A field comparison of multiple techniques to quantify groundwater–surface-water interactions

Abstract

Groundwater-surface-water (GW-SW) interactions in streams are difficult to quantify because of heterogeneity in hydraulic and reactive processes across a range of spatial and temporal scales. The challenge of quantifying these interactions has led to the development of several techniques, from centimeter-scale probes to whole-system tracers, including chemical, thermal, and electrical methods. We co-applied conservative and smart reactive solute-tracer tests, measurement of hydraulic heads, distributed temperature sensing, vertical profiles of solute tracer and temperature in the stream bed, and electrical resistivity imaging in a 450-m reach of a 3 rd -order stream. GW-SW interactions were not spatially expansive, but were high in flux through a shallow hyporheic zone surrounding the reach. NaCl and resazurin tracers suggested different surface-subsurface exchange patterns in the upper ⅔ and lower ⅓ of the reach. Subsurface sampling of tracers and vertical thermal profiles quantified relatively high fluxes through a 10-to 20-cm deep hyporheic zone with chemical reactivity of the resazurin tracer indicated at 3-, 6-, and 9-cm sampling depths. Monitoring of hydraulic gradients along transects with MINI-POINT streambed samplers starting ∼40 m from the stream indicated that groundwater discharge prevented development of a larger hyporheic zone, which progressively decreased from the stream thalweg toward the banks. Distributed temperature sensing did not detect extensive inflow of ground water to the stream, and electrical resistivity imaging showed limited large-scale hyporheic exchange. We recommend choosing technique(s) based on: 1) clear definition of the questions to be addressed (physical, biological, or chemical processes), 2) explicit identification of the spatial and temporal scales to be covered and those required to provide an appropriate context for interpretation, and 3) maximizing generation of mechanistic understanding and reducing costs of implementing multiple techniques through collaborative research.

River corridor science: Hydrologic exchange and ecological consequences from bedforms to basins

“…As a result many investigators are attempting to broaden detection by combining several approaches, each better suited for a particular time scale or spatial scale. This approach adds expense and logistical complications, but pays back in the greater understanding of relative contributions from different types of hydrologic exchange fluxes and how they contribute to ecologically meaningful outcomes such as stream metabolism [ González‐Pinzón et al ., ].…”

Combined use of thermal methods and seepage meters to efficiently locate, quantify, and monitor focused groundwater discharge to a sand‐bed stream

“…Temporally evolving physical features, such as meander bends, bar forms, pool‐riffle sequences [ Käser , ; Tonina and Buffington , ], and highly transient ripples and moving bedforms [ Käser et al ., ] grow and shrink at multiple temporal and spatial scales. This continually evolving porous medium imparts nested hyporheic‐scale exchange superimposed on longer flowpaths that confounds determination of larger‐scale distribution of groundwater discharge to a stream or river [ González‐Pinzón et al ., ; Hatch et al ., ; Karan et al ., ; Menció et al ., ; Rosenberry and Pitlick , ]. In addition to diffuse groundwater discharge controlled by reach‐scale hydraulic gradients and geologic properties, groundwater discharge also is focused in discrete areas where flow is orders of magnitude faster than diffuse flow [ Hare et al ., ; Kidmose et al ., ].…”

Determination of hyporheic travel time distributions and other parameters from concurrent conservative and reactive tracer tests by local‐in‐global optimization

“…Resazurin is a weakly fluorescent, phenoazine dye [ O'Brien et al ., ], which is transformed into the reaction product resorufin by metabolically active bacteria in the hyporheic zone. The resazurin‐to‐resorufin transformation can thus be used as a proxy for microbial activity, particularly aerobic respiration [ O'Brien et al ., ; González‐Pinzón et al ., , , ]. In order to quantify the reactivity of the metabolically active transient‐storage zone and its exchange with the stream, reactive transport models are fitted to concentration time series of the conservative and reactive tracers as well as the reaction product.…”