Effects of Soil Properties and Flooding on the Mobility and Transformation of Mercury in a Temperate Riparian Wetland

Abstract

Three fractions of mercury (mobile, semi-mobile, and non-mobile mercury) were detected in the soil of an estuarine wetland in Nansi Lake, which is on the east route of China's South-to-North Water Transfer Project. The correlations between these mercury fractions and soil properties were examined under different levels of toxicity. Furthermore, the effects of two flooding conditions (permanent flooding and seasonal flooding) on mercury mobility were analyzed. Results showed that soil pH was negatively correlated with mobile mercury, whereas semi-mobile mercury was positively correlated with total aluminum, iron, and manganese. Moreover, free alumina was positively correlated with all three fractions of mercury. Our study suggests that high contents of soil acid and free alumina might promote wetlands as “sinks” for mercury sequestration, along with low concentrations of organic matter and manganese. In addition, seasonally flooded wetland might limit the production of toxic mobile mercury more than permanently flooded wetland. Large areas of seasonally flooded wetlands in the watershed are permanently flooded by the water transfer project, which elevates the water level during the dry season. As a result, the potential toxicity of mercury may increase in the watershed during water transfer, which should gain more attention.