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  • Ground Water
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  • 1
    In: Fundamental and Applied Limnology / Archiv für Hydrobiologie, June 2014, Vol.184(3), pp.173-181
    Description: Heat is increasingly used as a natural tracer to quantify water fluxes at the groundwater-surface water-interface. We present a systematic approach to monitor and evaluate stream and streambed temperatures to derive daily-updated temperature-based water exchange fluxes between the stream and the streambed. Specifically designed multi-level temperature sensors coupled with a data logger and GSM modem are used to monitor temperature in the stream and streambed and transfer this data daily to a database. A suite of MATLAB scripts with structured query language (SQL) commands is applied to extract the data for processing using an inverse numerical model to estimate water flow based on the measured temperatures. Compared to common analytical approaches, which typically require sinusoidal diurnal temperature pattern, our numerical model can utilize temperature records without daily variations. Temperature-based calculations to quantify vertical water fluxes at the stream-groundwater interface can provide a supplement to, or even a replacement of, calculations based on vertical hydraulic gradients and Darcy' law.
    Keywords: Groundwater - Surface Water - Interface
    ISSN: 1863-9135
    E-ISSN: 23637110
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  • 2
    Language: English
    In: Journal of Hydrology, October 2015, Vol.529, pp.969-979
    Description: Coupling surface and subsurface water flow in fully integrated hydrological codes is becoming common in hydrological research; however, the coupling of surface–subsurface solute transport has received much less attention. Previous studies on fully integrated solute transport focus on small scales, simple geometric domains, and have not utilised many different field data sources. The objective of this study is to demonstrate the inclusion of both flow and solute transport in a 3D, fully integrated catchment model, utilising high resolution observations of dissolved organic carbon (DOC) export from a wetland complex during a rainfall event. A sensitivity analysis is performed to span a range of transport conditions for the surface–subsurface boundary (e.g. advective exchange only, advection plus diffusion, advection plus full mechanical dispersion) and subsurface dispersivities. The catchment model captures some aspects of observed catchment behaviour (e.g. solute discharge at the catchment outlet, increasing discharge from wetlands with increased stream discharge, and counter-clockwise concentration–discharge relationships), although other known behaviours are not well represented in the model (e.g. slope of concentration–discharge plots). Including surface–subsurface solute transport aids in evaluating internal model processes, however there are challenges related to the influence of dispersion across the surface–subsurface interface, and non-uniqueness of the solute transport solution. This highlights that obtaining solute field data is especially important for constraining integrated models of solute transport.
    Keywords: Solute Transport ; Surface–Subsurface Coupling ; Integrated Modelling ; Catchment Modelling ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 3
    Language: English
    In: Journal of Hydrology, 19 December 2012, Vol.475, pp.1-11
    Description: ► We developed a method to determine flow direction and velocity in the hyporheic zone. ► The method is based on a heat pulse technique with analytical data analysis algorithm. ► Error-proneness and accuracy of the method were assessed in the lab and . ► The first field application gives insight in hyporheic flow patterns of a lowland river. The hyporheic zone is strongly influenced by the adjacent surface water and groundwater systems. It is subject to hydraulic head and pressure fluctuations at different space and time scales, causing dynamic and heterogeneous flow patterns. These patterns are crucial for many biogeochemical processes in the shallow sediment and need to be considered in investigations of this hydraulically dynamic and biogeochemical active interface. For this purpose a device employing heat as an artificial tracer and a data analysis routine were developed. The method aims at measuring hyporheic flow direction and velocity in three dimensions at a scale of a few centimeters. A short heat pulse is injected into the sediment by a point source and its propagation is detected by up to 24 temperature sensors arranged cylindrically around the heater. The resulting breakthrough curves are analyzed using an analytical solution of the heat transport equation. The device was tested in two laboratory flow-through tanks with defined flow velocities and directions. Using different flow situations and sensor arrays the sensitivity of the method was evaluated. After operational reliability was demonstrated in the laboratory, its applicability in the field was tested in the hyporheic zone of a low gradient stream with sandy streambed in NE-Germany. Median and maximum flow velocity in the hyporheic zone at the site were determined as 0.9 × 10 and 2.1 × 10 m s respectively. Horizontal flow components were found to be spatially very heterogeneous, while vertical flow component appear to be predominantly driven by the streambed morphology.
