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.

平衡农业生产与其他生态系统服务是一项棘手的挑战。在威斯康星州南部的 Yahara 河流域，农民、政策制定者和广大市民之间的紧张局势加剧，因为少数人的农业实践造成的养分流失导致许多人的地表水受到损害。减少粪肥和化肥的施用，以及增加多年生草的覆盖，已被提议作为潜在的解决方案。使用 Agro-IBIS 农业生态系统模型，我们研究了到 2070 年 Yahara 河流域未来土地管理和气候的 48 个情景。情景包括在替代气候轨迹下牲畜减少和多年生草地增加的组合。结果表明，照常营业将导致环境进一步恶化，水道的磷负荷在基线、温暖和干燥以及温暖和潮湿的气候下分别增加 13%、7% 和 23%。流域范围内的磷产量和硝酸盐浸出量可减少 50%，但前提是养分施用量减少 50%，草地覆盖率增加 50%。此外，在最有可能的未来气候下实施改良的土地管理做法 50 年后，水质的改善才得以实现。我们的研究结果强调，在不断变化的气候下改善水质将需要长期投资以及对当前农业用地和土地覆盖的变革。