基于Mann-Kendall法的三峡库区长江干流入出库断面水质变化趋势分析

Trend Analysis with Mann-Kendall Test on Water Quality of the Mainstream Inflow and Outflow for the Three Gorges Reservoir of Yangtze River

三峡大坝对三峡库区水生态环境的影响广受国际关注,水质问题关乎三峡库区生态环境安全和社会经济发展。基于中华人民共和国生态环保部发布的2004～2017年三峡库区长江干流入库断面(重庆朱沱)和出库断面(湖北宜昌南津关)水质因子(DO、高锰酸钾指数和氨氮)监测数据,采用Mann-Kendall非参数统计检验法分析水库水质变化趋势。结果表明:入库和出库断面DO均保持Ⅰ级水质标准,均呈不显著下降趋势;入库断面高锰酸钾指数呈上升趋势,氨氮呈下降趋势,近年均保持Ⅱ级水质标准;出库断面高锰酸钾指数和氨氮呈显著下降趋势,近年保持Ⅰ级水质标准。相对于入库断面,出库断面水质在逐步改善,近年出库断面水质优于入库断面。突变趋势分析结果表明:入库断面各项水质因子均存在不显著的突变,突变时间主要发生在2005年和2008年;出库断面水质因子无突变,表明出库断面水质维持状况比入库断面平稳。库区水体中DO、高锰酸钾指数和氨氮含量与水情特征和库区生产生活方式密切相关;水库水位抬高,水流速度下降和泥沙沉积,有利于污染物沉入底泥。三峡水库水质维持及改善需要控制和削减农业面源污染、工业污水排放、城镇生活污水排放和船舶污染排放。

The impact of the Three Gorges Dam on aquatic ecosystem and environment in the Three Gorges Reservoir Area(TGRA)has received international attention.Water quality is an essential factor to the ecological security and sustainable socioeconomic development for TGRA.By setting Zhutuo section in Chongqing as inflow and Nanjinguan section in Yichang,Hubei province as the outflow of the TGRA,the Mann-Kendall method was applied to test the inflow and outflow water quality trend with the monitoring dataset(DO,CODMn,NH3-N)published by the ministry of environmental protection of the People’s Republic of China from 2004 to 2017.The results showed that DO of the inflow and outflow sections remained class I and under a not significant upward trend.CODMn of inflow was under an upward trend while NH3-N was under a downward trend,either maintained classⅡin recent years.CODMn and NH3-N of outflow had a significant downward trend and remained classⅡin recent years.Compared to the inflow,the water quality of outflow was better and gradually improved.The mutation trend analysis showed that the water quality monitoring factors of inflow had a non-significant mutation,mainly occurred in 2005 and 2008.No mutation in outflow which indicated the water quality of outflow remained more stable than inflow.The concentration of DO,CODMn and NH3-N are closely related to the characteristics of water situation,the production and lifestyle in the reservoir area.With the rising water level,declining water flow speed and sediment deposition,pollutant is sinking into the sediment effectively.In order to maintain and improve water quality of the Three Gorges Reservoir,the control and reduction in agricultural non-point source pollution,industrial sewage,urban sewage emissions and shipping emissions are in need.