    Keywords: Flow Patterns ; Flow Direction ; Flow Velocity ; Hyporheic Zone ; Heat Pulse Technique ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 4
    Language: English
    In: Journal of Hydrology, 13 February 2014, Vol.509, pp.601-614
    Description: An important prerequisite to better understand the transport of nutrients and contaminants across the river-aquifer interface and possible implications for biogeochemical transformations is to accurately characterize and asses the exchange fluxes. In this study we investigate how monsoonal precipitation events and the resulting variability in river discharge affect the dynamics of river-aquifer exchange and the corresponding flux rates. We evaluate potential impacts of the investigated exchange fluxes on local water quality. Hydraulic gradients along a piezometer transect were monitored at a river reach in a small catchment in South Korea, where the hydrologic dynamics are driven by the East-Asian Monsoon. We used heat as a tracer to constrain river-aquifer exchange fluxes in a two-dimensional flow and heat transport model implemented in the numerical code HydroGeoSphere, which was calibrated to the measured temperature and total head data. To elucidate potential effects of river-aquifer exchange dynamics on biogeochemical transformations at the river-aquifer interface, river water and groundwater samples were collected and analyzed for dissolved organic carbon (DOC), nitrate (NO ) and dissolved oxygen saturation (DO ). Our results illustrate highly variable hydrologic conditions during the monsoon season characterized by temporal and spatial variability in river-aquifer exchange fluxes with frequent flow reversals (changes between gaining and losing conditions). Intense monsoonal precipitation events and the associated rapid changes in river stage are the dominant driver for the observed riverbed flow reversals. The chemical data suggest that the flow reversals, when river water high in DOC is pushed into the nitrate-rich groundwater below the stream and subsequently returns to the stream may facilitate and enhance the natural attenuation of nitrate in the shallow groundwater.
    Keywords: River-Aquifer Exchange Fluxes ; Heat As a Natural Tracer ; Monsoonal-Type Climate ; Hydraulic Gradient Reversals ; Hydrogeosphere ; Natural Attenuation of Nitrate ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
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  • 5
    In: Hydrological Processes, 30 October 2013, Vol.27(22), pp.3240-3253
    Description: Exchange of groundwater and lake water with typically quite different chemical composition is an important driver for biogeochemical processes at the groundwater‐lake interface, which can affect the water quality of lakes. This is of particular relevance in mine lakes where anoxic and slightly acidic groundwater mixes with oxic and acidic lake water (pH 330 nmol g d) compared to alternating sites (〈220 nmol g d). Although differences in sulfate reduction rates could not be explained solely by different flux rates, they were clearly related to the prevailing groundwater‐lake exchange patterns and the associated pH conditions. Our findings strongly suggest that groundwater‐lake exchange has significant effects on the biogeochemical processes that are coupled to sulfate reduction such as acidity retention and precipitation of iron sulfides. Copyright © 2012 John Wiley & Sons, Ltd.
