Orals: Tue, 29 Apr | Room 2.31
The role of streams in dissolved organic matter (DOM) fluxes is widely acknowledged, yet the contribution of the hyporheic zone (Hz) to these dynamics remains unclear. For inorganic species of nitrogen, the Hz has been reported to be a sink, but what could be expected for DOM? We propose that the contribution of the Hz to stream DOM dynamics is conditioned by the water connectivity between surface and Hz (i.e., hyporheic flow). As hyporheic flow increases, DOM will tend to be removed by the microbial activity associated to the sediments in the Hz. While as hyporheic flow decreases, the microbial community will release DOM, acting as a source. We tested this hypothesis in two reaches, one with high hyporheic flow (connected reach) and another without hyporheic flow (disconnected reach), combining measurements at reach- and patch-scale of relative hyporheic flow with pore water sampling to determine DOM quantity and properties. We observed that at the reach scale, the connected reach tended to be a sink while the connected one was rather a source. Within the hyporheic zone, at the patch-scale, the areas with low hyporheic flow tended to have higher production of DOM than those more connected. Our results suggest that the contribution of the HZ to reach-scale DOM dynamics may be driven by hyporheic flow, and whether it is a source or a sink will result from the interplay among hyporheic areas with different degree of hyporheic flow.
How to cite: Mendoza-Lera, C., Pastor, A., Lupon, A., Catalán, N., and Datry, T.: Is the hyporheic zone a source or a sink of DOM?, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-8461, https://doi.org/10.5194/egusphere-egu25-8461, 2025.
Characterizing the spatio-temporal variability of water chemistry in the riparian zone is important for improving our understanding of the fundamental hydrological and biogeochemical processes that influence stream water quality. However, capturing this variability remains challenging due to the complexity of riparian environments, where dynamic surface water-groundwater exchanges, seasonal fluctuations in groundwater levels, subsurface heterogeneities, variability in flow paths and diverse land uses affect water chemistry.
In this study, we investigated small-scale variability in shallow groundwater chemistry within the riparian zones of three German headwater catchments located in the Black Forest, Sauerland, and Ore Mountains. These sites vary in land use, geology, climate, and other environmental attributes that potentially shape riparian water chemistry. Between summer and autumn 2022, we installed a total of 167 wells across nine riparian areas (three well fields per catchment). From 2023 to 2024, we conducted 10 snapshot sampling campaigns under a range of wetness conditions: three campaigns in the Black Forest and Sauerland, and four in the Ore Mountains. In total, we collected over 400 groundwater samples, which were analyzed for major cations, anions, and dissolved organic carbon.
Our comprehensive dataset showed pronounced variability in space and also between sampling times in all nine riparian areas. However, spatial variability often exceeded the temporal variability (i.e., the differences between the snapshot campaigns). The magnitude of both spatial and temporal variability differed among individual ions. In particular, ions primarily linked with weathering processes (Na, Mg, Ca, Si) exhibited lower spatial and temporal variability compared to biogeochemically active solutes (e.g., NO3-, SO42-, DOC). We also examined whether factors such as catchment wetness conditions, the well’s position relative to the stream, and groundwater levels at the time of sampling could explain variability of the individual ions. The results showed that catchment wetness conditions and well position relative to the stream did not consistently explain spatial variability across elements or sites, and groundwater levels at the time of sampling appeared to have an influence only in Sauerland. These findings highlight the complex interplay of factors driving the variability of riparian zone groundwater chemistry across seasons and study sites.
How to cite: Kuleshov, A., Gariremo, N., Hartmann, A., Blume, T., and Hopp, L.: Insights into Riparian Zone Water Chemistry, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-5588, https://doi.org/10.5194/egusphere-egu25-5588, 2025.
Surface water (SW) and groundwater (GW) interact with each other in almost all types of landscapes forming a hydrological continuum known as a hyporheic zone. Interest in these water exchanges has increased due to their impact on both resources. With changing climate and population growth, managing and understanding these exchanges becomes important as these have been strongly advocated to improve water quality.
