Urea can degrade water quality and stimulate toxic phytoplankton in P-rich lakes, yet little is known of its sources, abundance, or transportation in lotic systems, particularly within the Northern Great Plains. We measured physico-chemical parameters biweekly during May–September 2010–2012 at 16 stations along a 250 km lotic continuum to quantify spatial and temporal variation in urea concentrations and discharge, and to identify potential regulatory processes. Urea concentrations were similar to those in regional prairie lakes (range 5.2–792.1, median 78.6 μg N L⁻¹) with variable seasonal mean (± SD) concentrations (96.6 ± 96.1 μg N L⁻¹) and fluxes (4.22 × 10⁵ ± 257.6 μg N s⁻¹). Landscape analysis with generalized additive models explained 68.3% of deviance in urea concentrations, with high temporal variability predicted mainly by positive relationships with nutrient content and chlorophyte abundance, but not temperature, dissolved organic matter, bacterial abundance, or urban effluent. Seasonal analysis revealed that during spring, urea content was correlated negatively with leguminous forage cover (% area) and positively with stream discharge, oilseed and cereal crops, and shrubs or deciduous plants, while during summer, urea concentrations were correlated negatively with discharge and leguminous crop cover, as well as nutrient levels. Mean porewater urea concentrations (528.5 ± 229.8 μg N L⁻¹) were over five-fold greater than stream concentrations, suggesting that hyporheic production may offset declining influx from terrestrial sources during summer. We conclude that urea may be ubiquitous in eutrophic prairie streams and that management of its export from land may reduce detrimental effects on downstream lakes.

尿素可以降低水质并刺激富含磷的湖泊中的有毒浮游植物，但对其来源、丰度或在激流系统中的运输知之甚少，尤其是在大平原北部。我们在 2010 年 5 月至 2012 年 9 月期间每两周测量一次沿 250 公里连续流域的 16 个站点的物理化学参数，以量化尿素浓度和排放的空间和时间变化，并确定潜在的调节过程。尿素浓度与区域草原湖泊（范围 5.2–792.1，中值 78.6 μg NL ^-1）相似，具有可变的季节性平均 (± SD) 浓度（96.6 ± 96.1 μg NL ^-1）和通量（4.22 × 10 ⁵  ± 257.6）微克 N s ^-1）。使用广义加性模型的景观分析解释了 68.3% 的尿素浓度偏差，主要通过与养分含量和叶绿素丰度的正相关关系预测的高时间变异性，而不是温度、溶解有机物、细菌丰度或城市污水。季节性分析表明，春季尿素含量与豆科牧草覆盖率（%面积）呈负相关，与河流流量、油料和谷类作物、灌木或落叶植物呈正相关，而在夏季，尿素含量与流量和豆科牧草呈负相关。作物覆盖率以及营养水平。平均孔隙水尿素浓度 (528.5 ± 229.8 μg NL ^-1) 比溪流浓度大五倍以上，这表明低流产生可能会抵消夏季来自陆地源的流入量下降的影响。我们得出的结论是，尿素在富营养化的草原溪流中可能无处不在，并且从陆地出口的管理可能会减少对下游湖泊的不利影响。