干湿交替条件下三峡水库消落带土壤汞形态变化

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-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.

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

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 released. 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 bioavailable 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.