三峡水库蓄水以来库区干流水质变化(2004-2019年)研究

Water Quality Changes of the Mainstream in the Three Gorges Reservoir Region after Impoundment (2004-2019)

明晰三峡水库蓄水以来库区干流水质变化规律可为库区水环境保护与治理提供参考。基于2004-2019年库区干流多个断面逐月水质数据,采用Mann-Kendall检验法、水质质量指数(WQI)综合评估法和聚类分析对十项典型水质指标进行分析研究。结果表明:三峡水库蓄水以来库区干流各断面高锰酸盐指数、五日生化需氧量、氨氮及铅年均浓度值均满足Ⅲ类水质标准,库区水质总体趋好;根据水质指标年际波动特征,可划分2004-2006、2007-2014及2015-2019等3个时间阶段,且各阶段空间异质性规律不同。库区干流各断面总氮浓度范围为1.3~2.1 mg/L,库尾寸滩及清溪场断面粪大肠杆菌群浓度范围为10 735~79 000 A/L,均超Ⅲ类水质标准为库区干流主要污染指标;6个断面中寸滩断面水质最差需重点关注。长江上游溪洛渡-向家坝梯级水库的蓄水拦沙作用会减少三峡水库入库污染物通量,进而改善库区干流水质;三峡水库分期蓄水时的水位抬升有利于库区水质趋好,其年内常规调度则影响着库区干流水质的年内变化,位于变动回水区内的断面水质规律异于位于常年回水区内的断面水质规律。

Clarifying the variation law of water quality in the main stream of the Three Gorges Reservoir after impoundment can provide a ref⁃erence for water environment protection and management in the reservoir area.Based on the monthly water quality data of multiple sections of the mainstream of the reservoir area from 2004 to 2019,this paper uses Mann-Kendall test method,water quality index(WQI)comprehen⁃sive evaluation method and cluster analysis to analyze and study ten typical water quality indicators.The results show that since the impound⁃ment of the Three Gorges Reservoir,the annual average concentration of permanganate index,five-day biochemical oxygen demand,ammo⁃nia nitrogen and lead in each section of the main stream of the reservoir area have all met the Class III water quality standards,and the water quality in the reservoir area has generally improved.According to the inter-annual fluctuation characteristics of water quality indicators,it can be divided into three time stages: 2004-2006,2007-2014 and 2015-2019, and the spatial heterogeneity of each stage is different. Theconcentration of total nitrogen in each section of the reservoir mainstream ranged from 1.3~2.1 mg/L, and the concentration of fecal Esche⁃richia coli group in the section of Cuntan and Qingxichang is 10 735~79 000 A/L, which exceeds the Class III water quality standard as themain pollution index of the reservoir mainstream. The water quality of the Cuntan section is the worst among the six sections, which needs tobe paid attention to. The water storage and sediment retention effect of Xiluodu-Xiangjiaba cascade reservoirs in the upper reaches of theYangtze River will reduce the inflow pollutant flux of the Three Gorges Reservoir and improve the water quality of the mainstream of the reser⁃voir area. The water level rise during the impoundment of the Three Gorges Reservoir by stages is conducive to the improvement of water qual⁃ity in the reservoir area. The regular operation during the year affects the annual change of water quality in the mainstream of the reservoir ar⁃ea. The water quality law of the section located in the fluctuating backwater area is different from that in the perennial backwater area.