干湿交替条件下三峡水库消落带土壤汞形态变化

Mercury speciation transformation in soil of the water-level-fluctuating zone in the Three Gorges Area under alternative dry-wet condition

对三峡水库消落带干湿交替条件下土壤汞赋存形态变化、影响因素和生物可利用性进行了模拟研究．结果表明：干湿交替条件下土壤汞会发生形态转化和释放，总汞含量逐渐降低，两次“淹水一落干”后总汞含量降低了28．9％．土壤中不同汞形态所占比例分别为：水溶态汞（Hg—W）6．1％～16．8％；交换态汞（Hg—e）5．8％～12．9％；碳酸盐结合态汞（Hg．c）4．5％～17．7％；腐植酸结合态汞（Hg—h）12．5％～29．9％；有机质结合态汞（Hg—O）5．3％～12．8％，残渣态汞（Hg-r）34．5％～51．6％．土壤中汞形态以残渣态（Hg．r）为主，干湿交替条件下其所占比例有降低的趋势，腐植酸结合态汞（Hg-h）则逐渐增加，生物可利用态汞（Hg—W、Hg—e、Hg—C和Hg-h之和）总体呈增加趋势，易被水生生物利用并进入食物链，可能会增加水库生态系统的汞生态风险．

The speciation transformation, influencing factors, as well as bioavailability of mercury （Hg） in soil of the water-level-fluctuating zone in the Three Gorges Reservoir Area were simulated. The results showed that Hg in soil under alternative dry-wet condition could be transformed and re- leased. The total Hg content in the soil was decreased by 28.9% after two ＂wet-dry＂ cycles. The percentages of the six Hg species （water-soluble, exchangeable, carbonate-bound, humics-bound, organic-sulf and residual Hg） were 6.1% -16.8% , 5.8% -12.9% , 4.5% -17.7% , 12.5% - 29.9%, 5.3%-12.8%, and 34.5%-51.6%, respectively. It was found that Hg in soils was dominantly residue Hg, whose percentage tended to decrease under alternative dry-wet condition. The percentage of humics-bound Hg increased gradually and an increase of the percentage of bio- available Hg （ including water-soluble, exchangeable, carbonate-bound, and humics-bound Hg） after two wet-dry cycles were observed. Bioavailable Hg could be easily absorbed by aquatic orga- nisms to enter the food chain, which might increase the ecological risk of Hg in the reservoir.