Despite its importance, more standardized methods are needed. Traditional methods using chemical tracers or seepage meters are labour-intensive labor-intensive. Hence in recent times dependency on temperature as a tracer has gained significant attention. Different techniques and instruments have been developed to use temperature to detect these exchanges, which can collect sub-hourly data without human intervention. Whereas, these off-the-shelve instruments become expensive in the developing world context.
Hence, to have repeated observations catering to the socio-economic conditions of a region. We sought to develop a cost-effective probe for determining flux rates in the hyporheic zone using open source system, which can be deployed with high spatiotemporal coverage (amounts to ~100$ (that includes a data-logger, waterproof sensors (as many are required), Real-time clock, etc.). The hybrid probe developed can measure Vertical Hydraulic Gradient (VHG) values and temperature values at required depths. The probe is designed in such a way that, depending on the site of installation and depth of interest the sensor on the probe could be customized.
The probe has been tested with HOBO Tidbit sensors (off-the-shelve) at an upwelling location of a meander bend section at a headwater stream in the mountainous region of the Indian Himalayas. The values from the developed instrumentation had a strong correlation (>0.85) with those from the HOBO Tidbit sensor, indicating the reliability and accuracy of the newly developed probe.
Additionally, the flux values derived from the probe data provide us with valuable insights into GW-SW interactions, especially in the unexplored Himalayan headwater catchments. The probe’s low cost enables micro-monitoring of field sites with additional instrumentation, allowing for the collection of spatially and temporally robust data, thereby enhancing our physical understanding of GW-SW interfaces.
How to cite: Reddy, P. K. and Sen, S.: A Cost-Effective Probe for High-Resolution Monitoring of Hyporheic Zone Dynamics, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-9449, https://doi.org/10.5194/egusphere-egu25-9449, 2025.
Hyporheic fluxes are typically regarded as highly variable both in space and time at the stream‐groundwater interface. However, Active‐Distributed Temperature Sensing (DTS) experiments conducted in a losing river section demonstrated low spatial variability (one order of magnitude) and remarkable temporal stability. In this abstract, we investigate the potential reasons for the observed low variability and notable stability of hyporheic flows.
Experiments were conducted by burying several hundred meters of heatable Fiber‐Optic cables within streambed sediments in a large meander, where permanent stream‐losing conditions are observed. The absence of correlation between water fluxes in the hyporheic zone and variations in streambed topography suggests that the low spatial variability (one order of magnitude) of fluxes serves as an indicator of the low variability in streambed hydraulic conductivities. Repeated measurements taken during several field campaigns over three years demonstrated a remarkable stability of hyporheic flows throughout this period. To explain our findings, we analyzed the temporal variability of river stage and groundwater levels. Despite the rapid and sudden fluctuations of water levels, caused by upstream dam hydropeaking and groundwater pumping in the alluvial aquifer, the hydraulic gradients between the river and the aquifer remained relatively stable over time. Moreover, the speed at which the levels rebalance suggests that flows at the interface are primarily controlled by the high permeability of the streambed sediments rather than by the boundary conditions. These results can be considered for calibrating models that assess hyporheic processes.
How to cite: Bour, O., Simon, N., Heyman, J., and Crave, A.: About the stability of hyporheic flows in a losing river section, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12075, https://doi.org/10.5194/egusphere-egu25-12075, 2025.
Residence time distribution of solute in the hyporheic zone plays a key role in controlling the downstream transport and biogeochemical transformation of dissolved substances in river corridors. Riverbed morphology, hyporheic hydraulic conductivity, and groundwater upwelling/downwelling condition are crucial factors that control the resulting residence time distribution. In particular, these factors can exhibit spatial variations at different length scales leading to a complex multi-scale organization of hyporheic flow paths. In this context, we analyze the dominance or otherwise of spatial heterogeneity in the morphology of the riverbed, in the arrangement of hyporheic hydraulic conductivity, and in the organization of upwelling/downwelling flows. We frame our work in a stochastic context, i.e., we treat each factor as a spatially correlated random field, characterized by its degree of heterogeneity and its spatial correlation scale. We explore different combinations, in relative terms, of the degree of heterogeneity and the size of the correlation lengths of the different factors. We use a Monte Carlo approach for each combination to solve flow and solute transport for different realizations numerically. Results indicate the transition between the dominance of a given single factor and the complex interactions of all factors depending on (i) the target feature of the residence time distribution (e.g., mean, variance) and (ii) the relative degree of heterogeneity and spatial correlation of different single factors.
