HS2.1.12 | Advancing Critical Zone Science Across Scales through Synthesis and Collaboration
Advancing Critical Zone Science Across Scales through Synthesis and Collaboration
Co-organized by BG3/GM5/SSS5
Convener: Jeffrey Munroe | Co-conveners: David LitwinECSECS, Theresa Blume, Caroline FenskeECSECS, Claudia VoigtECSECS
Posters on site
| Attendance Tue, 16 Apr, 10:45–12:30 (CEST) | Display Tue, 16 Apr, 08:30–12:30
Hall A
Tue, 10:45
The Critical Zone (CZ) – the permeable near-surface layer of the Earth where the lithosphere, hydrosphere, atmosphere, and biosphere interact – is the place where cycles of carbon, nutrients, water and other biogeochemical processes intersect with ecosystems and society. Investigating the form and functioning of the CZ requires that insights from geology, hydrology, ecology, geochemistry, atmospheric science and other disciplines are integrated in a transdisciplinary manner. One successful approach to CZ research has been the development of intensively instrumented study areas, known as CZ observatories. Networks of observatories and interlinked thematically-focused projects have evolved to capitalize on advances possible through multifaceted collaborations across larger spatial scales. Processes that shape the critical zone also span wide ranges of temporal scales, from vegetation on seasonal timescales, to soil development and landscape evolution over thousands to millions of years. Because all of these processes together shape the critical zone and affect how it functions, bridging gaps between short term processes and longer-term environmental change is essential for understanding landscapes and maintaining their ability to sustain life.

This session will highlight the cutting edge of CZ science across spatial and administrative scales, from project, to observatory, to network levels. Submissions may also explore coupling across temporal scales, integrating relatively rapid processes with the longer-term evolution of the critical zone. Submissions are solicited that focus on integration of observations and modeling; hydrologic dynamics; geoecological interactions; biogeomorphology, mineral weathering and nutrient cycling; the rhizosphere; the societal relevance of CZ science; and other examples of how CZ research is evolving with new knowledge to face the challenges of our changing world. Contributions from early-career scientists are particularly encouraged.

Posters on site: Tue, 16 Apr, 10:45–12:30 | Hall A

Display time: Tue, 16 Apr 08:30–Tue, 16 Apr 12:30
Chairpersons: Jeffrey Munroe, David Litwin
Critical Zone Networks: Synthesis and Collaboration
Julien Ackerer, Sylvain Kuppel, Isabelle Braud, Sylvain Pasquet, Ophélie Fovet, Anne Probst, Marie Claire Pierret, Laurent Ruiz, Tiphaine Tallec, Nolwen Lesparre, Sylvain Weill, Christophe Flechard, Jean Luc Probst, Jean Marçais, Agnes Riviere, Florence Habets, Sandrine Anquetin, and Jerome Gaillardet

The French OZCAR critical zone network offers the opportunity to conduct multi-site studies and to explore the critical zone functioning under contrasted climate, geology, vegetation and land use. In this study, an integrated modeling of the water cycle is performed with the ecohydrological model EcH2O-iso in three long-term observatories: (1) the Naizin watershed characterized by an oceanic climate, a metamorphic bedrock and an intensive agriculture (north-west of France, AgrHyS observatory); (2) the Aurade watershed, a watershed with a warmer semi-continental oceanic climate, a sedimentary geological substratum and a crop cover with a wheat-sunflower rotation (south-west of France, Aurade observatory) and; (3) the Strengbach watershed characterized by a mountain climate, a granitic bedrock, and a beech-spruce forest cover (north-east of France, OHGE observatory).

Modeling robustness is evaluated by taking advantage of the large database for critical zone sciences including stream flow, water level in piezometers, and evapotranspiration fluxes measured from climatological stations and flux-towers located in the watersheds. Our comparative study brings these general outcomes: (1) the long term CZ evolution controlling the regolith thickness strongly impacts the total water storage in watersheds; (2) the Quaternary geomorphological evolution influences the current hydrological partitioning and the separation of hydrologically active and inactive water storage; (3) Both internal watershed characteristics and external forcings, such as current atmospheric forcing and recent land use need to be considered to infer stream persistence and to understand hydrological diversity; and (4) the observed hydrological diversity cannot be fully understood without considering a continuum of time scales in CZ evolution.


