Abstract It is understood that the major transport pathways for the soluble nutrients nitrate (NO3-N) and orthophosphorus (OP) from cropped fields to streams in the U.S. Cornbelt are tile drainage and groundwater seepage. The relative contribution of each, however, has not been well quantified and can vary between fields and watersheds. In this study, we used intermittent grab sample water quality monitoring and tile flow measurements, and the groundwater model MODFLOW to source dissolved nutrients from a cropped field to a low-order stream in the intensively-drained and cropped Des Moines Lobe landform of north central Iowa. Based on monitoring of eight tile outlets, nine groundwater wells and the receiving stream over a two-year period, nutrient loads from tiles were found to contribute approximately 98 % of the nitrate load to Hardin Creek. The loading pattern for OP was also dominated by discharge from constructed drainage, with 99.7 % sourced back to field tiles. Results from the farm field fit within the scaling pattern observed within the Des Moines Lobe region of Iowa showing that water yields and NO3-N loads are dominated by tile drainage at the field and local watershed scale. Loads dominated by tile flows suggest edge-of-field interception and treatment of tile water for mitigation of stream nutrients. Study results are consistent with local and regional assessments showing tile drainage to be an important pathway for both water and nutrients in the stream network of the US Cornbelt.

中文翻译：

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从农田到农业河流的地下养分输出：针对田间实践的影响

摘要 据了解，美国玉米带中可溶性养分硝酸盐（NO3-N）和正磷（OP）从农田到溪流的主要运输途径是瓷砖排水和地下水渗漏。然而，每个的相对贡献尚未得到很好的量化，并且可能因田地和流域而异。在这项研究中，我们使用间歇性抓样水质监测和瓦片流量测量，以及地下水模型 MODFLOW 将溶解养分从农田中提取到中北部密集排水和种植的得梅因洛贝地貌中的低阶河流爱荷华州。根据两年内对八个瓷砖出口、九个地下水井和接收流的监测，发现来自瓷砖的养分负荷贡献了哈丁溪约 98% 的硝酸盐负荷。OP 的装载模式也主要来自人工排水系统的排放，其中 99.7% 来自田间地砖。在爱荷华州得梅因洛贝地区观察到的尺度模式中的农田拟合结果表明，水产量和 NO3-N 负荷主要由田地和当地流域尺度的瓷砖排水决定。以瓦片流为主的负载表明田地边缘截取和处理瓦片水以减轻河流养分。研究结果与当地和区域评估一致，显示瓷砖排水是美国玉米带河流网络中水和养分的重要途径。在爱荷华州得梅因洛贝地区观察到的尺度模式中的农田拟合结果表明，水产量和 NO3-N 负荷主要由田地和当地流域尺度的瓷砖排水决定。以瓦片流为主的负载表明田地边缘截取和处理瓦片水以减轻河流养分。研究结果与当地和区域评估一致，显示瓷砖排水是美国玉米带河流网络中水和养分的重要途径。在爱荷华州得梅因洛贝地区观察到的尺度模式中的农田拟合结果表明，水产量和 NO3-N 负荷主要由田地和当地流域尺度的瓷砖排水决定。以瓦片流为主的负载表明田地边缘截取和处理瓦片水以减轻河流养分。研究结果与当地和区域评估一致，显示瓷砖排水是美国玉米带河流网络中水和养分的重要途径。