How to cite: Dell Oca, A. and Ackerer, P.: Hyporheic residence time distribution: scanning heterogeneity in riverbed morphology, hydraulic conductivity, and groundwater flux., EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6524, https://doi.org/10.5194/egusphere-egu25-6524, 2025.
The dynamic interaction between surface water and groundwater in the hyporheic exchange zone (HEZ) is crucial for regulating water quality, nutrient cycling, and ecosystem health. Nonetheless, understanding the impact of changing river discharge conditions—especially during peak flow events—and the diverse geometries of bedforms on flow dynamics and biogeochemical processes in the HEZ continues to be a substantial research challenge. This study aims to address this gap using a multiphysic framework to simulate bedform responses to distinct river flow conditions. The model assesses water exchange, pressure distribution, and solute transport under steady and transient states, providing insights into HEZ dynamics. Our study is grounded in extensive field data collected from the Krycklan Catchment in Northern Sweden. Key datasets include piezometer readings of water level and pressure measurements, hydraulic conductivity profiles, and tracer movement through the subsurface, which are used to validate the numerical model. Variables such as discharge intensities, flow duration, and bedform aspect ratios are systematically varied to investigate their effects on hyporheic exchange and residence times. Preliminary results indicate that variations in flow conditions and bedform geometries affect pressure distribution, velocity fields, and flow streamlines within the HEZ. These variations lead to changes in hyporheic exchange extents, especially under peak flow regimes. The findings will enhance our understanding of the impacts of peak flow events on HEZ expansion, contraction, and nutrient cycling. They hold significant implications for river management, particularly in predicting the impact of flood dynamics and preserving freshwater ecosystems.
How to cite: Alharbi, M., Krause, S., Han, S., Wu, L., and Li, Y.: Assessing the Impacts of Fluvial Flooding and River Bedform Geometry on Hyporheic Exchange Zones , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-21812, https://doi.org/10.5194/egusphere-egu25-21812, 2025.
Hydraulic structures affect rive environment, leading to changes in groundwater and surface water interactions. In South Korea, 8 weirs were installed in Nakdonggang River, in 2012, to secure sufficient water resources. This study aims to analyze the impacts of weir operation on the integrated water environment in the Nakdonggang River basin, South Korea. A basin-scale hydrological model for Nakdonggang River basin was developed to simulate the groundwater and surface water dynamics using HydroGeoSphere, three-dimensional fully integrated surface-subsurface hydrological model. Our results showed that the overall fluctuations in river flow decreased, while the river temperature increased during weir operation. In addition, groundwater delays hydrological responses within the integrated water environment of the study area and, in particular, plays a critical role in mitigating seasonal fluctuations in surface water flow. This study highlights the importance of integrated groundwater and surface water management to sustain the health of the integrated water environment, address future climate change, and reduce vulnerability to anthropogenic environmental changes and climatic variability.
How to cite: Lee, H., Lee, E., Park, D., and Hwang, H.-T.: Changes in Groundwater and Surface Water Interactions due to Weir Operation in the Nakdonggang River Basin, Korea, Using an Integrated Hydrological Model, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7594, https://doi.org/10.5194/egusphere-egu25-7594, 2025.
