The Origins and Dynamics of Phosphorus in Maine’s Lake Auburn Watershed

Land-use change and climate change-induced phosphorus (P) loading is a key driver of eutrophication in temperate lakes, including in Lake Auburn, the drinking water supply for more than 60,000 people in Lewiston and Auburn, Maine. Without decisive action to halt declining water quality, the cities could lose their EPA water filtration waiver and be required to build a $45+ million filtration plant within the next decade. Reversing the decline in water quality requires the identification of P loading hotspots and the development of targeted intervention strategies which maximize impact, minimize required staff time, and conserve scarce municipal resources. An examination of data collected since 2005 by the Auburn Water District/Lewiston Water Division (AWD/LWD) reveals that P concentrations in most Lake Auburn inlets have increased slightly in the past 15 years and are currently high enough to be of concern. Using the USDA\u27s Soil and Water Assessment Tool (SWAT), the 2019 P load was estimated to be 1671 kg, an increase of 198% from the estimated 1980 load of 560 kg. This increase reflects dramatic changes in land use and climate in the watershed over the past four decades. The P load is predicted to increase by an additional 66% to 2768 kg under the most-likely projected climate change and watershed development scenario. Thus, a rapid and sustained response is needed to avert regular summertime hypoxia. These results allow for a more nuanced understanding of current sources of P, as well as a prediction of where additional future loading is likely to originate, which will allow lake managers to both identify the most urgent and cost-effective solutions to current loading, and proactively implement measures to mitigate future loading