| As a typical heavy metal, mercury has multi-form, volatile, long-range transport, toxic and bioaccumulation characteristics. Its pollution has become one of the world's environmental problems. As important parts of terrestrial, soil and aquatic sediments are sources and sinks of mercury. Chaohu Lake is one of the five largest freshwater lakes in China, its basin has always been with concentration of population and intensive agricultural activities. With the accelerating urbanization and industrialization process, the environmental problems of Chaohu Lake Basin are becoming increasingly serious. At present, the research for heavy metal pollution of Chaohu Lake Basin is still limited, most studies focus on the single aspect of Chaohu Lake sediment or soil pollution in the region. In this study, we sample in soil and aquatic sediments, study distribution features of contents in mercury and other elements with purpose of revealing formation causes and regularities of element transfer or transformation and evaluating potential ecological risks.1. The spatial distribution of Hg in deep soil in Chaohu Lake Basin is determined by natural factors, such as soil type and type of parent material. Mercury content is low in the late Pleistocene loess and high in the parent material of river alluvial deposits. Compared to deep soil, mercury content in surface soil is much higher. The spatial distribution of mercury in surface soil is leading by human activities, high-value areas appear in the urban region. 2. From the lake inlets of rivers to internal lake area, mercury content in surface and deep Chaohu Lake sediments showed a decreasing trend. River is the role of the main factors affecting the distribution of mercury in lake sediments, there is a continuous exchange in sediment and water body of mercury. Meanwhile, hydrodynamic condition determines the physical properties of sediment particle size, specific gravity, shape etc., and thus affects the distribution of mercury content indirectly.3. Mercury level in river sediment is generally high, many sample sites appear serious pollution, especially in urban areas. However, under natural conditions, mercury level in river sediment and surface soil is very close, indicating a close relationship between them. Besides mercury from soil, the direct discharge of sewage to river is also the main source in river sediment.4. The migration ability of mercury in soil is weak, mercury content in surface soil is significantly higher than deep soil, mercury content will increase only when it is very high in surface soil. In the horizontal direction, mercury migration ability is also weak, high-value points show a pattern of discrete distribution.5. In vertical direction, migration ability of mercury is relatively strong in lake sediment. Mercury content in surface and deep lake sediments is basically the same. In the horizontal direction, migration of mercury mainly relies on water. In river sediment, from the sources of pollution, mercury content follows the exponential law. The migratory direction of mercury in the surface environment is from soil to water, and then to river sediment.6. Atmosphere plays an important role in the migration of mercury. In study area, the long-type distribution of mercury along the northwest-southeast direction is the embodiment of this effect. In the large-scale zone, atmospheric deposition of mercury cannot be ignored.7. Ecological risk assessment shows, because of the discharge of industrial wastewater and urban sewage, there is a high ecological risk in Nanfei River, which may cause harm to the ecosystem. |
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