Agricultural Landscape Transformation Needed to Meet Water Quality Goals in the Yahara River Watershed of Southern Wisconsin

Balancing agricultural production with other ecosystem services is a vexing challenge. The Yahara River watershed in southern Wisconsin is a place where tensions among farmers, policymakers, and citizens at-large run high because nutrient loss from the agricultural practices of a few drive the impairment of surface waters for many. Reducing manure and fertilizer application, as well as increasing perennial grass cover have been proposed as potential solutions. Using the Agro-IBIS agroecosystem model, we examined 48 scenarios of future land management and climate for the Yahara River watershed to the year 2070. Scenarios included combinations of reduced livestock and increased perennial grassland under alternative climate trajectories. Results suggested that business as usual will lead to further environmental degradation with phosphorus-loading to waterways increasing 13, 7, and 23% under baseline, warmer and drier, and warmer and wetter climates, respectively. Watershed-wide phosphorous yield and nitrate leaching could be reduced by 50%, but only when nutrient application was reduced 50% and grassland cover was increased 50%. Furthermore, water quality improvements only materialized 50 years after modified land management practices were implemented under the most likely future climate. Our findings highlight that improving water quality under a changing climate will require long-term investment and transformative changes to current agricultural land use and land cover. Agricultural management solutions exist but are unlikely to be implemented without policies that incentivize transformative agricultural change.