MODELING WATER, SEDIMENT AND ORGANIC-CARBON DISCHARGES IN THE HUDSON-MOHAWK BASIN - COUPLING TO TERRESTRIAL SOURCES

A previous modeling study (Howarth et al. 1991) showed the potential o f a simple watershed hydrology model, the Generalized Watershed Loadin g Function model (GWLF, Haith and Shoemaker 1987) for estimating annua l loads of sediment and organic carbon to the Hudson River from variou s land uses in the upper portion of the basin. We examined the quality and accuracy of model outputs after making two major modifications. F irst, we used a geographic information system (GIS) and several enviro nmental databases to improve model estimates of several parameters. Se cond, we evaluated alternative methods for incorporating weather data. We examined seasonal variation of model output as well as annual aver ages. Annual fluxes increased over those of Howarth et al. (1991) by 1 0% for sediment and 20% for TOC for the Hudson-Mohawk basin, resulting in closer agreement with measurement-based estimates. The estimated f luxes exhibited a strong seasonal component, with greatest sediment lo ad occurring during a few spring events. Finally, model estimates of f luxes associated with forested and agricultural scenarios, characteris tic of earlier periods of the region's history, predicted a doubling o f sediment and TOC loading in an agriculturally dominated Hudson basin but a reduction of sediment by 90% and of TOC by 60% in a completely forested basin.