A simulation study of mercury release fluxes from soils in wet-dry rotation environment

A simulative mesocosm study was conducted to evaluate the influence of wet-dry rotation on mercury (Hg) flux from soil/water to air and the distribution of Hg species in water as well as Hg chemical fractions in soil. Three types of soil were employed including two kinds of paddy soil, Typic Purpli-Udic Cambosols (TPUC) and Xanthi-Udic Ferralosols (XUF), as well as the Alluvial Soil (AS) from Three Gorge reservoir area in Chongqing, China. The results showed that Hg fluxes in wetting periods were significantly higher than that in drying periods. It might be due to the formation of a layer of stable air over the water surface in which some redox reactions promote evasion processes over the water surface. This result indicated that more Hg would be evaporated from the Three Gorge reservoir and paddy soil field during the flooding season. Hg fluxes were positively correlated with air temperature and solar irradiation, while negatively correlated with air humidity and the electronic conductivity of water. Hg fluxes from AS and TPUC were significantly higher than that from XUF, which might be due to the higher organic matter (OM) contents in XUF than TPUC and AS. The reduction processes of oxidized Hg were restrained due to the strong binding of Hg to OM, resulting in the decrease in Hg flux from the soil.