The critical zone comprises the Earth's permeable near-surface layer from the top of the canopy to the bottom of the groundwater. It is the zone where hydrosphere, atmosphere, pedosphere and geosphere interact with the biosphere. This fragile skin of our planet, which supports the life and survival of humans maintaining food production and drinking water quality, is endangered by threats such as climate change and land use change.
New approaches and innovative modeling strategies are needed to understand these complex interactions between hydrological, biogeochemical cycles and human resilience processes that may govern critical zone system dynamics, including sources, dynamics and chemistry of water, models to quantify external influences like human activities or erosion, weathering rate, water transfer in the frame of global change and biological feedback mechanisms.
This session focuses on the advancing proxies that may address pressing interdisciplinary scientific questions in coupling various disciplines like hydrology, soil science and biogeochemistry that cover single-site investigations, targeted experiments, remote sensing studies, large data compilations and modelling. This will be illustrated in this session through studies regarding the critical zone as a whole or within its different compartments, including the different environmental processes (geological, physical, chemical, and biological), their couplings and reactive transport modeling , and exploring the cities resilience.

Co-organized by HS10/SSS12
Convener: Gerd Gleixner | Co-conveners: Antonello Provenzale, Beatrice Bechet, Tamara Kolbe, Philippe Negrel
| Attendance Tue, 05 May, 08:30–10:15 (CEST)

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Chat time: Tuesday, 5 May 2020, 08:30–10:15

Chairperson: Gerd Gleixner, Antonello Provenzale, Beatrice Bechet, Tamara Kolbe, Philippe Negrel
D555 |
| solicited
| Highlight
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.

D556 |
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.



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.

D557 |
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.

D558 |
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.

D559 |
Swamini Khurana, Falk Heße, and Martin Thullner

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.

D560 |
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.

D561 |
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.

D562 |
| solicited
Nurit Agam and Dilia Kool

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.

D563 |
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.

D564 |
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.

D565 |
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.

D566 |
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.

D567 |
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.

D568 |
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.

D569 |
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.

D570 |
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.

D571 |
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.

D572 |
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.

D573 |
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.

D574 |
| Highlight
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.

D575 |
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.

D576 |
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.

D577 |
Shengli Liu and Wenbin Wu

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.

D578 |
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.

D579 |
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.

D580 |
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.

D581 |
Chun Dong

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.

D582 |
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.

D583 |
kang fengguang

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.

D584 |
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.


[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.

D585 |
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.

D586 |
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.

D587 |
saverio vicario, Maria adamo, Cristina tarantino, and palma blonda

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.

D588 |
Weihong Wang

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.

D589 |
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 km2 and an average soil bulk density of 1 Mg/m3 dark CO2 fixation will potentially account for the gross sequestration of 0.31 - 0.48 GtC/yr to a depth of 1 m. Furthermore, an increase in headspace CO2 concentration enhanced CO2 fixation rates by up to 3.4-fold under 20% v:v CO2 showing that dark CO2 fixation can be substantial in soils with higher CO2 concentrations.

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

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



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

D590 |
Stefano Ferraris, Davide Canone, Davide Gisolo, Mario Putti, Pietro Teatini, and Maurizio Previati

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

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

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

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

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

D591 |
Gaëlle Tallec, José Manuel Tunqui Neira, Andréassian Vazken, and Jean-Marie Mouchel

Discharge is one of the major factors influencing the evolution of solute concentration in river water. Different modeling approaches exist to characterize the dependency of concentration on discharge: the simplest require calibration, they are based on measurable quantities (stream discharge and stream water concentration) but do not allow for an explicit, physical, flow-path interpretation; the more complex are based on mixing assumptions with different end-member sources, but require knowledge of the (unmeasurable) flow components. Here, we present a combination between the simple concentration–discharge (C-Q) approach with the mass balance (MB) mixing approach, which we apply to a new high-frequency series on the Oracle-Orgeval Observatory (France) (Tunqui et al., submitted). This new methodology shows a better performance than the two approaches applied separately, allowing us to better describe the concentrations measured in the stream.

Reference : Tunqui et al. Combining concentration-discharge relationships with mixing models. Submitted to Journal of Hydrology

How to cite: Tallec, G., Tunqui Neira, J. M., Vazken, A., and Mouchel, J.-M.: Combining concentration–discharge relationships with mixing models , EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-9146, https://doi.org/10.5194/egusphere-egu2020-9146, 2020.