Lake Arendsee, a 50 m deep, monomictic lake in north-eastern Germany, has been suffering from anthropogenic eutrophication for more than 40 years. Lake eutrophication is generally associated with phosphorus (P) loads from surface inflows, direct sewage discharges, atmospheric deposition, surface runoff, bathers, waterfowl or other highly visible nutrient sources. In the case of Lake Arendsee previous research has shown that more than 50 % of the P load is due to excessive P inputs from groundwater. The aim of the study is to assess the changes in groundwater P concentrations over the last 15 years and to understand how the P load has changed between two measurement campaigns (2012 & 2022). P in groundwater was determined using permanent wells, temporary piezometers and private domestic wells, the latter sampled as part of Citizen Science campaigns. Lacustrine Groundwater Discharge (LGD) rates for 2022 were determined using temperature (T) lances, KSAT tests, Darcy calculations and hydraulic gradients, allowing the total annual P load to Lake Arendsee to be calculated. Despite a lower number of temporary piezometers installed along the lake shore in 2022 compared to 2012, the results showed similar spatial patterns, indicating the reliability of the method. High P concentrations were particularly common in the urban area. Both campaigns also showed similar patterns, despite using different domestic wells, indicating the reliability of the method. Unfortunately, two different methods for calculating LGD rates for 2012 (temperature lances) and 2022 (KSAT tests) were used. The comparability of the methods is limited but revealed that most groundwater discharge took place along the shore of the City of Arendsee. It is unlikely that the spatial LGD pattern changed within 10 years as there is no reason for a change of hydraulic conductivities. Therefore, the calculation of the annual P loads in 2022 was based on the patterns of exfiltration rates determined using T lances in 2012 but using hydraulic gradients of 2022 to adapt total LGD rates on the situation in 2022. The study shows that P in groundwater in the catchment has remained largely unchanged, with the exception of a few monitoring sites. Due to a decrease in both hydraulic gradients (consecutive dry years) and P in some near-shore temporary piezometers, P loads entering the lake in 2022 are lower than in 2012. Further studies are needed to determine whether the reduced P loads in 2022 will increase to levels similar to those observed in 2012 due to the increase in groundwater and lake water levels in 2024, or whether improvements (e.g. replacement of sewers) in the subsurface catchment of Lake Arendsee are the reason for the reduced P loads. Groundwater is still the major source of the high P concentrations of 180 μg/L in the lake.
How to cite: Lewandowski, J., Pfaff, M. J., and Hupfer, M.: Groundwater-borne phosphorus import into Lake Arendsee and its changes over the last 15 years, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-3989, https://doi.org/10.5194/egusphere-egu25-3989, 2025.
Aquifer sediments, formed under varying depositional conditions, exhibit significant heterogeneity in their sedimentary architecture causing variability in their hydraulic and biogeochemical properties. The spatial arrangement of these properties controls the net turnover of biogeochemically reactive and environmentally relevant solutes in floodplains. However, the interlinkage between reactive and hydraulic properties is still enigmatic. This study proposes using sedimentary facies analyses to reconstruct the paleoenvironmental conditions that control the abundance and spatial distribution of aquifer materials, their potential as electron donors, and their hydraulic conductivity. The approach is applied to a Holocene aquifer in the Ammer floodplain in South-West Germany, which consists mainly of organic-rich tufa successions with varying contents of total organic carbon (TOC), peat lenses, as well as of gravel- and clay layers. The spatial extent of sedimentary features and baseline reactive properties (TOC, hydraulic conductivity) were constrained by combining sedimentological observations and bulk geochemical analyses. Based on the insights gained from the paleoenvironmental reconstruction, a facies-based virtual aquifer resembling the sedimentological makeup of the Ammer floodplain was generated and used to perform flow and transport simulations, using exposure of groundwater to TOC as proxy for reactivity. The study demonstrates that the spatial arrangement of facies and their combined biogeochemical and hydraulic properties determine over which range of times the breakthrough of nitrate is to be expected, highlighting the importance of sedimentological insights for groundwater-quality projections.
How to cite: Holdt, J., Cantarella, V., Buchner, D., Mellage, A., Cirpka, O., and Duda, J.-P.: Holocene Floodplain Sediments: From depositional processes to biogeochemical pollutant turnover, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12177, https://doi.org/10.5194/egusphere-egu25-12177, 2025.
The hyporheic zone (HZ) is crucial for the stream and river ecosystem for attenuation of domestic, agricultural, and industrial pollution. Flow in the hyporheic zone occurs due to bedforms (dunes and ripples), meandering, and the presence of any obstruction. Water from the stream enters this zone and either returns or infiltrates deeper depending on the relative levels of surface water and groundwater. The zone is more reactive for biogeochemical processes due to the influx of nutrients and Pollutants and the mixing of surface water and groundwater. The sediment in HZ can adsorb the nutrients and pollutants, as well as support the growth and metabolism of microorganisms.
