Environmental Geochemical Behaviors Of Heavy Metal In Typical Tributary Sediments In Southwest High Dam Reservoir Area

The southwest high dam reservoir area can provide extremely convenient services for flood control,power generation,agricultural development,and water transportation.At the same time,it also brings a lot of ecological and environmental problems.Therefore,this study focuses on the typical tributaries in the high dam reservoir area.The spatial distribution of heavy metals in the sediment was analyzed to clarify the migration and transformation of heavy metals in the southwestern high dam reservoir area and the assessment of ecological environment risks.The conclusions are as follows:(1)The overlying water in xiangjiaba reservoir area is weakly alkaline.The distribution of temperature and conductivity along the difference is not big.However,the closer to the upstream,the higher the turbidity content will be.The path distribution of the heavy metals each are not identical,but the overall from upstream to downstream is constantly accumulation.However,the nutrient content from upstream to downstream is decreasing,and there is a tendency of eutrophication.Correlation analysis found that all heavy metals except Ni may come from the same source.(2)The nutrients in the sediments of zhongzhongdu river in xiangjiaba reservoir area will harm the environment,while only TN in xining river will harm the environment.The particle size is mainly silt,followed by clay,the least is sand.The minerals are mainly quartz,and there are dolomite,gismondine,calcium aluminum oxide hydrate,thaumasite,calcite,kilchoanite and so on.Most of the heavy metals in zhongdu river had a maximum value at 13 cm,and xining river had a maximum value at 22 cm.The comparison with the soil background value in China shows that Cd,Co,Fe and Mn in zhongdu river will cause pollution,while only Co and Fe in xining river are likely to cause pollution.The correlation analysis found that the heavy metals except Cr were strongly correlated with each other,and most of the heavy metals were similar or identical with TC,TOC and silt.The heavy metals in xining river are also strongly correlated,and most of the heavy metals are from the same sources as TC and clay.(3)There is a phenomenon of "surface enrichment" of total phosphorus in the sediments of xiangxi river in the three gorges reservoir area.And nutrients can cause ecological harm to the environment.Nutrients in the high dam reservoir area in southwest China are gradually accumulated from upstream to downstream,which is contrary to the law of overlying water.The particle size distribution is the same as that of xiangjiaba reservoir area.Mineral composition is mainly quartz,there are clinochlore,muscovite,chlorite,calcite,dolomite and so on.Most of the heavy metals peaked at 153 cm,and the heavy metal content in the high dam area was higher in the upstream than in the downstream.Correlation analysis found that most heavy metal pollution sources are the same or similar.Moreover,TP,TC and TOC can combine with most heavy metals to form complexes,thus affecting the heavy metal migration and transformation process.Heavy metal morphology analysis found that Cd,Co and Mn have high ecological risks and are easy to cause pollution.However,Zn,Ni,Cr,Cu and Fe are least likely to cause ecological harm.The unique hydrodynamic phenomenon formed after the construction of the Southwest High Dam Reservoir Area has caused the migration and deposition of heavy metals.Measures such as dredging sediments and limiting the number of tourists can be done to avoid greater harm to the surrounding environment.(4)The potential ecological environment assessment found that the overlying water of xiangjiaba reservoir area was not polluted by heavy metals and the water quality was good.Cd in the sediment of zhongdu river is at very high risk,Cu is heavily polluted,Co and Pb are moderately polluted,and Mn is also polluted.In the sediments of xining river,Cd is at high risk,Cu is moderately polluted,and Pb,Co,Ni,Zn and Mn are mildly polluted.Cd is a high risk in the sediments of xiangxi river in the three gorges reservoir area,and Pb,Zn,Ni,Co,Cu and Mn are mildly polluted.It can be seen that the heavy metal pollution in xiangjiaba reservoir area is more serious.In the morphological evaluation of the three gorges reservoir area,it was found that Mn was seriously polluted,Cd and Co were moderately polluted,and Pb and Ba were mildly polluted.