Focused Groundwater Controlled Feedbacks into the Hyporheic Zone During Baseflow Recession

Abstract

Groundwater surface water interaction in the hyporheic zone remains an important challenge for water resources management and ecosystem restoration. In heterogeneous stratified glacial sediments, reach-scale environments contain an uneven distribution of focused groundwater flow occurring simultaneously with diffusely discharging groundwater. This results in a variation of stream-aquifer interactions, where focused flow systems are able to temporally dominate exchange processes. The research presented here investigates the direct and indirect influences focused groundwater discharge exerts on the hyporheic zone during baseflow recession. Field results demonstrate that as diffuse sources of groundwater deplete during baseflow recession, focused groundwater discharge remains constant. During baseflow recession the hyporheic zone is unable to expand, while the high nitrate concentration from focused discharge changes the chemistry of the stream. The final result is a higher concentration of nitrate in the hyporheic zone as this altered surface water infiltrates into the subsurface. This indirect coupling of focused groundwater discharge and the hyporheic zone is unaccounted for in hyporheic studies at this time. Results indicate important implications for the potential reduction of agricultural degradation of water quality.

Assessing the importance of seepage and springs to nitrate flux in a stream network in the Wisconsin sand plains

“…We found evidence of focused groundwater discharge both among and within transects when seepage was estimated based on Darcy's Law. Several other investigators have observed a high degree of spatial variation in groundwater discharge (Binley et al, ; Lowry, Walker, Hunt, & Anderson, ; Malzone & Lowry, ; Rosenberry, Briggs, Delin, & Hare, ) or hydraulic conductivity (Genereux et al, ) in streambeds. Based on the finding of other investigators and our previous work in Emmons Creek (Stelzer, Drover, et al, ), the determination of focused discharge in the study reach was not surprising.…”

How does reach‐scale stream‐hyporheic transport vary with discharge? Insights from rSAS analysis of sequential tracer injections in a headwater mountain stream

“…However, the most common method used to characterize hyporheic exchange—the analysis of solute tracer breakthrough curves—has failed to identify consistent controls on hyporheic exchange under time‐variable hydrologic conditions [e.g., Ward et al ., ; Payn et al ., ]. To‐date, time‐variable hyporheic exchange has been reported in response to variable base flow conditions [ Ward et al ., ; Payn et al ., ; Ward et al ., ], diel fluctuations in discharge [ Loheide and Lundquist , ; Sawyer and Cardenas , ; Sawyer et al ., ; Wondzell et al ., ], and storm event responses [ Ward et al ., ; Malzone and Lowry , ; Schmadel et al ., ]. Several studies that include high replication in space or through storm events report that observed variations in reach‐scale tracer transport and inferred hyporheic exchange could not be explained by discharge alone [ Wondzell , ; Ward et al ., ; Payn et al ., ; Ward et al ., ].…”

Temporal Hyporheic Zone Response to Water Table Fluctuations

“…Elton Creek is a gaining stream; however, groundwater gradients are not high enough to contract the hyporheic zone completely. Heterogeneities in the sandy gravel deposit (clay lenses and gravel conduits) produce focused groundwater discharge in addition to diffuse groundwater discharge (Malzone and Lowry ). Pools and riffles comprise the majority of streambed topography with some steps and planar beds (Figure B).…”