Preferential Flow in Riparian Groundwater: Gateways for Watershed Solute Transport and Implications for Water Quality Management

Abstract

AbstractRiparian zones are key gateways for solutes in watersheds, including nutrients and pollutants moving toward the stream network. In human‐dominated landscapes, they are widely used as buffers to remove pollutants at substantial cumulative cost yet vary widely in their effectiveness, and much is unknown about the detailed processes involved and their controls. Preferential flow is widespread in riparian zones, oriented both horizontally toward the channel (often bypassing beneficial reactions in the soil during baseflow) or vertically (enhancing beneficial reactions by infiltrating surface flow during storms). Preferential flow thus contributes to widespread variability of riparian zone/buffer function, with implications for legacy nutrients stored in upland soils and aquifers. This creates a disconnect between functional riparian definitions based on flow and transport processes and common operational ones based on buffer width. Enhanced field characterization of preferential flow path spatial distribution and connectivity, together with developments in simulating preferential solute transport in soils, would allow better prediction of spatial and temporal variation in riparian zone function. Such prediction in turn would allow improved buffer function by tailoring buffer design to site specific conditions, thereby reconciling functional and operational viewpoints.