江湖关系演变对洞庭湖沉积物重金属污染时空分布的影响

对洞庭湖沉积物重金属的生态风险和污染负荷进行评价,探讨江湖关系演变对洞庭湖沉积物中重金属分布和生态风险的影响,为洞庭湖重金属污染防控决策和湖泊生态风险管理提供科学依据。监测的重金属为Cu、Zn、Pb、Cd、Hg、As,评价方法为潜在生态风险指数法和污染负荷指数法。结果表明,洞庭湖全湖沉积物重金属总体上呈"中度污染"并面临"较高"潜在生态风险,Cd、Hg是洞庭湖沉积物中污染程度和生态风险最大的重金属。在空间分布上,RI值和PLI值总体上均表现为南洞庭湖西洞庭湖东洞庭湖,但不同季节分布不一致,丰水期空间差别最大。在水期分布上,重金属含量、RI值和PLI值总体上均表现为丰水期枯水期,水文和水动力因素可能是产生此差异的重要原因。在季节分布上,RI值和PLI值总体上均表现为夏季最大,春秋季节次之,冬季最小,与洞庭湖水面面积、水位、"四水"径流量的季节变化规律基本吻合,洞庭湖的水情变化一定程度上影响着沉积物重金属污染水平。近年来随着江湖关系的演变,特别是三峡工程的运行,洞庭湖沉积物重金属污染变化显著,洞庭湖沉积物重金属含量相对于1984-2004年的递增趋势,2007-2015年递减趋势明显(Hg除外)。

Influence of River-lake Relation Evolution on Spatio-temporal Variation of Heavy Metal Pollution in Sediments in Dongting Lake

Heavy metals such as Cu, Zn, Pb, Cd, Hg and As in surface sediments of Dongting Lake were monitored during different seasons. The pollution level of heavy metal was evaluated by potential ecological risk index(RI) and pollution load index(PLI), and the influence of the river-lake relation evolution on the spatial and temporal variation of heavy metals in the surface sediments of Dongting Lake was investigated. The results showed that heavy metals in the sediments of Dongting Lake were generally moderately polluted and facing high potential ecological risks. The pollution grade and ecological risk of Cd and Hg were most serious. The spatial distribution of RI values and PLI values were as follows: South Dongting Lake>West Dongting Lake>East Dongting Lake. The distribution of the different water periods were inconsistent, and the spatial difference of wet period was the most obvious. The RI values, PLI values and contents of heavy metals in the sediments of Dongting Lake in dry period was lower than that in wet period, and the the main reason of these differences may be the disparity of hydrology and hydrodynamics in the different water periods. Seasonal distribution of heavy metals in the sediments of Dongting Lake showed that RI values and PLI values pretended the largest in summer, followed by spring and autumn, and the smallest in winter, which was in accordance with the seasonal variation of the area, water level and the runoff of "four inlets" of Dongting Lake. Change of the water regimen may affect the pollution of heavy metals in sediments of Dongting Lake to some extent. In recent years, with the evolution of river-lake relationship, especially the operation of the Three Gorges project, the degree of heavy metals pollution in sediments of Dongting had Lake changed significantly. Compared with the increasing trend of the heavy metals contents in Dongting Lake sediments during 1984 to 2004, the decreasing trend during 2007 to 2015 was obvious (except for Hg).