Abstract:

In order to study the impact of 172 m trial impoundment of the Three Gorges Reservoir (TGR) on soluble heavy metals，heavy metal concentration (Cu,Pb,Cd and Cr) of eleven sections in the Yangtze River within the Three Gorges Reservoir was monitored between 2008 and 2010.According to the spatial distribution of TGR,a total of eleven stations from Fuling to Badong covering the upstream and downstream sites of TGR,were selected for this study．The main focus was to examine patterns in spatial distribution and seasonal variability.The influence of water environmental condition on soluble heavy metal concentrations was discussed.The results indicated that the concentration of soluble heavy metals in wet season was higher than that in even and dry season,and the concentration of heavy metals still met the GradeⅠof Environmental Quality Standard for Surface Water (GB38382002).Thus,soluble heavy metal concentration in river water was low,and no apparent pollution was observed. Spatial distributions of heavy metals in sediments and soils showed the decrease in Cu,Pb,Cd,and Cr from upstream to downstream,which was due to an intensification of agricultural and urban industrial practices in upstream area.No significant relationship was found between the heavy metal concentration in water body and that in soil/sediments,and heavy metals of soil/sediments had little effect on water body.Water environmental conditions changed after wet season,especially SS concentration decreased significantly.Soil erosion was considered related to the high SS concentration in wet season.Soil erosion was recognized as one of the major environmental problems in the Three Gorges Region,which had an average annual soil loss of approximately 157 million tons equivalent to a loss of 25 tons of soil per hectare.Soil erosion was one of the main factors for heavy metal transport.In addition to soil erosion,flow rate also affected heavy metal concentrations in the dissolved phase.There were significant seasonal changes in pH levels,dissolved oxygen,water temperature and oxidation reduction potential values except SS concentration.After wet season,water temperature and Eh dropped,but pH and DO increased.pH,dissolved oxygen,water temperature and oxidationreduction potential values were known to be the most important parameters that influence heavy metals removal and transform in water environment system.Water environmental condition had significant effect on distribution patterns of soluble heavy metal in wet season and after that.Overall,the distribution of soluble heavy metal concentrations in the TGR varied in different seasons due to factors such as soil erosion,hydrodynamic conditions,pH,ORP,temperature,SS and so on.These results provide fundamental information for developing better water pollution control strategies for the Three Gorges Reservoir