DETECTING CHANGES IN WATER QUALITY IN THE LAPLATTE RIVER WATERSHED FOLLOWING IMPLEMENTATION OF BMPS

Abstract

The LaPlatte River Watershed in northwestern Vermont is the focus of an intensive land treatment program to control agricultural runoff and a long-term monitoring program to evaluate the effect of these treatments on water quality. Best Management Practices for controlling dairy manure and cropland erosion have been implemented on 90 percent of the priority areas in the Watershed. The 11-year monitoring program includes precipitation and streamflow recording and water sampling for suspended solids, phosphorus, and nitrogen analysis. Interpretation of monitoring data is confounded by incremental implementation of best management practices, climatic and hydrologic variation, and lack of pre-implementation water quality data. Application of four exploratory trend analysis techniques to six years of data from one monitored subwatershed is described. These techniques are (1) linear regression against time; (2) comparison of annual means; (3) analysis of frequency distributions; and (4) paired watershed regression. Results of these analyses suggest significant decreases in sediment and nutrient concentrations and loads since the project began.