Abstract Lake Winnipeg has undergone rapid eutrophication over the last several decades with a large portion of the associated nutrient loads delivered via the Red River. Consequently, subcatchments of the Red River Valley (RRV) are priorities for nutrient management, an aim that requires identification of key nutrient sources to stream food webs. We identified the primary sources of nitrogen to food webs of rural streams of the RRV, as well as variation in nitrogen input between spring and summer. We measured δ15N of particulate organic matter (POM) and collector-gatherer invertebrates collected in spring and summer from 20 subcatchments, which exhibited a range of agricultural intensity and size of municipal wastewater lagoons. δ15N values of POM and collector-gatherer invertebrates were best predicted by the presence of wastewater treatment lagoons, with δ15N values increasing with the number of people served by lagoons in spring and summer. When present, wastewater contributed a greater proportion of nitrogen to stream food webs than agricultural sources. Waste sources also had a greater relative contribution to food webs in summer than spring. Despite wastewater lagoons releasing nitrogen in short-term, pulsed discharges, the influence of wastewater on food web nitrogen persisted from the summer release into the following spring. Based on the observed importance of wastewater as a source of nitrogen to stream food webs, we recommend management agencies consider additional actions to reduce nutrient losses from wastewater treatment facilities as well as agricultural lands to more effectively protect aquatic ecosystems.

中文翻译：

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马尼托巴省红河谷支流食物链中的氮源

摘要 在过去的几十年里，温尼伯湖经历了快速的富营养化，大部分相关的养分负荷通过红河输送。因此，红河谷 (RRV) 的子汇水面积是养分管理的优先事项，这一目标需要确定关键的养分来源以形成食物网。我们确定了 RRV 农村河流食物网中氮的主要来源，以及春季和夏季之间氮输入的变化。我们测量了春季和夏季从 20 个子汇水面积收集的颗粒有机物 (POM) 和收集-收集无脊椎动物的 δ15N，显示了一系列农业强度和城市污水泻湖的大小。污水处理泻湖的存在可以最好地预测 POM 和收集-收集无脊椎动物的 δ15N 值，δ15N 值随着春季和夏季泻湖服务的人数增加而增加。当存在时，与农业来源相比，废水为食物网提供了更大比例的氮。与春季相比，夏季废物源对食物网的相对贡献更大。尽管废水泻湖在短期脉冲排放中释放氮，但废水对食物网氮的影响从夏季释放一直持续到第二年春天。基于观察到的废水作为流动食物网的氮源的重要性，