Export mechanisms for dissolved organic carbon and nitrate during summer storm events in a glaciated forested catchment in New York, USA

Nitrate and dissolved organic carbon (DOC) concentrations during a summer storm for a forested catchment in the Adirondack Mountains displayed a clear separation in trajectories and timing of maximum values. Nitrate concentrations peaked early on the rising limb of the hydrograph, whereas DOC concentrations gradually increased through the rising limb with maximum concentrations following the discharge peak. Solute data from precipitation, throughfall, soilwater, and ground/till water indicated till water and near-surface soil waters as the controlling end members for stream NO3- and DOC concentrations respectively. Streamflow concentrations of major base cations (Ca2+ and Mg2+), which were assumed to represent water originating from deep flow paths, matched the NO3- trajectory. These data suggest that streamflow NO3- concentrations are derived from till groundwater and that DOC is derived from near-surface soil waters. We attributed the early expression of NO3- to the displacement of till waters by infiltrating precipitation. In contrast, we hypothesized that the delayed DOC concentrations occurred with surface and near-surface runoff from near-stream wetlands/peatlands and isolated saturated areas that became connected only under conditions of maximum water content in the catchment. Copyright (C) 2004 John Wiley Sons, Ltd.