Overall, this work illustrates the strength of critical zone networks, allowing a new level of multi-site and comparative studies that are crossing several observatories and encompassing a wide diversity of geology and climate.


How to cite: Ackerer, J., Kuppel, S., Braud, I., Pasquet, S., Fovet, O., Probst, A., Pierret, M. C., Ruiz, L., Tallec, T., Lesparre, N., Weill, S., Flechard, C., Probst, J. L., Marçais, J., Riviere, A., Habets, F., Anquetin, S., and Gaillardet, J.: Exploring the landscape heterogeneity and the hydrological diversity in three contrasted observatories of the French critical zone research infrastructure OZCAR, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-419, https://doi.org/10.5194/egusphere-egu24-419, 2024.

Steffen Zacharias, Theresa Blume, Heye Bogena, Ralf Kiese, Erik Borg, Peter Dietrich, Susanne Liebner, Hans Peter Schmid, Martin Schrön, and Harry Vereecken

The need to develop and provide integrated observation systems to better understand and manage global and regional environmental change is one of the major challenges facing Earth system science today. In 2008, the German Helmholtz Association took up this challenge and launched the German research infrastructure TERrestrial ENvironmental Observatories (TERENO). The aim of TERENO is to establish and to maintain a network of observatories as a basis for an interdisciplinary and long-term research programme to investigate the effects of global environmental change on terrestrial ecosystems and their socio-economic consequences. State-of-the-art methods from the field of environmental monitoring, geophysics, and remote sensing are used to record and analyze states and fluxes in different environmental compartments from groundwater through the vadose zone, surface water, and biosphere, up to the lower atmosphere. To date, four observatories are part of the network, and over the past 15 years we have gained collective experience in running a long-term observing network, thereby overcoming unexpected operational and institutional challenges, exceeding expectations and facilitating new research. Today, the TERENO network is a key pillar for environmental modelling and prediction in Germany, an information hub for regional stakeholders, a nucleus for international collaboration, an important anchor for large-scale experiments, and a trigger for methodological innovation and technological progress. We will present the main lessons learned from this 15-year endeavour, and illustrate the need to continue long-term integrated environmental monitoring programmes in the future.

How to cite: Zacharias, S., Blume, T., Bogena, H., Kiese, R., Borg, E., Dietrich, P., Liebner, S., Schmid, H. P., Schrön, M., and Vereecken, H.: Lessons learned from 15 years of TERENO: the integrated TERrestrial ENvironmental Observatories in Germany, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-4999, https://doi.org/10.5194/egusphere-egu24-4999, 2024.

Holly Michael, Dannielle Pratt, Yu-Ping Chin, Sergio Fagherazzi, Keryn Gedan, Matthew Kirwan, Angelia Seyfferth, Lee Slater, Stephanie Stotts, and Katherine Tully

Ghost forests and abandoned farms are stark indicators of ecological change along world coastlines, caused by sea level rise (SLR). These changes adversely affect terrestrial ecosystems and economies, but expanding coastal marshes resulting from SLR also provide crucial ecosystem services such as carbon sequestration and mediate material fluxes to the ocean. A US-NSF Critical Zone Network project was designed to understand the hydrological, ecological, geomorphological, and biogeochemical processes that are altering the functioning of the marsh-upland transition in the coastal critical zone. We have instrumented six sites in the mid-Atlantic region of the US, along the coastlines of the Atlantic Ocean, Delaware Bay, and Chesapeake Bay where marshes are rapidly encroaching into forests and farmland. Field observations, laboratory experiments, and modeling are revealing the drivers and impacts of coastal change, as well as feedbacks among competing processes that accelerate or reduce rates and magnitude of change. We discuss examples of processes and feedbacks and highlight the importance of interdisciplinary exploration and synthesis in advancing process understanding at the land-sea transition.

How to cite: Michael, H., Pratt, D., Chin, Y.-P., Fagherazzi, S., Gedan, K., Kirwan, M., Seyfferth, A., Slater, L., Stotts, S., and Tully, K.: Hydrological, biogeochemical, and ecological linkages at the land-sea margin: Insights from a coastal critical zone network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13095, https://doi.org/10.5194/egusphere-egu24-13095, 2024.

