盐度对典型滨海湿地沉积物汞甲基化的影响

Effect of Salinity on Mercury Methylation in Sediments of A Typical Coastal Wetland

盐度是滨海湿地最重要的环境特征之一,然而滨海湿地盐度的变化如何影响汞甲基化过程目前仍缺乏相关研究。基于室内培养的方法,研究了厌氧条件下江苏盐城滨海湿地沉积物甲基汞质量分数和硫酸盐还原菌绝对含量随盐度梯度(0、0.6%、1.2%、1.8%、2.4%和3.0%)的变化特征。结果表明,海盐处理下,随着盐度的升高,甲基汞质量分数总体呈现先增加后减少的趋势,1.2%盐度下,沉积物汞甲基化程度最高;随着培养时间(1—29 d)的增长,甲基汞质量分数总体也呈现出先增加后减少的趋势,培养8 d时,沉积物汞甲基化程度最高。海盐处理下,随着盐度的升高,硫酸盐还原菌的绝对含量总体增加,表明海水盐度未对硫酸盐还原菌生长产生盐胁迫;随着培养时间(1—29 d)的增加,硫酸盐还原菌的绝对含量表现为先增加后减少的趋势,当培养时间超过15 d时,硫酸盐还原菌的生长会受到抑制。该实验条件下,硫酸盐还原菌绝对含量与甲基汞质量分数间无显著线性相关,可溶性有机碳对甲基汞质量分数随时间的变化具有较高的解释度。该研究表明滨海湿地盐度的时空变化对汞甲基化过程有较重要的影响。研究结果可为预测盐度变化所带来的甲基汞生态风险提供了依据。

Salinity is one of the most typical environmental features in coastal wetlands. However, how salinity affects the process of mercury methylation under anaerobic condition in coastal wetland sediments remains unclear. Using a microcosm experiments, we investigated the effects of simulated salinity(0, 0.6%, 1.2%, 1.8%, 2.4% and 3.0%) on methylmercury contents and absolute abundance of sulfate-reducing bacteria in sediments from the coastal wetland of Yancheng, Jiangsu Province, China. The results showed that the methylmercury content in the sediments had an overall increase at the beginning and then decreased during the entire incubation period(1-29 d), and it reached the highest value at the 8th day. In addition, the methylmercury content first increased and then decreased with the increase of salinity, and was the highest at the salinity of 1.2%. Similarly, the absolute abundance of sulfate-reducing bacteria showed a unimodal pattern with the incubation time. The salinity used in this study probably did not cause salt stress to the growth of sulfate-reducing bacteria. However, the abundance of sulfate-reducing bacteria decreased after being incubated for 15 days. There was no significant linear correlation between the absolute abundance of sulfate-reducing bacteria and methylmercury content. Dissolved organic carbon could explain a large proportion of the changes in the methylmercury content over time. These findings highlight the important role of the spatio-temporal changes in salinity for the production of methylmercury in coastal wetlands, and can provide a basis for predicting the ecological risk of methylmercury caused by the variation in salinity.