School of Environmental Science and Engineering, Tianjin University, 300072 Tianjin, China.
Global Ecology Unit Centro de Investigación Ecológica y Aplicaciones Forestales (CREAF)-Consejo Superior de Investigaciones Científicas (CSIC)-Universitat Autònoma de Barcelona (UAB), CSIC, Bellaterra, Barcelona, 08193 Catalonia, Spain.
Proc Natl Acad Sci U S A. 2020 May 26;117(21):11566-11572. doi: 10.1073/pnas.1920759117. Epub 2020 May 8.
Large-scale and rapid improvement in wastewater treatment is common practice in developing countries, yet this influence on nutrient regimes in receiving waterbodies is rarely examined at broad spatial and temporal scales. Here, we present a study linking decadal nutrient monitoring data in lakes with the corresponding estimates of five major anthropogenic nutrient discharges in their surrounding watersheds over time. Within a continuous monitoring dataset covering the period 2008 to 2017, we find that due to different rates of change in TN and TP concentrations, 24 of 46 lakes, mostly located in China's populated regions, showed increasing TN/TP mass ratios; only 3 lakes showed a decrease. Quantitative relationships between in-lake nutrient concentrations (and their ratios) and anthropogenic nutrient discharges in the surrounding watersheds indicate that increase of lake TN/TP ratios is associated with the rapid improvement in municipal wastewater treatment. Due to the higher removal efficiency of TP compared with TN, TN/TP mass ratios in total municipal wastewater discharge have continued to increase from a median of 10.7 (95% confidence interval, 7.6 to 15.1) in 2008 to 17.7 (95% confidence interval, 13.2 to 27.2) in 2017. Improving municipal wastewater collection and treatment worldwide is an important target within the 17 sustainable development goals set by the United Nations. Given potential ecological impacts on biodiversity and ecosystem function of altered nutrient ratios in wastewater discharge, our results suggest that long-term strategies for domestic wastewater management should not merely focus on total reductions of nutrient discharges but also consider their stoichiometric balance.
在发展中国家，大规模和快速改善废水处理是常见做法，但很少在广泛的时空尺度上考察这种做法对受纳水体营养状况的影响。在这里，我们提出了一项研究，将湖泊的营养监测数据与相应的、随时间变化的其周边流域的五种主要人为营养排放物的估计值联系起来。在一个涵盖 2008 年至 2017 年期间的连续监测数据集内，我们发现，由于 TN 和 TP 浓度的变化率不同，46 个湖泊中的 24 个（主要位于中国人口稠密地区）表现出 TN/TP 质量比增加；只有 3 个湖泊表现出减少。湖泊内营养浓度（及其比值）与周边流域人为营养排放物之间的定量关系表明，湖泊 TN/TP 比值的增加与城市污水处理的快速改善有关。由于与 TN 相比，TP 的去除效率更高，因此，总城市污水排放量中的 TN/TP 质量比已从 2008 年的中位数 10.7（95%置信区间，7.6 至 15.1）持续增加到 2017 年的 17.7（95%置信区间，13.2 至 27.2）。改善全球城市污水收集和处理是联合国设定的 17 个可持续发展目标中的一个重要目标。鉴于改变污水排放中营养比可能对生物多样性和生态系统功能产生潜在影响，我们的研究结果表明，国内废水管理的长期策略不仅应注重减少营养物排放总量，还应考虑其化学计量平衡。
