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.

全球半干旱地区尤为易发生水体富营养化，由此引发严重的生态与经济问题。地处中华人民共和国的京津冀干旱流域区域正处于转型阶段，亟需开展系统性研究以实施有效干预。本研究针对覆盖特大城市北京的海河流域，开展了为期一年的调查，解析了各类氮、磷污染物的来源及时空负荷分布。尽管近年来污水处理水平有所提升，但辖区河流水体污染仍十分严重：总磷浓度介于0.3~5.3 mg·L⁻¹，总氮浓度介于3.0~49 mg·L⁻¹，且亚硝酸盐（≥1 mg NO₂⁻-N·L⁻¹）与氨氮（≥0.6 mg NH₃-N·L⁻¹）含量均达到毒性阈值。氨氮（NH₄⁺）平均浓度达16.9 mg N·L⁻¹，较1996年水平提升160%。质量通量与氮稳定同位素δ¹⁵N特征分析结果显示，流域内营养盐几乎全部来源于生活污水。此外，水量平衡分析表明，超过90%的受污染河流水体被用于农业灌溉，由此对食品安全与地下水水质构成威胁。研究区域的人均氮负荷达1.42 kg·a⁻¹、人均磷负荷达115 g·a⁻¹，与1970-1990年代欧洲及美国的污染物峰值排放水平相当，但京津冀地区的污染物浓度较欧美同期水平高出2~3倍。本研究证实，生活污水是该半干旱区域营养盐污染的主要来源，这意味着采用当前最先进的污水处理技术，可大幅缓解水体富营养化问题，且其见效速度将快于欧洲此前的治理实践。