Imaging hyporheic zone solute transport using electrical resistivity

Traditional characterization of hyporheic processes relies upon modelling observed in-stream and subsurface breakthrough curves to estimate hyporheic zone size and infer exchange rates. Solute data integrate upstream behaviour and lack spatial coverage, limiting our ability to accurately quantify spatially heterogeneous exchange dynamics. Here, we demonstrate the application of near-surface electrical resistivity imaging (ERI) methods, coupled with experiments using an electrically conductive stream tracer (dissolved NaCl), to provide in situ imaging of spatial and temporal dynamics of hyporheic exchange. Tracer-labelled water in the stream enters the hyporheic zone, reducing electrical resistivity in the subsurface (to which subsurface ERI is sensitive). Comparison of background measurements with those recording tracer presence provides distributed characterization of hyporheic area (in this application, ∼0·5 m2). Results demonstrate the first application of ERI for two-dimensional imaging of stream-aquifer exchange and hyporheic extent. Future application of this technique will greatly enhance our ability to quantify processes controlling solute transport and fate in hyporheic zones, and provide data necessary to inform more complete numerical models. Copyright  2010 John Wiley & Sons, Ltd.