“十三五”期间长江干流沿程水质变化规律

The Variation Trend of Water Quality of the Yangtze River during the 13th Five-Year Plan Period

为掌握“十三五”期间长江水质的总体情况和变化趋势,开展了2016—2020年长江干流水质变化特征研究,总结了5年间长江干流地表水水质变化情况,以高锰酸盐指数(COD_(Mn))、氨氮(NH_(3)-N)和总磷(TP)为研究因子,掌握长江水质现状及污染物浓度随季度变化的特征;同时,采用局部加权回归散点平滑(Locally weighted scatterplot smoothing,Loess)等方法研究了5年间长江干流沿程水环境质量变化规律。结果表明:(1)“十三五”期间长江水质逐年变好,到2020年干流所有断面均满足Ⅱ类水质;(2)ρ(COD_(Mn))、ρ(NH_(3)-N)和ρ(TP)各季度表现为沿程上升趋势,其中第三季度的ρ(COD_(Mn))最大,ρ(NH_(3)-N)最大值在第一季度;(3)长江干流上游水质明显好于中下游水质,ρ(COD_(Mn))和ρ(TP)在岷江出口(挂弓山断面)开始明显增高,在三峡库区内保持平稳,出三峡库区后云池(白洋)断面显著上升。

In order to master the overall situation and variation trend of water quality of the Yangtze River during the 13th Five-Year Plan period,the water quality variation characteristics of the main stream of the Yangtze River from 2016 to 2020 were studied.The variation of surface water quality of the main stream of the Yangtze River in the past five years was summarized.The permanganate index(COD_(Mn)),ammonia nitrogen(NH_(3)-N)and total phosphorus(TP)were used as the research factors to master the characteristics of water quality and pollutant concentration changing with seasons in the Yangtze River;At the same time,the variation law of water environmental quality along the main stream of the Yangtze River in the past five years was studied by using the weighted regression method of the Loess(Locally weighted scatterplot smoothing,Loess).The results show that:(1)The water quality of the Yangtze River has got better year by year during the 13th Five-Year Plan period,and all sections of the main stream meet the quality of class Ⅱ by 2020;(2)ρ(COD_(Mn)),ρ(NH_(3)-N)andρ(TP)showed an upward trend in each quarter,with the maximumρ(COD_(Mn))in the third quarter and the maximumρ(NH_(3)-N)in the first quarter;(3)theρ(COD_(Mn))andρ(TP)of the upper reaches of the Yangtze River were obviously better than those of the middle and lower reaches.Theρ(COD_(Mn))andρ(TP)of the Yangtze River began to increase obviously at the exit of Minjiang River(Gua Gongshan section).It was stable in Three Gorges Reservoir area,and increased significantly after the Three Gorges Reservoir area at the Yunchi(Baiyang)section.