Happel Austin, Gallagher Dustin
Daniel P. Haerther Center for Conservation and Research, John G. Shedd Aquarium, Chicago, IL, USA.
Metropolitan Water Reclamation District of Greater Chicago, Chicago, IL, USA.
Sci Total Environ. 2022 Jun 10;824:153776. doi: 10.1016/j.scitotenv.2022.153776. Epub 2022 Feb 10.
Throughout much of the globe, rivers are used to dispatch treated and untreated wastewater to the detriment of receiving ecosystems. Surprisingly, few studies directly relate water quality variables to fish community responses in receiving waterways on timescales that encompass the incremental and compounding improvements to wastewater infrastructure over time. Chicago (Illinois, USA) represents one such city, within which sits a series of waterways whose flows are primarily controlled by effluent discharges from three large wastewater treatment plants. Random forest regressions were used to construct models which predict changes in fish species richness within the Chicago Area Waterways over a period of 35 years from data on water quality and weather. The average number of species found at any one location across the Chicago Area Waterway system increased from ~5 to ~12 between 1985 and 2019. Decreases in concentrations of variables related to wastewater effluents (i.e., phenols, fecal coliforms, and nitrogenous compounds) were identified as highly informative, allowing increases in species richness to be predicted with a relatively high accuracy (R ≥ 0.49). Weather variables (particularly those related to snow and freezing temperatures) were only important predictors in a section of waterway which does not receive wastewater effluent, although consistent increases in rainfall were noted for Chicago and in chloride concentrations within the waterways. Increased rainfall events and harsher winter conditions (induces greater chloride runoff) threaten the progress made to lessen the effects of wastewater on the region. Improvements to how wastewater is treated, and subsequent reductions to harmful constituents of effluents, have improved the aquatic ecosystem and are likely responsible for the increased species richness over the 35-year timeframe studied.
在全球大部分地区，河流被用于排放经过处理和未经处理的废水，这对受纳生态系统造成了损害。令人惊讶的是，很少有研究在涵盖废水基础设施随时间的渐进式和复合式改善的时间尺度上，直接将水质变量与受纳水道中鱼类群落的反应联系起来。美国伊利诺伊州的芝加哥就是这样一个城市，市内有一系列水道，其水流主要受三座大型废水处理厂的废水排放控制。利用随机森林回归构建模型，根据水质和天气数据预测芝加哥地区水道35年内鱼类物种丰富度的变化。1985年至2019年间，芝加哥地区水道系统中任一地点发现的物种平均数量从约5种增加到了约12种。与废水排放相关的变量（即酚类、粪大肠菌群和含氮化合物）浓度的降低被确定为信息量很大，能够以相对较高的准确度预测物种丰富度的增加（R≥0.49）。天气变量（特别是与降雪和冰冻温度相关的变量）仅在一段未接收废水排放的水道中是重要的预测因子，不过芝加哥的降雨量持续增加，水道中的氯化物浓度也在上升。降雨事件增加和冬季条件更加恶劣（导致更大的氯化物流失）威胁着在减轻废水对该地区影响方面取得的进展。废水处理方式的改进以及随后废水中有害成分的减少，改善了水生生态系统，很可能是在所研究的35年时间框架内物种丰富度增加的原因。
