Abstract
Traditional characterization of hyporheic processes relies upon modelling observed inโstream 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 nearโsurface 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. Tracerโlabelled 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, โผ0ยท5 m^2^). Results demonstrate the first application of ERI for twoโdimensional imaging of streamโaquifer 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 ยฉ 2010 John Wiley & Sons, Ltd.