Elizabeth W. Boyer, Bhavna Arora, Emma Aronson, Holly Barnard, Steven Holbrook, Jeffery S. Horsburgh, Lixin Jin, Praveen Kumar, Holly Michael, Jeff Munroe, Julia Perdrial, Claire Welty, and Jordan Read

The Critical Zone Collaborative Network (CZ Net) is a national research initiative in the United States supporting investigations of the Earth's critical zone (CZ) -- the vital near-surface environment extending from the top of the vegetation canopy to the weathered bedrock beneath. CZ Net fosters collaboration, data sharing, and interdisciplinary research to understand complex landscapes. The network comprises nine thematic clusters covering diverse geological, climatic, and land use settings. The thematic clusters explore many areas, including bedrock geology's effects on landscapes and ecosystems, ecosystem responses to climate and land-use disturbances, processes occurring between land and sea affected by sea-level rise, land-water interactions in agricultural regions, water and carbon cycles in arid regions, the impact of mineral dust transported in the atmosphere on ecosystems, water storage's influence on landscape and ecosystem processes, relationships between landscapes and microbial communities, and ecosystem processes in cities. A coordinating hub provides cross-cluster support. In the presentation, we introduce CZ Net and the focal research areas of each thematic cluster. We consider synthesis work addressing environmental challenges faced by the CZ, which is under increasing pressure to meet societal needs while safeguarding the environment for future generations. Further, we discuss opportunities for engagement with the network, reflecting CZ Net's dedication to advancing knowledge and addressing critical environmental issues through collaborative efforts. International coordination through developing a network of networks can foster collaborative research that transcends national boundaries, allowing scientists to combine expertise, data, and resources for a deeper understanding of CZ processes. Such collaboration is imperative for addressing pressing global environmental challenges.

How to cite: Boyer, E. W., Arora, B., Aronson, E., Barnard, H., Holbrook, S., Horsburgh, J. S., Jin, L., Kumar, P., Michael, H., Munroe, J., Perdrial, J., Welty, C., and Read, J.: Exploring Earth's Critical Zone Through the U.S. Critical Zone Collaborative Network, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-13395, https://doi.org/10.5194/egusphere-egu24-13395, 2024.

Christoff Andermann, Kristen Cook, Basanta Raj Adhikari, Niels Hovius, and Rajaram Prajapati

Mountains are hotspots for earth surface processes, with very fast erosion rates, mass movements, catastrophic flooding and enhanced geochemical weathering rates. These landscapes respond quickly to external forcing by tectonics and/or climate. As a consequence, the hazard potential in mountains is very high, and mountains produce a wide range of large catastrophes which often have wide-reaching impacts on infrastructure and human lives. Furthermore, mountains can be considered as the water towers of the world, as they are very effective at harvesting water from the atmosphere, storing it, and redistributing it to the adjacent lowlands. The key role of mountain regions can be extended endlessly to other disciplines such as ecology, climatology, social sciences and so forth. Yet, despite their importance, high mountains remain inaccessible and notoriously understudied. High elevation terrains are only lightly covered by monitoring systems, with elevations >2500 m asl. widely underrepresented in global monitoring networks (Shahgedanova et al., 2021). The Himalayan mountains are particularly poorly covered by coordinated monitoring observatories.

In this contribution we present the set up and overview results of the ~last 10 years of integrated critical zone monitoring in the Kaligandaki Catchment in the central Himalayas in Nepal.

Motivated by fundamental research questions on coupled surface process and the high mountain water cycle in the Himalayan mountain range, we began observation in the Kaligandaki Catchment with two major stations for climatological and hydrological monitoring that have operated continuously over the past 10 years. At each location trained personal conducted manual river water sampling for river water geochemistry and suspended sediment monitoring as well as water discharge and bulk meteorological parameters. These observations were complemented by targeted short-term deployments and field sampling campaigns to cover the full spatial extent as well as the seasonal variability. Research question range from organic carbon export, climate and erosion feedback as well as water pathways in high mountains to large mass-movements and intramountain sediment storage and feedbacks with landscape evolution.

