Nutrient Enrichment, Water Clarity, and Ecological Risk in Lakes, Ponds, and Reservoirs of the Winooski River Basin

The Winooski River Basin is a watershed with a long history of eutrophication and associated ecological risk. This study evaluated nutrient dynamics, trophic state, and ecological risk across lakes, ponds, and reservoirs using a combination of water quality indicators and statistical analyses. Nutrient-related Risk Quotients (RQs) were used to quantify the extent to which observed conditions exceeded established ecological thresholds, enabling comparison of phosphorus, nitrogen, chlorophyll-a, and worst-case risk conditions across waterbodies. Results demonstrated that phosphorus is the primary driver of algal biomass, as evidenced by a strong relationship between total phosphorus (TP) and chlorophyll-a (Chl-a), as well as consistent patterns across trophic indices derived from the Carlson Trophic State Index. Trophic conditions ranged from oligotrophic to eutrophic, with most sites classified as oligotrophic to mesotrophic. Principal Component Analysis (PCA) revealed a dominant eutrophication gradient defined by TP, Chl-a, and water clarity, while secondary variation was associated with physicochemical conditions including temperature and dissolved oxygen (DO). Ecological risk assessment indicated that sites with elevated nutrient concentrations exhibited higher RQ values, with the worst-case metric (RQₘₐₓ) identifying moderate to high risk in several waterbodies. Overall, results demonstrate that nutrient enrichment—particularly phosphorus—and reduced water clarity are strongly associated with variation in ecological conditions across the basin. These findings underscore the importance of targeted nutrient management and watershed-scale processes in maintaining freshwater ecosystem health.