Chemical‐hydrologic interactions in the near‐stream zone

Abstract

The chemical and hydrologic responses of a 9.9‐ha Pennsylvania hill‐land watershed to a typical summer storm event were determined and compared. Patterns and the relative magnitudes of NO 3 , NH 4 , total phosphorus (P), and orthophosphate (PO 4 ) concentrations observed in seepage, surface runoff, storm flow, base flow, and rainfall fit those hypothesized from the storm hydrograph and associated water table responses observed in the near‐stream zone. Nitrate concentrations in seepage and base flow were similar and, typically, exceeded those in surface runoff, rainfall, and peak storm flow by 5–20 times. Conversely, NH 4 , total P, and PO 4 concentrations in surface runoff from the seep zone and in peak storm flows exceeded those in seepage and base flow by 2–20 times. The findings, presented in a hydrologically based framework for this watershed, provide a conceptual model of how the near‐storm zone operates during and following storm events.