The Distribution Of Heavy Metals In Dianchi Lake And Ecological Risk Assessment

Heavy metals were highly concerned in Pollution Ecology with their toxicity,not degradation and bioaccumulation.Sediments are both sink of heavy metals in water ecosystems and are also an important source of heavy metals pollution.Therefore,it is necessary to investigate the concentration,time-space distribution,stability and biological availability of heavy metals in sediments and the accumulation of heavy metals in food chain.The results would make a great contribution to figure out heavy metals sources,pollution status and the risk of ecosystems,and also have a great significance to management and ecological restoration of water ecosystems polluted by heavy metals.The whole studied area in Dianchi Lake was divided into five representative regions:CaoHai,HaiGeng,HuiWan,GuanZhong and DianNan.Surface sediment,surface water,plankton and fish sample were collected from five sites respectively in October 2015 and May 2016.In addition,we explored the actual ecological risk of heavy metals with the change of physiological characteristics of Vallisneria which planted in sediments samples from Dianchi Lake.The main conclusions of this paper show as follows:(1)The concentration of heavy metals in the surface sediments of Dianchi Lake exceeded the soil background value,except for Fe and Mn.The source of heavy metals was similar,which was mainly caused by human activities,particularly industrial discharges.RI and Igeo showed that CaoHai have high ecological risk which were polluted with a variety of heavy metals.Waihai region still have a considerate ecological risk and the southern part was mainly polluted by Mn and Ni.The whole region of Dianchi Lake were polluted in Cd and Hg.The SQGs showed that Hg,Ni,Zn in CaoHai and Cd in whole region of Dianchi Lake were more likely to have a negative effect on the organism.(2)The bioavailability of Fe,Mn and Zn in the sediments of Dianchi Lake is the highest,while the bioavailability of Hg and Cr is relatively small.The bioavailability of heavy metals in sediments has a seasonal variation,which is controlled by Eh and organic matter.The increase of the organic matter content or the decrease of Eh can enhance the bioavailability.Cd is stable,which have a low risk in sediments.And the migration ability of Zn is the highest,which may be harmful to aquatic organisms.SEM of Zn,Cu,Pb,Ni and Cd had similar sources,and they mainly existed in the form of sulfide and carbonate precipitates.(3)The concentration of heavy metals in the surface water of Dianchi Lake is much lower than that of sediments,but the concentration of heavy metals in the pore water of sediments affects the heavy metals in surface water.The content of Cd in surface water of Dianchi Lake is lowest,and the content of Hg exceeded the ? class of the environmental quality standards of surface water in china,and it has certain ecological risk.In addition,the content of heavy metals in the pore water also has seasonal changes,and there is a tendency to diffuse to the surface water.(4)Plankton and fishes had biological enrichment of heavy metal.The enrichment of heavy metals were related to the organs of fishes.Pb,Cr and Cd were enriched in scales of Carassius auratus in CaoHai,Pb,As,Cr,Ni,Cd were enriched in the kidney,and As,Hg were enriched in brain and skin,where contains phospholipids.The concentration of Cd and As in muscles of Erythroculter ilishaeformis,Carassius auratus,Hypophthalmichthys molitrix were exceeded,which had edible safety risk.The length of fishes and different sampling sites will affect the concentrations of heavy metal in the fishes.(5)The actual ecological risk test showed that the root system of Vallisneria can affect Eh of sediment,formed Fe-plaque,and then alter the morphology and concentration of heavy metals in sediments and pore water.Besides,the heavy metal can significantly inhibit the root activity of Vallisneria and change the intensity of the oxygen production,and then inhibit the influence of Eh in sediment and the morphology and concentration of heavy metals in pore water.