FLOW AND NUTRIENT EXPORT PATTERNS FOR AN AGRICULTURAL HILL-LAND WATERSHED

Nutrient patterns and export in streamflow were determined for a 7.4-k m(2) agricultural hill-land watershed located in Pennsylvania. P expor t, whether associated with sediment or water phase, was dominated by s torm periods. About 70% of water phase P was exported during the 10% o f time defined as storm flow. P export during storms becomes less cont rolled by water phase P as the P fraction being exported is expanded f rom 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 exporte d in total flow. Nitrate export was mostly in nonstorm periods (60%) w ith the higher concentrations in elevated base flows. The elevated bas e flow appears to result from increased drainage from a shallow fractu re layer that underlays cropland. Because storm periods dominate P exp ort, control of the hydrologically active P source areas within the wa tershed provides the greatest opportunity for controlling export of al gal-available P.