[Temporal and Spatial Variation of Mercury in the Water of the Ruxi River Estuary, a Typical Tributary of the Three Gorges Reservoir Area].

Four typical estuaries located in the Ruxi River, a tributary of the Yangtze River, were selected to investigate the possibility of mercury pollution in tributary estuaries from the Three Gorges reservoir water storage. Water samples were collected during the water storage period (September to October), the flooding period (November to December), the water withdrawal period (February to March), and the drying period (May to June) to determine the levels of mercury species including total mercury (THg), particulate mercury (PHg), dissolved mercury (DHg), reactive mercury (RHg), total methylmercury (TMeHg) and dissolved methylmercury (DMeHg). The results showed that the concentration of THg and TMeHg in the estuary of the Ruxi River was comparable with that of other reservoirs or natural waters in China. There was a significant difference in the concentration of DHg and TMeHg in the water at different depths, because DHg and TMeHg might be derived from the release of sediment to the overlying water. Comparing the concentrations of different mercury species in the four estuaries during the same period, it was found that the difference of water flow direction during the water storage period could lead to an uneven concentration distribution of THg and PHg in the estuary areas. During the water withdrawal period, the particles in the estuary water could adsorb and carry a large amount of PHg, resulting in higher THg concentration in the water in comparison with other periods. The concentration of TMeHg in the flooding and the drying periods was higher than in the other two periods, indicating that the stable water level might be conducive to the accumulation of methylmercury in the water, and the severe disturbance of the water level could significantly reduce the concentration of TMeHg in the water.

[Effects of Agricultural Activities on Soil Mercury Changes in the Water-Level-Fluctuating Zone of the Three Gorges Reservoir].

Farming in the water-level-fluctuating zone (WLFZ) of the Three Gorges reservoir, China, may result in a wide range of environment problems when the sediment is exposed to air. In this study, Qukou, Chongqing, was selected as the research site due to its large WLFZ area and significant agricultural activities. Four kinds of land use types, including rice, maize, vegetables, and grassland, were selected to investigate the distribution of mercury (Hg) in the surface soil. The results showed that the mean concentrations of soil total Hg (THg), bioavailable Hg (Hg-wh), and methylmercury (MeHg) in the surface soil were 25.80-68.74 ng ·g-1, 0.44-0.88 ng ·g-1, and 0.08-0.85 ng ·g-1, respectively. The concentrations of THg, Hg-wh, and MeHg in non-cultivated soil were higher than those in cultivated soil, indicating that farming disturbances could accelerate soil Hg loss. The MeHg concentrations in both non-cultivated and cultivated soil increased up to the maximum value 1-2 months after drying, and then gradually decreased to a relatively stable level. The peak value was approximately four times higher than that at the end of flooding. The percentage of MeHg to THg (% MeHg) was similar to the distribution of soil MeHg, and the peak value occurred at 1 month after drying. However, when% MeHg decreased to the stable level, no significant difference was found compared to the value at the end of flooding (P>0.05). Furthermore, the soil% MeHg had a significantly positive correlation with Hg-wh (r=0.642, P<0.01), while there was no significant correlation with THg (P>0.05), suggesting that Hg methylation was mainly affected by the bioavailability of Hg in the seasonally inundated soil of the WLFZ.

[Distribution Characteristics and Risk Assessment of Heavy Metals in the Sediments of the Estuary of the Tributaries in the Three Gorges Reservoir, SW China].

To investigate the pollution status of sediments at the junction of the Three Gorges Reservoir area, sediment samples were collected over four seasons from the junction of the estuary located at a tributary of the Ruxi River and the Yangtze River. The content of eight heavy metals (HMs), including Cr, Zn, Mn, Ni, Cu, As, Cd, and Pb, in sediments was determined by ICP-MS. The results showed the average levels of investigated HMs (in mg·kg-1) were Cr (45.24), Zn (46.46), Mn (406.14), Ni (20.885), Cu (12.49), As (7.02), Cd (0.253), and Pb (11.042). The distribution analysis indicated that the levels of HMs at the river mouth were higher than that of the tributaries of the middle reaches and the two sections nearby. The seasonal distribution shows that the heavy metal content in the spring sediment is higher than in summer, autumn and winter. In addition, the correlation analysis indicated that the eight HMs possessed similar homologous characteristics and had common exogenous inputs. The assessment of the Geo Accumulation Index showed slight Cd pollution in the estuary of Ruxi River, and the Potential Ecological Risk index showed that Cd presented moderate ecological risks. The toxic effect of benthonic organisms was possibly correlated to Ni contamination at the intersection of the tributary and main stream, which was supported by the evidence from the sediment quality criteria. In conclusion, the rating of ecological risk at the mouth of the Ruxi River tributary is slight.