Agriculture intensification in Northeast US to meet food demands of the growing population must be sustainable, balanced against the pressure to continually improve water quality for use by that same population. Climate models predict increases in temperature and precipitation in the Northeast throughout the 21st century, further complicating temporal planning toward agricultural sustainability. As of 2017, highly productive agricultural regions within the Upper Chesapeake Bay Basin struggled to meet nutrient reduction goals set by the USEPA Total Maximum Daily Load (TMDL) for the Bay. We evaluated historic and future trends and variations in nutrient loadings from an agricultural watershed in southeastern PA under two land use scenarios: A) locally-detailed baseline management from 2007-2014, and B) the PA phase II Watershed Implementation Plan for meeting the TMDL goals. Both scenarios were represented with spatially and temporally detailed agricultural management in a variable source area version of the Soil and Water Assessment Tool and simulated over 2000-2100 using nine climate forecasting models. Under baseline management, we predicted that nitrogen, phosphorus, and sediment loadings will rise by 0.12, 0.04, and 40 kg/ha/year, respectively, over the 21st century. Under historic climate estimates, scenario B provides watershed-wide average reductions of 16%, 25%, and 33% in nitrogen, phosphorus and sediment loadings, respectively. Predictions maintain this reduction level until the 2030’s, but suggest significant reduction decrease for N and sediment loadings near the 2070’s. Findings from this study highlight the value of customizing land use plans to local physiographic and climate conditions, to reduce pollutant loadings.
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