D592 |
Beate Michalzik, Alexander Tischer, and Robert Lotze

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

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

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

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

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

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

D593 |
Qian Chen and Sining Zhong

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

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

D594 |
Danièle Valdés, Ningxin Chen, Marc Dumont, Christelle Marlin, Hélène Blanchoud, Cyrille Fauchard, Fabrice Alliot, Ayoub Saydy, Emmanuel Aubry, Julien Guillemoteau, Roger Guérin, and Pierre Ribstein

The Chalk aquifer is a crucial, vital resource for water supply in France, Belgium and England. However, since several decades, this resource is threatened by high anthropogenic pressures: inducing a degradation of the groundwater’s quality.

The aim of our multidisciplinary study is to understand the transfer processes of the water and associated elements - solutes and contaminants (nitrate, pesticides) - throughout the critical zone (CZ) of chalk from the topsoil to the water table.

This study is focused on the underground quarry of Saint Martin le Noeud which is located in the Upper Cretaceous chalk layer of the Paris Basin. A layer of clay-with-flints covers the chalk of the quarry with a variable thickness. At a depth from 16 to 30m, the quarry is about 1200 m long and 150 m wide, giving a direct access to different groundwater compartments: (1) the Chalk water table through a series of 16 underground lakes, and (2) the vadose zone thanks to infiltration water percolating at the ceiling of the quarry. The set-up of this site allows to study the behaviors of both compartments.

Surface geophysical measurements: electrical resistivity tomography  and electromagnetic induction  mapping, have allowed to describe precisely the structure of the critical zone: in particular the geometry of the clay layer which has a variable thickness from 0 to about 5m.

The hydrodynamic and the quality of the groundwaters of both compartments (vadose zone and Chalk water table) have been characterized in time and space: (1) time series of flow percolation, water level, electrical conductivity and temperature, (2) geochemical analyses (major elements, nitrate, pesticides). The hydrodynamic and geochemical properties of the groundwaters vary spatially along the quarry highlighting different transfer processes.

Time series analysis and geochemical data allow to estimate the transfer velocities of the water and the contaminants and to precise the biogeochemical reactions (degradation, adsorption/desorption, storage …) that occurs in the CZ. These processes vary spatially depending on the properties of the CZ. The precise description of the clay layer compared to the groundwater behaviors allows to better characterize the infiltration processes. (1) a thin layer of clay induces a “diffuse infiltration”, low velocities, and low degradation of the pesticides in the subsurface, (2) a thick layer of clay induces a perched groundwater in the near-surface, degradation processes, concentrated infiltration and higher velocities.

How to cite: Valdés, D., Chen, N., Dumont, M., Marlin, C., Blanchoud, H., Fauchard, C., Alliot, F., Saydy, A., Aubry, E., Guillemoteau, J., Guérin, R., and Ribstein, P.: Transfer processes in the chalk critical zone – Multidisciplinary study of the undergound quarry of Saint Martin le Noeud, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-20390, https://doi.org/10.5194/egusphere-egu2020-20390, 2020.

D595 |
Marta Magnani, Ilaria Baneschi, Mariasilvia Giamberini, Brunella Raco, Pietro Mosca, and Antonello Provenzale

In high mountains, the Critical Zone (CZ) is a thin layer sustaining the whole local ecosystem. Here, however, the effects of climate change are manifesting most rapidly than in the surrounding lowlands. This is especially critical for the high-altitude carbon cycle, for which our knowledge is still patchy and new feedbacks could possibly be triggered. In particular, models of the processes that control carbon fluxes in mountain grasslands and Alpine tundra need to be improved. To contribute to fill this knowledge gap, in 2017 a new Critical Zone Observatory was established at the valley of the Nivolet Plain (CZO@Nivolet) in the Gran Paradiso National Park (GPNP), in the western Italian Alps, at about 2700 m asl. Three measurement sites were identified along the flanks of the valley.  The sites are characterized by soils developed over carbonate rocks, gneiss rocks and glacial deposits. Since 2017, every year, from July to October, fluxes of carbon dioxide (CO2) were measured using a portable accumulation chamber, together with basic meteo-climatic and environmental variables, such as soil and air temperature and moisture, air pressure and solar radiation. This work is focused on a novel empirical model that uses unbiased and rigorous statistical analysis of these data to identify the environmental variables that control CO2 fluxes in Alpine tundra. The modelling approach is applied to the full dataset of simultaneous in situ measurements of the net exchange, ecosystem respiration and environmental variables for the three sites and the three measurement years. Since a large year-to-year variability in the dependencies on solar irradiance and environmental temperature is observed, a multi-regressive model has been implemented, where additional variables are introduced as perturbations of the standard functions. The multi-regressive model identifies the main drivers, highlighting the crucial role of soil moisture, and largely explains the temporal variability of the fluxes, with explained variance up to 90%. This model provides a basis for estimating future scenarios of carbon fluxes in high-altitude Alpine ecosystems.

