Flow and nutrient export patterns for an agricultural hill‐land watershed

Nutrient patterns and export in streamflow were determined for a 7.4‐km 2 agricultural hill‐land watershed located in Pennsylvania. P export, whether associated with sediment or water phase, was dominated by storm periods. About 70% of water phase P was exported during the 10% of time defined as storm flow. P export during storms becomes less controlled by water phase P as the P fraction being exported is expanded from labile P (50–70%) to algal‐available P (20–40%) to total P (10–20%). Water phase P accounted for 25–50% of the algal‐available P exported in total flow. Nitrate export was mostly in nonstorm periods (60%) with the higher concentrations in elevated base flows. The elevated base flow appears to result from increased drainage from a shallow fracture layer that underlays cropland. Because storm periods dominate P export, control of the hydrologically active P source areas within the watershed provides the greatest opportunity for controlling export of algal‐available P.