have more than doubled the rate of N input into the nitrogen cycle and this could alleviate N limitation thus stimulating plant growth. However, it has been suggested that when N availability exceeds biotic demand and abiotic sinks, additional N can trigger a negative cascade effect: nutrient imbalance, reduced productivity, increased losses of N, eutrophication and acidification of soil and water, leading toward forest decline and net greenhouse gases emissions. The consequences of increased N deposition on forest depend in large share on the fate of N in the ecosystem, which can be simulated and quantified by a fertilization at a known isotopic signature. Nevertheless, most of the tracer experiments performed so far added the fertilizer directly to the forest floor, neglecting the potential role of N uptake by the forest canopy. In the Italian Alps, we are conducting an experiment where both types of N additions (above and below the canopy layer) are performed in two different forest stands, to understand if canopy fertilization better simulates ecological consequences of increased atmospheric N deposition. These field-scale manipulation experiments are willing to test two different hypotheses: i) the N uptake by trees in the above-canopy N addition experimental sites is higher than under-canopy N addition ii) forest growth rate varies with the type of treatment. To describe the fate of the applied N, stable isotope techniques have been adopted: the forest sites, fertilized with NH4NO3 at a known isotopic signature, are sampled for all the ecosystem components (plant, soil and water) periodically to determine the total N content and its isotopic signature. The δ15N values permit to calculate the recovery of N-fertilizer in tree tissues, soil and leaching-water, allowing us to understand how N allocation varies under these two fertilization strategies and how this affects C sequestration potential. Results regarding the short-term effects over the first 6 years of data collection will be presented.

How to cite: Da Ros, L., Ventura, M., Rodeghiero, M., Gianelle, D., and Tonon, G.: Fate of atmospheric nitrogen depositions in two Italian temperate mountain forests assessed by isotopic analysis, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13067, https://doi.org/10.5194/egusphere-egu2020-13067, 2020.

EGU2020-17258 | Displays | BG1.2

Effects of nitrogen deposition on greenhouse gas fluxes from the soil: results from an innovative experimental design

Anna Bortolazzi, Maurizio Ventura, Pietro Panzacchi, Flavio Fornasier, Claudio Mondini, and Giustino Tonon

In the last decades, the effects of nitrogen (N) deposition on temperate forests have received much interest. Studies recorded several changes in soil carbon (C) and N cycles due to extra reactive N available. For instance, past studies reported that N deposition, may influence CO2 emission, lower CH4 consumption by the soil and increase the emission of N2O. Nevertheless, the mechanistic understanding of these ecological responses is still far to be reached. However, most of the studies neglected to include the canopy interception in the experiments simulating N addition, notwithstanding tree canopy have shown to change both the amount and the chemical composition of the N deposition. Hence, experiments simulating this process by applying fertilization above the canopy are needed.

The aim of this study is to explore how N deposition influences greenhouse gas (GHG) emissions in a temperate oak forest (Quercus petraea Liebl.) located in Monticolo (Bolzano, Italy). In this site, a set of three plots was created and replicated three times. Each set includes a control plot, a plot with below-canopy fertilization (NBL) and a plot with above-canopy fertilization (NAB). The fertilization is applied, since 2015, from May to September, for a total annual N addition of 20 kg N ha-1.

Since April 2018, CO2 emission has been monthly measured with a portable infrared gas analyzer. Measurements were performed on three points per plot, for a total of 27 measurement points. During measurements, soil moisture and soil temperature at 10 cm depth were measured as well.

The measurements of CH4 and N2O started during the growing season in 2019 and are performed on a monthly basis by a static chamber method. Three chambers were installed per plots, for a total of 27 chambers.

We will present the preliminary results of this study. The results showed that the 5-year N fertilization did not lead to significant differences between plots in terms of GHG fluxes. The sensitivity of CO2 emission to temperature was not influenced by extra N. The differences were not significant between fertilized and unfertilized plots, nor between the two fertilization methods.

How to cite: Bortolazzi, A., Ventura, M., Panzacchi, P., Fornasier, F., Mondini, C., and Tonon, G.: Effects of nitrogen deposition on greenhouse gas fluxes from the soil: results from an innovative experimental design, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-17258, https://doi.org/10.5194/egusphere-egu2020-17258, 2020.

EGU2020-12706 | Displays | BG1.2

Response of N2O and N2 Emissions in Forest Soils to Temperature Change across China

Haoming Yu, Yunting Fang, and Ronghua Kang

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 21.5oC 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 35oC with an interval of 5oC 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.

EGU2020-20450 | Displays | BG1.2

Response of N2O emissions to logging residue piles of Norway spruce, Scots pine and silver birch

Tiina Törmänen, Antti-Jussi Lindroos, Veikko Kitunen, and Aino Smolander

Utilization of forest bioenergy is increasing; however, the overall environmental impacts of forest bioenergy utilization are not fully understood. Especially effects on N2O emissions in mineral soils are less studied. With current harvesting practices, either whole-tree-harvest or stem-only-harvest, piles of logging residues are left on the forest floor. As a result, soil nitrogen (N) cycling processes can be accelerated on clear cut area under the piles, especially net nitrification. When N is transformed to more mobile form, the risk for N losses via nitrous oxide (N2O) emissions from the forest floor may increase.

We studied how logging residue piles of three tree species, Norway spruce (Picea abies (L.) Karst.), Scots pine (Pinus sylvestris L.) and silver birch (Betula pendula Roth.), influence gaseous losses of N after clear-cut. A Norway spruce dominated mixed stand on a mineral soil site was clear-cut and N2O emissions were monitored. There were four treatments; three tree species treatments consisting of 40 kg m-2 of fresh logging residues and control plot without residues as an additional treatment. Effects of logging residue piles on N2O emissions were monitored over 4 growing season with closed chamber technic. Simultaneously soil temperatures were recorded over 2 growing season. Soil denitrification activity and the contribution of nitrification and denitrification to N2O production were determined in laboratory experiments.

Logging residue piles lowered and balanced fluctuation of soil temperatures. N2O fluxes peaked under the piles during the second and third growing season after the establishment of the piles; however inconsistent fluxes tended to be low. The production of N2O was driven by both nitrification and denitrification processes, the proportion depending on the tree species. Our results indicate that logging residue piles accelerate N losses as gaseous form; however studies on the same field experiment shows that most of the N losses occur through soil percolation waters. Spruce residues tend to stimulate N2O emissions longer compared to other tree species. There was a positive correlation with net nitrification and microbial biomass C (Törmänen et al. 2018, FORECO). These results have implications for sustainable and productive forest management practices and nutrition of re-growing vegetation.

How to cite: Törmänen, T., Lindroos, A.-J., Kitunen, V., and Smolander, A.: Response of N2O emissions to logging residue piles of Norway spruce, Scots pine and silver birch , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20450, https://doi.org/10.5194/egusphere-egu2020-20450, 2020.

EGU2020-22205 | Displays | BG1.2

Effects of drying and rewetting cycles on denitrification and greenhouse gas emissions in normally saturated organic substrate

François Birgand, Bryan Maxwell, Augustin Thomas, Louis Schipper, David Williams, Laura Christianson, Shying Tian, Matthew Helmers, Chip Chescheir, and Mohamed Youssef

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.

EGU2020-6628 | Displays | BG1.2 | Highlight

The effect of boichar on the emission of N2O from a calcareous soil

Wenxu Dong, Anna Walkiewicz, Caohui He, Andrzej Bieganowski, and Chunsheng Hu

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.

EGU2020-2760 | Displays | BG1.2

Denitrification induced by plant residues is driven by water-soluble organic carbon

Ronny Surey, Corinna M. Schimpf, Leopold Sauheitl, Carsten W. Mueller, Pauline S. Rummel, Klaus Dittert, Klaus Kaiser, Jürgen Böttcher, and Robert Mikutta

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.

EGU2020-15158 | Displays | BG1.2

Response of soil N2 and N2O fluxes to denitrification control factors in two agricultural soils

Amanda Matson, Stefan Burkart, Balazs Grosz, Jan Reent Köster, Simone Merl, and Reinhard Well

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.

