Non-point source pollution of phosphorus (P) is a primary cause of eutrophication of aquatic ecosystems, and poses a persistent management challenge due to the dynamic and poorly understood processes controlling the transport and transformation of P at the watershed scale. We examined phosphorus inputs, retention, and riverine losses in 62 diverse watersheds that included a wide range of land cover and use (minimally disturbed to human dominated) and human P inputs in Minnesota, USA. Fertilizer inputs from row crop cultivation were the dominant source of P to agricultural watersheds. A large majority of P inputs was retained in watershed soils or removed in agricultural products. However, fertilizer input was the most important factor associated with average annual river transport of total, dissolved, and particulate phosphorus (PP). Mean annual runoff increased total and dissolved P yields and decreased P retention. Dissolved P made up a significant portion of annual river loads at sites with high rates of P inputs and river TP export, with the ratio of dissolved to PP export increasing with crop cover and fertilizer inputs. PP export rose with larger extents of eroding bluffs near channels. Bluffs constitute only a small proportion of watershed area, but make a disproportionately high contribution to sediment loads due to their close proximity to river channels that are increasingly affected by human and climate-driven changes to river hydrology. Together, our results suggest that rising discharge and flow variability due to climate change and agricultural intensification coupled with high rates of P inputs will maintain elevated fluvial P export into the future. Without reductions in P inputs and reductions in both soluble P losses and stream bank erosion, reversal of water quality degradation will be difficult to achieve.

中文翻译：

---

肥料、景观特征和气候调节不同中西部流域的磷保留和河流输出

磷 (P) 的非点源污染是水生生态系统富营养化的主要原因，并且由于控制流域尺度 P 运输和转化的动态和知之甚少的过程，它构成了持续的管理挑战。我们研究了 62 个不同流域的磷输入、保留和河流损失，这些流域包括美国明尼苏达州的各种土地覆盖和利用（对人类主导的干扰最小）以及人类磷输入。来自中耕作物种植的肥料投入是农业流域磷的主要来源。大部分磷投入物被保留在流域土壤中或在农产品中被去除。然而，化肥投入是与年平均总磷、溶解磷和颗粒磷 (PP) 河流运输相关的最重要因素。年平均径流增加了总磷和溶解磷的产量，并减少了磷的保留。在 P 输入和河流 TP 输出率高的地点，溶解磷占年度河流负荷的很大一部分，溶解磷与 PP 输出的比率随着作物覆盖和肥料输入的增加而增加。PP 出口上升，通道附近的断崖面受到更大程度的侵蚀。断崖仅占流域面积的一小部分，但由于它们靠近河道，而河道对河流水文的人类和气候变化的影响越来越大，因此对沉积物负荷的贡献不成比例。总之，我们的结果表明，由于气候变化和农业集约化导致的排放量和流量变异性增加，再加上高磷投入率，将在未来维持河流磷出口的增加。