The Patterns Of Diatom Community Responses To Pollution And Hydrological Regulation In Low-latitude Plateau Lakes Of Southwest China

In the context of expanding anthropogenic disturbances,subtropical plateau lakes in Yunnan province have suffered the affects of multiple environmental pressures,such as industrial pollution,eutrophication,hydrology regulation,extreme drought,which led the biodiversity decreased and ecosystem structure and function changed obviously.In recent years,large-medium lakes,Yangzong Lake and Datun Lake,are threatened by increasing inputs of pollutants,particularly nutrients and heavy metals.In addition,two stable states,macrophytic and algal state,exist in a middle-small lake,Changqiao Lake,simultaneously.Under the stress of nutrient enrichment and hydrological regulation,Changqiao Lake is facing a threat that ecosystem stablility is decreasing and regime shifts.We applied multi-proxy sediment analyses for Yangzong Lake,Datun Lake and Changqiao Lake combining with modern investigation and history records,aiming to reconstruct the history of the ecological environment change of three lakes and revealing the long-term response of the diatom communities to eutrophication,arsenic pollution and hydrological regulation.Main research results:(1)The characteristic of diatom community responding to eutrophication is that oligotrophic species disappeared and replaced by eutrophic species.For instance,the oligotrophic species(Cyclotella rhomboideo-elliptica)in Yangzong Lake disappeared completely as nutrient levels increased,and the species abundance of eutrophic diatom(Aulacoseira ambigua)increased in Datun Lake and Changqiao Lake.Furthermore,the increasing of nutrient is beneficial to aquatic macrophyte in Datun Lake and Changqiao Lake,and benthic diatom community succession is related with the changes of aquatic macrophyte.(2)Arsenic pollution has made similar affects to diatoms communities in Yangzong Lake and Datun Lake,respectively.Firstly,the arsenic concentration reached the peak maximum in 2006~2008 in those two lakes,and planktonic diatom abundance decreased,but metal-resistant species(Achnanthes minutissima)increasedrapidly.In addition,the curve of benthic diatom abundance changed consistently with sediment arsenic concentration.It showed that A.minutissima is a indicator species for water heavy metal pollution.(3)Hydrological regulation not only changed the diatom community structure directly,but also driven the benthic diatom community succession indirectly by affecting the growth of aquatic plants.Water diversion project implemented since1965 provide a ecological diffusion channel for endemic species,C.rhomboideo-elliptica,and led to a significant increase in Yangzong Lake.Lake hydrodynamic receded and water levels rose because of damming in Changqiao Lake in 1936,which caused the diatom community succession from benthic diatom to planktonic diatom(Aulacoseira ambigua).Then,Changqiao Lake was divided into two parts by a dam after 1998,and precipitation continuely declined simultaneously,which made hydrodynamic receded,water level decreased.These factors combined with the heavy growth of aquatic plants resulted in the abundance of benthic diatom increasing in east area of Changqiao Lake.(4)The ecosytem structure,function and the ecological system stability of three lakes have changed over the past century on account of the multiple environmental pressure.For example,because of the influence of long-term eutrophication and hydrological regulation,the diatom community structure and species abundance displayed a catastrophic shift when the lake-water arsenic reached a threshold level,suggesting that the Yangzong Lake and Datun Lake have experienced a shift of stable state.The multi-analysis results of sediment organic carbon isotope and the characteristics of diatom community succession in Changqiao Lake indicated that the ecosystem stale state in west area transform into algal lake since 1936,and east area have experienced two shifts around the year 1936 and 1936,respectively.Therefore,the change of hydrological conditions is the main driving factor that lead shallow water lake ecosystem steady state changed and resulted in serious space difference space difference.