APPLICATION OF A GIS-BASED NONPOINT-SOURCE NUTRIENT LOADING MODEL FORASSESSMENT OF LAND-DEVELOPMENT SCENARIOS AND WATER-QUALITY IN OWASCO LAKE, NEW-YORK

The magnitude and water quality implications of nonpoint source phosph orus loadings to Owasco Lake (New York) are evaluated through the appl ication of a methodology which links geographic characteristics, long- term average runoff loads and a set of critical lakewide water quality response parameters. The approach utilizes the Universal Soil Loss Eq uation together with empirical loading functions to derive representat ive phosphorus export coefficients for the local drainage system. Cumu lative loadings from individual sub-basins within the watershed serve as input to a simple water quality model of Owasco Lake, showing the e xpected lake response in terms of average total phosphorus concentrati ons, trophic state, water transparancy, and minimum hypolimnetic disso lved oxygen concentration. The methodology facilitates easy and rapid assessment of general watershed management and development scenarios o f interest. A unique aspect of the approach is its dependence upon des criptive data supplied by a Geographic Information System (GIS) to est ablish the coincidence of specific land use, soil texture and surface slope attributes within each of the hydrologic sub-basins comprising t he overall watershed. The GIS-generated attribute matrices provide a m uch more accurate depiction of critical geographic characteristics kno wn to impact nonpoint source runoff loadings, thereby improving the re liability of current and projected phosphorus loads to Owasco Lake.