Water quality is affected by croplands. The Conservation Reserve Program (CRP), where farmers convert croplands to natural land cover (e.g., trees), is expected to improve water quality. However, whether such improvements are achieved alongside cropland area change has not been verified at river-basin scales, due to challenges in large scale observations. Therefore, aiming to quantify the relationship between CRP enrollment, cropland area, and the downstream water quality, we propose an approach that combines archived survey data, water quality monitoring data (total nitrogen content, TN), and remote sensing observations. By constructing the long-term datasets (1999–2014 annually) in Google Earth Engine and conducting multiple linear regression, we explained 79% variation in TN by the area of total CRP enrollment (CRP_all), area of corn and soybeans croplands, and discharge. Moreover, 78% is explained if we consider only water quality targeted conservation practices (CRP_WQ). Our results indicate significant positive correlation between CRP enrollment (both CRP_all and CRP_WQ) and the downstream water quality. Nevertheless, it should be noted that correlation does not necessarily represent causation. While this pioneer effort of quantifying impacts of the CRP on water quality from large scale observations has achieved some success, we call for more research to expand the spatial and/or temporal scales and consider more water quality variables, so as to further enhance our understanding of the coupled natural-and-human system.

水质受到农田的影响。预计保护储备计划（CRP）可使农民将耕地转换成自然土地覆盖物（例如树木），从而改善水质。但是，由于大规模观测的挑战，尚未在河流流域范围内证实是否与耕地面积变化同时实现了这种改善。因此，为了量化CRP注册量，耕地面积和下游水质之间的关系，我们提出了一种将存档的调查数据，水质监测数据（总氮含量，总氮）和遥感观测资料相结合的方法。通过在Google Earth Engine中构建长期数据集（每年1999-2014年）并进行多元线性回归，我们解释了总CRP注册面积（CRP_all）TN的79％变化，玉米和大豆的耕地面积和排放量。此外，如果仅考虑以水质为目标的保护措施（CRP_WQ），可以解释78％。我们的结果表明，CRP注册量（CRP_all和CRP_WQ）与下游水质之间呈显着正相关。然而，应该指出的是，相关性不一定代表因果关系。尽管从大规模观测中量化CRP对水质影响的开创性工作取得了一些成功，但我们呼吁开展更多研究以扩大空间和/或时间尺度，并考虑更多水质变量，以进一步增进我们的理解。自然与人类系统的耦合。我们的结果表明，CRP注册量（CRP_all和CRP_WQ）与下游水质之间呈显着正相关。然而，应该指出的是，相关性不一定代表因果关系。尽管从大规模观测中量化CRP对水质影响的开创性工作取得了一些成功，但我们呼吁开展更多研究以扩大空间和/或时间尺度，并考虑更多水质变量，以进一步增进我们的理解。自然与人类系统的耦合。我们的结果表明，CRP注册量（CRP_all和CRP_WQ）与下游水质之间呈显着正相关。然而，应该指出的是，相关性不一定代表因果关系。尽管从大规模观测中量化CRP对水质影响的开创性工作取得了一些成功，但我们呼吁开展更多研究以扩大空间和/或时间尺度，并考虑更多水质变量，以进一步增进我们的理解。自然与人类系统的耦合。