Hydrogeochemical Response of a Forested Watershed to Storms: Effects of Preferential Flow Along Shallow and Deep Pathways

Abstract

Hydrology and solute chemistry were monitored during four storms in a forested watershed in karst terrain in eastern Tennessee at spatial scales ranging from a 0.5‐ha upper hillslope subcatchment to a 38.4‐ha watershed drained by a first‐order stream. Storm flow was generated from large portions of the watershed as a result of subsurface preferential flow initiated by zones of perched saturation in the soil profile. For most storms, runoff per unit area increased with increasing catchment size, indicating that preferential flow was primarily vertical along relatively deep pathways that emerged in the lower portions of the watershed. However, when antecedent soil moisture was high and rainfall was large, runoff was similar across catchment sizes, indicating that preferential flow was largely lateral along shallow paths (4, and dissolved organic carbon and lower exports of alkalinity, Ca, Mg, and soluble reactive phosphorus than an equivalent amount of runoff generated by preferential flow via deeper flow paths.