EGU2020-6822 | Displays | BG1.2

The effects of living roots and arbuscular mycorrhiza fungi (AMF) on soil N2O emissions

Yawen Shen, Tianle Xu, and Biao Zhu

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.

EGU2020-9218 | Displays | BG1.2

Analysis of N2O emissions and isotopomers to understand nitrogen cycling associated with multispecies grassland swards at a lysimeter scale

Conor Bracken, Gary Lanigan, Karl Richards, Saoirse Tracy, Christoph Müller, and Paul Murphy

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.

EGU2020-19445 | Displays | BG1.2

NO3- uptake and C exudation – do plant roots stimulate or inhibit denitrification?

Pauline Sophie Rummel, Reinhard Well, Birgit Pfeiffer, Klaus Dittert, Sebastian Floßmann, and Johanna Pausch

Growing plants affect soil moisture, mineral N and organic C (Corg) availability in soil and may thus play an important role in regulating denitrification. The availability of the main substrates for denitrification (Corg 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 Corg 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 Corg 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.

EGU2020-8609 | Displays | BG1.2

Optimising Fertilisation Strategy for Nitrogen Uptake Efficiency

Daniel McKay Fletcher, Siul Ruiz, Simon Duncan, Dave Chadwick, David Jone, and Tiina Roose

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.

 

There is growing evidence that liming reduces the magnitude of N2O emissions in acidic soils. Here we report N2O emissions from a liming experiment with olivine, dolomite and calcite and of maintenance liming with the same materials in clay loam soil at Norwegian University of Life Sciences research farm. The field was bulk limed in 2014 and monitored for N2O fluxes by an autonomous filed flux robot (FFR). Over the course of four years, the fluxes varied but showed a potential of lime as a mitigation tool, with calcareous treatments (dolomite and calcite) displaying a clear decline in N2O emissions compared to unamended plots. To explore the effect of maintenance liming, subplots were maintenance limed and compared with bulk limed controls after sowing the field to winter wheat (Triticum aestivum L.) in summer and fertilizing with 50 kg NPK-N.

Growing-season N2O emissions (June-September) in maintenance limed dolomite plots were on average 26% lower than bulk limed plots and the corresponding reduction in calcite plots was 16%. There was no effect of maintenance liming in the olivine treatment. N2O emissions decreased in the order unlimed control > olivine > dolomite > calcite, covering a pHCaCl2 range of 4.9 to 6.5.

Our results suggest that maintenance liming, as a component of good agricultural practice, is important to maintain the N2O reducing effect of liming over time. However, the amount of CO2 released by the dissolution of lime should be investigated in order to fully explore the mitigation potential of soil pH management in crop production.

How to cite: Todorcic Vekic, T., Bakken, L., and Dörsch, P.: Effect of maintenance liming with olivine, dolomite and calcite on growing-season N2O emissions in an arable soil of SE Norway , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11023, https://doi.org/10.5194/egusphere-egu2020-11023, 2020.

EGU2020-8818 | Displays | BG1.2

Interaction of decreased crop growth and retarded mineralisation of 15N 13C labelled green manure under decreased precipitation patterns

Andreea Spiridon, Weronika Kisielinska, Rebecca Hood-Nowotny, Simon Leitner, Maria Heiling, Anna Wawra, Johannes Hösch, Erwin Murer, Herbert Formayer, Wolfgang Wanek, Judith Prommer, and Andrea Watzinger

Changes in climate will bring along changes in precipitation patterns, and as such, it will determine the availability of water in agricultural systems. We aimed to investigate the impact of climate-induced altered precipitation regimes on crop performance and soil processes such as organic matter mineralisation and nutrient release. The experiment took place at the lysimeter station located in Hirschstetten, Vienna, Austria (48° 15' 22" N, 16° 289 3" E, 160 m a.s.l.) where a future precipitation scenario was compared with current precipitation patterns on two different soil types – a sandy calcaric Phaeozem and a calcic Chernozem, both being representative for the Marchfeld region in Lower Austria. The future precipitation regime was calculated from four regionalised scenarios from Euro-Cordex out of the ÖKS 15 ensemble following the GHG emission scenarios RCP 4.5 and RCP 8.5.

Stable isotope analysis has become a useful tool for sensitively tracing biogeochemical processes in soils. In this study, plant residues of white mustard (Sinapis alba), isotopically labelled with carbon 13C and nitrogen 15N in a controlled laboratory environment were applied as organic fertiliser (green manure) on the lysimeter soils in April 2018. Soil, plant, gas and groundwater samples were collected from the lysimeters throughout the growing season of 2018 and 2019 and analysed using cavity ring-down spectrometry (CRDS) for 15N-N2O in the field and by isotope ratio mass spectrometry.

Crop results showed an increase in the shoot 13C signatures, indicative of drought stress, which resulted in diminished plant production by -20 to -50% under the decreased precipitation. Isotope analysis showed lower decomposition and mineralisation rates of labelled green manure only during the first few days under the future precipitation treatment, followed by an increase in 15N enrichment of soil solution NO3- during summer, emphasising the importance of plant biomass production on root NO3- uptake from the soil. N2O emissions were higher after the application of synthetic fertiliser during the first year, highlighting the importance of available NO3- in agricultural systems for nitrification and denitrification processes. However, lower N2O emissions were observed during the second year, indicating possible N stress. Overall we found that N losses through NO3- leaching and N2O emissions were most sensitive to reduced precipitation when NO3- is available, which can cause aggravating environmental problems in the future.

The stable isotope labelling technique proved to be successful for tracing and identifying drought stress effects on plant and soil processes in agricultural systems, allowing for a better understanding of soil-plant processes under changing climate conditions.

How to cite: Spiridon, A., Kisielinska, W., Hood-Nowotny, R., Leitner, S., Heiling, M., Wawra, A., Hösch, J., Murer, E., Formayer, H., Wanek, W., Prommer, J., and Watzinger, A.: Interaction of decreased crop growth and retarded mineralisation of 15N 13C labelled green manure under decreased precipitation patterns, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-8818, https://doi.org/10.5194/egusphere-egu2020-8818, 2020.

The amount of bioavailable nitrogen is directly linked to anthropogenic activity (Kuypers, Marchant, & Kartal, 2018), particularly with the intensive application of synthetic nitrogen fertilisers. Although high nitrogen inputs are required to support the ever-increasing need for food production, nitrogen use efficiency is in many cases low, to the extent that even with extra nitrogen inputs over time, increases of food production are small and slow (Battye, Aneja, & Schlesinger, 2017).

It has been suggested that roughly 40% of reactive nitrogen is denitrified in the soil (Seitzinger, et al., 2006), and most of the reactive nitrogen that results from human activities is removed by denitrification, with consequent production of N2 and N2O. However, even if most reactive N forms are removed by denitrification, this is an indicator that N use efficiency is not at optimum levels.

A study is being conducted in field and controlled conditions, that aims to understand denitrification and nitrogen use efficiency in a long-term experiment (running continuously since 2013) at Rothamsted Research. The experiment was designed to provide a clearer look at the effect of applications of organic amendments and/or inorganic fertilisers on nitrogen dynamics and crop yields in a conventional cereal-based cropping system.

Simultaneously, using yield data from the same trial, we aim to understand a) if the application of organic amendments leads to a reduction of the nitrogen threshold for optimum yields and, by using a modelling approach, b) if the eventual higher yields obtained with organic amendment application are due to the effect of the extra nutrients contained in the amendment or to some other effect caused by the amendments.

Soil and gas samples are being collected from a) different treatments of the field experiment (four different organic amendments: anaerobic digestate, compost, farmyard manure, straw and unamended control; and different nitrogen application rates; area of each plot: 54 m2) to assess nitrogen dynamics, and b) from soil columns (height 35 cm; width 25.5 cm)  placed in a controlled environment using soil collected from the same trial. Different measurements are being taken including leachate (measurements of mineralised nitrogen), microbiology and gas emissions (using a Picarro device that measures NH3, N2O, CO2, CH4, O2, H2O). Simultaneously, underground sensors are being used to understand moisture and temperature evolution in the soil column, while electrochemical nitrate sensors are being used to understand nitrate dynamics before and after application of organic amendments and inorganic fertilisers.