Our findings from the past 10 years of monitoring motivate the development of a more substantial observatory in the Kaligandaki catchment, which is particularly suited as a critical zone observatory in the Himalayas. The Kaligandaki is a trans-Himalayan river that connects the Tibetan Plateau through the Himalaya to the low elevation foreland. The river crosses distinct climatological, ecological, tectonic, and geomorphic zones, including the arid high elevation plateau, the rapidly uplifting high Himalaya and monsoon precipitation maxima, and the middle hills. The river corridor is highly prone to flood and landslide hazards, and is experience increasing development and human impact, particularly road construction and hydropower. In addition, the river basin is highly sensitive to changing precipitation patterns, which have brought anomalous rainfall and flooding in recent years, and to changing melting patterns, which affect water resources. Together with local partners and the international research community we are proposing this unique catchment as potential integrated mountain critical zone observatory in order to close the monitoring gap in the highest mountain range on Earth.


Shahgedanova, M., et al. 2021, https://doi.org/10.1659/MRD-JOURNAL-D-20-00054.1

How to cite: Andermann, C., Cook, K., Adhikari, B. R., Hovius, N., and Prajapati, R.: High Mountain Plateau Margin Critical Zone Observatory, Kaligandaki River Nepal, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15453, https://doi.org/10.5194/egusphere-egu24-15453, 2024.

Critical Zone Hydrology: Dynamics and Evolution
Philippe Steer, Lucas Pelascini, Laurent Longuevergne, and Min-Hui Lo

Landslides represent a pervasive natural hazard, exerting a significant influence on hillslope morphology in steep regions. Intense rainfall events are well-established as primary triggers for landslides, particularly those characterized by high rainfall intensity, intermediate to long durations, and substantial cumulative precipitation during and before the event. While the evolving roles of soil saturation and mechanical properties are well-identified in shallow landslide occurrences, the influence of groundwater dynamics on the triggering of deep-seated or bedrock landslides remains less understood. Despite this knowledge gap, deep-seated landslides play a dominant role in the volume budget of landslide catalogs and serve as the primary geomorphological process shaping hillslope evolution in steep regions. In this study, we explore the impact of groundwater dynamics on landslide triggering. Our investigation focuses initially on landslides triggered during Typhoon Morakot, examining their relationship with water table fluctuations derived from the HydroModPy 3D hydrogeological model, forced by water recharge data obtained from the Community Land Model CLM 4.0. Analyzing several contrasting catchments, we demonstrate a strong correlation between the locations and depth of deep-seated landslides and the instability predicted by a simple landslide model that integrates pore pressure and water table depth. Notably, these predictions are valid within specific ranges of hydrogeological (i.e., aquifer thickness, porosity, and conductivity) and mechanical (i.e., cohesion and friction angle) parameters, providing valuable insights into the hydrogeological and mechanical properties of the studied catchments. In an exploratory study, we then shift our focus to the longer-term geomorphological impact of rainfall-triggered landslides on hillslope evolution and morphology. Using a coupled 2D model of water table evolution and landsliding, we investigate topographic changes at the hillslope scale, under different scenarios. Our investigation considers the influence of seasonal recharge, intense rainfall events, and hillslope hydrological convergence or divergence perpendicular to the hillslope orientation on resulting hillslope morphology and dynamics. Overall, our results particularly highlight the role of groundwater dynamics on hillslope finite shape.

How to cite: Steer, P., Pelascini, L., Longuevergne, L., and Lo, M.-H.: The impact of groundwater dynamics on landsliding and hillslope morphology: insights from typhoon Morakot and landscape evolution modelling, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15523, https://doi.org/10.5194/egusphere-egu24-15523, 2024.

