Study On The Effect Of Cyanobacteria Aggregation Grown On The Migration And Release Of Heavy Metals In Chaohu Lake

China is one of the most lakes and resource-rich countries in the world.Water resource can bring a lot of convenience.Chaohu Lake is one of the five freshwater lakes and the most important lakes in Anhui Province,with road transport,fishing and agricultural irrigation and other functions.In recent years,the rapid development of economic level,making the discharge into the Chaohu area of pollutants increased year by year.Chaohu Lakeg radually transit into heavily eutrophic lakes.Every summer,algal bloom outbreaks at a wide range.Also,the influxing of heavy metals into the lake,Chaohu Lake heavy metals concentration exceed background values,so the aera ecosystem health is seriously affected.Cyanobacteria have a strong adsorption due to its special physical and chemical structure.As a gathering area of Cyanobacteria,sediment samples and Cyanobacteria were collected from the western-half area of Chaohu Lake.The distribution patterns of seven heavy metals（Cd,Cr,Cu,Zn,Pb,Ni and Mn）were studied.The pollution levels were evaluated by the potential ecological risk index and the fractions of Cd and Mn were analyzed using BCR（European Communities Bereau of Reference）sequential extraction procedure for correlations analysis.The fresh Cyanobacteria was collected to simulat natural algae growth and humification process.The effects of Cyanobacteria on the adsorption and release of heavy metals were explained.Finally,heavy metal.cadmium on the toxicity of cultured purebred Microcystis aeruginosa were studied in order to monitor the degree of heavy metal pollution in water.The main conclusions are as follows:（1）The heavy metal contents of surface sediments exceed background values to a different degree at each sampling site,the closer near the Nanfei River,the pollution degree were higher.The vertical distribution of sediments showed that the content of heavy metal elements in the sediments of Nanfei River was more moderate from the bottom to 10cm,while above the surface was generally high and volatile.Compared with the Nanfei River,Hangbu River was no significant change.That’s due to the Nanfei River water level is shallow,the water flows slowly making sediments accumulate easily.At last,heavy metals and other pollutants deposited in the estuary.In addition,the impact of summer southeast wind and hydrodynamic,Nanfei River is as a gathering area of Cyanobacteria,because of the huge algal biomass and adsorbing heavy metals.After death,heavy metal released,making heavy metals significant migrate in the water.（2）Heavy metal potential ecological risk index showed that for a single heavy metal,Chaohu Lake in the west half of the lake and the entrance into the lake were subject to different levels of heavy metal Cd pollution,Nanfei River and the west half of the lake pollution were heavy,Tangxi River high pollution was a significant representative,but others had low pollution levels.The comprehensive ecological risk index（RI）showed that there were moderate polluted in the Nanfei River and Tangxi river.Due to the small amount of water exchange,other rivers pollution sources into the lake,the west-half of the lake was also moderate polluted.（3）Potential Mobile Index（PMI）analysis showed that compared to Mn,Cd was more likely to cause the secondary pollution in the western-half area of Chaohu Lake.sediments’ TOC/TN range was from 2 to 4,belonging to the typical algae lake,it can be considered that the vast majority of organic matter in Chaohu Lakesediments was contributed to Cyanobacteria.Both two heavy metal（Cd and Mn）showed a significant positive correlation between metal speciation,heavy metals contents TOC and TN.Therefore,it is believed that the source of heavy metals（Cd and Mn）in the western half-lake are consistent and related to algae boom.（4）The study of Cyanobacteria during humification,water content of pH changed constantly,affecting the ability of Cyanobacteria to adsorb heavy metals.Cyanobacteria humification could influence the adsorption,release and migration of Cd and Mn.In the study of algal toxicity,the biomass,chlorophyll a（Chl-a）,superoxide anion content and malondialdehyde（MDA）content were measured after heavy metal Cd²⁺ exposure for 96h.The cell membrane and antioxidant system were damaged and the cell proliferation was greatly weakened.