鄂东南云中湖近50 a沉积物微量元素记录

摘要

近年来湖北省通山县九宫山风景区的云中湖污染日益严重,已引起诸多关注,然而目前并不清楚该湖生态环境变化轨迹以及原因.通过对云中湖沉积物年代学、微量元素、有机碳和粒度分析,结合聚类分析和地质累积指数等方法,揭示近50 a云中湖环境变化历史.结果表明,云中湖沉积物中14种微量元素含量随深度呈相似的变化趋势,且两两之间呈显著正相关关系,反映元素输入物源的一致性.在20世纪80年代前,湖底沉积物中微量元素含量变化很小,表明流域环境变化较小,20世纪80年代以来微量元素含量呈波动变化,其中在10和4 cm深度出现2次明显低值,下部低值与沉积物粒度增粗相对应,这可能是由于气候和人为旅游开发原因所致;顶部低值与有机碳含量增加相一致,反映了水体富营养化过程以及有机质输入对沉积元素的稀释作用.1993年以来元素V/Cr比值明显增加并超过2.0,反映底层水体向缺氧状态转变.各元素的地质累积指数小于0.5,表明云中湖重金属污染程度处于较轻水平.综合分析云中湖沉积物研究记录可知,20世纪90年代之前云中湖湖泊环境相对稳定,20世纪90年代以后流域环境发生明显变化,水体环境呈恶化趋势.%The pollution of the Yunzhong Lake in the Jiugongshan Scenery Spot of Tongshan County,Hubei Province has been aggravating with each passing day in the recent years,which has aroused concerns from all walks of life.However,it is still unclear about trajectory and the main causes of the changes in ecological environment of this lake.The history of the environmental changes in the Yunzhong Lake during the past fifty years were reconstructed based on chronological and physic-chemical analyses of the sediments in the lake for trace elements,organic carbon and particle size composition,coupled with cluster analysis and geo-accumulation indexes.Results show that 14 trace elements were found in the sediment of the lake and their contents varied with depth of the sediment in similar trends with depth and correlated positively with each other,indicating that the fourteen elements come from the same material source.The trace elements in the sediment before the 1980s varied very slightly in content,indicating that the environment of the catchment did not change much during that time period,but they began to fluctuate in content after the 1980s,with two drops at the depths of 10 cm and 4 cm.The low value in the lower layer corresponded to the trend of the sedimentary becoming coarser in particle size,which could probably be attributed to climatic changes and the development of tourism,while the low value in the upper layer was concurrent with an increase in organic carbon content,reflecting the eutrophication process of the water body and dilution effect of the input of organic matter on contents of the trace elements.V/Cr ratio of the elements increased significantly and exceeded 2.0 after 1993,reflecting that the bottom layer of the water body turned to be oxygen deficient.Geoaccumulation indices of all the elements are lower than 0.5,indicating that the lake is only slightly polluted with heavy metals.Comprehensive analysis of the research data reveals that the environment was relatively stable before the 1990s,and then the catchment environment underwent significant changes,particularly the water body environment,showing a trend of deterioration.Therefore,it is essential and urgent for us to strengthen water pollution control in the Jiugongshan tourist areas,in order to protect this precious alpine lake ecosystem.