NUTRIENT RETENTION IN RIPARIAN ECOTONES

Nutrient retention mechanisms in riparian buffer strips are reviewed w ith emphasis on surface runoff and subsurface flows, the main pathways of exchanges between the stream and its surroundings. Unique physical and biogeochemical properties prevailing in these riparian ecotones d ictate the flux of water, nutrients and other exogenous substances bet ween the upland areas and the stream. Removal of nutrients from surfac e inflows is induced by deposition of sediment bound nutrients and exc hange of dissolved nutrients with the soil/litter surface. Removal of nitrogen in subsurface flows can partly be explained by vegetation upt ake, but the main mechanism for removal is usually denitrification. In channelized streams, the subsurface inflows have, in most cases, been altered to discharges via drainage tiles, with the exchange flows (wa ter leaving and re-entering the open-channel via the stream bed and ba nks) being greatly decreased. Consequently, to improve nitrogen remova l in these systems, these flows have to be intercepted or reestablishe d either through restoration of the old stream valley or through manag ed structures in the buffer strips.