Environmental Science & Technology fertilizer and wastewater seeping from the irrigated ﬁelds into the aquifers, groundwater contamination is already evident in several regions of northern China.3,9,50,51 A successful mitigation strategy therefore includes long-term chemical monitoring programs for the rivers and groundwater resources, to assess the eﬃciency of intervention measures.45 This would ideally tackle a representative set of both inorganic and organic pollutants in the aquatic environment. ASSOCIATED CONTENT *S Supporting Information Information regarding geopositions of the sampling sites, sample preparation and procedures of chemical analyses, database of chemical species quantiﬁed in river waters, plots of nutrient species variation along the river system, plot of water isotope signatures (δ2H and δ18O), and plot of δ15N and δ18O signatures of NO3− in Beijing wastewater and river water. This material is available free of charge via the Internet at http://pubs.acs.org. AUTHOR INFORMATION Corresponding Author *Phone: +41-58-765 5078; e-mail: michael.berg@eawag.ch. Notes The authors declare no competing ﬁnancial interest. ■ ■ ■ ACKNOWLEDGMENTS ■ We thank Jiuhui Qu and Min Yang (RCEES) for their constant and generous support. Huachun Lan, Huimin Ren, Xiaobin Liu, Cui Li, Mingzhu Zhu, Xiaoli Du, Wenxin Gong, Xiaoyu Wu, Pengfei Xia, Meng Qiao, Caroline Stengel, and Ruth Stierli are acknowledged for their excellent assistance in sampling campaigns and instrumental analyses, and Guoying Bai, Yajuan Wang (Central Hydrology Station of Beijing), and Wenhao Chai (Bureau of Hydrology and Water Resource Survey of Langfang, Hebei Province) for providing discharge data. Yongjun Jiang and two anonymous reviewers provided valuable suggestions to the manuscript. 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