Analysis And Verification Of The Influencing Factors And Changes Of Cladocera Community In Dianshan Lake

Human activities and social development are closely related to climate change.Natural change factors and human activities can affect the development and succession of lake ecosystems.Under the background of the global warming,the increase of air temperature leads to the increase of water temperature,which further affects the distribution of organisms and the composition of the community structure in the lake ecosystem.At the same time,with the increase of human activities,the nitrogen and phosphorus nutrients in the water increased significantly.The phenomenon of eutrophication also appeared,and "water bloom" is often accompanied by rich phytoplankton.Many researchers have applied biomanipulation technology to ecological restoration of eutrophic waters,and control or remove fish that feed on plankton and benthic organisms in various ways to promote the development of macrozooplankton,especially large-bodied cladocerans.which can effectively feed on phytoplankton,but based on zooplankton surveys and ecological restoration studies in lakes around the world,the number of cladocera species is continuously decreasing in various lakes,and the reason for their absence in lakes is still a mystery.Based on this purpose,we carried out the field investigation,combined with relevant literature data of Dianshan Lake since 1958,analyzes the changes of cladocera community and its relationship with environmental factors in Dianshan lake.The influencing factors were verified and analyzed by laboratory experiments.The main results are as follows:1 Dianshan Lake is the largest freshwater lake and important water source in Shanghai.The community structure of cladocera can reflect certain water quality conditions.Further exploration requires long-term and regular investigations.This study is based on the survey data of Dianshan lake from March 2004,March 2005 to February 2006,2007 to 2008,2015 to 2018 and relevant reports since 1958.There were significant differences in the structure of the cladocera community betwen 2004 to 2009 and 2015 to 2018.The main dominant species are Bosmina,Ceriodaphnia,and Diaphanosoma;the results of the Aggregated Boosted Trees show that the environmental factor affecting the Bosmina coregoni is soluble phosphorus,with relative influence of 25.73,the most important factor affecting the Simocephalus Vetulus.are chlorophyll-a and total nitrogen,with relative influence of 21.78 and 22.29.COD and transparency is the most important environmental factors affecting the Diaphanosoma brachyurum,which are 24.09 and 20.2.The first impact factor of the Moina micrura is water temperature,and the relative influence is 40.11.Ammonia nitrogen mainly affects Bosmina longirosiris,with relative influence of 19.07.Human activities,such as fishing activities,and ecological restoration engineering,have an impact on the number of species of cladocerans.2 Global warming leads to an increase in the temperature of the water environment,and algae blooms easily break out.At the same time,it has a dramatic impact on the growth and reproduction of zooplankton.D.magna are effective feeders of algae,and the presence of D.magna in water bodies has a significant impact on the changes of aquatic ecosystems.In this study,D.magna were used as the research object,and 5?,15 ?,20 ?,25?,and 30 ? were set to observe the body length and reproduction parameters.The results obtained are as follows:(1)As the temperature increases,the growth rate of body length of D.magna increased,and the order of the largest body length of D.magna was 15?> 20 ?> 25?> 30?> 5 ?;(2)Except the 5? treatment group,the spine length of D.magna increased first and then decreases with time.The maximum spine length of D.magna has a negative correlation with temperature.The maximum spine length is 15?> 20?> 25?> 30?> 5?;(3)With the increase of temperature,the decrease rate of the ratio of body length to spine length is increased,and with the increase of time,the ratio of body lenghth to spine length in each treatment group becomes smaller and smaller.(4)It has the largest total reproduction amount at 15?.With increasing temperature,the time of first reproduction of D.magna was shortened,from 101 days at 5? to 8 days at 30 ?.Meanwhile,their body length at first reproduction was gradually shortened.The length at first reproduction of the 15? treatment group was the largest,3.25 mm,which was not significantly different from the 5? treatment group.3 In recent years,more and more studies show the reasons for the miniaturization of zooplankton and the lack of large-bodied cladocerans is inclined tothe predation pressure which is temperature before.But most of the results come from observations of field experiment and speculation,the experiments in this paper use Pseudorasbora parva as predator,using D.magna.to represent large-bodied cladocerans,by setting with or without visual stress and kairomones treatment,the following conclusions are obtained:(1)The growth rate of D.magna in the free kairomones treatment group was faster than that in the kairomones treatment group.(2)The difference of the body length in first reproduction is prior appear in visual stress treatment group than that in the kairomones treatment group.The D.magna.in visual stress treatment group grew faster;(3)The effects of kairomones on the D.magna.were sustained,while the effects of visual stress on the D.magna.may be transient;(4)In general,it showed that the spine length of D.magna.grew faster in no kairomones treatment,on the other hand,there were different responses on the setting of visual stress.The spine length of D.magna was longer in no kairomones and visual stress treatment group than that in the no visual stress and in kairomones treatment group,the group without visual stress had better growth.The results of this study provide a reference for the quality of the water environment,the current situation of the aquatic ecology,and the evolutionary trends of the Dianshan Lake in the future;provide data support for the discussion of the survival status of largebodied cladocerans in the context of global warming,so as to provide a reference for prediction about the structural change and succession of aquatic ecosystem communities.by climate change;simultaneously,it provides a theoretical basis for the successful application of biomanipulation technology to control lake eutrophication in subtropical lake...