How to cite: Magnani, M., Baneschi, I., Giamberini, M., Raco, B., Mosca, P., and Provenzale, A.: Drivers of carbon fluxes in high-altitude Alpine Critical Zone: a novel data-based model, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-3919, https://doi.org/10.5194/egusphere-egu2020-3919, 2020.

D596 |
Dinusha Eshvara Arachchige and Kai Uwe Totsche

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

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

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

D597 |
Johanna Menges, Niels Hovius, Stefanie Poetz, Helena Osterholz, and Dirk Sachse

On long timescales, carbon fluxes in and out of rock, soil and biological reservoirs control carbon dioxide concentrations in the atmosphere and therefore modulate global climate. For example, the transfer of particulate organic matter (POM) from mountain ranges into rivers and subsequent burial in the ocean constitutes a carbon sink from the atmosphere if the eroded POM is sourced from vegetation and soils. In contrast, the transfer and burial of rock-derived petrogenic POM has no effect on atmospheric carbon concentrations. However, if petrogenic POM is remineralized during transfer, often mediated by microorganisms, it constitutes a carbon source to the atmosphere. To evaluate the net effect of these processes, it is essential to understand sourcing, mobilization and fluxes of POM. Bulk stable and radiogenic isotopes as well as a range of lipid biomarkers and their stable isotope ratios have been used to trace the sourcing and transfer of POM. However, these methods are limited to the distinction of broad classes of source materials and do not contain information on potential molecular transformations during organic matter mobilization and transport.

Fourier Transform Ion Cyclotron Resonance Mass Spectrometry (FT-ICR-MS) allows the simultaneous measurement of a large range of compounds (i.e. hundreds to thousands) and has been applied in dissolved organic matter research to trace different sources as well as to identify transformations. FT-ICR-MS measurements on solvent-extractable POM provide direct information on the compositional variability of POM with a much larger analytical window than single biomarker or bulk isotope analysis and additionally might allow to trace transformations of POM upon mobilization.

Here, we test this method to decipher the different sources of POM and their mobilization in the upper catchment of the trans-Himalayan Kali Gandaki River, which sources petrogenic POM from abundant Jurassic sediments as well as biospheric POM from aged and modern soils. We evaluate the potential of the high-resolution molecular dataset to identify new marker compounds for specific organic matter sources and, by applying indicator species analysis, to statistically identify indicator compounds. In a second step, we evaluate the potential to trace transformations across the mobilization step from each specific organic matter source to particulate organic matter in river sediments.

We found a large number of source-specific elemental formulas for biospheric carbon and strong heterogeneity for bedrock-derived organic carbon which highlights that petrogenic carbon varies in molecular composition depending on its (geological) origin. Regarding transformations, we found a loss of source-specific formulas during mobilization of organic matter, related to intrinsic chemical properties. These formulas were characterized by a higher number of double bond equivalents, a higher nominal oxidation state and higher oxygen content than formulas shared between riverine POM and source organic matter for all sources, which is consistent with the preferential loss of more labile organic matter during transport and/or mobilization. Overall, our study highlights the potential of FT-ICR-MS to identify molecular-level transformations of solvent extractable lipids along the source-to-sink pathway of sedimentary organic matter.

How to cite: Menges, J., Hovius, N., Poetz, S., Osterholz, H., and Sachse, D.: Evaluating the potential of FT-ICR-MS to identify source-specific markers and trace molecular transformations in particulate organic matter, EGU General Assembly 2020, Online, 4–8 May 2020, EGU2020-18089, https://doi.org/10.5194/egusphere-egu2020-18089, 2020.

D598 |
Katharina Lehmann, Robert Lehmann, and Kai Uwe Totsche

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

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