Determination of critical source areas for phosphorus loss: Lake champlain basin, vermont

Lake Champlain, located between Vermont, New York, and Quebec, exhibits eutrophication due to continuing phosphorus (P) inputs from upstream nonpoint-source areas. To address the effects of this eutrophication and as part of total maximum daily load (TMDL) requirements, state-level P reduction goals have been established by both the Vermont and New York Departments of Environmental Conservation. Unfortunately, remedial measures undertaken thus far have been mostly based on voluntary participation by the landowners and have not been guided by a systematic technique to implement remedial measures where they could provide the greatest P loss reduction. Consequently, P reduction goals have not been achieved in most segments of Lake Champlain. The main objective of this study was to identify and quantify critical source areas (CSAs) of P loss using a model-based approach. The Soil and Water Assessment Tool (SWAT) is used for this objective. This study focuses on the Rock River watershed, which is one of the highest contributors of P to Lake Champlain. Spread over 71 km ², the watershed is dominated by dairy agriculture and has fertile periglacial lacustrine and alluvial soils with an old tile drainage system. In this agriculture-dominated watershed, 80% of total P loss occurs from only 24% of the watershed area, signifying the need for focused remedial measures on CSAs of P loss. The identification of CSAs for P loss is expected to support the next phase of our project, which involves exploring cost-effective P management strategies with the highest potential for P loss reduction applicable to the study watershed and Lake Champlain basin.