Sources and Pathways of Nutrients in the Semi-Arid Region of Beijing–Tianjin, China

Semiarid regions worldwide are particularly prone to eutrophication, which causes immense ecological and economic problems. One region that is in transition and requires systematic research for effective intervention is the dry landscape of Beijing-Tianjin (P. R. China). We investigated the sources and spatiotemporal loads of nitrogen and phosphorus species over a one-year period in the Haihe catchment that drains the megacity of Beijing. Although wastewater treatment was improved in recent years, the rivers were heavily contaminated by 0.3–5.3 mgP L^–1 and 3.0–49 mgN L^–1, with toxic levels of nitrite (≥1 mgNO₂–N L^–1) and ammonia (≥0.6 mgNH₃–N L^–1). The average NH₄⁺ (16.9 mgN L^–1) increased by 160% compared to 1996-levels. Mass fluxes and δ¹⁵N-signatures revealed that nutrients originated almost exclusively from sewage. Furthermore, the water balance demonstrated that >90% of the polluted river water was diverted for irrigation, thereby threatening food safety and groundwater quality. Per capita loads of 1.42 kgN/yr and 115 gP/yr were comparable to the peak discharges typical of Europe and the United States in 1970–1990, but concentrations were 2–3 times higher in the Beijing–Tianjin region. Our research identified sewage as the predominant nutrient source in this semiarid region, which suggests that state-of-the-art wastewater treatment would drastically mitigate eutrophication and even more rapidly than was previously observed in Europe

Sources and Pathways of Nutrients in the Semi-Arid Region of Beijing–Tianjin, China

Semiarid regions worldwide are particularly prone to eutrophication, which causes immense ecological and economic problems. One region that is in transition and requires systematic research for effective intervention is the dry landscape of Beijing-Tianjin (P. R. China). We investigated the sources and spatiotemporal loads of nitrogen and phosphorus species over a one-year period in the Haihe catchment that drains the megacity of Beijing. Although wastewater treatment was improved in recent years, the rivers were heavily contaminated by 0.3–5.3 mgP L^–1 and 3.0–49 mgN L^–1, with toxic levels of nitrite (≥1 mgNO₂–N L^–1) and ammonia (≥0.6 mgNH₃–N L^–1). The average NH₄⁺ (16.9 mgN L^–1) increased by 160% compared to 1996-levels. Mass fluxes and δ¹⁵N-signatures revealed that nutrients originated almost exclusively from sewage. Furthermore, the water balance demonstrated that >90% of the polluted river water was diverted for irrigation, thereby threatening food safety and groundwater quality. Per capita loads of 1.42 kgN/yr and 115 gP/yr were comparable to the peak discharges typical of Europe and the United States in 1970–1990, but concentrations were 2–3 times higher in the Beijing–Tianjin region. Our research identified sewage as the predominant nutrient source in this semiarid region, which suggests that state-of-the-art wastewater treatment would drastically mitigate eutrophication and even more rapidly than was previously observed in Europe

Organic Micropollutants in Rivers Downstream of the Megacity Beijing: Sources and Mass Fluxes in a Large-Scale Wastewater Irrigation System

The Haihe River System (HRS) drains the Chinese megacities Beijing and Tianjin, forming a large-scale irrigation system severely impacted by wastewater-borne pollution. The origin, temporal magnitudes, and annual mass fluxes of a wide range of pharmaceuticals, household chemicals, and pesticides were investigated in the HRS, which drains 70% of the wastewater discharged by 20 million people living in Beijing. Based on Chinese consumption statistics and our initial screening for 268 micropollutants using high-resolution mass spectrometry, 62 compounds were examined in space and time (2009–2010). The median concentrations ranged from 3 ng/L for metolachlor to 1100 ng/L for benzotriazole and sucralose. Concentrations of carbendazim, clarithromycin, diclofenac, and diuron exceed levels of ecotoxicological concern. Mass-flux analyses revealed that pharmaceuticals (5930 kg/year) and most household chemicals (5660 kg/year) originated from urban wastewaters, while the corrosion inhibitor benzotriazole entered the rivers through other pathways. Total pesticide residues amounted to 1550 kg/year. Per capita loads of pharmaceuticals in wastewater were lower than those in Europe, but are expected to increase in the near future. As 95% of the river water is diverted to irrigate agricultural soil, the loads of polar organic micropollutants transported with the water might pose a serious threat to food safety and groundwater quality

Assessment and Identification of Primary Factors Controlling Yangtze River Water Quality

Challenges for rapid dam construction remain, including pollutant trajectories after construction, how socioeconomic developments drive long-term water quality and large spatial changes, and which indicators primarily control these changes. Here, high-density sampling and socioeconomic data were integrated to assess primary factors controlling Yangtze River water quality. Our results indicated that the pollutant trajectories in the upper and lower sections differ, owing to the Three Gorges Dam. From 2003 to 2020, the decreased TP, NH4+-N, and CODMn concentrations were strongly correlated to the per capita gross domestic product, drainage pipe length, number of wastewater treatment plants, and fertilizer consumption. Moreover, Se and Cd concentrations decreased, whereas Ni and Zn concentrations increased from 2007 to 2020. The water quality index (WQI) demonstrated that Yangtze River water quality varies from levels “good” to “excellent”, is better in the winter, and deteriorates with decreasing distance from the estuary. Furthermore, an optimized WQI model consisting of six crucial parameters (TN, Pb, Cd, Zn, NO3––N, and As) was built using the random forest method, which exhibits excellent performance in water quality assessment. The approach proposed in the present study can significantly reduce the number of parameters required to assess water quality without compromising the results