The experiments were conducted in a recirculating hyporheic zone flume of 5 m effective length connected to a groundwater reservoir, which allowed us to simulate gaining, losing, and neutral streams by independently adjusting the surface water and groundwater levels. Three artificial sediment dunes were constructed in the shape of asymmetric triangles, 1 m in length and 0.15 m in height at 0.75 m length.
The objective of the experiments was to investigate the transport of a conservative tracer (Br-) and nutrients (NO3-, PO43-, NH4+) within the hyporheic zone and estimate the dispersion and retardation coefficients with the help of simulation. All the experiments were conducted in duplicate. The flow was simulated using the two-dimensional steady-state classical groundwater flow equation, and the transport was simulated using the two-dimensional time-dependent advection-dispersion equation using grid sizes of 0.5 cm x 0.5 cm. The dispersivity and horizontal and vertical dispersion coefficients were estimated using the experiments with the conservative tracer. The retardation coefficients of the nutrients were computed for each of the nutrients. All the parameter estimations were carried out by minimizing the least square errors between the experimental measurements and simulation. Since the transport is time-dependent, parameters were estimated using the data from the measurements at two times and validated using the data from subsequent measurements. Uncertainties of the estimated parameters were also computed.
How to cite: Gupta, V. K. and Guha, S.: Reactive Transport of Nutrients in the Hyporheic Zone: Experiment and Simulation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6111, https://doi.org/10.5194/egusphere-egu25-6111, 2025.
Transformation and removal of dissolved nutrients and pollutants in streams strongly depends on microbial processes in streambed sediments. The contact between these solutes and microbial communities is mediated by the physical transport from the bulk stream to, and through, the streambed, a process broadly referred to as hyporheic exchange. Even though multiple physical and biological processes influence the rate of hyporheic exchange, we here show that many hyporheic exchange mechanisms can be represented simply as a one‐dimensional diffusion process, where the diffusion coefficient decays exponentially with depth into the streambed. This framework is applied to a classic study of nitrate removal in 72 headwater streams across the United States, showing how the interplay among land‐use, stream physics, and stream biology collectively influence nutrient transformation in streambeds. The proposed modeling framework can help the upscaling of hyporheic exchange and promote better understanding of its role for processing and removal of contaminants in streams.
How to cite: Boano, F., Monofy, A., Grant, S., Rippy, M., Gomez-Velez, J., Kaushal, S., Hotchkiss, E., and Shelton, S.: Toward a universal model of hyporheic exchange and nutrient cycling in streams, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-13630, https://doi.org/10.5194/egusphere-egu25-13630, 2025.
Hyporheic zones (HZs), where surface water (SW) and groundwater (GW) mix underneath and adjacent to streams, are known for their inherent ability to attenuate contaminants. Mixing of reactants from SW and GW enables the occurrence of mixing-dependent reactions, mixing-dependent denitrification is commonly regarded as the last defense against groundwater-bone nitrate before it enters to streams. However, the impact of mixing-dependent DNRA on nitrate transformation is often overlooked. In this study, we conducted a flume experiment to generate downwelling of SW with dissolved organic carbon (DOC) into the sediments and create a hyporheic exchange flow (HEF) cell. We added nitrate to anoxic upwelling GW to stimulate mixing-dependent reactions. Hydrodynamics, hydrochemical conditions, microbial community and its biogeochemical function with respect to nitrogen transformation were tested and analyzed. The SW and GW mixing zone was situated along the fringe of HEF cell. The mixing zone represented a transition zone between the HEF cell and deeper GW in microbial community structure, and hosted active mixing-dependent reaction potentials. Both mixing-dependent denitrification and DNRA occurred, with the hotspots for these processes appearing predominantly on the right side (closer to the GW) and the left side (closer to the HEF cell) of the mixing zone, rather than evenly within it. The downstream and upstream movement of the mixing zone enhances the mixing-dependent denitrification and DNRA reactions. The NH4+ produced by mixing-dependent DNRA would undergo further nitrification within the HEF cell because higher concentrations of nitrification functional genes present upstream. Disregarding the mixing-dependent DNRA would lead to an overestimation of HZs’ capacity to attenuate groundwater-borne nitrate. This study enhances our understanding of nitrate processing within HZs and contributes valuable insights for the effective management of watershed contaminants.
