College of Environmental Science and Engineering, Tongji University, Shanghai 200092, China.
Environ Sci Process Impacts. 2019 Sep 18;21(9):1477-1488. doi: 10.1039/c9em00201d.
Excessive dissolved inorganic nitrogen (DIN) added to urban river systems by point-source (PS) inputs, including raw sewage and wastewater treatment plant (WWTP) effluent, constitutes a water-quality problem of growing concern worldwide. However, the quantification of their impacts on DIN retention capacity and pathways in receiving water still remains partial. In this study, a spatially intensive water quality monitoring campaign was conducted to support the application of a water quality model to a PS-impacted urban river in Hefei City, China. The DIN retention capacities and pathway of a reference upstream Reach A, a raw-sewage-impacted Reach B and a WWTP-effluent-dominated Reach C were quantified using the model results after a Bayesian approach for parameter estimation and uncertainty analysis. The results showed that the raw sewage discharge elevated the assimilatory uptake rate but lowered its efficiency in Reach B, while the WWTP effluent discharge elevated both the denitrification rate and efficiency and made Reach C a denitrification hotspot with an increased nitrate concentration and hypoxic environment. The effects of the PS inputs on the DIN retention pathways (assimilatory uptake vs. denitrification) were regulated by their impacts on river metabolism. Despite different pathways, the total DIN retention ratios of Reaches A, B and C under low-flow conditions were 30.3% km-1, 14.3% km-1 and 6.5% km-1, respectively, which indicated that the instream DIN retention capacities were significantly impaired by the PS inputs. This result suggests that the DIN discharged from PS inputs to urban rivers will be transported with the potential to create long-term ecological implications not only locally but also more distant downstream.
过量的溶解无机氮（DIN）通过点源（PS）输入进入城市河流系统，包括未经处理的污水和污水处理厂（WWTP）的出水，这构成了全球日益关注的水质问题。然而，对于 PS 输入对受纳水体中 DIN 保持能力和途径的影响的量化仍然不完全。在这项研究中，进行了空间密集的水质监测活动，以支持将水质模型应用于中国合肥市受 PS 影响的城市河流。使用贝叶斯方法进行参数估计和不确定性分析后，通过模型结果量化了参考上游河段 A、受 raw-sewage 影响的河段 B 和以 WWTP 出水为主的河段 C 的 DIN 保持能力和途径。结果表明，raw-sewage 排放提高了河段 B 中的同化吸收速率，但降低了其效率，而 WWTP 出水排放提高了反硝化速率和效率，使河段 C 成为反硝化热点，硝酸盐浓度增加，缺氧环境。PS 输入对 DIN 保持途径（同化吸收与反硝化）的影响受河流代谢的影响调节。尽管途径不同，但在低流量条件下，河段 A、B 和 C 的总 DIN 保留率分别为 30.3% km-1、14.3% km-1 和 6.5% km-1，这表明 PS 输入显著损害了河流中的 DIN 保持能力。这一结果表明，从 PS 输入到城市河流的 DIN 将随着水流被运移，不仅在当地，而且在更下游的地方都有可能产生长期的生态影响。
