Actualities And Problems Of Water Environment In The Dam-site Of Yongding Bridge Reservoir

The proposed Yongding Bridge reservoir is located on the Liusha River,and it can provide water for a new city,Hanyan,and the surrounding rural areas.The water also will be used for the rural resettlement and enterprises along the channels,which is reasonable arranged.What's more,the water needed by the environment and ecology must also be considered.Therefore,for rational exploition,utilization of water resources and protection of water resources,it is necessary for us to fully understand the chemical characteristics,heavy metal pollution and other kinds of pollutions.This paper showed the groundwater systems distribution,chemical characteristics, content of heavy metal and the pollution levels of nitrogen in the water body of dam-site,Yongding Bridge,through the use of geological-hydrogeological surveys, hydro-geochemical methods etc.It also provides a simple assessment of the ecological environment and presents the following conclusions:(1)Dam-site area groundwater can be divided into several water systems,which are Taishanshi ditch,Noâ… ditch,Noâ…¡ditch,and Feishui ditch groundwater systems in the left bank and Yongding bridge-Yudong ditch,shattered fault zone of Yudong ditch groundwater systems in the right bank.(2)pH scale of surface water in dam-site is in the range from 7.5 to 8.6,while the groundwater is in the range from 6.4 to 8.4.Both is in the normal range of 6 to 9,which showed by the natural water.Temperature of water in dam-site changes between 7.2℃and 12.0℃.From the relationship of temperature versus pH scale,one can determined if the water body has been affected by man-kind according to temperature changing. The composition of quantity element of water in dam-site shows that the chemistry forms of water bodies mainly is HCO₃-Ca·Mg type,except individuals to be SO₄·HCO₃-Ca and HCO₃·SO₄-Ca·Mg type.The Cation of water in dam-site mainly be Ca²⁺,Mg²⁺,whose average ion mole-equivalent is 65.5 percent and 25.5 percent respectively;while the anion mainly be HCO₃^-,whose average ion mole-equivalent is 71.3 percent.The degree of mineralization of the water in dam-site changes in the range of 52.31～337.6mg/L.and the majority is relatively low salinity water.From the correlation beteen the various ions and the salinity,the water salinity in the study area increases mainly by Ca²⁺,Mg²⁺,HCO₃^-.SO₄^2-.K⁺,Na⁺ contribute little to the degree of mineralization,which shows that the chemical composition and formation of the groundwater in the region,related to outcropping formation lithology.(3)The chemical characteristic of the water in dam-site is mainly affected by the weathering of dolomite rock.Some samples are also affected by the oxidation of pyrite.Simultaneity,groundwater hydrodynamic conditions,weathering of evaporates and digestions of Ca in the soil also affect the water.Apart from the stratum and the groundwater hydrodynamic conditions,agricultural production and frequent human activity are also important factors.(4)Among the heavy metals(Pb,Cu,Cd,Fe and Mn)in the water in dam-site, except for the Pb sampling attained the state's third-level quality,the content of other heavy metals are low and lower than the national standard for the second-level waters environmental quality.The content of Pb changes in the range of 0.009mg/L～021mg/L,The content of Cd changes in the range of 0.001mg/L～0.005 mg/L,which is higher than the others.(5)The concentration of the nitrate nitrogen content(N)of water in dam-site changes in the range of 0.628mg/L～1.747mg/L.Nitrite nitrogen are not detected except H₇ and Q₈.Apart from individual samples,nitrate nitrogen and nitrite nitrogen are below national standards for the first-level waters environmental quality. Ammonia concentration changes in the range of 0.009mg/L～0.466mg/L,except samples H₁₇,H₁₈,Q₁ and Q₅,and is below the national standard for the third-level waters environmental quality.(6)Based on the conclusion above,this paper devided the region to be three protection zones considering the specific geology,hydro-geological conditions and the degree of water pollution,and presented specific ecological and environmental protection measures.