    Keywords: Groundwater‐Lake Exchange ; Acid Mine Lake ; Seepage Flux ; Ph‐Profiles ; Chloride Profiles ; Acid Neutralization Processes
    ISSN: 0885-6087
    E-ISSN: 1099-1085
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  • 6
    Language: English
    In: Journal of Hydrology, 12 December 2013, Vol.507, pp.149-162
    Description: The linkage between hydrologic dynamics and the delivery of nitrate and DOC (dissolved organic carbon) to streams was studied in the Haean catchment, a mixed land-use mountainous catchment in South Korea. Three monsoonal precipitation events were analyzed, which varied in total rainfall amount (39–70 mm) and intensities (mean: 1.6–5.6 mm h ), by high-resolution (2–4 h interval) stream water-quality sampling along the topographic elevation gradient of the catchment, from an upland deciduous forest stream, over areas intensively used for agriculture (dryland farming and rice paddies) down to the catchment outlet. The dynamics of river-aquifer exchange were investigated at two piezometer transects at mid and lower elevations. DOC and nitrate sources and their transport pathways to the receiving surface waters differed between the forested and the agricultural stream site. In the forest stream, elevated DOC concentrations (max: 3.5 mgC l ) during precipitation events were due to hydrologic flushing of soluble organic matter in upper soil horizons, with a strong dependency on pre-storm wetness conditions. Nitrate contributions to the forested stream occurred along shallow subsurface transport pathways. At the agricultural sites stream DOC concentrations were considerably higher (max: 23.5 mgC l ) supplied from adjacent rice paddies. The highest in-stream nitrate concentrations (max: 4.1 mgN l ) occurred at river reaches located in the lower agricultural part of the catchment, affected by groundwater inputs. Groundwater nitrate concentrations were high (max: 7.4 mgN l ) owing to chemical fertilizer leaching from dryland fields forced by monsoonal rainfalls. Overall, this study demonstrates that the hydrologic dynamics resulting from the monsoonal climate drive the in-stream DOC dynamics in the forested 1st-order catchment whereas sources and mobilization of DOC in downstream agricultural areas are mainly controlled by the prevailing land-use type and irrigation management. Nitrate dynamics in higher order agricultural streams and their connected aquifers reflect combined effects of land-use type and monsoonal hydrology.
    Keywords: Nitrate ; Dissolved Organic Carbon ; Monsoonal-Type Climate ; Land-Use Type ; River-Aquifer Exchange Dynamics ; Topography ; Geography
    ISSN: 0022-1694
    E-ISSN: 1879-2707
    Source: ScienceDirect Journals (Elsevier)
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  • 7
    In: Water Resources Research, January 2017, Vol.53(1), pp.779-798
    Description: In this study, we investigate the impact of single stream discharge events on water exchange, solute transport, and reactions in the hyporheic zone below a natural in‐stream gravel bar. We set up a reactive transport groundwater model with streamflow scenarios that vary by event duration and peak discharge. A steady ambient groundwater flow field is assumed that results in losing, neutral, or gaining stream conditions depending on the stream stage. Across the streambed dissolved oxygen, organic carbon, and nitrate are transported into the subsurface. Additional nitrate is received from upwelling groundwater. Aerobic respiration and denitrification are simulated for scenarios with different stream solute concentrations. Results show that hyporheic exchange flux, solute transport, and consumption increase during events. However, their intensities depend highly on the interplay between event characteristics and ambient groundwater conditions. During events where reversals in the hydraulic gradient occur stream water and solutes infiltrate deeper into the aquifer where they have more time to react. For those events, the reactive efficiency of the hyporheic zone (solute consumption as fraction of influx) for aerobic respiration and denitrification is up to 2.7 and 10 times higher compared to base flow conditions. The fraction of stream nitrate load consumed in the hyporheic zone increases with stream discharge (up to 150 mg/m/h), but remains below the value under base flow conditions for weak events. Events also increase denitrification of groundwater borne nitrate, but groundwater nitrate flux to the stream decreases by up to 33% due to temporary gradient reversals. Transient reactive transport groundwater model of the hyporheic zone for various single discharge events Aerobic respiration and denitrification occur at different timing and locations in the hyporheic zone Reversal in hydraulic gradient direction (gaining to neutral to losing) significantly increases reactive efficiency
    Keywords: Hyporheic Zone ; Discharge Events ; Transient Groundwater Model ; Reactive Transport ; Denitrification
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 8
    Language: English
    In: Advances in Water Resources, 2010, Vol.33(11), pp.1291-1295
    Description: Interest in groundwater (GW)-surface water (SW) interactions has grown steadily over the last two decades. New regulations such as the EU Water Framework Directive (WFD) now call for a sustainable management of coupled ground- and surface water resources and linked ecosystems. Embracing this mandate requires new interdisciplinary research on GW-SW systems that addresses the linkages between hydrology, biogeochemistry and ecology at nested scales and specifically accounts for small-scale spatial and temporal patterns of GW-SW exchange. Methods to assess these patterns such as the use of natural tracers (e.g. heat) and integrated surface-subsurface numerical models have been refined and enhanced significantly in recent years and have improved our understanding of processes and dynamics. Numerical models are increasingly used to explore hypotheses and to develop new conceptual models of GW-SW interactions. New technologies like distributed temperature sensing (DTS) allow an assessment of process dynamics at unprecedented spatial and temporal resolution. These developments are reflected in the contributions to this Special Issue on GW-SW interactions. However, challenges remain in transferring process understanding across scales. ►Rapidly growing interest in groundwater-surface water exchange processes. ►Research on groundwater-surface water interactions has become multidisciplinary. ►New focus on linkages between hydrology, biogeochemistry and ecology. ►Development of new methods and models to quantify spatial and temporal patterns. ►Challenges remain in transferring process understanding across scales.
