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  • Krause, Stefan
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  • 1
    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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  • 2
    Language: English
    In: Advances in Water Resources, 2010, Vol.33(11), pp.1309-1319
    Description: Analytical solutions to the one-dimensional heat transport equation for steady-state conditions can provide simple means to quantify groundwater surface water exchange. The errors in exchange flux calculations that are introduced when the underlying assumptions of homogeneous sediments and constant temperature boundary conditions are violated were systematically evaluated in a simulation study. Temperatures in heterogeneous sediments were simulated using a numerical model. Heterogeneity in the sediments was represented by discrete, binary geologic units. High contrasts between the hydraulic conductivities ( ) of the geologic units were found to lead to large errors, while the influence of the structural arrangement of the units was smaller. The effects of transient temperature boundary conditions were investigated using an analytical equation. Errors introduced by transient boundary conditions were small for Darcy-velocities 〉 0.1 m d in the period near maximum and minimum annual surface water temperatures. For smaller fluxes, however, errors can be large. Assuming steady-state conditions and vertical flow in homogeneous sediments is acceptable at certain times of the year and for medium to high exchange fluxes, but pronounced geologic heterogeneity can lead to large errors.
    Keywords: Groundwater–Surface Water Interaction ; Streambed Temperatures ; Geologic Heterogeneity ; Heat Transport Modelling ; Engineering
    ISSN: 0309-1708
    E-ISSN: 1872-9657
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  • 3
    In: Water Resources Research, February 2014, Vol.50(2), pp.1847-1855
    Description: This paper introduces the special section on “new modeling approaches and novel experimental technologies for improved understanding of process dynamics at aquifer‐surface water interfaces.” It is contextualizing the framework for the 27 research papers of the special section by firth identifying research gaps and imminent challenges for ecohydrological research at aquifer‐surface water interfaces and then discussing the specific paper contributions on (i) new developments in temperature/heat tracing at GW‐SW interfaces, (ii) new methods to capture the temporal and spatial variability of groundwater—surface water exchange, (iii) new approaches in modeling aquifer‐river exchange flow, and (iv) new concepts and advanced theory of groundwater—surface water exchange.
    Keywords: Groundwater ; Surface Water ; Hyporheic Zones ; Lacustrine Groundwater Discharge
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 4
    Language: English
    In: Ecosystems, 2015, Vol.18(6), pp.1101-1120
    Description: Denitrification is the main process removing nitrate in river drainage basins and buffer input from agricultural land and limits aquatic ecosystem pollution. However, the identification of denitrification hotspots (for example, riparian...
    Keywords: Environmental Sciences ; Biodiversity and Ecology ; Denitrification ; Biogeochemical Hotspot ; Upscaling ; Residence Time Distribution ; Damköhler Ratio ; Diffuse Pollution Control ; Environmental Sciences ; Ecology
    ISSN: 1432-9840
    E-ISSN: 1435-0629
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  • 5
    In: Journal of Geophysical Research: Biogeosciences, March 2017, Vol.122(3), pp.628-644
    Description: Transient storage zones for water represent potential hot spots for metabolic activity in streams. In lowland rivers, the high abundance of submerged vegetation can increase water transient storage, bioreactive surface areas, and, ultimately, in‐stream metabolic activity. Changes in flow resulting from climatic and anthropogenic factors that influence the presence of aquatic vegetation can also, thereby, impact in‐stream metabolism and nutrient cycling. We investigated the effects of water column depth on aquatic vegetation cover and its implications on water transient storage and associated metabolic activity in stream mesocosms ( = 8) that represent typical conditions of lowland streams. Continuous injections of metabolically reactive (resazurin‐resorufin) tracers were conducted and used to quantify hydraulic transport and whole‐mesocosm aerobic respiration. Acetate, a labile carbon source, was added during a second stage of the tracer injection to investigate metabolic responses. We observed both higher vegetation coverage and resazurin uptake velocity, used as a proxy of mesocosm respiration, with increasing water column depth. The acetate injection had a slight, positive effect on metabolic activity. A hydrodynamic model estimated the water transport and retention characteristics and first‐order reactivity for three mesocosms. These results suggest that both the vegetated surface water and sediments contribute to metabolically active transient storage within the mesocosms, with vegetation having a greater influence on ecosystem respiration. Our findings suggest that climate and external factors that affect flow and submerged vegetation of lowland rivers will result in changes in stream respiration dynamics and that submerged vegetation is a particularly important and sensitive location for stream respiration. Ecosystem respiration is positively correlated with water depth, discharge, and vegetation coverage In‐stream vegetation beds are significant sites of metabolically active transient storage Declining stream flows may negatively impact aquatic vegetation and ecosystem function in lowland rivers