Sylvain Kuppel, Yves Goddéris, Jean Riotte, and Laurent Ruiz

Water is the first order controlling factor of the weathering reactions. In the recent years, efforts have been made towards the building of model cascades able to simulate the water fluxes and the residence time of the water in the various compartments of the critical zone. Those hydrological constrains are then injected into numerical models simulating the water-rock interactions from the surface down to the impervious bedrock. In this contribution, we describe such a model cascade, where the water-rock interaction model WITCH is fed by the process-based ecohydrological model EcH2O-iso. This model cascade, WITCH2O, is designed for the modeling of water fluxes & stores, as well as the weathering reactions and transport of weathering products (including atmospheric CO2 consumption), from the vertical profile to the catchment scale, and from the submonthly to decadal time scales. We deployed WITCH2O along a gneiss-saprolite-ferralsol profile in a small tropical forested catchment in peninsular India. Long-term observations of water and geochemical fluxes are available, allowing for a 2-step model calibration and evaluation (hydrological and geochemical) across the different processes simulated. Using various temporal averages of simulated water fluxes and stores, preliminary results highlight that seasonal hydrological variability (driven by monsoon dynamics and deep root water uptake) is key for capturing groundwater nutrient concentrations, despite highly-buffered water table variations. We also explore how this non-linear dependence of weathering fluxes upon hydrological states is modulated by the propagation of uncertainties regarding i) modeled hydrology and ii) uncertainties in geohydrochemical properties (e.g. reactive surface and mineral abundance).

How to cite: Kuppel, S., Goddéris, Y., Riotte, J., and Ruiz, L.: Hydroclimatic versus geochemical controls on silicate weathering rates, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17490, https://doi.org/10.5194/egusphere-egu24-17490, 2024.

Kapiolani Teagai, John Armitage, Léo Agélas, Christoff Andermann, and Niels Hovius

In many watersheds of various sizes, the role played by groundwater to sustain river flow is still misunderstood. This is the case in mountainous areas where geological features as fractures, altered or unaltered bedrocks and steep slopes notably play an important role for storing groundwater into the subsurface. The groundwater support to low flows was considered for a long time as a minor contribution, due to the steep slopes in those areas. But in Nepal, it is estimated that 2/3 of the volume of rivers comes from the exfiltration of groundwater through resurgences. Though several attempts were made with numerical modelling based on data monitoring and field surveys to quantify river-groundwater exchanged fluxes, some ambiguities remain. Especially regarding the impact of landscape change in a mountainous topography. The aim of this work is to characterize the subsurface infiltration, recharge, and storage mechanisms of a mountainous hydrogeological system in the Himalayas using field investigations and numerical modelling. In the Kahule Khola watershed (Nepal), a steep catchment of 33 km² whose altitudes range between 1000 and 3500 masl, various field experiments were made to identify groundwater pathways into the altered subsurface and to catch the river/groundwater interactions: seismic and electric surveys (ERT), infiltration tests, physical and isotopic measurements of springs/streams and the water tracking on the surface with loggers installed along gullies in the overall watershed. The region is submitted to intense rainfall as monsoon, intercalated by dry periods in which the river flow is still sustained. Moreover, by closing ancient fractures and opening new ones, earthquakes can deviate springs and change the surface water/groundwater pathways. This contributes to reshaping the landscape. However, the spatial and temporal contribution of groundwater to maintain a baseflow in the river is not quantified yet, in space and time. The ERT data from a time-lapse realized before and after monsoon show a deep alteration zone with a shallow humid layer of 10 m thick at least all year long under the slopes. Areas of low resistivity reveal infiltration zones and preferential flow paths. These areas are recharged in the wet season and drained in the dry season. At the surface, we estimate an average hydraulic conductivity at saturation of 3,5.10-5 m.s-1 in 150 cm depth which suggest an infiltration rate higher than the average rainfall rate (~3000 mm.year-1). In order to quantify the groundwater storage into the subsurface, a numerical groundwater model in 2D has been developed (Python) and is able to simulate and quantify the water storage dynamics of a spatial and temporal pre-defined domain. The data measured on the field will be used to define the initial conditions of future scenarios.

How to cite: Teagai, K., Armitage, J., Agélas, L., Andermann, C., and Hovius, N.: Link between groundwater storage and landscape changes in mountainous areas: the Kahule Khola watershed (Nepal), EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9375, https://doi.org/10.5194/egusphere-egu24-9375, 2024.

