NONPOINT SOURCE POLLUTION ASSESSMENT USING A NESTED WATERSHED APPROACH

The Little Chazy River watershed in northeastern New York, like other medium-sized (100 to 200 km²) watersheds in the Champlain Lowland, exhibit increased phosphorus loadings to Lake Champlain, in spite of agricultural best management practices. The upper sections of the watershed are predominantly forested, transitioning to predominantly agricultural lands in the lower watershed.

The Little Chazy River watershed was divided into fifteen subwatersheds to isolate nutrient loadings from different areas. Outflows from nine subwatersheds on the mainstream and major tributaries were recorded at 15-minute intervals using TruTrack WT-HR water level and temperature dataloggers. Nutrient chemistry and outflow for 6 additional first-order agricultural tributaries were measured manually. Daily phosphorus loadings were determined for gaged watershed outflows, with upstream contributions subtracted out for each stream reach. Unit loadings for each subwatershed were calculated by dividing total loading by subwatershed area.

Unit subwatershed nutrient loadings were low in the upper, forested segments, increasing in some of the lower agricultural main branch segments. Nutrient loadings for first-order agricultural tributaries, however, were generally low, in spite of high concentrations, due to their low discharge. The lowermost subwatershed on the main branch, which includes the village of Chazy, a publicly owned treatment works, and a large farm with attendant manure handling facilities, had very high loadings. This subwatershed was later subdivided to isolate these effects, with preliminary data suggesting that the largest proportion of these increases arose from areas near the manure holding facilities. This study was funded by the National Science Foundation Research for Undergraduates Program.