Chemical fluxes between catchments and streams are influenced by biogeochem
ical processes in the groundwater-stream water (GW-SW) ecotone, the interfa
ce between stream surface water and groundwater. Terminal electron acceptin
g processes (TEAPs) that are used in respiration of organic C in anoxic env
ironments may have a strong effect on nutrient dynamics and water chemistry
. Concentrations of oxidized and reduced forms of terminal electron accepte
rs (dissolved O-2, NO3-, Fe2+, SO42-, and CH4) were measured in networks of
vertically nested wells installed beneath the surface stream and in the ne
ar-stream aquifer of a headwater catchment. Tracer addition experiments wer
e conducted in surface and groundwater environments of a Ist-order montane
stream to characterize hydrologic fluxes between the stream and aquifer, an
d to quantify ecosystem retention of terminal electron accepters (NO3- and
SO42-) in the GW-SW ecotone. Sulfate retention was evident in both hyporhei
c and groundwater environments. Distribution of important redox sensitive s
olutes varied predictably with changing hydrologic residence time of water
in the GW-SW ecotone. Results suggest a strong hydrologic control of TEAPs
and ecosystem retention of biologically important solutes in the GW-SW ecot
one related to characteristics of GW-SW mixing and residence time of water
in the hyporheic zone.