The Variations Of Plankton And Zoobenthos Communities On Different Time Scales In Nansi Lake And Dongping Lake

Ecosystem health of lakes had been undermined by water pollution,biodiversity decline and eutrophication caused by economic development and human activities.Biodiversity,which is one of the fundamental elements of ecosystem functioning,has been considered an important indicator that could be applied in biological restoration as well as assessment of ecosystem health of lake.Plankton and zoobenthos,as important functional groups in lake ecosystem,had profound influence on energy flowing,information transfer and material cycling.As a consequence,studies on variations of plankton and zoobenthos in lakes on annual and seasonal time scales and the main influence factors were benefited to biological recovery and management of lake ecosystem.Biodiversity samples of Nansi Lake and Dongping Lake were collected in 2015 in spring and summer respectively,and then measured in laboratory.In addition,water samples,collected in Nansi Lake and Dongping Lake respectively,were carried back to laboratory for total nitrogen?TN?,total phosphorus?TP?,chemical oxygen demand?CODcr?,NH₄⁺-N and permanganate index?COD_Mn?measure.Water temperature?WT?,transparency?SD?,pH,chlorophyll a and dissolved oxygen?DO?were measured in filed.Combined with the data of biodiversity and water physico-chemical parameters in Nansi Lake from 2011 to 2014,this research aims to study the annual variations of plankton and zoobenthos in Nansi Lake and seasonal variations of that in Nansi Lake and Dongping Lake.Furthermore,we attempt to reveal the main influence factors which resulted in different variations of plankton and zoobenthos.Also we studied the bottom-up and top-down effects on phytoplankton community in this two lakes.Finally,we assess the water quality and eutrophication status of Nansi Lake and Dongping Lake using water physico-chemical paraneters,Shannon-Wiener index and comprehensive nutritive index respectively.The main conclusions of this research are shown as follows:?1?Different annual dynamics were found among phytoplankton,zooplankton and zoobenthos in terms of density,biomass and biodiversity in Nansi Lake.Density and biomass of phytoplankton decreased from 2011 to 2013 and increased significantly in 2014.Finally,they reached the minimum in 2015.Biodiversity?Shannon-Wiener index and Simmpson's diversity index?of phytoplankton were roughly unchanged from 2011 to 2014 and decreased in 2015.Zooplankton density increased from 2011-2013 and decreased during 2014 to 2015.Zooplankton biomass showed opposite tendency compared with zooplankton density.The Shannon-Wiener index of zooplankton remained steady during 2011-2013 and increased in 2014-2015,whereas Simpson's diversity index was steady during the whole survey period.Density and biomass of zoobenthos showed tendency to ascend during 2011-2012 and began to decline in 2013.They decreased significantly in spring in 2014,and the declined trend continued to 2015.Shannon-Wiener index of zoobenthos in Nansi Lake decreased significantly in 2014 and increased significantly in 2015,while Simpson's diversity index of that decreased significantly in spring in 2014.Total phosphorus was the main factor that influenced on annual variation of phytoplankton in Nansi Lake.Zooplankton density and biomass were mainly affected by total phosphorus and NH₄⁺-N respectively.Zoobenthos of Nansi Lake was influenced by the increased concentration of total nitrogen,total phosphorus and organic matter.Our results suggest that density and biomass of phytoplankton were more sensitive to water quality change than zooplankton and zoobenthos.?2?Density and biomass of phytoplankton and zoobenthos showed significant increase in summer in Nansi Lake,while that of zooplankton showed non-significant difference.Moreover,biodiversity?Shannon-Wiener index and Simpson's diversity index?of plankton had no significant difference in spring and summer,as well as zoobenthos.The main influence factors on phytoplankton density and biomass were water temperature and total phosphorus.Water temperature also play an important influence on phytoplankton diversity.In addition,zooplantkton density was influenced by total nitrogen and zooplankton diversity was affected by water temperature,dissolved oxygen and transparency.Zoobenthos density and biomass were influenced by water temperature and total phosphorus.?3?Density and biomass of phytoplankton in summer were significantly higher than that in spring in Dongping Lake.Shannon-Wiener index of phytoplankton decreased significantly in summer while Simpson's diversity index had no significant change.Zooplankton biomass were significantly higher in summer than that in spring in Dongping Lake,whereas density and biodiversity?Shannon-Wiener index and Simpson's diversity index?of zooplankton showed non-significant difference.The variations of density,biomass and biodiversity of zoobenthos in summer were not significant.Water temperature had influence on phytoplankton density and zooplankton biomass.Result of Pearson's correlation analysis revealed that zooplankton density negatively correlated with pH.Zoobenthos density and biomass were affected by total phosphorus,and biodiversity were affected by transparency.?4?Phytoplankton community was mainly influenced by nutrients?bottom-up effect?rather than predation of zooplankton?top-down effect?in Nansi Lake and Dongping Lake.Study also showed that bottom-up and top-down effect varied with seasons.In Nansi Lake,both of bottom-up and top-down effect weakened in summer.In Dongping Lake,nutrients which had influenced on phytoplanton by bottom-up control changed from TN?in spring?to TP?in summer?,and top-down effect weakened in summer.?5?Water quality of Nansi Lake and Dongping Lake in 2015 was mainly in accordance with the national water quality standards of grade ?.But the water quality became worse in summer,showing higher concentrations of TP,TN and COD_cr.There were different results when using Shannon-Wiener index of different taxa to evaluate water quality,which indicated that the combination of Shannon-Wiener index and physico-chemical parameters could give an overall and credible assessment of water quality.Water in this two lakes was slight pollution when using Shannon-Wiener index of plankton for evaluation while water was clean when using Shannon-Wiener index of zoobenthos for evaluation.The nutrition levels of the two lakes which were evaluated by using the comprehensive nutritive index were moderate in 2015.Moreover,the eutrophication degree became worse in summer.In conclusion,our research showed differentiated responses of plankton and zoobenthos to water quality on both annual and seasonal time scales.Phytoplankton showed significant and rapid variations on annual and seasonal time scales in terms of density,biomass and biodiversity.This result could contributed to selecting effective bio-indicators for water quality assessment.Phytoplankton community was mainly influenced by nutrients?bottom-up effect?rather than predation of zooplankton?top-down effect?in Nansi Lake and Dongping Lake.Water quality of Nansi Lake and Dongping Lake were relatively good.The nutrition levels of the two lakes which were evaluated by using the comprehensive nutritive index were moderate.In addition,the eutrophication degree became worse in summer.The results could contribute to predicting the dynamics of plankton and zoobenthos in freshwater lakes and the responses patterns to variation of water quality,which provided theoretical foundation of biological recovery and protection of ecosystem health of lakes.