How to cite: Ping, X., Wen, Z., Xian, Y., Krause, S., Yuan, S., Zhang, Z., and Jin, M.: Nitrate fate in mixed surface water and groundwater: Role of mixing-dependent denitrification and DNRA in hyporheic zones, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-15101, https://doi.org/10.5194/egusphere-egu25-15101, 2025.
Nitrate pollution of groundwater represents a critical environmental concern, with many aquifers exceeding ecological and health-related concentration limits. Microbial driven denitrification represents the primary mechanism for nitrate attenuation in aquifers. Despite a robust understanding of individual transformation steps, predicting nitrate turnover in the complex and heterogeneous subsurface environment of aquifers remains challenging. This is primarily due to the uneven distribution of potential electron donors (e.g., organic carbon) and the variability in local biogeochemical conditions on the aquifer scale. To assess the spatial variability of denitrification at field-relevant scales, we conducted laboratory microcosm experiments were conducted with distinct sedimentary facies from a Holocene aquifer which we previously characterized by paleo environmental reconstruction. The denitrification capacity of anaerobically incubated sediments (n=40) from eight distinct sedimentary facies with varying TOC contents was evaluated by monitoring the concentrations of NO₃⁻, NH₄⁺, N₂O, SO₄²⁻, and DOC over time. Microcosm replicates of the same sedimentary facies at a specific sampling location showed consistent nitrate removal. However, microcosms of the same sedimentary facies at different locations showed significant variability of nitrate removal. The observed variability of a particular sedimentary facies was found to be within the same range as the mean variability observed across different sedimentary facies. Our study indicates that the denitrification potential of heterogenous aquifers is far more complex and variable than commonly assumed and cannot be gauged by evaluating the electron donor distribution.
How to cite: Buchner, D., Holdt, J., Cantarella, V., Mellage, A., Cirpka, O., and Duda, J.-P.: Unravelling the Spatial Variability and Complexity of Denitrification in Heterogeneous Aquifer Sediments , EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-18208, https://doi.org/10.5194/egusphere-egu25-18208, 2025.
Climate change and water resource management may result in the temporary drying up of streams or stream reaches. Such flow interruption has significant effects on biogeochemical processes, particularly on oxygen dynamics in the hyporheic zone. We hypothesized that the hyporheic zone may quickly return to the pre-interruption oxygen pattern once the original flow conditions are restored. To test this, oxygen concentrations were measured in situ in the surface water and pore water of the hyporheic zone using flow-through cells (every 2 cm down to 14 cm in the sediment) and a planar optode placed in the streambed of an urban river. Measurements were taken five days before and fifteen days after a one-day flow interruption at different streamwater velocities ranging from 0.1 m/s to 0.5 m/s. We found that the flow interruption reduced the diurnal amplitude of oxygen in the surface water. At high flow velocities (> 0.3 m/s), the changes in surface water oxygen concentration propagated into the pore water, leading to lower diurnal oxygen amplitudes throughout the sediment depth profile. This alteration affects the biogeochemical milieu in the hyporheic zone and thus the nutrient dynamics and functioning of the ecosystem as a whole. Contrary to the hypothesis, the oxygen dynamics did not return to the pre-interruption oxygen pattern, even three weeks after the streamflow interruption. Both, surface water and pore water had lower oxygen concentrations, which were about 2 mg/L O2 lower than before the flow interruption. The altered vertical gradient and the two-dimensional oxygen patterns in the hyporheic zone caused by even short dry fall of streams highlight the impact on the oxygen dynamics of river ecosystems. It also emphasizes the need for sustainable water management strategies to mitigate the long-term ecosystem consequences of flow intermittency.
How to cite: Villa, A., Baume, C., Spahr, S., Arnon, S., and Lewandowski, J.: Effects of a short-term dry fall of streams on oxygen dynamics in the hyporheic zone, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-16345, https://doi.org/10.5194/egusphere-egu25-16345, 2025.
