Effects of environmental changes on the succession of diatom assemblage during the last 50 years in Lake Chaohu

Abstract

Ecosystem in shallow lakes is generally subjected to the effects of multiple stressors,including nutrient,hydrology and climate.It is important to identify the impacts of multi-stressors for understanding the mechanism of environmental change in the lakes.Based on sedimentary proxies(i.e.,210Pb and 137Cs dating,diatom,geochemical indicators and particle size) from Chaohu sediment core and documentary data(i.e.,hydrology,climate,population and agriculture) in Chaohu basin,this study estimated quantitatively the effects of nutrient,hydrology and climate on diatom succession since 1950 using the redundancy analysis.Before 1978 diatom assemblages were dominated by Aulacoseira granulata,followed by an abrupt increase in eutrophic species(i.e.Cyclostephanos dubius).Since 2000 diatom assemblages were characterized by C.dubius,with increases in eutrophic species(e.g.,Cyclostephanos tholiformis and Stephanodiscus parvus).Results showed that sedimentary total phosphorus,total nitrogen,annual mean temperature,annual mean wind speed and annual water level amplitude were five significant variables,explaining solely 6.5%,4.7%,4.5%,4.7% and 3.0% of the variances in diatoms respectively.Therefore,nutrient input was the most important factor on diatom succession.Meanwhile,changes in climate and hydrological conditions also imposed an effect on diatom succession in Lake Chaohu during the last 50 years.