Data for: Long-Term Trends Show Improvements in Water Quality in the Chicago Metropolitan Region with Investment in Wastewater Infrastructure, Deep Tunnels, and Reservoirs

Compiled water quality data of the Chicago, Calumet, and Des Plaines River Systems from 1975 to 2018. Data were collected as part of the Metropolitan Water Reclamation District's Ambient Water Quality Monitoring program. A study was carried out to evaluate water quality trends from 1975 to 2012 and from 2013 to 2018 in the Chicago, Calumet, and Des Plaines River Systems in Cook County, Illinois, in order to investigate the outcome of practices carried out by the Metropolitan Water Reclamation District of Greater Chicago. Data from 41 monitoring locations were compiled and analyzed for 11 water quality parameters. The seasonal Kendall test was performed on each variable at each location to analyze for long-term monotonic trends. Wilcoxon Rank-Sum test was used to test for significant differences in water quality constituents between time periods to point to practices that changed water quality during the study period. For most sampling locations, long-term trend analyses showed significant downward trends for total organic carbon (TOC), total Kjeldahl nitrogen (TKN), ammonium nitrogen (NH4-N), total suspended solids (TSS), fecal coliform (FC), and sulfate and significant upward trends for dissolved oxygen (DO), chloride, and temperature. Total phosphorus (TP) concentrations increased downstream of the Stickney, Kirie, and Calumet WRPs from 1975 to 2012, but decreased downstream of the Kirie WRP and had no trends downstream of the Stickney and Calumet WRPs from 2013 to 2018. Improvements in TKN, NH4-N, TOC, TSS, FC, TP, and DO concentrations over four decades demonstrated the beneficial outcome from the expansion of secondary treatment systems at water reclamation plants, implementation of the Tunnel and Reservoir Plan System, instream and side-stream elevated pool aeration stations, and effluent disinfection. The study is described in the article entitled "Long-Term Trends Show Improvements in Water Quality in the Chicago Metropolitan Region with Investment in Wastewater Infrastructure, Deep Tunnels, and Reservoirs". Supporting Information for this manuscript is attached.本数据集整合了1975年至2018年芝加哥、卡卢梅特（Calumet）河系与德斯普兰斯（Des Plaines）河系的水质监测数据。该数据由芝加哥大都会水回收区（Metropolitan Water Reclamation District）的环境水质监测项目采集获取。为探究芝加哥大都会水回收区实施的各类管控措施对水质的影响效果，本研究针对伊利诺伊州库克县境内的上述三条河系，分别对1975-2012年与2013-2018年两个时段的水质变化趋势开展评估。研究整合了41个监测点位的数据，针对11项水质参数展开分析。针对每个点位的各水质参数，采用季节性肯达尔（Seasonal Kendall）检验法分析其长期单调变化趋势；采用威尔科克森秩和（Wilcoxon Rank-Sum）检验法对比不同时段间水质组分的显著差异，以此识别研究期内对水质产生影响的管控措施。多数监测点位的长期趋势分析结果显示：总有机碳（TOC, total organic carbon）、凯氏总氮（TKN, total Kjeldahl nitrogen）、氨氮（NH4-N, ammonium nitrogen）、总悬浮固体（TSS, total suspended solids）、粪大肠菌群（FC, fecal coliform）以及硫酸盐浓度呈显著下降趋势；而溶解氧（DO, dissolved oxygen）、氯化物浓度与水温则呈显著上升趋势。1975年至2012年，斯图尼（Stickney）、基里（Kirie）与卡卢梅特（Calumet）污水处理厂（WRP, Water Reclamation Plant）下游区域的总磷（TP, total phosphorus）浓度呈上升趋势；但2013年至2018年期间，基里污水处理厂下游总磷浓度转为下降，斯图尼与卡卢梅特污水处理厂下游则无显著变化趋势。四十年来凯氏总氮、氨氮、总有机碳、总悬浮固体、粪大肠菌群、总磷与溶解氧浓度的改善情况，印证了以下措施的积极效果：污水处理厂二级处理系统扩容、隧道与水库计划（Tunnel and Reservoir Plan System）的落地实施、河道内与侧流高位池曝气站的建设，以及出水消毒工艺的推广。 本研究相关成果已发表于题为《长期趋势表明：芝加哥都会区污水基础设施、深层隧道与水库投资助力水质提升》的学术论文，该论文的支撑材料随附于本数据集说明中。