Institute of Geology and Palaeontology - Applied Geology, University of Münster, Corrensstrasse 24, 48149 Münster, Germany.
Institute of Geology and Palaeontology - Applied Geology, University of Münster, Corrensstrasse 24, 48149 Münster, Germany.
Sci Total Environ. 2022 Apr 20;818:151730. doi: 10.1016/j.scitotenv.2021.151730. Epub 2021 Nov 17.
Medium-sized rivers, which are used for intensive agriculture and urban infrastructure, are subject to manifold hydrochemical stressors. Identifying and monitoring these stressors is important for river basin management and a functioning ecosystem. To understand the spatiotemporal variation of surface water quality in a highly modified lowland river, the Münstersche Aa River (Northwestern Germany) with 62% of land used for agriculture and 26% urban/residential area, was exemplarily studied. A total of 519 samples were collected using two automated high-frequency samplers and five catchment-wide sampling campaigns. They covered the five-year period 2015-2020 and included two extremely dry summers. The Münstersche Aa catchment is dominated by low permeable strata resulting in surface water runoff (Baseflow Index: 0.41) which leads to a high amplitude of discharge variation (mean discharge: 0.7 m/s) with high flow conditions in winter/spring, and low discharge during summer/fall. In wintertime, maximum nitrate concentrations (up to 73 mg NO/L) and loads (up to 1300 t NO/a; up to 98% in winter) correlate with high-flow conditions. δO and δN isotopic analysis indicated manure from farmland as the major source of nitrate whereas the impact of municipal wastewater treatment plants was neglectable. Increased nitrate concentrations are linked to the higher proportion of farmland in the upper catchment (77%) compared with the lower catchment (47%). In summertime, at extremely low flow conditions, surface water consisted of up to 100% of treated wastewater, resulting in the highest measured chloride, sodium and potassium concentrations. The river is impacted by strongly seasonal and different stressors, which can be expected to intensify with ongoing climate change. Results from this study may help to adapt monitoring schemes for the Münstersche Aa but also for other lowland streams with comparable land-use targeting the goals of the Water Framework Directive.
中型河流用于集约型农业和城市基础设施，受到多种水化学胁迫因素的影响。识别和监测这些胁迫因素对于流域管理和生态系统的正常运行至关重要。为了了解高度改造的低地河流——德国西北部的明斯特阿河（Münstersche Aa River）的地表水水质的时空变化，对其进行了示例研究。该河 62%的土地用于农业，26%的土地用于城市/居民区，使用两个自动化高频采样器和五次全流域采样活动共采集了 519 个样本。这些样本覆盖了 2015 年至 2020 年的五年时间，包括两个极其干旱的夏季。明斯特阿河流域主要由低渗透性地层组成，导致地表水径流量大（基流指数：0.41），这导致了流量变化幅度大（平均流量：0.7 立方米/秒），冬季/春季流量高，夏季/秋季流量低。冬季，最大硝酸盐浓度（高达 73 毫克/升）和负荷（高达 1300 吨/年；98%的硝酸盐负荷在冬季）与高流量条件相关。δO 和 δN 同位素分析表明，农田中的粪肥是硝酸盐的主要来源，而城市污水处理厂的影响可以忽略不计。硝酸盐浓度的增加与上流域（77%）中农田的比例较高有关，而下流域（47%）中农田的比例较低。夏季，在极低的流量条件下，地表水由高达 100%的处理后的废水组成，导致氯化物、钠和钾的浓度达到最高测量值。这条河受到强烈季节性和不同胁迫因素的影响，随着气候变化的持续，这些因素可能会加剧。本研究的结果可能有助于适应明斯特阿河的监测计划，但也可能有助于适应其他具有类似土地利用的低地河流，以实现《水框架指令》的目标。