Estimating in-stream mixing lengths is important in the context of salt dilution gauging, but also in the context of stream water quality assessments. Underestimating the mixing length can lead to large errors and misinterpretations of your data. Playing it safe and going with an overly long mixing length can also introduce errors. For example, the underlying assumption of salt dilution gauging of conservation of mass might be violated when stream losses become significant. However, despite their importance, mixing length estimates are often only based on experience or empirical equations.
In this study we estimated the mixing lengths for 10 different stream reaches in two mid-mountain headwater streams. Three tracer experiments were carried out at each stream reach: dye injection and salt injections, here both as slug and constant rate injections. Breakthrough curves of the salt injections were monitored using 20 electric conductivity sensors. The results of the tracer injections are then compared to other common methods of mixing length estimation and the implications are discussed.
How to cite: Blume, T. and Adeberg, F.: A systematic analysis of in-stream mixing lengths in two mid-mountain headwater streams: incongruities, insights and implications, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-17972, https://doi.org/10.5194/egusphere-egu25-17972, 2025.
The Cuneo Plain (Piedmont, NW Italy), like the whole Po Plain, is characterized by intense agricultural activities that heavily rely on seasonal water availability, which is now challenged by the climate crisis. In the study area, groundwater resources represent a great tool to buffer temporary water scarcity and mitigate the drought risk. The connection between the irrigation network and the unconfined aquifer is made available by the historical drainage trenches, known as fontanili. They were constructed starting from the 11th century with the aim of reclaiming swamps, by lowering the water table, and to provide water for irrigation and drinking purposes. Their configuration was later improved by adding screened boreholes, known as tubi calandra, along the furrows, as they enhance the groundwater flow towards the surface.
This study presents the development of a conceptual and numerical model capable to describe the groundwater - surface water flow interaction in the presence of such structures. The model results were compared to field monitoring data of a fontanile located in the Cuneo province, Italy. The flow model was developed in Hydrus (PC-Progress), solving the Richard’s equation and allowing to model the water flow also in the vadose zone. The Finite Element Mesh consists of a network of triangular (2D) or tetrahedral (3D) elements, refined at the base of the furrow and around the tubi calandra. The 2D model of a transversal section of the trench was implemented to study the hydraulic connection to the phreatic aquifer, whereas, the 3D model was used to estimate evolution of the drainage capacity, and therefore of the discharge, along the furrow. The model was forced with head boundary conditions, applied upstream of the fontanile and at the screened boreholes, instead, an aquiclude was imposed at the bottom of the saturated thickness. Afterwards, a sensitivity analysis was conducted to determine the drainage capacity of the trench under different scenarios of aquifer hydraulic conductivity, upstream hydraulic head and, finally, length and radius of the tubo calandra.
The numerical model allowed to have a clearer picture of the mechanisms controlling the discharge in the fontanili, both in terms of their connection directly to the water table, as well as the contribution of the tubi calandra. In particular, for the latter a suitable range of granulometry and conductivity of the soil was identified to maximize their performance. The results are particularly meaningful as they contribute to the sustainable management of water resources in the area, coupling groundwater and surface water, so that a careful planning of the resource to meet the irrigation demand can be developed.
How to cite: Amendola, A., Tosco, T. A. E., Casasso, A., and Sethi, R.: A flow model of groundwater-surface water interaction in a drainage trench used for irrigation, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-6475, https://doi.org/10.5194/egusphere-egu25-6475, 2025.
Well drilling for aquifer tests creates a skin zone with hydraulic properties distinct from the surrounding aquifer formation. The skin zone affects the tests and interpretations of hydraulic properties of the formation. Traditional models attempt to address this issue by incorporating a governing equation to describe flow or transport in the skin zone. However, these methods face challenges such as parameter correlation, where multiple parameter estimates produce the same agreement between measured data and model predictions, making it impossible to obtain reliable and objects parameter estimates. Additionally, numerical solutions for traditional models require fine grids to discretize skin zone and coarse grids for the formation, resulting in excessive grid numbers, and high computational costs. This study introduces new models for slug test and tracer test. Both analytical and numerical solutions of the models are developed. Results indicate the new models achieve predictions comparable to the traditional models while effectively addressing the issues of parameter correlation and the need for fine skin discretization. This study provides theoretical insights and practical applications for groundwater remediation and resource management.
