不同类型DOM对三峡库区消落带土壤汞甲基化的影响

三峡水库特殊的调度方式导致了消落带的形成,在落干期,消落带上会生长大量以狗牙根为主的植物.在淹没期,狗牙根会发生腐解并释放出溶解性有机质(Dissolved Organic Matter,DOM),消落带作为汞的敏感区,狗牙根释放的DOM对汞甲基化的影响值得关注.为此,本文以狗牙根提取液中的DOM(记为DOM_g)为研究对象,同时选取猪粪中的DOM(记为DOM_z)作为比较,利用室内模拟实验,研究这两种不同类型的DOM对土壤汞甲基化影响的差异,并分析两种DOM的光谱特征,探讨其作用机制.结果表明,两种DOM的光谱特征存在明显的差异,DOM_z的有色可溶解性有机物(Chromophpric Dissolved Organic Matter,CDOM)浓度、芳香性及疏水性组分都高于DOM_g.同时,两种DOM均以类蛋白组分为主,但DOM_z的生物可利用性高于DOM_g.并且这两种DOM均能促进土壤的汞甲基化,且在培养后期促进效果更加显著.但两种DOM的促进效果存在差异,DOM_z的促进效果优于DOM_g.

Effects of different DOMs on mercury methylation in soil in water-level-fluctuating zone of the Three Gorges Reservoir area

The special water level management of the Three Gorges Reservoir has led to the formation of the water-level-fluctuation zone (WLFZ). During the drying period, a large number of plants dominated by Cynodon dactylon (L.), grow on the WLFZ, which would be submerged and release dissolved organic matter (DOM) into soil, sediment or water when the water level increased. However, little is known about the mechanism of the effect of DOM released by Cynodon dactylon (L.) on mercury methylation. Thus, this study takes the DOM from Cynodon dactylon (L.) named as DOM_g as the research object, meanwhile, DOM from pig manure named as DOM_z was selected as comparison. The effects of different types of DOM on soil mercury methylation were studied through laboratory simulation experiments. Significant differences were observed between these selected DOM, and the concentrations of chromophpric dissolved organic matter (CDOM), aromatic and hydrophobic components of DOM_z were higher than DOM_g. At the same time, the main components of both DOMs were protein-like substances, but the bioavailability of DOM_z was higher than DOM_g. Moreover, both DOMs could promote mercury methylation in the soil and the effect was more obvious in the later culture stage. In addition, there were differences in the promotion effects between these two DOMs, and the promotion effect of DOM_z was significantly higher than that of DOM_g.