With this, we aim at having a better understanding on denitrification processes and nitrogen use efficiency issues that may occur when using a joint regime of organic amendments and inorganic fertilisers. The main objectives of the project are the validation of the effect of organic amendments in the Fosters long-term experiment and the quantification of nitrogen gas emissions with the application of organic amendments and nitrogen fertilisers.

How to cite: Albano, X., Sakrabani, R., and Haefele, S.: Effect of organic amendments and inorganic fertiliser application on nitrogen use efficiency and denitrification in controlled and field conditions, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15032, https://doi.org/10.5194/egusphere-egu2020-15032, 2020.

EGU2020-2543 | Displays | BG1.2

Evaluation and adjustment of description of denitrification in the CoupModel, DNDC and DeNi model based on N2 and N2O laboratory mesocosm incubation system measurements

Balázs Grosz, Reinhard Well, Rene Dechow, Jan Reent Köster, M. Ibrahim Khalil, Hongxing He, Simone Merl, Andreas Rode, and Bianca Ziehmer

Quantifying soil nitrogen processes – especially denitrification – are critical for the adequate prediction of the produced and emitted N2O and N2 gasses and the production and consumption of NO3- and NH3. Biogeochemical models are useful tools for the description of these N processes, but recent research progress is not considered on the denitrification sub-modules of these models. Denitrification typically occurs in hot-spots of the soils but the models describe the soils as a homogenized system. Another critical problem is the calibration of the decomposition sub-modules. Suitable soil N2 flux data were not available during the development of the extensively used models but new measurement techniques provide appropriate N2 gas flux data.

In this study we investigate the N2 and N2O fluxes from mesocosm experiments of different complexity and use the measured data and experimental settings for testing the denitrification sub-module of existing biogeochemical models.

Two arable soils – a silty loam and a sandy soil – were used for the experiments and varied with N fertilization and organic matter amendment. The soils were incubated in laboratory incubation systems over 42 and 58 days, respectively. N2, N2O and CO2 fluxes were quantified by gas chromatography and isotope-ratio mass spectrometry. Seven moisture and three NO3- contents were set up to the loamy soil and only the temperature was manipulated during the experiment, while other factors were kept constant. In the experiment with the sandy soil, incubations were conducted with or without incorporation of organic litter (ryegrass) and initial water content was adjusted equivalent to 80% water-filled pore space. Temperature, water content and NO3- content were manipulated during that experiment.

Three commonly used biogeochemical models – namely CoupModel, DNDC and DeNi (a self programmed early stage version of the nitrification and denitrification sub-model of the DailyDayCent) – were tested on the experimental data.

The average N2+N2O fluxes of the loamy soil as given by measurements, DNDC, DeNi and CoupModel calculations was 287.5±202.3, 1.8±0.5, 779.1±282.2, 67.9±8.4 gN ha-1 day-1, respectively. For the sandy soil, these fluxes were 166.6±377.7, 23.7±34.7, 491.2±819.9 and 13.3±7.8 gN ha-1 day-1, respectively. The results show that the models did not calculate the same magnitude of the measured values. The DeNi model overestimated and the DNDC and CoupModel underestimated the measured fluxes. However, in some cases the temporal patterns of the measured and the modeled emission were similar. Most cases of over- or underestimations by the models could be explained by certain deficiencies of the models or of the experimental data.

How to cite: Grosz, B., Well, R., Dechow, R., Köster, J. R., Khalil, M. I., He, H., Merl, S., Rode, A., and Ziehmer, B.: Evaluation and adjustment of description of denitrification in the CoupModel, DNDC and DeNi model based on N2 and N2O laboratory mesocosm incubation system measurements, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2543, https://doi.org/10.5194/egusphere-egu2020-2543, 2020.

EGU2020-19467 | Displays | BG1.2

Understanding the Dynamics of Denitrification with high-resolution Simulations

Olaf Ippisch, Jan Zawallich, Peter Dörsch, Steffen Schlüter, Marcus A. Horn, and Hans-Jörg Vogel

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.

EGU2020-1763 | Displays | BG1.2

Effects of the nitrification inhibitor nitrapyrin on urea-based fertilizers in a Mediterranean calcareous soil: N dynamics and microbial functional genes.

Georgios Giannopoulos, Lars Elsgaard, Georgios Zanakis, Rima B. Franklin, Bonnie L. Brown, and Nikolaos Barbayannis

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.

EGU2020-6567 | Displays | BG1.2

Seasonal comparison of potential denitrification rates and nitrogen functional genes with sediment depths in the wetland, Korea

Ji Yeon Han, Dong-Hun Kim, Seolran Oh, and Hee Sun Moon

EGU2020-20866 | Displays | BG1.2

Advancing our understanding of novel nitrous oxide reducers

Jun Shan, Sean Ooi, Robert A Sanford, Joanne Chee-Sanford, Frank Löffler, Kostas Konstantinidis, and Wendy H. Yang

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.

EGU2020-12613 | Displays | BG1.2

Formation and succession of microbial community structure in different ecological niches under reclaimed water acclimation

Jie Li, Yujiao Sun, Xiaoyu Wang, Meng Yin, and Shangwei Xu

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.

EGU2020-5713 | Displays | BG1.2

Responses to dissolved organic nitrogen compounds by recently isolated freshwater microalgae species

Catherine E. Bayliss, Penny Johnes, Richard P. Evershed, Patricia Sanchez-Baracaldo, and Stephen C. Maberly

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 (δ13Corg) 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 (δ13Corg) 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.

BG1.3 – Do geochemical background values still exist?

EGU2020-761 | Displays | BG1.3

Determination of geochemical backgroud of waters of Kola Peninsula in order to decrease anthropogenic pollution in analysed area

Dorota Moroniak-Wawryszuk, Mateusz Wawryszuk, Stanisław Chmiel, Miłosz Huber, Paweł Kramarz, Lesia Lata, and Sebastian Skupiński

In this study the geochemical background of waters of Kola Peninsula in the context of decreasing the athropogenic pollution in that region was indicated. The study was conducted on 14 water samples from different phases of hydrological cycle- precipitation water, snow-melting water, ground water, river water, lake water, sea water; also 12 samples of rocks and soils were used. pH of waters, conductivity, isotopic ratio of δ18O i δD, concentration of ions (anions and cations) along with metal ions were analysed. For conductivity measure InoLab 1 (WTW) was used, cations and anions were indicated by ions chromatograph (Metrohm MIC 3), metal ions were indicated by spectrometer ICP-MS (Thermo Xseries2). Laser analyzer PICARRO L2130 was used for defining the isotopic ratio of δ18O i δD. Soils and rocks samples were analysed using scanning electrone microscope (Hitachi SU6600) with EDS add-on and spectroscope XRF Epsilon 3 (Pananalytical).

The study showed significant impact of bedrock and soils on ion composition of waters in different locations in Kola Peninsula in example on several geogenical metal ions of P, F, Cl, Fe, Mn, Cu, Ni, S. Chemical composition of water backround is strictly related to polymetalic rocks and metal ores of the Baltic Shield which build analysed area. The waters' richness in alkali minerals is due to alkaline bedrock occuring in numerous areas of Kola Peninsula. The content of metal ions like Zn, Pb, Cr, Cd in numerous water samples indicates severe anthropogenic influence on water composition which can be especially noticed in the composition of surface water affected by the nearby heavy industry plants thus pollution of surface water.

Analisys of water samples proves significant impact of geological structure on chemical composition of water and should be considered in reclamation of natural environment of Kola Peninsula from anthropogenic pollution.

How to cite: Moroniak-Wawryszuk, D., Wawryszuk, M., Chmiel, S., Huber, M., Kramarz, P., Lata, L., and Skupiński, S.: Determination of geochemical backgroud of waters of Kola Peninsula in order to decrease anthropogenic pollution in analysed area, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-761, https://doi.org/10.5194/egusphere-egu2020-761, 2020.

