1990~2016年湘江流域水质时空变化及驱动因素分析

Analysis of Spatiotemporal Variation and Driving Factors of Water Quality in the Xiangjiang River Basin from 1990 to 2016

为探讨湘江全流域水质时空变化特征及其驱动机制,收集湘江流域1990~2016年共26年113个站点16个水质参数数据,采用水质指数法等对流域水质进行综合评价并识别其主要污染物,分析其形成机制,重点剖析水位和土地利用格局对水质的驱动作用.结果表明:(1)研究期间湘江流域整体水质等级为“良好”.时间上,水质呈现出先恶化再改善的变化态势,1990~2003年为水质恶化阶段,2004~2016年为水质改善阶段;水质季节变化不明显,丰水期水质波动较大.空间上,干流水质污染负荷从中游、下游和上游依次减小.上游支流水质最好,水质较差区域主要分布在中下游支流河口处,尤其是有多条支流汇流的地方.(2)有毒重金属具有毒性、持续性和生物累积性的特点,在水体中若超过一定浓度就难以净化,对自然环境和人类健康都危害极大.毒性金属指标(CI1)是影响湘江水质的主导因素,其中汞(Hg)和镉(Cd)是影响湘江流域整体水质的主要参数.(3)水位通过稀释环境参数对湘江水质产生正面影响,土地类型对重金属浓度影响不大,林地可以起到改善水质的作用,草地在较大尺度范围(≥5 km)与高锰酸盐指数存在负相关,流域内水体、耕地和不透水面面积的增加使得水体粪大肠菌浓度偏高的概率增加.(4)土地利用方式对水质的解释能力呈现出随缓冲区尺度增大而增强的态势,在河岸带10 km缓冲区尺度上,土地利用方式对水质的解释度最高,是湘江水质治理的有效尺度.研究显示,湘江流域重金属污染与其他污染驱动因素不同但区域差异均较明显,因此污染治理应分类和因地施策.

In order to explore the spatiotemporal variation characteristics and driving mechanism of water quality in the Xiangjiang River Basin,the data of 16 water quality parameters at 113 stations over 26 years from 1990 to 2016 in the Xiangjiang River Basin were collected for synthetically assessing the water quality and identifying its main pollutants through the water quality index and other methods.The causal mechanism of water quality,especially the driving effect of water level and land use pattern,was analyzed.The results showed that:①The overall water quality grade of the Xiangjiang River Basin during the study period was“good.”However,the water quality deteriorated first(from 1990 to 2003)and then improved(from 2004 to 2016).The season variation in water quality was not obvious,but the water quality fluctuation of the wet season was larger.The water pollution load of the main stream decreased successively from the middle reaches,downstream reaches,and upstream reaches.The upstream tributaries had the best water quality,whereas areas with poor water quality were mainly distributed at the mouth of the middle and downstream tributaries,especially in areas where multiple tributaries converged.②Toxic heavy metals had the characteristics of toxicity,persistence,and bioaccumulation.If they exceeded a certain concentration in water,they were difficult to purify,posing great harm to the natural environment and human health.The toxic metal index(CI1)was the leading factor affecting water quality,in which Hg and Cd were the main parameters affecting the overall water quality of the Xiangjiang River Basin.③The water level had a positive impact on the water quality of the Xiangjiang River by diluting environmental parameters.Land type had little effect on heavy metal concentration,whereas forest land could improve water quality.Grassland had a negative correlation with permanganate index over a large scale range(≥5 km).The increase in water bodies,arable land,and impermeable surface areas within the watershed increased the probability of high fecal coliform concentration in the water body.④With the increase in buffer distance,the water quality explained by the land use pattern increased.On the scale of 10 km buffer zone in the riparian zone,the explanation degree by land use pattern on water quality was the highest,which was an effective scale for water quality control of the Xiangjiang River.This research showed that the driving factors of heavy metal pollution and other pollution were different,but their regional differences were all obvious in the Xiangjiang River Basin.Therefore,pollution control should be classified and taken according to local conditions.