BMP IMPACTS ON WATERSHED RUNOFF, SEDIMENT, AND NUTRIENT YIELDS

To quantify the effectiveness of best management practice (BMP) implem entation on runoff, sediment, and nutrient yields from a watershed, th e Nomini Creek watershed and water quality monitoring project was init iated in 1985, in Westmoreland County, Virginia. The changes in nonpoi nt source (NPS) loadings resulting from BMPs were evaluated by compari ng selected parameters from data series obtained before, during, and a fter periods of BMP implementation. The results indicated that the wat ershed-averaged curve number, sediment, and nutrient (N and P) concent rations were reduced by approximately 5, 20, and 40 percent, respectiv ely, due to BMP implementation. The nutrient yield model developed by Frere et al. (1980) was applied to the water quality parameters from 1 75 storms, but it failed to adequately describe the observed phenomena . Seasonal changes in nutrient availability factors were not consisten t with field conditions, nor were they significantly different in the pre- and post-BMP periods. An extended period of monitoring, with inte nsive BMP implementation over a larger portion of the watershed, is re quired to identify BMP effectiveness.