The need for effective water quality models to help guide management and policy, and extend monitoring information, is at the forefront of recent discussions related to watershed management. These models are often calibrated and validated at the basin outlet, which ensures that models are capable of evaluating basin scale hydrology and water quality. However, there is a need to understand where these models succeed or fail with respect to internal process representation, as these watershed-scale models are used to inform management practices and mitigation strategies upstream. We evaluated an ensemble of models—each calibrated to in-stream observations at the basin outlet—against discharge and nutrient observations at the farm field scale to determine the extent to which these models capture field-scale dynamics. While all models performed well at the watershed outlet, upstream performance varied. Models tended to over-predict discharge through surface runoff and subsurface drainage, while under-predicting phosphorus loading through subsurface drainage and nitrogen loading through surface runoff. Our study suggests that while models may be applied to predict impacts of management at the basin scale, care should be taken in applying the models to evaluate field-scale management and processes in the absence of data that can be incorporated at that scale, even with the use of multiple models.

需要有效的水质模型来帮助指导管理和政策，并扩展监测信息，这是与流域管理有关的最新讨论的重中之重。这些模型通常在流域出口处进行校准和验证，从而确保模型能够评估流域规模的水文学和水质。但是，由于这些分水岭规模模型用于向上游的管理实践和缓解策略提供信息，因此有必要了解这些模型在内部过程表示方面成功或失败的地方。我们评估了一组模型（每个模型都根据流域出口处的流内观测值进行了校准），针对农田规模的排放量和养分观测值进行了确定，以确定这些模型在多大程度上捕获了田间规模动态。尽管所有模型在分水岭出口处均表现良好，但上游性能却有所不同。模型倾向于高估通过地表径流和地下排水的流量，而低估通过地表排水的磷负荷和通过地表径流的氮负荷。我们的研究表明，尽管可以将模型用于预测流域规模管理的影响，但在缺乏可以整合到该规模的数据的情况下，应谨慎应用模型来评估流域规模的管理和流程。使用多种模型。