2016—2019年长江流域水质时空分布特征

为掌握“十三五”以来长江流域的水环境质量时序变化和空间分布特征，基于国家生态环境监测网2016—2019年长江流域615个可比断面监测数据，从流域主要污染特征、主要超标指标浓度时空变化等方面分析了长江流域水质变化情况.结果表明:2016—2019年，长江流域水质总体好转.依据GB 3838—2002《地表水环境质量标准》评价，Ⅰ~Ⅲ类水质断面比例上升7.2百分点，劣Ⅴ类下降2.8百分点.TP、NH₃-N和COD是长江流域的主要超标指标，2019年三者的浓度较2016年分别下降了28.3%、35.0%和8.0%；从流域不同级别河流来看，三者浓度在干流均为最低；从干流来看，三者浓度较高的断面主要分布在长江中游；TP和COD污染主要来自面源，NH₃-N主要来自点源.研究期间，TP对长江流域水环境污染贡献最大，其断面超标率一直排在首位.针对流域水质分布特征，建议继续加强流域内TP防控，重点加强中游污染治理；同时，优化流域产业结构，进一步改善流域水质和生态环境质量. 

Spatiotemporal Characteristics of Surface Water Quality of the Yangtze River Basin during 2016-2019

In order to study the temporal-spatial characteristics of water quality in the Yangtze River Basin (YRB), since 2016 (the first year of the 13th Five-Year Plan), monitoring data from 615 comparable sections of the YRB in the national monitoring network during 2016-2019 were analyzed, the main pollution characteristics and the spatiotemporal characteristic changes of the concentrations of main indicators were summarized. The results showed that the water quality of the YRB improved during 2016-2019. According to the Environmental Quality Standards for Surface Water (GB 3838-2002), the percentage of water sections meeting Grade Ⅰ-Ⅲ water quality standard increased by 7.2 percentage points, and those inferior to Grade Ⅴ dropped by 2.8 percentage points. The main exceeding standard indicators of the YRB were TP, NH₃-N and COD. Compared with 2016, the concentration of TP, NH₃-N and COD in 2019 decreased by 28.3%, 35.0% and 8.0%, respectively. These were the lowest concentrations of the three pollutants in the main stream of Yangtze River. The sections with higher concentrations of the three pollutants mainly distributed in the middle reaches of the Yangtze River. The pollution of TP and COD mainly came from non-point sources and NH₃-N came from point sources. TP was always the main indicator affecting the water quality of the YRB, and the exceedance rate of TP cross sections always ranked first. According to the spatiotemporal characteristics of water quality in the YRB, in order to improve the water quality and ecological environment quality of the basin, prevention and control of TP should be strengthened continuously, pollution control in the middle reaches needs to be strengthened, and industrial structure of river basin should be optimized.