Mostaquimur Rahman, Ross Woods, Francesca Pianosi, Fai Fung, and Rafael Rosolem

Chalk forms one of the most important aquifers in the UK. Extending over large parts in the south-west, chalk aquifers account for more than half of the groundwater used for drinking in England and Wales. Groundwater held in these aquifers supports flows in chalk rivers. Hence, chalk aquifers play an important role in sustaining the riverine ecosystem. It is, therefore, important to assess and manage freshwater resources in these catchments. Here we develop and evaluate a distributed numerical model for simulating coupled subsurface and land surface hydrological processes including soil moisture variability, flow, and groundwater dynamics in chalk catchments. The parsimony and computational efficiency of this model make it possible to perform numerous simulations within a reasonable time. This allows for sensitivity analysis, calibration, and multiple scenario analysis that are useful in management decision making.

How to cite: Rahman, M., Woods, R., Pianosi, F., Fung, F., and Rosolem, R.: Developing a coupled hydrological model for UK chalk catchments, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-7396, https://doi.org/10.5194/egusphere-egu24-7396, 2024.

Boris Gailleton, Philippe Steer, Philippe Davy, and Wolfgang Schwanghart

Surface processes control mass transfer efficiency on Earth, responding to tectonic and climatic forcings. These forcings impact landscape dynamics across a wide range of temporal scales, from individual events (e.g., storms) to geological time spans (e.g., Cenozoic climate cooling). Bridging these temporal scales poses a significant challenge for Landscape Evolution Models (LEMs). While LEMs are conventionally employed to study the effects of climate or tectonics on landscape dynamics over geological time, numerical methods simulating short-term processes such as landslides, floods, erosion, and sediment transport struggle to be projected beyond a few hundred years. 

In this contribution, we address this challenge by leveraging a recent model development—graphflood—that enables the computation of hydro-stationary water surfaces and discharge using a simplified shallow water approximation. This new model shows an order-of-magnitude improvement in speed over its predecessors, achieved through the efficiency of algorithms applied to directed acyclic graphs. Through testing induced subgraph dynamic traversals for initial calculations of a stationary state and employing GPU techniques to maintain the state to slower erosion and deposition processes, we demonstrate the potential for an additional order-of-magnitude reduction in computation time for fluvial dynamics. We also investigate how the computation of landslide runout using a shallow water approximation with a friction coefficient modified to account for velocity-weakening can be introduced within the same numerical framework. 

First, we explore various sets of fluvial erosion and deposition laws (e.g., stream power, Meyer Peter Muller) to determine the minimal representation needed for fluvial morphodynamics and projecting them across scales at the lowest computational cost. We then perturb the system with landslides processes and observe the controls on its resilience to external forcings. Lateral dynamics (e.g., lateral erosion, deposition, interaction with valley walls) and the model's ability to capture different river states (e.g., high flow vs low flow, flood) emerge as crucial elements in understanding the complexity of river responses to climato-tectonic perturbations. 

How to cite: Gailleton, B., Steer, P., Davy, P., and Schwanghart, W.: Exploring fluvial morphodynamics through scales , EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-15452, https://doi.org/10.5194/egusphere-egu24-15452, 2024.

Adriane Hövel, Christine Stumpp, Heye Bogena, Andreas Lücke, and Michael Stockinger

A catchment’s runoff response to precipitation largely depends on the antecedent soil moisture in the catchment, but also on hydro-meteorological conditions in terms of, e.g., evapotranspiration. Studies investigating the effects of hydro-meteorological conditions on runoff event characteristics at the small catchment scale with daily temporal resolution mostly used surrogate measures for soil moisture, e.g., derived from hydrological models or using the antecedent precipitation index (API). Here, we applied a time-series based pattern search to 11 years of daily in-situ measured soil moisture in three depths (5, 20, 50 cm) at 33 locations in the Rollesbroich catchment (40 ha) in Germany to identify key variables influencing runoff event characteristics under similar wetness patterns. After identifying wetness patterns, we split the corresponding runoff responses into similar and dissimilar ones by means of goodness-of-fit criteria and analyzed their respective hydro-meteorological variables and event runoff coefficients (ERC), i.e., the proportion of rainfall that transforms into runoff during an event. Results showed that for similar soil moisture patterns, mean potential evapotranspiration, and antecedent soil moisture in all three depths had a smaller standard deviation for similar runoff responses than for dissimilar. This indicates a larger influence on the runoff response compared to rainfall-derived variables such as total event rainfall, maximum event rainfall intensity, or API. Furthermore, during runoff events under similar wetness conditions, the Spearman rank correlation coefficient (ρ) indicated a low average correlation between ERC and API (ρ=0.17). In terms of antecedent soil moisture conditions, the highest correlation between ERC and antecedent soil moisture was observed in the topsoil at 5 cm depth (ρ=0.43), while at 20 cm (ρ=0.16) and 50 cm (ρ=0.30) depths, the correlations were comparatively lower. Our study indicates that using the API as a substitute for antecedent wetness conditions may not be able to comprehensively reflect the relation between the runoff response and antecedent soil moisture conditions in the topsoil in the given catchment. Consequently, the results show that topsoil moisture measurements are more suitable than the surrogate API for assessing the impact of hydro-meteorological variables on daily runoff characteristics.

