| Due to the rapid advancement of industrialization and urbanization,a large amount of pollutants is discharged into the lake,which leads to the deterioration of water quality of Lake Taihu and the bloom of cyanobacteria blooms year after year.Zooplankton is an important component of the lake ecosystem.Its species composition,quantitative changes,dominant species and pollution indicator species are greatly affected by the lake's natural geographical environment,water body type and human activities.Different species have different sensitivity and adaptability to the environment and respond differently.Therefore,this study selected Lake Taihu as the research object.Based on the monthly continuous monitoring data of the zooplankton community structure of the National Lake Scientific Observation and Research Station of Taihu Lake Ecosystem from 1997 to 2017,we analyzed the long-term variation characteristics,spatial variation characteristics,main influencing factors of zooplankton community structure and the effects of wind-driven wave turbulence on the interspecific competition and balance of zooplankton in Lake Taihu under the combined effects of human activities and climate change.It is hoped to provide reference for the long-term variation characteristics of zooplankton in Lake Taihu and important scientific basis for the research and management of Lake Taihu ecosystem.The main results are as follows.The study of long-term variation characteristics of zooplankton and its influencing factors in Meiliang Bay in Lake Taihu showed that the abundance and biomass of zooplankton in Meiliang Bay significantly decreased from 1997 to 2017(P < 0.05).In particular,the abundance and biomass of rotifer and copepod slowly declined,and the abundance of cladocerans fluctuated but its biomass presented a significant decreasing trends(P < 0.05).The results showed that the average size of zooplankton was significantly reduced(P < 0.05)and indicated that zooplankton were becoming smaller.In addition,zooplankton abundance and biomass showed an upward trend in spring and decreased in autumn and winter.In the summer,their changes were the opposite.Pearson correlation analysis showed that zooplankton community structure was significantly related to water physical characteristics(alkalinity,electrical conductivity,suspended substance and water temperature),Chlorophyll a and nitrogen(P < 0.05).Studies on spatial variation characteristics of zooplankton and its influencing factors in different lake areas of Lake Taihu showed that the spatial distribution of nutrients and Chl a concentrations were significantly higher in the western coast than in the northern bays,and significantly higher in the northern bays than in the lake center and southern coast,while the eastern lake was lower than other lake areas(P <0.05).From 2005 to 2017,the abundance of zooplankton in Lake Taihu and the five lake areas fluctuated,while the biomass displayed a downward trend,indicating that the zooplankton in the five lake areas of Lake Taihu might have a trend of miniaturization.In addition,the Lake Taihu zooplankton community exhibited strong spatial differences.In particular,the northern bays and the western coast were mainly dominated by rotifer and cladocerans.The number of three types of zooplankton in the lake center and the southern coast were equivalent,while the eastern lake was dominated by rotifer and copepods.The results of field simulation experiments showed that the Wind-driven wave turbulence was not conducive to the growth and biomass accumulation of zooplankton,and had an important impact on the competition between zooplankton.Cladocerans and copepod maintained high abundance and biomass levels in stationary or low turbulence intensity water bodies,while rotifer was more suitable for survival under strong turbulence intensity,but long-term strong turbulence also caused damage accumulation to rotifer,which was not conducive to their growth.In addition,under stable and persistent strong turbulence intensity,small rotifer gradually replaced planktonic crustaceans as the dominant species,and this process took about 3 days.In summary,zooplankton in Lake Taihu showed a miniaturized evolution characteristic from 1997 to 2007,especially large cladocerans and copepod.There was obvious spatial heterogeneity in Lake Taihu.There were significant differences of nutrient salt content in different eutrophication lake areas,and the zooplankton community structure in different lake areas also changed significantly.The northern bays and the western coast(high eutrophication)were mainly dominated by rotifer and cladocerans.The three types of zooplankton were similar in the lake center and the southern coast,while rotifer and copepod dominated the eastern lake(low eutrophication).In addition,water temperature was the most important environmental factor that affected the longterm variation characteristics of zooplankton community structure in Lake Taihu.In short-term experimental studies,the Wind-driven wave turbulence had a greater impact on zooplankton community structure.The results of field simulation experiments of wind wave turbulence revealed that cladocerans and copepod maintained higher abundance and biomass levels in stationary or low turbulence intensity water bodies,but rotifer were more suitable for survival under strong turbulence conditions. |
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