Environmental Geochemistry Of Heavy Metals In Yueliang Lake In West Jilin Province

Lake is an important ecosystem on the earth surface, with multiple functions forregulating climate, maintaining ecosystem balance, rearing aquatic animals, irrigation andflood prevention, etc. With the rapid development of industry and agriculture and theincrease of population, the pollution of water including the lake becomes increasinglyserious. Among water pollutions heavy metal pollution is characterized by the concealment,persistence, irreversibility and non-degradability, so the pollution has been highly focusedby environmental sector.Yueliang Lake is located in the hinterland of Songnen Plain. The lake is not only thesecond largest freshwater lake in the western Jilin province, and also the major freshwaterfish production base and famous resort area, so its water quality has a great impact onfarming, livestock breeding, fishing productions, and resident the health within the area.Therefore, the comprehensive investigation of heavy metal distribution within YueliangLake is of great significance.The heavy metal in water, suspended solids in water, superficial layer of bottomsediment, sediment core and aquatic products were measured in this study in order toinvestigate the heavy metals distribution within Yueliang Lake, with which theenvironmental quality of the water body is evaluated, and to provide a scientific basis forthe healthy developments of the regional economics and society, and the ecological andenvironmental protections. The result obtained in this study is as follows:（1） The content order for major cations in seasons is nearly the same in the water ofYueliang Lake, which is Na⁺>Ca²⁺>Mg²⁺>K. In contrast, the content order of major anionsis changed with seasons. In high water season, the content order for major anions wasHCO₃^->SO₄^2->CO₃^2->Cl-; in dry season, the content order was HCO₃^-> SO₄^2->Cl->CO₃^2-.The hydrochemical type for Yueliang Lake is HCO₃^--Na⁺. The content order for heavymetals in lake water of seasons is Zn>As>Cu>Pb>Hg. The content order for heavy metals in suspended solids material in different seasons is Mn>Zn>Pb> Cu>As>Cd>Hg.（2）The relative mineral content in superficial layer of bottom sediment of YueliangLake is quartz>plagioclase> K-feldspar> illite/smectite mixed-layer minerals> calcite>illite> kaolinite> dolomite. The order of heavy metal content is: Mn>Zn>Pb>Cr>Cu>As>Cd>Hg. The variation coefficient is less than0.5, indicating that the heavymetal content is not varied too much. The contents of As, Cd, Cr, Cu, Hg, Mn and Zn insuperficial layer of bottom sediment are significantly correlated each other, andsignificantly correlated with N, P, organic carbon, Al₂O₃, and Fe₂O₃too. As, Cd, Cr, Cu,Hg, Mn and Zn are mainly derived from the rocks and soils around the lake, and theirgeochemical behaviors are constrained by the contents of organic carbon, Al₂O₃, and Fe₂O₃.Pb has poor relationship with As, Cd, Cr, Cu, Hg, Mn, Zn and N, P, organic carbon, Al₂O₃,Fe₂O₃, suggedting that the origin of Pb is different from the other heavy metals, which maybe probably derived from man-made pollution.（3） There are two obvious accumulation peaks of¹³⁷Cs in the sediment core: the mainaccumulation peak at position of32cm is corresponding to the year of1963; and thesecondary accumulation peak at position of18cm is corresponding to the year of1986, theaverage deposition rate calculated during1986-2006is0.90cm/a. Using three models of²¹⁰Pbex, we can get the result of depositional age of the sediment core with a length of156cm: the CIC model （74years）<the CFCS model （120years）<the CRS model （172years）. Compared with the time scale of¹³⁷Cs, the dating result of CIC model issignificantly deviated from it; the dating result of CFCS model is not reliable when thesediment depth is greater than64cm; and the dating result of CRS model is more reliablethan the results of CIC and CFCS model. The average deposition rates of Yueliang Lakecalculated by using the dating results of CRS model of²¹⁰Pbexare:0.33cm/a during theyear of1835-1898,1.09cm/a during the year of1898-1920,2.21cm/a during the year of1920-1961, and0.94cm/a during the year of1961-2006. The yearly variations ofdeposition rates reflect the impact of environmental changes and human activities aroundYueliang Lake and its watershed. The contents of As, Hg, Mn, Cu, Pb, Zn, Cr show adecreasing trend with increasing depth in the sedimentary core, but at the position12-16cm （during the year of1992-1995）, the contents of As, Hg, Cu, Zn, etc. reached the maximumvalue.（4） The contents of As, Pb, Hg, Cr and Cd are relatively low in different types fishesin different seasons and of Yueliang Lake, and their contents are roughly in the order ofZn>Mn> Cu>Hg>Cr>Pb>As>Cd.（5） The water quality of Yueliang Lake is good, and it is up to the surface waterstandard one in different seasons. Both the geo-accumulation index and the potentialecological risk index of heavy metals in bottom sediment are lower, indicating that thepotential ecological risk of heavy metals in the sediments is very low. The contents of As,Cd, Cr, Pb, Cu in the fish from the low and high water seasons of Yueliang Lake are lowerthan those levels of the national and industry food standards. In general, the ecologicalenvironment of Yueliang Lake is safe.