Linking watershed and sub-basin characteristics to in-lake TP concentrations in the Lake Winnipesaukee watershed

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Tarpey, Patricia E.
As a key natural and economic resource for the state and local communities, degradation of the water quality of Lake Winnipesaukee would have a major impact on the entire NH tourism economy. Efforts to protect the water quality of Lake Winnipesaukee and its surrounding land area have challenged planners and decision makers for several decades. A primary concern for Lake Winnipesaukee is TP loading from the land into the lake and its impact on lake water quality. One of the difficulties in discerning problems with excessive TP loading for Lake Winnipesaukee is that, due to its size and volume, in-lake effects of TP loading like reduced clarity and algae blooms are slow to appear. The physical structure and shape of Lake Winnipesaukee has been described as more a system of interconnected bays rather than a single cohesive body of water. Utilizing established TP loading and in-lake response models, the differing characteristics, land-based influences and in-lake response to nutrient inputs were determined for the 10 Lake Winnipesaukee sub-watersheds to evaluate whether Lake Winnipesaukee should remain classified as one assessment unit for water quality reporting purposes to the U.S. EPA. Key findings of the analysis indicate that while approximately 18% of the study sub-watershed area is developed, the TP loading has shown a 2.5 to four-fold increase over pre-development conditions with a corresponding estimated increase in in-lake TP concentrations; the water quality of Paugus Bay is currently positively impacted by Lake Winnipesaukee; and although preliminary findings indicate that the lake should remain classified as one assessment unit, target goals for in-lake TP should be set at the sub-watershed level.