三峡库区消落带甲基汞变化特征的模拟

Simulation on the variation characteristics of methylmercury of the water-level-fluctuating zone in the Three Gorges Area

为探寻三峡水库消落带在干湿交替条件下甲基汞的变化规律,以库区典型消落带土壤为研究对象,采用模拟试验,研究了干湿交替条件下消落带土壤和水体甲基汞含量和动态变化趋势及其影响因素.结果表明:淹水过程会促进土壤无机汞向有机汞转化,土壤甲基汞含量在淹水和落干过程均呈现先增加后减少的趋势;随着干湿交替周期的增加,土壤甲基汞含量增加,第二次淹水后土壤甲基汞平均含量比第一次淹水增加了22.13%,第二次落干后土壤甲基汞平均含量比第一次落干增加了58.17%.第二次淹水过程土壤甲基汞占总汞的比例明显高于第一次淹水,土壤中汞的甲基化主要与干湿交替循环有关.土壤淹水后会迅速向水体释放甲基汞,水体中甲基汞含量明显增加,两次淹水过程增幅分别为119.42%和334.72%,水体甲基汞和土壤甲基汞之间无显著相关.干湿交替环境土壤甲基汞含量主要受pH值、有机质含量、Eh和土壤含水量等因素的影响;水体中甲基汞含量的影响因素则主要有水体pH值、DO、DOM、水温等.

To investigate variation of methylmercury of the water-level-fluctuating zone in the Three Gorges Reservoir Area, dynamic changes of methylmercury contents and influencing factors were analyzed in soil and water by simulation experiment. The results showed that the methylmercury contents in soil initially increased but then decreased in both the flooding and drying process. Flooding could promote the transformation of inorganic mercury into organic forms. Methylmercury contents in soil increased with the number of wet-dry cycles. The average methylmercury content in soil during the second flooding phase was 22.13% higher than the first one, whereas the average methylmercury content increased by 58.17% in the second drying phase. The ratio of methylmercury to total mercury in soil during the second flooding phases was significantly higher than that during the first, and the alternate wet-dry environment was beneficial to mercury methylation. Methylmercury in soil was rapidly released into water, resulted in an obvious increase of methylmercury content in water. Methylmercury contents in water increased by 119.42% after the first flooding cycle and 334.72% after the second. The results showed that there was no correlation between methylmercury contents in water and methylmercury contents in soil. Methylmercury contents in soil were significantly affected by soil pH, organic matter content, Eh and soil moisture. Meanwhile, water pH, DO, DOM and temperature considerably influenced methylmercury contents in water.