How to cite: Hövel, A., Stumpp, C., Bogena, H., Lücke, A., and Stockinger, M.: The importance of in-situ soil moisture observations to evaluate the main drivers of event runoff characteristics in a small-scale catchment, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-9338, https://doi.org/10.5194/egusphere-egu24-9338, 2024.

Ronny Figueroa, Clément Roques, Ronan Abherve, Landon Halloran, and Benoit Valley

The occurrence of springs and their connectivity within stream networks is typically associated with three key controlling factors: climate, topography and the distribution of hydraulic properties. In crystalline media, this distribution is often related to lithology and the presence of fractures. In addition, tectonic and topographic stresses can modify properties through compressive and extensional forces acting on the rock mass and fractures. However, these controls are rarely considered for hillslope scale applications. The aim of this research is to investigate the effects of stress on bedrock hydraulic properties and their implications for groundwater flow and transport at the hillslope scale. A numerical experiment has been designed that combines linear poroelasticity to simulate the distribution of permeability and porosity, together with groundwater flow and transport simulations. Different slope and stress conditions are examined, providing a comprehensive sensitivity analysis framework.

Our results show that vertical stress leads to a decrease in permeability and porosity at depth, following an exponential-like trend. Increasing the proportion of lateral stresses relative to the total vertical stresses reduces the mean permeability and porosity and increases the variance in the distribution along the hillslope. For high values of lateral stress, a low permeability domain develops downslope at the valley bottom due to the accumulation of compressive stresses, while the extensive regime at the crest provides higher permeabilities. As expected, groundwater flow simulations revealed that the partitioning of flow paths is strongly influenced by such heterogeneous stress-induced permeability and porosity fields. As stress increases, groundwater flow becomes more channelized in the near subsurface, strongly deviating from the classical Dupuit model. We also found that the distribution of normalized groundwater discharge rates shows higher values in the upper part of the seepage zone than in the lower part. By analyzing the results of particle tracking simulations, we found that mean residence times increase with higher external stress due to a decrease in mean permeability. In addition, the shape of the residence time distribution is strongly modified by the channeling of groundwater flow with increasing lateral stress, with the probability of shorter residence times increasing as stress increases. We discuss the implications of these fundamental results for our understanding of the role of stress in groundwater-dependent systems, with important insights into the recharge, storage and discharge mechanisms that may control the resilience of landscapes to the effects of climate change.

How to cite: Figueroa, R., Roques, C., Abherve, R., Halloran, L., and Valley, B.: Assessing the impact of stress–dependent hydraulic properties on hillslope-scale groundwater flow and transport, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-17282, https://doi.org/10.5194/egusphere-egu24-17282, 2024.

Patricia Saco, Juan Quijano Baron, Jose Rodriguez, Mariano Moreno de las Heras, and Samira Azadi

Feedback effects between hydrology, vegetation and erosion processes are pervasive across landscapes. These tight interactions lead to the coevolution of landscape patterns that modulate landform shape and regulate many other critical zone processes. We study these feedbacks and interactions using simulations from landform evolution models that account for the effect (and feedbacks) of spatially and temporally varying hydrologic pathways and vegetation over landscapes displaying a variety of vegetation patterns. 