Environmental geochemistry is playing an increasingly important role in mineral exploration, environmental management, agricultural practices as well as links with health. With rapidly growing databases available at regional, national, and global scales, environmental geochemistry is facing the challenges in the “big data” era. One of the main challenges is to find out useful information hidden in a large volume of data, with the existence of spatial variation found at all the sizes of global, regional (in square kilometers), field (in square meters) and micro scales (in square centimeters). Meanwhile, the rapidly developing techniques in machine learning become useful tools for classification, identification of clusters/patterns, identification of relationships and prediction. This presentation demonstrates the potential uses of a few practical spatial machine learning techniques (spatial analyses) in environmental geochemistry: neighborhood statistics, hot spot analysis and geographically weighted regression.

 

Neighborhood (local) statistics are calculated using data within a neighborhood such as a moving window. In this way, spatial variation at the local level can be quantified and more details are revealed. Hot spot analysis techniques are capable of revealing hidden spatial patterns. The techniques of hot spot analysis including local index of spatial association (LISA) and Getis Ord Gi* are investigated using examples of geochemical databases in Ireland, China, the UK and the USA. The geographically weighted regression (GWR) explores the relationships between geochemical parameters and their influencing factors at the local level, which is effective in identifying the complex spatially varying relationships. Machine learning techniques are expected to play more important roles in environmental geochemistry. Challenges for more effective “data analytics” are currently emerging in the era of “big data”.

 

How to cite: Zhang, C.: Towards spatial machine learning to reveal hidden patterns and relationships in national and international geochemical databases, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-2179, https://doi.org/10.5194/egusphere-egu2020-2179, 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.

Urban areas are typical examples of disturbed natural environments where human development has significantly altered the geochemical background of trace elements in surface soil and sediment. Road dusts and gully sediments are reflective of a wide range of anthropogenic activities in cities and are a useful resource for evaluating the level and distribution of trace metal contaminants in the surface environment. The evaluation of contamination in these sinks provides useful information of how the drainage system of the cities contributes to urban pollution.

A total of 26 urban road deposited sediment samples were collected from different altitudes within the Athens basin based on the hydrographic network of the area. The samples were analyzed for 33 elements following an aqua regia dissolution. Sample organic carbon content, pH and grain size distribution have been determined and magnetic susceptibility measurements and mineralogical analysis by powder X-ray diffraction were also performed in order to identify possible factors explaining the variability of elemental concentrations. Also, sixteen samples were analyzed for polycyclic aromatic hydrocarbons (PAHs) in order to detect their sources in the Athens urban environment.

Aqua regia concentrations in the analyzed sediments reached maximum values of 18 mg/kg for As, 2 mg/kg for Cd, 14 mg/kg Co, 193 mg/kg Cr, 640 mg/kg Cu, 25600 mg/kg Fe, 112 mg/kg Ni, 3092 mg/kg Pb and 1469 mg/kg Zn. The median values of the studied elements were estimated to be 13 mg/kg for As, 1 mg/kg for Cd, 8 mg/kg Co, 98 mg/kg Cr, 215 mg/kg Cu, 17154 mg/kg Fe, 70 mg/kg Ni, 267 mg/kg Pb and 598 mg/kg Zn, respectively. With the exception of Co and As, both maximum and median values were found to be much higher than those in Athens soils from a previous study. Cluster analysis on the results identified two major groups of elements based on an over 43.59% criterion of similarity. The first cluster contains elements of geogenic origin including Co, Fe, Mn and Ni. The parameters of % organic carbon, magnetic susceptibility, Cu and Cr are grouped together in a second cluster showing a similarity level over 65% while a third cluster groups together Pb, Zn and Cd and is interpreted as anthropogenic.

In a previous systematic baseline study of Athens, it was found that the major factor controlling variability of the chemical composition of surface soil was the bedrock chemistry, resulting in a significant enrichment in concentrations of Ni, Cr, Co and possibly As. Anthropogenic influences were also significant in soil, controlling a spectrum of elements that are typical of human activities, i.e. Pb, Zn, Cu, Cd, Sb, and Sn. The clustering of elements in the present study indicates that although the geogenic origin of some elements is retained in road sediments, a greater number of elements indicate anthropogenic influence in their distribution. Briefly, it was documented that road deposited sediments reflect the characteristics of the anthropogenic activities taking place, and that traffic- related activities are the primary sources of contaminants.

How to cite: Kourgia, P.-M. and Argyraki, A.: Trace element concentrations in road deposited sediments of Athens, Greece: A comparison with baseline soil data, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-13246, https://doi.org/10.5194/egusphere-egu2020-13246, 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.

EGU2020-21458 | Displays | BG1.3

Spatial anomalies of uranium background levels in groundwater of Lower Saxony

Roland Stumpf, Dörte Budziak, Nico Deus, and Jörg Elbracht

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.

EGU2020-22687 | Displays | BG1.3

Extending the concept of background to soil gas: natural radon concentrations in soils of Campania region.

Stefano Albanese, Annalise Guarino, Daniela Zuzolo, Antonio Aruta, Domenico Cicchella, Antonio Iannone, Raffaele Melito, Francesco Verrilli, and Alessandro Fedele Gianvito

Radon is an ubiquitous radioactive gas proceeding from the decay of some radionuclides, mostly abundant in igneous rock and volcanic soils; it is the main source of natural radiation to which human beings are exposed during their life. Campania, a region located on the south-western sector of the Italian peninsula, has a territory mostly characterized by the presence of volcanic lithotypes and sediments. 
An empirical method was applied to determine the concentration of Rn-222 in soils of Campania region by using radiometric  and compositional data recorded in two extensive different environmental prospecting campaigns completed in 2003 and 2015, respectively.

Radiometric surveys were carried out with a nominal density of 1 station per 5 sqkm with a GRS-500 portable scintillometer produced by Scintrex Ltd (Ontario, Canada); topsoil samples were collected at 3535 sites regularly spread across the whole regional area with a nominal density of 1 sample per sqkm. Samples destinated to chemical analyses were analysed by ICP-MS after an aqua regia digestion at the ACME Analytical Laboratories Ltd (now Bureau Veritas) in Vancouver, Canada.  

Specifically, the concentrations of  U, Th and K  in topsoil samples  and the activity (gamma radiation) generated by the decay of U-238, Th-232 and K-40 (expressed as Bq) at  each measurement station were used as proxies in order to determine the variation of Rn-222 flux from the ground and to estimate the distribution pattern of geogenic radon potential (GPR) across the region.

The use of a sequence of specific equations led to estimate the terrestrial gamma dose rate (nSv/h) at 1 m above the ground surface starting from both datasets and, therefore, allowed the generation of the Rn-222 flux and GPR maps for the whole regional territory.

Both Radon flux and GPR raster maps were produced by mean of some specific geospatial elaborations and the estimated values were compared among them and validated trough the completion of some field measurements.

How to cite: Albanese, S., Guarino, A., Zuzolo, D., Aruta, A., Cicchella, D., Iannone, A., Melito, R., Verrilli, F., and Gianvito, A. F.: Extending the concept of background to soil gas: natural radon concentrations in soils of Campania region., EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-22687, https://doi.org/10.5194/egusphere-egu2020-22687, 2020.

BG1.6 – Functions and functioning of the Critical Zone

EGU2020-12689 | Displays | BG1.6 | Highlight

How deep do signals of surface conditions extend into the subsurface Critical Zone?

Susan Trumbore, Kai Uwe Totsche, and Kirsten Küsel

Fluids (water and gases) connect surface and subsurface compartments of the Critical Zone by transporting matter, including chemical energy and organisms. In the AquaDiva Collaborative Research Center, one of our research goals is to use a variety of tracers to determine how the subsurface and the organisms inhabiting it reflect and depend on surface conditions.  This research is performed at the Hainich Critical Zone Exploratory (CZE), a hillslope transect in limestone and marlstone sedimentary rocks where a network of surface observations is linked to routinely monitored groundwater wells.   This CZE is especially interesting because its different rock units and hydrogeologic conditions create environments with different microbiomes and conditions.