    Keywords: Resazurin ; Metabolism ; Ecosystem Respiration ; Transient Storage ; Lowland Rivers ; Vegetation
    ISSN: 2169-8953
    E-ISSN: 2169-8961
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  • 6
    In: Water Resources Research, April 2016, Vol.52(4), pp.3227-3245
    Description: Improved understanding of stream solute transport requires meaningful comparison of processes across a wide range of discharge conditions and spatial scales. At reach scales where solute tracer tests are commonly used to assess transport behavior, such comparison is still confounded due to the challenge of separating dispersive and transient storage processes from the influence of the advective timescale that varies with discharge and reach length. To better resolve interpretation of these processes from field‐based tracer observations, we conducted recurrent conservative solute tracer tests along a 1 km study reach during a storm discharge period and further discretized the study reach into six segments of similar length but different channel morphologies. The resulting suite of data, spanning an order of magnitude in advective timescales, enabled us to (1) characterize relationships between tracer response and discharge in individual segments and (2) determine how combining the segments into longer reaches influences interpretation of dispersion and transient storage from tracer tests. We found that the advective timescale was the primary control on the shape of the observed tracer response. Most segments responded similarly to discharge, implying that the influence of morphologic heterogeneity was muted relative to advection. Comparison of tracer data across combined segments demonstrated that increased advective timescales could be misinterpreted as a change in dispersion or transient storage. Taken together, our results stress the importance of characterizing the influence of changing advective timescales on solute tracer responses before such reach‐scale observations can be used to infer solute transport at larger network scales. Advection is the primary control on observed stream solute tracer responses The influence of spatial heterogeneity in morphology is muted by advection Interpretation of solute transport requires consideration of tracer timescales
    Keywords: Stream Solute Transport ; Transient Storage ; Conservative Tracer ; Storm Event ; Statistical Moments ; Advective Timescale
    ISSN: 0043-1397
    E-ISSN: 1944-7973
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  • 7
    Language: English
    In: Hydrological Processes, 15 July 2009, Vol.23(15), pp.2103-2107
    Description: Abstract not available.
    Keywords: Hydrology ; Hydrologic Analysis ; Hydrology ; Hydrology ; Interfaces ; Hydrology ; General ; General ; General ; General (556);
    ISSN: 0885-6087
    E-ISSN: 1099-1085
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  • 8
    Language: English
    In: Hydrological Processes, 15 July 2009, Vol.23(15), pp.2252-2263
    Description: Despite the widely accepted importance of the hyporheic zone as a habitat for stream macroinvertebrates during floods, few data exist regarding community composition and distribution during periods of low flow or drought in perennial streams. Integrating research on hyporheic invertebrates with results from a long‐term study of a UK river provided the opportunity to examine how benthic and hyporheic macroinvertebrate communities respond to inter‐annual variability in river flow and periods of groundwater drought. Changes in the riverine macroinvertebrate community associated with low flow included a reduction in species richness and the number of individuals per sample, particularly aquatic insects. The hyporheic community was characterized by a relatively homogeneous composition during a period of severe low flow, punctuated by short‐term changes associated with variation in water temperature rather than changes in discharge. We present a conceptual model of the processes influencing benthic and hyporheic invertebrates under low‐flow conditions. Previous studies have seldom integrated these two assemblages and their interactions. The model presented highlights the potential importance of surface water and hyporheic zone linkages for riverine invertebrate communities under a range of flow conditions. Copyright © 2009 John Wiley & Sons, Ltd.