We first present results from a landscape evolution modelling framework, that accounts for a comprehensive representation of hydrology and vegetation, including the effect of various vegetation pools on erosion processes. The model includes interacting modules for hydrology, dynamic vegetation, biomass pools partition, and landform evolution. Our simulations indicate that each of the biomass pools provides a specific erosion protection mechanism at a different time of the year. As rainfall events and the resulting vegetation growth and protection are asynchronous, the maximum values of erosion are associated with runoff at the beginning of the rainy season when vegetation protection is not as its maximum. These results show how rapid hydrological processes affecting vegetation have long term implications for landform development. Results for a Eucalyptus savanna landscape study site in the Northern Territory (Australia) showed that models that do not account for the vegetation dynamics can result in prediction errors of up to 80%.  

We also present simulations of the coevolution of landforms and vegetation patterns in selected sites with patchy Acacia Aneura (Mulga) vegetation.  These sites display a sparse vegetation cover and strong patterns of surface water redistribution, with runoff sources located in the bare areas and sinks in the vegetation patches. This effect triggers high spatial variability of erosion/deposition rates that affects the evolving topography and induces feedbacks that shape the dynamic vegetation patterns. We run simulations using rainfall, vegetation and erosion data, and vegetation parameters previously calibrated for Mulga sites in the Northern territory. We further investigate the effect of alterations in hydrologic connectivity induced by climate change and/or anthropogenic activities, which affect water and sediment redistribution and can be linked to loss of resources leading to degradation. We find that an increase in hydrologic connectivity can trigger changes in vegetation patterns inducing feedbacks with landforms leading to degraded states. These transitions display non-linear behaviour and, in some cases, can lead to thresholds with an abrupt reduction in productivity. Critical implications for management and restoration are discussed.  

How to cite: Saco, P., Quijano Baron, J., Rodriguez, J., Moreno de las Heras, M., and Azadi, S.: Coevolution in the critical zone: the key role of fast hydrologic processes, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-20178, https://doi.org/10.5194/egusphere-egu24-20178, 2024.

Franz Zehetner, Martin H. Gerzabek, J. Gregory Shellnutt, Pei-Hao Chen, I Nyoman Candra, Kuo-Fang Huang, and Der-Chuen Lee

The Galápagos archipelago, a chain of islands formed by hotspot volcanism on the Nazca tectonic plate, exhibits a pronounced rock age gradient with distance from the volcanic hotspot from west to east. Here, we investigate chemical weathering along a soil chronosequence (1.5 to 1070 ka) under humid conditions. Our results show considerable loss of base cations already in the early to intermediate phases of weathering (e.g. 95% of Na and 78% of Mg lost from the topsoil after 26 ka) and almost complete loss from the entire profile in soils older than 800 ka. Depletion of Si was less pronounced, with topsoil losses of 24% and 63-68% after 26 ka and >800 ka, respectively. Total weathering flux and associated CO2 consumption rates estimated from profile-scale element losses in this study exceeded catchment-scale estimates reported for other volcanic islands or global averages during the early weathering phase, but were much lower in the intermediate and late phases. Nevertheless, total C drawdown was dominated by soil organic C sequestration (70-90% share) rather than inorganic, weathering-induced CO2 consumption during early pedogenesis (≤4.3 ka), and the relative importance switched in the intermediate and late phases (90-95% share of weathering-induced C drawdown at ≥166 ka). Dust deposition derived from a nearby ocean sediment core was <20% of total basalt mass loss at the young and intermediate-aged sites, but reached 40-60% at the older sites (>800 ka). Our results suggest that (1) young volcanic surfaces are very efficient (inorganic and organic) C sinks, (2) the development of thick soil covers at advanced pedogenic stages effectively shields the underlying rocks from further weathering, and (3) dust inputs become an increasingly important biogeochemical factor in such highly weathered environments.

How to cite: Zehetner, F., Gerzabek, M. H., Shellnutt, J. G., Chen, P.-H., Candra, I. N., Huang, K.-F., and Lee, D.-C.: Time matters: photosynthetic vs. weathering-induced C drawdown and the role of dust inputs along a one-million-year soil weathering gradient on the Galápagos Islands, EGU General Assembly 2024, Vienna, Austria, 14–19 Apr 2024, EGU24-2143, https://doi.org/10.5194/egusphere-egu24-2143, 2024.