Study On Release Characteristic Of Mercury From Soil In Water Level Fluctuation Zone Of Three Gorges Reservoir

In the last decades, dam foundation has resulted in the increase of mercury contents in fish, which has get international attraction. The Three Gorges dam was huge project and considerable attention has been focused on its impact on human beings. Mercury pollution brought by dam building has become an active field of research worldwide by scientists engaged in relevant subject. According to existing studies and forecasts, mercury pollution source was due to more mercury in soik exploitation of mercury mine and higher mercury in coal; after impounding, mercury reactivity of the reservoir will increase by 0.35—1.5 times, and mercury contents in fish will be 1.4².5times higher than the present amount. After flooding, large area of soil was drowned in drawdown area, and existed in alternate wetting and drying for a long time, which affected greatly transportation and transformation of mercury in soih water and air. However, release characteristic and mechanism are not fully understood and further studies are required. In this paper, typical soils of water level fluctuating zone of the Three Gorges Reservoir were collected and then mercury adsorption-desorption characteristics were studied depending on adsorption-desorption experiments. On the other hand, mercury release characteristics and relations with environment factors were discussed in different type of soils with different pollution during flooding and air-drying respectively by simulated experiments.The results of Hg²⁺ adsorption to five soils could be fitted to three isothermal adsorption equations including Langmuir, Freundlich, Temkin, among which Langmuir equation was the most effective. The order of the maximal amount of Hg²⁺ adsorption was: purple alluvial soil > neutral purple soil>yellow soil>grey-brown alluvial soil>acid purple soil. The order of the adsorption forces of Hg²⁺ was: yellow soil > acid purple soil > neutral purple soil > purple alluvial soil> grey-brown alluvial soil. Langmuir and Freundlich equations explained better Hg²⁺ desportion characteristics of five soils, except that neutral purple soil was not fitted to Freundlich equation. The order of the maximal amount of Hg²⁺ desorption was: grey-brown alluvial soil>purple alluvial soil >neutral purple soil > acid purple soil>yellow soil.Mercury contents in water have two peak values after flooding, and the more mercury the same kind of soil has, the more was mercury content of water. The first peak occurred earlier, the second appeared relatively later. In whole course, the order of the maximal release flux of mercury was: acid purple soil > neutral purple soil > purple alluvial soil > grey-brown alluvial soil > yellow soil. Among assayed factors in this experiment, only conductivity , Fe²⁺ and Mn²⁺ contents of alluvial soils were better correlative with mercury content in water, others were not obvious. Dissolution...