This talk will synthesize information collected by AquaDiva researchers on how different kinds of ‘signals’ identify important mechanisms connecting surface and subsurface.   Biologically dominated signals, such as cell counts, metagenomics, metabolomics, the molecular composition and properties of dissolved organic matter,  change with distance from the surface.   While some individual compounds and organisms can be found across the different critical zone compartments, it is clear that that ground water and its inhabitants are not just diluted from the surface but reflect and co-evolve with microbial communities and subsurface environmental conditions.   Isotopic tools trace elements rather than chemical compounds and provide independent information on the timescales for surface-subsurface transport or the sources of energy or metabolites.  For example, we used bomb-radiocarbon as a tracer for surface carbon recently fixed by plants.  The 14C in dissolved or particulate organic matter and inorganic C demonstrate how newly fixed, recycled or even fossil (rock derived) C is incorporated into microbial food webs. Finally, surface conditions, including structure, influence the subsurface metabolism by regulating the transfer of electron acceptors like O2, excess nutrients from fertilizers, or reactive nanocrystalline Fe, through soils and unsaturated zones into groundwaters.  

How to cite: Trumbore, S., Totsche, K. U., and Küsel, K.: How deep do signals of surface conditions extend into the subsurface Critical Zone?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12689, https://doi.org/10.5194/egusphere-egu2020-12689, 2020.

EGU2020-18437 | Displays | BG1.6

Exploring the hydrogeological functioning and microbial habitats of the deep hillslope aeration zone in limestone-mudrock alternations

Robert Lehmann, Cassandre Sara Lazar, Kirsten Küsel, and Kai Uwe Totsche

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.

EGU2020-14556 | Displays | BG1.6

Nitrate sources and sinks in oligotrophic groundwater

Martina Herrmann, Markus Krüger, Bo Thamdrup, and Kirsten Küsel

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.

EGU2020-18141 | Displays | BG1.6

Characterizing denitrification in the aquifer and transit times based on spatially-distributed measurements in streams

Camille Vautier, Christophe Petton, Ronan Abhervé, Gilles Pinay, Anniet Lavermann, and Jean-Raynald de Dreuzy

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.

Biogeochemical cycles are extensively studied as they control the flow of matter (carbon and nitrogen, specifically) up to the global scale, further impacting ecosystem functions and services. To be able to predict carbon and nitrogen budgets, it is necessary to study carbon and nitrogen cycles in all compartments of the biosphere, from forests to water, to soil and deep subsurface. Since the soil and deeper subsurface compartments store a high share of the global carbon and nitrogen budget, it is necessary to study the carbon and nitrogen cycles in the subsurface at a higher resolution. Given the spatial heterogeneity and temporal dynamics exhibited by the subsurface, coupled with lack of observational opportunities, the prediction of these cycles in the subsurface is a challenge. For this purpose, this study aims to resolve microbial mediated carbon and nitrogen dynamics in the subsurface with respect to spatial and temporal heterogeneity using a numerical modeling approach. The model considers the response of microbial growth and activity to varying environmental conditions such as access to nutrients and energy sources.

The obtained results show a linear relationship between the relative impact on carbon and nitrogen removal and relative difference in breakthrough times between homogeneous scenarios and the spatially heterogeneous scenarios. In contrast, the temporal dynamics of changing flow rates induces minimal aggregated impact on the carbon and nitrogen cycles in the subsurface. This implies that short term temporal dynamics do little to influence the long-term nutrient cycles, given the same average water flux through the entire simulation period. The findings of this study can assist in identification of drivers of microbial dynamics and nutrient cycling in the Critical Zone. This, in turn, can assist towards the regional scale modeling of biogeochemical cycles resulting from microbial dynamics.

How to cite: Khurana, S., Heße, F., and Thullner, M.: Predicting microbial redox dynamics and nutrient cycling in the subsurface considering spatio-temporal heterogeneities, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3389, https://doi.org/10.5194/egusphere-egu2020-3389, 2020.

EGU2020-15958 | Displays | BG1.6

Water as a critical zone currency: linking water storage and age to root uptake and biogeochemical transport

Sylvain Kuppel, Isabelle Braud, Yves Goddéris, Sekhar Muddu, Jean Riotte, and Laurent Ruiz

Efforts to grasp hydrological functioning in landscapes have gradually been evolving from inferring when water output fluxes respond to precipitation and energy inputs in catchments, towards tracking down which water is present in the different flow pathways of the critical zone (CZ). In the CZ where almost all terrestrial life developed, quantifying water storage and age (residence times in stores and transit times in fluxes) is key to the understanding of how water is i) available to supply root uptake, ii) in interaction with regolith minerals and biota, and iii) a medium for solute transport. We propose an approach to characterize the dynamics and non-linearities of CZ functioning first by mapping time-varying transit times of water exiting as plant transpiration as well as soil evaporation and stream discharge, against the corresponding water storage states. This picture is then extended by assessing the resulting relationships between hydrological states and patterns of nutrient concentration in, and export out of, the critical zone. This analysis considers several spatial scales, from the hillslope to the whole catchment. To this end, we use simulations from a cascade of spatially-distributed numerical tools: a process-based ecohydrological model – accounting for the coupling between energy balance, critical zone hydrology and vegetation dynamics, and a modular chemical weathering model – simulating dissolution/precipitation rates of mineral phases based on kinetics laws. We particularly focus on the long-term experimental tropical catchment of Mule Hole in Peninsular India (part of both the Indian Kabini CZ observatory and the French CZ observatory network OZCAR), with a highly seasonal hydroclimate and deep unsaturated profile, and where extensive hydrometric and chemical datasets are available for model calibration and evaluation. We discuss the interplay between distinctively mobilized critical zone compartments for each output flux, and the time-varying spatial organization of flow pathways.

How to cite: Kuppel, S., Braud, I., Goddéris, Y., Muddu, S., Riotte, J., and Ruiz, L.: Water as a critical zone currency: linking water storage and age to root uptake and biogeochemical transport, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-15958, https://doi.org/10.5194/egusphere-egu2020-15958, 2020.

EGU2020-11400 | Displays | BG1.6

Main knowledge gaps in critical zone processes and behaviour: Extracting information from water quality time-series data and models outputs

Zahra Thomas, Ophélie Fovet, Qian Zhang, Channa Rajanayaka, Christian Zammit, and Chantal Gascuel-Odoux

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.

In drylands, the annual amount of non-rainfall water inputs (NRWIs), i.e., a gain of water to the surface soil layer that is not caused by rainfall, can exceed that of rainfall.  They thus significantly contribute to the water cycle and to biogeochemical dynamics.  However, the small magnitude of the fluxes involved in the formation and evaporation of NRWIs challenges their measurement.  Various methods were applied in attempting to quantify NRWIs amount and duration, all being point/local measurements.  Given the large heterogeneity of soils, both at local and at regional scale, upscaling from the small point measurement methods to larger scales is necessary in order to fully understand the environmental factors controlling NRWIs and the role of NRWIs in dryland ecosystems.  Numerous remote sensing-based models have been developed to assess spatially distributed latent heat fluxes, greatly varying in complexity.  Unfortunately, the magnitude of diurnal fluxes due to NRWIs is too small to be detected by any of the existing models.  Hypothesizing that soil surface emissivity is sensitive to very small changes in water content at the top soil layer, our objective was to quantify NRWIs by analyzing the temporal changes in land surface emissivity over bare loess soil in the Negev desert, Israel.  Proven successful, this can be utilized over large areas. 

Intensive measurements using a longwave infrared radiometer (CLIMAT 312-2n ASTER, Cimel Electronique, Paris, France) were conducted in summer 2019 at the Wadi Mashash Experimental Farm (31o08’N, 34o53’E).  Radiance and temperature measurements were obtained for a broad band (8.01-13.34 μm) and 5 subsections of this bandwidth.  The radiometer was mounted at 0.5 m directly above one of four microlysimeters (undisturbed soil samples installed flash with the soil surface and weighed continuously).  Radiometer readings were automatically taken every 15 min for 24-h cycles. 

Initial results indicate an agreement between the diurnal cycle of NRWIs detected by the microlysimeters and between the diurnal cycle of an index derived from the radiometer bands: (e11.3-e8.3)/ e10.6 (the numbers are the center of the band in µm).  These preliminary results show the potential to upscale quantifying NRWIs to regional scale.