    Keywords: Benthos ; Hyporheos ; Low Flows ; Drought ; Hyporheic Processes ; Invertebrates ; Groundwater
    ISSN: 0885-6087
    E-ISSN: 1099-1085
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  • 9
    Language: English
    In: Hydrological Processes, 15 July 2009, Vol.23(15), pp.2138-2149
    Description: Subsurface flow in streambeds can vary at different scales in time and space. Recognizing this variability is critical for understanding biogeochemical and ecological processes associated with the hyporheic zone. The aim of this study was to examine the variability of hydraulic conductivity (), vertical hydraulic gradients (VHGs), and subsurface fluxes, over a riffle–step–pool sequence and at a high spatio‐temporal resolution. A 20 m reach was equipped with a network of piezometers in order to determine the distribution of VHGs and . During a summer month, temporal variations of VHGs were regularly surveyed and, for a subset of piezometers, the water level was automatically recorded at 15 min intervals by logging pressure transducers. Additionally, point‐dilution tests were carried out on the same subset of piezometers. Whereas the distribution of vertical fluxes can be derived from and VHG values, point‐dilution tests allow for the estimation of horizontal fluxes where no VHG is detectable. Results indicate that, spatially, VHGs switched from upwelling to downwelling across lateral as well as longitudinal sections of the channel. Vertical fluxes appeared spatially more homogeneous than VHGs, suggesting that the latter can be a poor indicator of the intensity of flow. Finally, during flow events, some VHGs showed little or no fluctuations; this was interpreted as the result of a pressure wave propagating from upstream through highly diffusive alluvial sediments. Copyright © 2009 John Wiley & Sons, Ltd.
    Keywords: Hyporheic Exchange Flow ; Heterogeneity ; Hydraulic Conductivity ; Vertical Hydraulic Gradient ; Groundwater–Surface Water Interactions
    ISSN: 0885-6087
    E-ISSN: 1099-1085
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  • 10
    Language: English
    In: Hydrological Processes, 15 July 2009, Vol.23(15), pp.2212-2224
    Description: The hydrochemistry of sulphur in the active outwash plain of Skeiðarársandur, SE Iceland shows considerable variety reflecting differences in sources and processes, and is investigated in this article using δS values of dissolved sulphate and igneous sulphide minerals, δO, and ionic concentrations in waters. Seawater‐derived sulphate is a notable component only in the lower sandur (δS = +6·8‰ VCDT). δS in the Skeiðará glacial melt river range from +3·4 to +8·8‰δS. The higher values occur during a flood event and reflect geothermal sulphate contributions from the Grímsvötn caldera. ‘Kettle‐hole lakes’ formed since the November 1996 jökulhlaup form important ecological niches and show evidence of coupled sulphide oxidation and carbonate and possibly silicate dissolution and have the lowest δS values (average −0·8‰) attributed to higher proportions of sulphide oxidation‐derived SO and/or bacterially mediated sulphide oxidation. The hydrochemistry of eastern sandur groundwater is influenced by a hydrothermal source of reduced sulphur from the Grímsvötn caldera or a localized area of geothermal springs, and contrasts with the hydrochemistry of the majority of groundwaters and the Sulá and Gígjukvísl rivers in western and central Skeiðarársandur. These have lower [Ca + Mg], [Na + K] and SO concentrations and δS values consistent with sulphate derived from the oxidation of igneous sulphides. In comparison to catchments dominated by atmospherically transported sulphate, catchments such as this where the sulphur system is dominated by internal sources (rock‐derived and geothermal) will not be sensitive to the temporal decreasing trends in contributions from long‐range airborne sulphate resulting from reductions of sulphur emissions in North America and Europe. Copyright © 2009 John Wiley & Sons, Ltd.
    Keywords: Sulphur Isotopes ; Sulphate ; Kettle‐Hole Lakes ; Geothermal Water ; Jökulhlaups ; Chemical Weathering
    ISSN: 0885-6087
    E-ISSN: 1099-1085
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