| At present,the Three Gorges reservoir is the largest reservoir in China.Its construction and operation have changed the original hydrological and hydraulic characteristics of the main stream of the reservoir area.There are many distributed in Three Gorges Reservoir area the size of a tributary of the reservoir impoundment in the backwater situation under the influence of the formation of the Bay entrance tributary backwater area,and has become an important area of sediment deposition.In the process of sediment deposition,pollutants will enter the estuarine sediments due to physical and chemical actions such as adsorption,ion exchange,flocculation,redox and so on.The existing research shows that the reservoir is a typical"Mercury sensitive ecosystem".Therefore,the dynamic characteristics of mercury in the tributary estuary of the Three Gorges Reservoir area should be paid attention to.Therefore,this paper selects typical tributaries in Three Gorges Reservoir area.The area of the Ruxi River Estuary as the research object,set up 4 monitoring points in the estuary,once a month for one year,the hierarchical collection water,sediment and sediment pore water samples were analyzed for total mercury in water?THg?,dissolved mercury?DHg?,the activity of mercury?RHg?and methylmercury?TMeHg?and dissolved methylmercury?DMeHg?concentration;total mercury in sediment samples was determined?THg?and methylmercury?MeHg?content,discusses the dynamic characteristics of different forms of mercury in the branch river,in order to provide research foundation for further study of Three Gorges Reservoir mercury environmental geochemical cycle and ecological risk.The results of the study are as follows:?1?The average content of THg was 2.48±1.43 ng?L-1,of DHg was 0.79±0.34ng?L-1,RHg was 0.21±0.15 ng?L-1 in Ruxi River estuary.The average content of THg is in the normal level of mercury in unpolluted natural water,but it is obviously lower than the water body of the Three Gorges Reservoir Area in the same area.The average content of DHg compared with the other areas of China is high,the RHg content is lower than the content of active mercury in nature;estuary is the average content of TMeHg was 0.31±0.19 ng·L-1,of DMeHg was 0.09±0.06 ng?L-1.The content of TMeHg is obviously higher than that of unpolluted natural water in other areas.The changes of the content of TMeHg and DMeHg in the four sections were basically the same as the time.The TMeHg content appeared in December,May,June and September,and the content of DMeHg was the highest in March,May and June.However,the rule of TMeHg content varies with season and DMeHg content varies with time.The TMeHg content in spring is significantly lower than that in the other three seasons,and the DMeHg content in summer is significantly higher than that in the other three seasons.?2?From the vertical direction,the contents of THg,DHg and RHg showed different degrees of fluctuation in the vertical direction,indicating that there was obvious water stratification in the estuary.The increase of TMeHg content in the bottom water shows that there is a favorable condition for the existence of TMeHg in the TMeHg source or the bottom water body in the bottom water body.?3?The content of THg in the estuarine sediments of average:76.32±9.45 ng?g-1,slightly lower than a survey in Chongqing section of the Three Gorges District WLFZ soil THg content.It shows the same rule as water THg,that is,the mercury content of the tributary is lower than that of the main stream.The average content of TMeHg is0.29±0.05 ng?g-1.Compared with the soil TMeHg content in the area adjacent to the reservoir area,the content of TMeHg in this study area is generally in the middle low level.?4?From the vertical distribution,the content of THg in the surface sediments of the?a‘section sediments is obviously higher than that of the middle and lower sediments,and the content of THg in the surface sediments is enriched.The changes of TMeHg content and TMeHg content in the upper and lower layers of the four sections of the sediments were different.With the increase of the depth of deposition,the content of TMeHg in the surface sediments is decreasing,and the regularity of the change of the middle and deep sediments is not obvious.The content of DHg in the pore water of sediment average:16.31±4.87 ng?L-1.The average value of DMeHg is:1.49±0.50ng?L-1.The overall performance of DHg and DMeHg content in pore water with the change of sediment depth is that the surface sediments are obviously higher than the bottom sediments. |
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