长江流域重点断面水质时空变异特征及污染源解析

为明晰长江流域水质时空分布特征并解析污染源，基于长江流域21个水质监测断面2008—2018年的pH、溶解氧(DO)、高锰酸盐指数(COD_Mn)及氨氮质量浓度([NH₃-N])数据，采用M-K趋势检验、相关性分析和层次聚类分析，对流域内水质时空动态变化趋势及特征进行综合识别，并结合绝对主成分回归分析法(APCS-MLR)解析污染物来源。结果表明，研究区内重点断面水质类别以II类为主，占71.39%。在时间上，水质污染程度表现为汛期(5—10月)劣于非汛期(1—4月和11、12月)，汛期主要污染指标为DO和COD_Mn，非汛期主要污染指标为[NH₃-N]；在空间上，21个监测断面聚类为3组，其水质优劣排序为GⅢ(四川乐山岷江大桥、湖南长沙新港、江西南昌滁搓站点)>GⅡ(中下游及下游)>GⅠ(上游及中上游)。结合主成分分析和多元回归分析得出，在所基于的指标中COD_Mn和NH₃-N是研究区内典型污染物，GⅠ组水体主要受营养盐面源污染和耗氧有机物蓄积污染；GⅡ组水质受工业生产和人类活动影响其营养盐和有机物污染严重，而自然因素影响较弱；GⅢ组站点属局部污染严重，污染源主要是有机物，其次是营养盐。上述研究结果可为长江流域针对性水环境治理、污染控制和改善提供参考。

Spatial and temporal variability of water quality at key cross-sections in the Yangtze River Basin and analysis of pollution sources

In order to clarify the spatial-temporal distribution characteristics of water quality in the Yangtze River Basin and analyze the pollution sources, Mann Kendall test, correlation analysis, and hierarchical clustering analysis were adopted based on the pH, dissolved oxygen (DO), permanganate index (CODMn) and ammonia nitrogen (NH3-N) data of 21 water quality monitoring sections in the Yangtze River Basin from 2008 to 2018. The spatial and temporal dynamic change trend and characteristics of water quality in the basin were identified comprehensively, and the sources of pollutants were analyzed by absolute principal component regression analysis (APCS-MLR). The results showed that the water quality of key sections were class II, accounting for 71.39%. In terms of time, the water pollution degree in flood season (May-October) was worse than that in non-flood season (January-April, November and December). The main pollution indexes in flood season were DO and CODMn, and the main pollution indexes in non-flood season was NH3-N. In terms of space, the 21 monitoring sections were grouped into 3 groups, and the quality of water quality was ranked as GⅢ(Minjiang Bridge in Leshan, Sichuan Province, Changsha Xingang in Hunan Province, Nanchang Chuzhu station in Jiangxi Province)>GⅡ(middle and lower reaches)>GⅠ(upper and middle reaches). The results of principal component analysis and APCS-MLR showed that CODMn and NH3-N were typical pollutants in the study area, and the water quality of group GⅠ was mainly polluted by the non-point source nutrients and the accumulation of oxygen-consuming organic matter. The water quality of group GII was seriously polluted by nutrients and organic matter due to industrial production and human activities, while the influence of natural factors were relatively weak. The sites of group GIII were seriously polluted, and the pollution sources were mainly organic matter, followed by nutrients. The findings from this study can provide theoretical basis for targeted water environment management, pollution control and improvement in the Yangtze River Basin.