How to cite: Agam, N. and Kool, D.: Prospective upscaling of quantification of non-rainfall water inputs to regional scale, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-12486, https://doi.org/10.5194/egusphere-egu2020-12486, 2020.

EGU2020-11430 | Displays | BG1.6

Dissolved gas (CO2, alkanes, O2, N2) in critical zone developed on claystone

Catherine Lerouge, Michaela Blessing, Mathieu Debure, Frédérick Gal, Wolfram Kloppmann, and Jean-Charles Robinet

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 δ13CCO2, 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 δ13CCO2 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 δ13CCO2 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.

EGU2020-10078 | Displays | BG1.6

Lithium isotopes tracing weathering processes in a time series through soil porewaters

David Wilson, Philip Pogge von Strandmann, Gary Tarbuck, Jo White, Tim Atkinson, and Philip Hopley

Chemical weathering is a key process that controls Earth’s geochemical cycles and global climate, yet at present the climate-weathering feedback is poorly understood. Lithium (Li) isotopes are sensitive to silicate weathering processes [1] and can be applied in a range of settings to improve our understanding of weathering mechanisms and timescales, and hence to quantify the role of weathering in the global carbon cycle. While marine carbonates [2] and speleothems [3] are suitable for recording changes over million year and thousand year timescales, respectively, it is equally important to assess how weathering operates over seasonal [4] and shorter [5] timescales.

In order to explore seasonal variability in a natural system, we analysed Li isotopes and major/trace elements in a time series of cave drip-water samples from Ease Gill and White Scar caves (Yorkshire Dales, U.K.). Since the drip-waters are sourced from the overlying soil porewaters, these measurements provide a record of the evolving weathering fluid chemistry at approximately monthly intervals. Our data reveal striking temporal variations in ∂7Li of 4 to 8 permil, hinting at rapid changes in weathering processes over monthly to seasonal timescales. We assess the sources of Li using isotope measurements on local rocks and soils, which enables a first order quantification of the temporal changes in Li removal by clay formation. Comparison to records of temperature, precipitation, drip rates, and drip-water chemistry allows the local controls on weathering to be assessed and indicates that a dominant control is exerted by the fluid residence time.

These data are further complemented by batch reactor experiments, which were conducted to replicate rock weathering over timescales of hours to weeks. In combination, the time series and experiments contribute to a better understanding of weathering changes over short timescales and their influence on Li isotopes. In addition, results from the drip-waters provide key ground-truthing for interpreting our ongoing Li isotope measurements on speleothems, which will provide new records of weathering changes over longer timescales in response to regional climate forcing.

[1] Pogge von Strandmann, P.A.E., Frings, P.J., Murphy, M.J. (2017) Lithium isotope behaviour during weathering in the Ganges Alluvial Plain. GCA 198, 17-31.

[2] Misra, S. & Froelich, P.N. (2012) Lithium isotope history of Cenozoic seawater: changes in silicate weathering and reverse weathering. Science 335, 818-823.

[3] Pogge von Strandmann, P.A.E., Vaks, A., Bar-Matthews, M., Ayalon, A., Jacob, E., Henderson, G.M. (2017) Lithium isotopes in speleothems: Temperature-controlled variation in silicate weathering during glacial cycles. EPSL 469, 64-74.

[4] Liu, X.-M., Wanner, C., Rudnick, R.L., McDonough, W.F. (2015) Processes controlling δ7Li in rivers illuminated by study of streams and groundwaters draining basalts. EPSL 409, 212-224.

[5] Pogge von Strandmann, P.A.E., Fraser, W.T., Hammond, S.J., Tarbuck, G., Wood, I.G., Oelkers, E.H., Murphy, M.J. (2019) Experimental determination of Li isotope behaviour during basalt weathering. Chemical Geology 517, 34-43.

How to cite: Wilson, D., Pogge von Strandmann, P., Tarbuck, G., White, J., Atkinson, T., and Hopley, P.: Lithium isotopes tracing weathering processes in a time series through soil porewaters, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10078, https://doi.org/10.5194/egusphere-egu2020-10078, 2020.

EGU2020-20605 | Displays | BG1.6

Urban sediment: a specific geochemical signature compared to natural sediments?

Qiufang Zhan, Vincent Chatain, Jean-Baptiste Aubin, Gislain Lipeme Kouyi, Mathieu Gautier, Thierry Winiarski, and Cécile Delolme

Detention and infiltration basin has been increasingly implemented in France in order to provide additional storage of runoff from impervious surfaces due to rapid urbanization. These sustainable urban drainage systems also ensure quality of stormwater infiltrated into groundwater. In urban areas, these devices accumulate suspended particles eroded from city watershed and represent a geochemical signature of these urban watershed. Urban sediments are known to be polluted by high organic and inorganic substance contents, but their geochemical properties and specificities are insufficiently informed. The objective of this work is to study whether geochemical properties of urban sediment accumulated in detention and infiltration basins is distinguished from other natural sediments (from rivers, lake, marine environment). For this purpose, this study focused on relating watershed characteristics and physico-chemical properties of sediment using multivariate analyses based on rank data values. Data were notably collected from the national programs GESSOL (GEStion du patrimoine SOL, i.e. soil environmental functions - soil heritage management) and EC2CO (Ecosphère Continentale et Côtière, i.e. continental and coastal ecosphere) based on 19 infiltration basins around Lyon (France) and from literature (lake, basin, river etc.). Principal Component Analysis (PCA) was used to identify the most important sources of variation between trace metals and organic matters in different sediments. Cluster analysis was performed to group samples of similar sediment characteristics between major variables and trace metals contents. A significant amount of Fe (from 2.52 to 3.92 wt.%) and organic matters (from 18 to 27 wt.%) was found in the urban sediment. The results of PCA showed the influence of grain size on metal variability. Metals are more associated with the aluminosilicates (<63μm fraction), Fe and organic matters. Cluster analysis shows that Ti, Ni, Zn, Cd and Pb are originated from anthropogenic sources, especially discharged from commercial and industrial watershed. This work highlights the singularity of the urban sediment, as they are highly contaminated compared to natural sediments. Hence, the specific treatments are needed to tackle this problematic contamination.

How to cite: Zhan, Q., Chatain, V., Aubin, J.-B., Lipeme Kouyi, G., Gautier, M., Winiarski, T., and Delolme, C.: Urban sediment: a specific geochemical signature compared to natural sediments?, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20605, https://doi.org/10.5194/egusphere-egu2020-20605, 2020.

EGU2020-17490 | Displays | BG1.6

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.

Camille Banc, Mathieu Gautier, Blanc Denise, Lupsea-Toader Maria, Marsac Rémi, and Gourdon Rémy

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.

EGU2020-10953 | Displays | BG1.6

Impact of Sustainable Urban Drainage Systems (SUDS) on Vadose Zone Water
not presented

Arne Reck, Eva Paton, and Björn Kluge

Sustainable Urban Drainage System (SUDS), like bioretention for stormwater runoff infiltration, offer several advantages compared to the traditional centralised sewage drainage. Such approaches maintain the natural water cycle in the urban critical zone and help to mitigate climatic extremes impact on urban areas by retarding, storing and evaporating stormwater runoff. Although SUDS are established since longer time (>25 years for example in Germany) we lack systematic investigations on the hydrological functionality and pollutant retention performance of these systems after long-term operation. We employed laboratory and field experiments coupled with numerical simulations to investigate three long-term operated bioretention systems in Germany with following objectives: (i) a detailed mapping of spatial contamination patterns; (ii) a soil hydrological and -chemical substrate characterisation; (iii) an event-based influent and effluent trace metal concentrations monitoring covering 36 months in total; and (iv) a soil water balance simulation using HYDRUS-1D. Regarding the pollution patterns, we found significantly enhanced trace metal contents in the soil substrate mainly as a function of the drainage area type and kind of inflow regime. Nonetheless, average free metal ion concentrations in the soil seepage water extracted below the upper soil layers (30-45 cm) fall below German trigger values considering the soil-groundwater pathway at all three investigated sites. Compared to influent concentrations, average load reduction of the major pollutants Cu and Zn was 55-95 % within the upper soil layers. With regard to infiltrated runoff volumes, simulated water balances revealed hydraulic load reductions of 10-40 % by evapotranspiration. Our current findings demonstrate no risk of groundwater degradation suggesting bioretention as a powerful tool in terms of maintaining the natural water cycle in the urban vadose zone even after long-term operation. Debatable might be the handling of soil substrates modified by stormwater infiltration showing enhanced trace metal contents and a certain amount of technogenic sediments like tyre wear. On the one hand, a big metal pool is specifically bound meaning it can easily turn into free ions during changing conditions like the application of de-icing agents. On the other hand, these substrates perfectly fulfil pollutant retention and water conductivity requirements as mandatory for an effective stormwater treatment using SUDS approaches.