    Keywords: Groundwater-Surface Water Interactions ; River-Aquifer Exchange ; Engineering
    ISSN: 0309-1708
    E-ISSN: 1872-9657
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  • 9
    In: Water Resources Research, March 2018, Vol.54(3), pp.2317-2335
    Description: The analysis of transit/residence time distributions (TTDs and RTDs) provides important insights into the dynamics of stream‐water ages and subsurface mixing. These insights have significant implications for water quality. For a small agricultural catchment in central Germany, we use a 3D fully coupled surface‐subsurface hydrological model to simulate water flow and perform particle tracking to determine flow paths and transit times. The TTDs of discharge, RTDs of storage and fractional StorAge Selection (fSAS) functions are computed and analyzed on daily basis for a period of 10 years. Results show strong seasonal fluctuations of the median transit time of discharge and the median residence time, with the former being strongly related to the catchment wetness. Computed fSAS functions suggest systematic shifts of the discharge selection preference over four main periods: In the wet period, the youngest water in storage is preferentially selected, and this preference shifts gradually toward older ages of stored water when the catchment transitions into the drying, dry and wetting periods. These changes are driven by distinct shifts in the dominance of deeper flow paths and fast shallow flow paths. Changes in the shape of the fSAS functions can be captured by changes in the two parameters of the approximating Beta distributions, allowing the generation of continuous fSAS functions representing the general catchment behavior. These results improve our understanding of the seasonal dynamics of TTDs and fSAS functions for a complex real‐world catchment and are important for interpreting solute export to the stream in a spatially implicit manner. Transit times of discharge strongly related to storage Strong seasonality in discharge selection preference Seasonally changing SAS functions are well captured by Beta distributions
    Keywords: Transit Time ; Subsurface Mixing ; Sas Functions
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 10
    In: Journal of Geophysical Research: Biogeosciences, May 2014, Vol.119(5), pp.910-928
    Description: At the interface between stream water, groundwater, and the hyporheic zone (HZ), important biogeochemical processes that play a crucial role in fluvial ecology occur. Solutes that infiltrate into the HZ can react with each other and possibly also with upwelling solutes from the groundwater. In this study, we systematically evaluate how variations of gaining and losing conditions, stream discharge, and pool‐riffle morphology affect aerobic respiration (AR) and denitrification (DN) in the HZ. For this purpose, a computational fluid dynamics model of stream water flow is coupled to a reactive transport model. Scenarios of variations of the solute concentration in the upwelling groundwater were conducted. Our results show that solute influx, residence time, and the size of reactive zones strongly depend on presence, magnitude, and direction of ambient groundwater flow. High magnitudes of ambient groundwater flow lower AR efficiency by up to 4 times and DN by up to 3 orders of magnitude, compared to neutral conditions. The influence of stream discharge and morphology on the efficiency of AR and DN are minor, in comparison to that of ambient groundwater flow. Different scenarios of O and NO concentrations in the upwelling groundwater reveal that DN efficiency of the HZ is highest under low upwelling magnitudes accompanied with low concentrations of O and NO. Our results demonstrate how ambient groundwater flow influences solute transport, AR, and DN in the HZ. Neglecting groundwater flow in stream‐groundwater interactions would lead to a significant overestimation of the efficiency of biogeochemical reactions in fluvial systems. Coupling of CFD model to reactive transport model Losing and gaining conditions reduce aerobic respiration and denitrification HZ has higher potential for aerobic respiration compared to denitrification
    Keywords: Hyporheic Zone ; Pool‐Riffle ; Streambed ; Reactive Transport Modeling ; Denitrification
    ISSN: 2169-8953
    E-ISSN: 2169-8961
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