Abstract In the Lake Winnipeg Basin (LWB), at both basin and regional scales, there are currently gaps regarding the significance of groundwater as a mediator of nutrient and contaminant fluxes to Lake Winnipeg. During 2018, surface water and groundwater samples were collected from various locations across the largest sand and gravel aquifer (Assiniboine Delta Aquifer [ADA]; 3800 km2) in the LWB as well as from surface water courses flowing above this aquifer. The samples collected during spring and fall were analyzed for anions and cations as well as for a series of isotopic and geochemical tracers (e.g. water isotopes, carbon 14, artificial sweeteners, pesticides, etc.). The results reveal that groundwater and the small watercourses flowing above the ADA have a similar chemical composition, which is in contrast with the chemical composition of the main watercourse flowing above the aquifer (Assiniboine River [AR]). When corroborated with stream discharge measurements this indicates that groundwater plays a significant role at local scale in controlling both the flow and the chemical composition of the AR tributaries. Nitrate showed low to non-detectable concentrations in both groundwater and surface water. With respect to groundwater, this could be related to the reducing conditions in the deeper aquifer in conjunction with relatively large groundwater travel times of up to 2400 years.

中文翻译：

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Assiniboine Delta 含水层 (ADA) 中地下水对地表水的贡献：水量和质量的观点

摘要 在温尼伯湖流域 (LWB) 中，在流域和区域尺度上，目前关于地下水作为温尼伯湖养分和污染物通量的中介的重要性存在差距。2018 年期间，从 LWB 中最大的沙砾含水层（Assiniboine Delta Aquifer [ADA]；3800 平方公里）的不同位置以及从该含水层上方流动的地表水道收集了地表水和地下水样本。对春季和秋季收集的样品进行阴离子和阳离子以及一系列同位素和地球化学示踪剂（例如水同位素、碳 14、人造甜味剂、杀虫剂等）的分析。结果表明，地下水和流经 ADA 上方的小水道具有相似的化学成分，这与在含水层上方流动的主要水道（阿西尼博因河 [AR]）的化学成分形成对比。当与河流流量测量证实时，这表明地下水在局部尺度上在控制 AR 支流的流量和化学成分方面发挥着重要作用。硝酸盐在地下水和地表水中都显示出低至不可检测的浓度。关于地下水，这可能与较深含水层中的减少条件以及长达 2400 年的相对较大的地下水流动时间有关。当与河流流量测量证实时，这表明地下水在局部尺度上在控制 AR 支流的流量和化学成分方面发挥着重要作用。硝酸盐在地下水和地表水中都显示出低至不可检测的浓度。关于地下水，这可能与较深含水层中的减少条件以及长达 2400 年的相对较大的地下水流动时间有关。当与河流流量测量证实时，这表明地下水在局部尺度上在控制 AR 支流的流量和化学成分方面发挥着重要作用。硝酸盐在地下水和地表水中都显示出低至不可检测的浓度。关于地下水，这可能与较深含水层中的减少条件以及长达 2400 年的相对较大的地下水流动时间有关。