How to cite: Reck, A., Paton, E., and Kluge, B.: Impact of Sustainable Urban Drainage Systems (SUDS) on Vadose Zone Water, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-10953, https://doi.org/10.5194/egusphere-egu2020-10953, 2020.

EGU2020-8668 | Displays | BG1.6

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

Paul Hamer, Heidelinde Trimmel, Philipp Weihs, Stéphanie Faroux, Herbert Formayer, Kristofer Hasel, Johannes Laiminghofer, David Leidinger, Valéry Masson, Imran Nadeem, Sandro Oswald, Michael Revesz, and Robert Schoetter

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 21st 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.

EGU2020-11645 | Displays | BG1.6

Hydroclimatic control on global weathering regimes

Salvatore Calabrese and Amilcare Porporato

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.

EGU2020-11100 | Displays | BG1.6

Regolith production rates from 238U-234U-230Th disequilibrium in a deep granitic weathering profile (Longnan, SE China)

Guodong Jia, François Chabaux, Jérôme van der Woerd, Eric Pelt, Raphaël di Chiara, Julien Ackerer, Zhi-Qi Zhao, Ye Yang, Sheng Xu, and Cong-Qiang Liu

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.

EGU2020-11626 | Displays | BG1.6

Lithological controls on soil formation rates and the implications for soil sustainability

Daniel Evans, John Quinton, Andrew Tye, Angel Rodes, Jessica Davies, and Simon Mudd

Soils deliver multiple ecosystem services and their long-term sustainability is fundamentally determined by the rates at which they form and erode. Our knowledge and understanding of soil formation is not commensurate with that of soil erosion, but developments in cosmogenic radionuclide analysis have enabled soil scientists to more accurately constrain the rates at which soils form from bedrock. To date, all three major rock types – igneous, sedimentary and metamorphic lithologies – have been examined in such work. Soil formation rates have been measured and compared between these rock types but the impact of rock characteristics such as mineralogy or porosity on soil formation rates has seldom been explored. In this UK-based study, we addressed this knowledge gap by using cosmogenic radionuclide analysis to investigate whether the lithological variability of sandstone governs pedogenesis. Soil formation rates from two arable hillslopes underlain by different types of arenite sandstone were calculated. Rates ranged from 0.090 to 0.193 mm yr-1 and although the sandstones differed in porosity, no significant differences in soil formation rates were found between them. On the contrary, these rates significantly differed from those measured at two other sandstone-based sites in the UK, and with the rates compiled in global inventory of cosmogenic studies on sandstone-based soils. We suggest that this is due to the absence of matrix and the greater porosities exhibited at our UK sites in comparison to the matrix-abundant, less porous wackes that have been studied previously. We then used soil formation rates to calculate first-order soil lifespans for both of our hillslopes. In a worst case scenario, the lifespan of the A horizon at one of our sites could be eroded in less than 40 years, with bedrock exposure occurring in less than 190 years.  This underlines the urgency required in ameliorating rates of soil erosion. However, we also demonstrate the importance of measuring soil erosion and formation in parallel, at the site of interest, rather than calculating a mean rate from the literature, as we demonstrate soil formation rates can vary significantly among variants of the same rock type.

 

How to cite: Evans, D., Quinton, J., Tye, A., Rodes, A., Davies, J., and Mudd, S.: Lithological controls on soil formation rates and the implications for soil sustainability, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-11626, https://doi.org/10.5194/egusphere-egu2020-11626, 2020.

EGU2020-20385 | Displays | BG1.6

Lithium isotopes as a probe of anthropogenic activities: Dommel River

Philippe Negrel, Romain Millot, and Emmanuelle Petelet-Giraud

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.

EGU2020-12113 | Displays | BG1.6

Soils in the urban critical zone - Analyse of anthropogenic pressures and current proposals to preserve soil functions and ecosystem services

Beatrice Bechet, Laure Beaudet, Philippe Branchu, Patrice Cannavo, Cécile Delolme, Liliane Jean-Soro, Thierry Lebeau, Cécile Le Guern, Fabienne Marseille, and Christophe Schwartz

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.

EGU2020-14486 | Displays | BG1.6 | Highlight

Observil - A French network project of urban critical zone observatories

Fabrice Rodriguez, Jean Nabucet, Jules Kouadio, Beatrice Bechet, Nadege Blond, Emmanuel Bozonnet, Ghassan Chebbo, Damien David, Sihem Guernouti, Thomas Houet, Pascal Keravec, Thierry Lebeau, Gislain Lipeme-Kouyi, Valery Masson, Anne Puissant, Yves Richard, Christophe Schwartz, and Zahra Thomas

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.

EGU2020-2956 | Displays | BG1.6

A Critical Zone Approach to Carbon Fluxes in the Arctic Tundra

Mariasilvia Giamberini, Ilaria Baneschi, Matteo Lelli, Marta Magnani, Brunella Raco, and Antonello Provenzale

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.

EGU2020-21791 | Displays | BG1.6

From the Critical Zone to decision support tools for China's agriculture

Paul Hallett and the China/UK Critical Zone Obervatory Team

A number of critical zone observatories across China have focussed on human impacts caused by agriculture, particularly the sustainability of soil and water resources.   Using the CZO approach of measuring from the top of vegetation, through soil, to the bedrock below, joint China/UK projects at these CZOs have quantified large pools of previously undocumented nitrogen stored at depth, pathways for water loss and pollutant transport and drivers of accentuated soil erosion.  Socioeconomic studies have found that these challenges to land and water resources tie in well with the concerns of farmers.  In two different regions of China, farmers identified fertilisers as their greatest cost and water availability as their biggest challenge.  Using large data-sets generated over the past 4 years in these projects, we are developing Decision Support Tools (DSTs) underpinned by CZO science that can guide farmers and policy makers.  The work addresses food and water security in the context of climate change and diminishing resources, with an aim to improve livelihoods and sustainable economic development.  We have been guided by a review of over 400 DSTs designed for agriculture and the environment, which have been ranked in terms of their outputs and data requirements.  A goal at the EGU will be to develop links with other CZO projects to help with our DST development.

How to cite: Hallett, P. and the China/UK Critical Zone Obervatory Team: From the Critical Zone to decision support tools for China's agriculture, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21791, https://doi.org/10.5194/egusphere-egu2020-21791, 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.

EGU2020-4423 | Displays | BG1.6

Coupling model of ecohydrology and simulation of typical shrub ecosystems on the Loess Plateau

Yu Zhang, Xiaoyan Li, Wei Li, Weiwei Fang, and Fangzhong Shi

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.

EGU2020-8931 | Displays | BG1.6

Energy demand estimates in large Russian cities and its biometeorological characteristics

Iya Belova, Liudmila Krivenok, and Sergy Dokukin

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.

