Richards Samia, Bidgood Lucy, Watson Helen, Stutter Marc
The James Hutton Institute, Craigiebuckler, Aberdeen, AB15 8QH, Scotland, UK.
University of Dundee, Nethergate, Dundee, DD1 4HN, Scotland, UK.
J Environ Manage. 2022 Jun 1;311:114891. doi: 10.1016/j.jenvman.2022.114891. Epub 2022 Mar 16.
Discharge of treated sewage effluent to rivers can degrade aquatic ecosystem quality, interacting with multiple stressors in the wider catchment. In predominantly rural catchments, the river reach influence of point source effluents is unknown relative to complex background pressures. We examined water column, sediment and biofilm biogeochemical water quality parameters along river transects (200 m upstream to 1 km downstream) during summer at five wastewater treatment works (WWTW) in Scotland. Treated sewage effluent (subset, n = 3) pollutant concentrations varied between sites. Downstream concentration profiles of water and sediment biogeochemical parameters showed complex spatial changes. A hypothesised point source signature of elevated concentrations of pollution immediately downstream of WWTW then a decaying pollution 'plume' did not commonly occur. Instead, elevated soluble reactive phosphorus (SRP), ammonium and coliforms (maximum 0.23 mgP/l, 0.33 mgN/l and >2 × 10 MPN/100 ml) occurred immediately downstream of two WWTW, whereas some downstream pollutant concentrations decreased. Microbial substrate respiration responses only differed 1 km downstream. Significantly greater concentrations of sediment metal occurred >500 m downstream, likely due to the redeposition of historic contaminated sediments. Significantly lowered chlorophyll-a downstream of one WWTW coincided with elevated metals, despite water SRP and sediment P increases. Overall, stress caused to microbes and algae by effluent contaminants outweighed the subsidy effect of WWTW nutrients. We observed variable effluent flows to the rivers limited localised pollution downstream of WWTW and overall influence of arable land cover on river water quality. Together, this challenges views of consistently discharging point sources impacting low dilution sensitive rivers in summer contrasting with 'diffuse' sources. Thus, river water column and benthic compartments are altered at varying scales by point source effluents in combination with rural catchment pollution sources, both discrete (e.g. farmyards and septic tanks) and diffuse.
将经处理的污水排放到河流中会降低水生生态系统质量，并与更广泛集水区中的多种压力源相互作用。在以农村为主的集水区，相对于复杂的背景压力，点源污水对河段的影响尚不清楚。我们在夏季对苏格兰的五座污水处理厂（WWTW）沿河流断面（上游200米至下游1公里）的水柱、沉积物和生物膜生物地球化学水质参数进行了检测。各污水处理厂处理后的污水（子集，n = 3）污染物浓度因地点而异。水和沉积物生物地球化学参数的下游浓度分布呈现出复杂的空间变化。一种假设的点源特征，即污水处理厂下游立即出现污染浓度升高，然后是污染“羽流”衰减，这种情况并不常见。相反，两座污水处理厂下游立即出现可溶性活性磷（SRP）、铵和大肠菌群升高（最高分别为0.23 mgP/l、0.33 mgN/l和>2×10 MPN/100 ml），而一些下游污染物浓度则下降。微生物底物呼吸反应仅在下游1公里处有所不同。下游500米处沉积物金属浓度显著更高，可能是由于历史污染沉积物的再沉积。一座污水处理厂下游叶绿素-a显著降低，尽管水体SRP和沉积物磷含量增加，但金属含量升高。总体而言，污水污染物对微生物和藻类造成的压力超过了污水处理厂营养物质的补贴效应。我们观察到流入河流的污水流量变化，这限制了污水处理厂下游的局部污染以及耕地覆盖对河流水质的总体影响。综合起来，这挑战了关于夏季持续排放点源影响低稀释度敏感河流与“面源”形成对比的观点。因此，点源污水与农村集水区污染源（包括离散源，如农家院和化粪池，以及面源）相结合，在不同尺度上改变了河流水柱和底栖生物区。
