Succession Of Water Ecological Environment And Its Response To Climate Change In Typical Lakes,China

The evolution of lake eco-environmental quality is dramatically influenced by climate change and anthropogenic activities.Revealing the evolution of lake eco-environment and its driving mechanism under the background of climate change,and quantitatively assessing the relative contribution of climate change and human activities on the evolution,are the crucial scientific problem at the forefront of the current research on lake ecology,as well as the national demand for environmental protection and management of lakes and reservoirs.The typical lakes in different regions of the country were selected as research object,including Lake Chaohu,Lake Chenghai,Lake Qionghai,Lake Jingbohu and Reservoir Changtan.The specific objectives of this study were to:(1)reveal the historical succession process of algae community,heavy metal and persistent organic pollutants(POPs)pollution process and its driving mechanism by using sedimentary algae pigments,carbon and nitrogen stable isotopes,toxic and harmful pollutants and other multi-index methods;and(2)establish the quantitative model by generalized additive models(GAMs)and other methods,to quantify the contribution of climate change and human activities on phytoplankton succession and pollution processes of typical lakes.The main findings are as follows.(1)The historical phytoplankton community succession in the lake and reservoir were reconstructed by analyzing pigment molecules in sediment cores.The profile changes of algae degradation indexes,Pheopigment-a/Chl a and Tcaro/Tpigment,indicate that algae pigment can effectively identify the structure variation of phytoplankton communities on the interannual scale.Historical phytoplankton community of Lake Chaohu,a typical shallow water eutrophic lake,has experienced two stages.Before the 1960s,the algae community in Lake Chaohu was dominated by diatoms and dinoflagellates,and algae biomass was low.After the construction of Chaohu Dam in the 1960s,specific pigment content of cyanobacteria and green algae increased significantly and the phytoplankton community showed obviously succession.The proportion of cyanobacteria and green algae increased from 5%to?35%and?40%,respectively,and the proportion of diatom dinoflagellates dropped from?90%to?15%.Dominant algae population of Lake Chaohu changed from diatom and dinoflagellate to cyanobacteria and green algae in the 1960s.(2)The algal biomass of Reservoir Changtan,a typical mesotrophic reservoir,increased significantly from the middle of 2000s,and the mean values of ??-Car and Ch1 a increased from 0.115 and 0.35 to 0.525?g g-1 and 5.77 ?g g-1,respectively.Cyanobacteria,green algae,diatoms and cryptophyta were the main dominant populations,accounting for 33.8%,22.5%,17.9%and 16.3%,respectively.The obvious succession of phytoplankton community structure was not observed during the past 30 years in this reservoir.The extreme high temperatures in the eastern region of China in 2007 may be the main driving factor for the significant increase in planktonic algae biomass.(3)The contribution of climate change and human activities to the succession of phytoplankton community in Lake Chaohu and Reservoir Changtan were quantified.The contribution of TP concentration in Lake Chaohu to total algae,cyanobacteria,green algae,cryptophyta and diatom dinoflagellate was 42.27%,40.27%,40.77%,41.01%and 72.58%,respectively.Increased TP concentration,as the main influencing factor of algal community succession,promoted the growth and reproduction of cyanobacteria and green algae in the lake.The contribution of temperature on total algae,cyanobacteria,green algae,cryptophyta and diatom dinoflagellate was 7.29%,7.56%,7.07%,9.78%and 20.74%,respectively,which indicated that warmer temperature exacerbated the structure succession and biomass increase of planktonic algae community in Lake Chaohu.(4)The profiles variations of metals in the sediment cores of Lake Chenghai,Lake Qionghai and Lake Jingbohu,and their EF,Igeo and AF factors analysis displayed the concentration of metals in sediment cores increased gradually,except for Cd,Pb and Hg.Evidence proved that human activities,temperature and precipitation all affected the accumulation process of metal deposits in these lakes.The concentration of Hg in the sediment cores of Lake Chaohu can be divided into three stages(before 1960s,1960s?1980s and after 1980s).After 1960s,the Hg deposition flux accounted for 69?74%of the total deposition in the past 100 years.The analysis found that Hg has the same artificial source as some heavy metals,and the sedimentation process is affected by hydrodynamic conditions and temperature rise.(5)The profiles variations of DDTs,PAHs and PCBs in Lake Chaohu experienced a stable period,a rapid growth period and a slow decline period.The contribution of TP concentration,watershed GDP and temperature to sedimentary DDT was 16.7%,13.4%,and 2.6%,respectively.TP concentration and watershed GDP as explanatory variables for characterizing human activities have a significant impact on the three sedimentary POPs concentrations in the Lake.