EGU2020-9272 | Displays | BG1.6

Spatiotemporal analysis of the housing bubble’s contribution to the proliferation of illegal landfills – The case of Gran Canaria

Lorenzo Carlos Quesada-Ruiz, Liliana Perez, Victor Rodriguez-Galiano, and David Aragones

The management of disposed waste in illegal landfills (ILs) is a significant problem in contemporary societies due to respective hazards for the environment and human health. This study investigates the spatiotemporal distribution of IL occurrence for 2000, 2006 and 2012 in two representative areas of Gran Canaria island: northwest (Zone A) and east (Zone B). The interannual growth rate of surfaces affected by ILs for the period between 2000 and 2006 was 4.5% and 9.5% and between 2006 and 2012 it was 6.6% and 6.7%, for Zone A and Zone B respectively. The growth of ILs between 2000 and 2006 was higher in urban areas, spaces under construction, and industrial zones, and may be closely related to the process of urban expansion linked to the real estate boom. The latter would have a deep impact on the landscape due to the proliferation of illegal construction and demolition waste. The growth rate of ILs in urban environments fell during the later period of urban expansion. Besides, this work shows the application of cellular automata (CA) in the analysis of IL occurrence, with ILs considered to be a dynamic and complex system. This may supply added value to policies for environmental repair and protection as well as territorial planning (land use and management), by delimiting possible future areas of IL occurrence. In this regard, IL occurrence was simulated over a long timescale (18 years), to estimate and spatially locate the surface growth of ILs based on CA-Markov and Multiobjective Land Allocation models. The modelling of IL proliferation was divided into three phases: calibration, validation and simulation of the future 2018 scenario. Synchronic data series were used, along with Markov chains and transition rules, in all phases. In the calibration phase the suitability analysis was done and the transition rules and transition potential maps were obtained. The use of dynamic characteristics such as those associated to land uses and static characteristics such as elevation and slope helped model the ILs’ growth. Models’ accuracy was assessed using Kappa index and landscape metrics. Simulation outputs were not highly accurate when reproducing the exact location of ILs, however, they did correctly reproduce the distribution patterns for IL proliferation. Obtaining the best validation results, the CA_Markov model was used to simulating IL proliferation in 2018, predicting that increases of 52.3 ha and 81.5 ha affected by ILs in Zone A and Zone B respectively.

How to cite: Quesada-Ruiz, L. C., Perez, L., Rodriguez-Galiano, V., and Aragones, D.: Spatiotemporal analysis of the housing bubble’s contribution to the proliferation of illegal landfills – The case of Gran Canaria, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9272, https://doi.org/10.5194/egusphere-egu2020-9272, 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.

EGU2020-22557 | Displays | BG1.6

A case study aiming to promote cities resilience based on urban critical zone management as a whole

Marion Diaz, Zahra Thomas, Alain Prenveille, and Nicolas Floch

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.

EGU2020-19992 | Displays | BG1.6

Study of metallic trace elements in attic dust from two former industrial cities, Salgótarján and Ózd (Hungary)

Nelson Salazar, Gorkhmaz Abbaszade, Davaakhuu Tserendorj, Péter Völgyesi, Dóra Zacháry, Katalin Szabó, and Csaba Szabó

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.

EGU2020-17524 | Displays | BG1.6

Nitrate transfer in the Critical zone view through N & O isotopes of NO3 and CFC-SF6 groundwater residence time assessment

Emmanuelle Petelet-Giraud, Nicole Baran, Virginie Vergnaud, Flora Lucassou, and Jean-Michel Schroetter

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.

EGU2020-21141 | Displays | BG1.6

Microbial role in N2O-NO2 production and CH4 oxidation under active hypogenic settings

Tamara Martin-Pozas, Soledad Cuezva, Valme Jurado, Raul Perez-Lopez, Cesareo Saiz-Jimenez, Jose Maria Calaforra, Sergio Sanchez-Moral, and Angel Fernandez-Cortes

The hydrothermal caves linked to active faulting have subterranean atmospheres with a distinctive gaseous composition containing deep endogenous gases, such as carbon dioxide, methane and nitrogen oxides (NOx). Ascending fluids through associated near-surface hydrothermal processes can mobilize endogenous gases into the Critical Zone and, ultimately, to the lower troposphere.
Nitrogen oxides are polluting gases and can have adverse effects on human health, especially inhaled NO2. They also catalyse ozone (O3) production in the lower layers of the atmosphere and the greenhouse effect, when they react with volatile organic compounds. The largest source of NOx emissions is anthropogenic. The rest is produced naturally by microbial processes in soil and water, by lightning, volcanic activity, storms, etc. Production of N2O and NO2 is associated with soil and other active-geothermal ecosystems, far less is known about the sources and sinks of these gases within subterranean locations. Here, we report high N2O and NO2 concentrations detected along a hypogenic system associated with an active faulting (Vapour Cave, southern Spain), which enables direct gas exchange with the low-atmosphere. These anomalous concentrations of N2O and, NO2 are about ten and five times higher than the typical atmospheric background, respectively.
Gaseous composition analyses of subterranean atmosphere were conducted by high precision field-deployable CRDS and FTIR spectrometers for measuring in situ the target tracer gases (NO2, N2O, CH4, CO2) and δ13C of both carbon-GHGs. DNA extraction, sequencing and phylogenetic analyses were conducted to characterize the microbial community of cave sediments. The results showed that N2O and NO2 emission depends on the activity of nitrification by ammonia oxidizing microorganisms (such as members of the family Nitrosomonadaceae and phylum Thaumarchaeota) and/or as a result of incomplete denitrification by heterotrophic denitrifying bacteria (such as Bacillus, Acinetobacter and Cupriavidus) from this hydrothermal and hypoxic ecosystem.
On the other hand, CH4 concentrations and δ13CH4 vary along the cave (with the deep), in deepest cave locations CH4 values are higher with lighter δ13C values in comparison with the more superficial areas, which indicates a deep endogenous origin of methane. However, in areas near the entrance we observe lower concentrations of methane and heavier δ13C values (CH4<1 ppm and δ13C close to −30‰), as a result of methane oxidation by denitrifying methanotrophs of the NC10 phylum during gas migration from the deepest areas to the surface.

These new findings reveal the sourcing of these nitrogenous gases into the upper vadose zone of a hypogenic/geothermal ecosystem, and its potential release to the lower troposphere. A better understanding of biogeochemical processes controlling the production of nitrogenous gases in subterranean environments will be useful to identify and characterize new possible
sources, reservoirs and sinks of greenhouse gases (CO2, CH4, N2O and NOx) in order to calculate more accurately the budgets and for the design of new mitigation strategies of these gases.

How to cite: Martin-Pozas, T., Cuezva, S., Jurado, V., Perez-Lopez, R., Saiz-Jimenez, C., Calaforra, J. M., Sanchez-Moral, S., and Fernandez-Cortes, A.: Microbial role in N2O-NO2 production and CH4 oxidation under active hypogenic settings, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21141, https://doi.org/10.5194/egusphere-egu2020-21141, 2020.

In Murgia Alta National Park the repeated fire perturb the stability of the environment and it s capacity to be a carbon sink. Thanks to the Landsat archive we can observed change in phenology t over the two decade (2000-2019). Unfortunately the phenological signal extracted from Landsat time series bear several uncertainties caused by missing data and error in atmospheric correction that makes difficult to reconstruct the trajectory of each pixel. Applying a Bayesian Harmonic model we can obtain not only expected values for the vegetation index time series but also confidence interval both for vegetation index and derived statistics. We took the phenological statistical framework of the Ecological Functional Attributes (EFA) to obtain annual statics and evaluate the time of recovery to obtain EFA with no statistical difference from the pre-perturbation time.

The results highlighted that only of subset of burned forest recover EFA values after 10 years of critical events. In particular the values of intra year variability tend to be higher due to the different trajectory of young shoots. The burned grassland time of recovery is much shorter given that the vast majority of pixel recover pre-event EFA in less than 4 year.

How to cite: vicario, S., adamo, M., tarantino, C., and blonda, P.: Estimating the Vegetation phenology Time of recovery after a critical perturbation from Landsat time series within the frame of a Bayesian Harmonic model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-21794, https://doi.org/10.5194/egusphere-egu2020-21794, 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 kmdecrease 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.

EGU2020-22447 | Displays | BG1.6

Significance and driving forces of dark CO2 fixation for organic carbon inputs in temperate forest soils

Rachael Akinyede, Martin Taubert, Marion Schrumpf, Susan Trumbore, and Kirsten Küsel

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