| There are three main research topics in this thesis, namely, (1) the foundation and application of methylmercury in natural water by means of the distillation-ethylation combined with gas chromatography (GC)-cold vapor atomic fluorescence spectrometer (CVAFS); (2) a preliminary study on speciation and distribution of mercury in Wujiang River; (3) studies on reservoir effect on the mercury distribution in the Wujiang River and the mercury transformation within the reservoir-a case study from Wujiangdu Reservoir and Dongfeng Reservoir, two different aged hydroelectric reservoirs both located on the up-mid mainstream of the Wujiang River. Through the detailed studies reported in this thesis, some main conclusions were obtained as follows:1. An analysis technique is established for determination of methylmercury in natural water based on the distillation-ethylation combined with gas chromatography (GC)-cold vapor atomic fluorescence spectrometer (CVAFS). Methylmercury in water sample reacted with sodium tetraethyl borate after distillation, forming volatile methylethyl mercury, catched and concentrated in by nitrogas gas blowing; then determined with GC-CVAFS. The recovery rate of the technique is 88.2%~108.4%, and the average relative standard deviation is 5.4%. The methylmercury detection limit is 0.009ng/L for 45mL sample determined. This method is sufficient to accurately measure methylmercury in most ambient water, and quite simple, fast compared to other earlier methods in China.2. The mercury concentration in the Wujiang River was much higher than those reported about other undisturbed rivers in North American and Europe. The average total mercury was 65.9 ng/L in high flow period and 16.9 ng/L in low flow period, respectively. The mercury in Wujiang River was mostly associated with suspended particles, and the particulate mercury constituted on an average of84% of the total mercury in high flow period, of 52% of the total mercury in low flow period, respectively. The pilot study indicated that Wujiang River is contaminated in terms of mercury in a certain extent.3. Using input-output budgets, annual net yields of total mercury in Dongfeng Reservoir was - 57785.1 g/yr, constituting 40.2% of the total inputted mercury; while in Wujiangdu Reservoir, annual net yields of total mercury was - 23273.7 g/yr, constituting 14.0% of the total inputted mercury. Both hydroelectric reservoirs were believed to be the "reservoir" of the total mercury. Contrary to the total mercury, the two hydroelectric reservoirs acted as the "source" of the methylmercury. Annual net yields of methylmercury in Dongfeng Reservoir was +284.7g/yr, accounted for 4.4% of the total inputted methylmercury; while in Wujiangdu Reservoir, annual net yields of methylmercury was +6622.0 g/yr, accounted for 80.1% of the total inputted methylmercury. Wujiangdu Reservoir was a significant methylmercury source compared to the Dongfeng Reservoir.4. Obviously seasonal changes of total mercury and methylmercury in water body within the two reservoirs were obtained during the three sampling periods, with the concentrations in spring were generally higher than that of the winter and the summer. In winter, spring and summer, the averaged total mercury levels in water-column in Wujiangdu Reservoir were 9.0 ng/L, 16.0 ng/L and 7.9 ng/L, respectively; while in Dongfeng Reservoir the averaged total mercury levels were 8.2 ng/L, 12.5 ng/L and 9.4 ng/L, respectively. In view of methylmercury, the averaged concentration in Wujiangdu Reservoir was 0.74 ng/L in winter, 0.97 ng/L in spring and 0.89 ng/L in summer, respectively; and in Dongfeng Reservoir was 0.74 ng/L in winter, 1.12 ng/L in spring and 0.38 ng/L in summer, respectively. The methylmercury correlated with the total mercury in both reservoirs, but only significant at the 0.05 level (r=0.451 *, n=24, in Wujiangdu Reservoir; r=0.471 *, n=27, in Dongfeng Reservoir). The distribution, speciation and levels of mercury within the reservoir water body were governed by severalfactors, such as t...
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