Nutrient dynamics at the interface between surface waters and groundwaters

1. The surface water/groundwater (SW/GW) interface is a crucial control point for lateral nutrient ̄uxes between uplands and aquatic ecosystems and for upstream/ downstream (longitudinal) processes in lotic ecosystems. 2. Hydrological and biogeochemical dynamics of the SW/GW ecotone are linked to the degree of channel constraint and the sediment characteristics of the ̄oodplain and stream bed. 3. The availability of speci®c chemical forms of electron donors and electron acceptors affects the spatial distribution of biogeochemical processes at the SW/GW interface. Temporal change in discharge is also a major factor affecting the rate and extent of these processes. 4. The magnitude of SW/GW interactions in lotic ecosystems is predicted to be a major determinant of solute retention. Channel morphology, stream bed composition and discharge are predicted to be important controls on SW/GW interactions. 5. Interdisciplinary research involving hydrologists, geomorphologists, aquatic ecologists, microbial ecologists and landscape ecologists is needed to further our present understanding of this critical interface linking terrestrial and aquatic ecosystems.