How to cite: Wang, C. and Huang, C.-S.: New Models Simulating Aquifer Tests with No Parameter Correlation and Low Computational Cost, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-7823, https://doi.org/10.5194/egusphere-egu25-7823, 2025.
This review is motivated by deep concern over the current, relatively fragmented state of lake and groundwater research. For example, Chinese mega lake basins such as Lake Taihu, Dongting, Poyang, Hongze, and Chaohu are not only major cropland areas but also habitats for over 120 million residents. These lakes have faced serious issues for decades, such as the rapid shrinking of water areas and volume in Poyang, and severe eutrophication and algal blooms in Taihu and Chaohu. Despite significant efforts by environmental and limnology scientists to prevent these eco-environmental problems and restore ecosystem services, these uninvited guests continue to harass the lake systems. This underscores the need for optimal management, protection, and restoration of lake eco-environments, which should encompass both visible surface water and invisible groundwater.
Lakes are always the outcrops of the regional groundwater system. To gain a comprehensive understanding of hydrological and biogeochemical functions, and to pave the way for better lake eco-environmental protections and restoration, we must carefully consider the role of groundwater inflow, specifically lacustrine groundwater discharge (LGD), and the associated biogeochemical fluxes. In this review, we first provide a historical and comprehensive overview of groundwater-lake water interaction studies in China. Our main finding shows that over 22% of lakes, among the 673 lakes with areas exceeding 10 km², were identified as groundwater discharge lakes prior to the 2000s. Subsequently, the increased study of groundwater-lake water interaction study is discussed in main study areas, e.g. Badain Jaran Desert, Qinghai-Tibetan Plateau (QTP), the middle-lower Yangtze plains, Volcanic and Maar lakes etc. The current state of study is encapsulated by examining the study methods and techniques employed, with a particular emphasis on the study of lacustrine groundwater discharge (LGD). Finally, we discuss the major challenges and problems remaining in LGD studies, including driving mechanisms, scale differentiations, and temporal evolutions. This review also aims to advocate for close collaboration between multidisciplinary scientific communities and stakeholders to protect lake environments from a hydrogeological perspective.
How to cite: Zuo, J. and Luo, X.: Lacustrine Groundwater Discharge Studies in China:History, Current State & Future Vision, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-12379, https://doi.org/10.5194/egusphere-egu25-12379, 2025.
The world’s largest freshwater resource - groundwater is essential for irrigation and food security. However, unsustainable groundwater pumping, exceeding recharge from precipitation, has led to significant groundwater depletion, particularly in intensively irrigated regions like north India, with cascading impacts on streamflow. Groundwater storage losses reduce groundwater discharge to streams, reverse flow directions, or cease discharge entirely, thereby reducing streamflow. Despite its critical implications on water security, ecosystem health, and agricultural sustainability, the relative influence of groundwater pumping and climate variability in driving streamflow variability remains poorly understood. Most previous studies often relied on coarse-resolution models that overlook groundwater-surface water interactions and lateral groundwater flow. To address these limitations, we applied the physically based, integrated land surface-groundwater model ParFlow-CLM at a 5 km resolution from 1970 to 2022 across the Ganga and the Indus basins. This physically based model simulates three-dimensional groundwater flow using the Richards equation and couples it with land surface processes, enabling robust analysis of groundwater-streamflow interactions. We find that streamflow variability in north India is primarily driven by groundwater abstraction for irrigation, modulated by precipitation variability. Excessive pumping has shifted streams from gaining groundwater to losing it, approaching critical environmental flow thresholds. The study underscores that prolonged groundwater pumping has significantly reduced baseflow contributions, which has critical implications for water management in India.
How to cite: Roy, R. and Mishra, V.: Strong Influence of Groundwater Pumping on Streamflow Depletion across North India, EGU General Assembly 2025, Vienna, Austria, 27 Apr–2 May 2025, EGU25-14587, https://doi.org/10.5194/egusphere-egu25-14587, 2025.
