Study On The Response Of Plankton Stability To Biodiversity Of Shallow Eutrophic Lakes In Semi-Arid Area

Plankton has the characteristics of high species abundance and fast reproduction in lakes.It can not only become an indicator of lake water quality,but also provide good innate conditions for studying species diversity and stability.In this study,we selected eutrophic lake Ulansuhai as the research area,and continuous sampling was conducted in January,April,July,and October of 2019.The impact of diversity on community stability was studied through two diversity indicators of species richness and evenness;CCA was applied Analyze the impact of environmental factors on the diversity and stability of plankton.The main results are as follows:(1)A total of 344 phytoplankton species belonging to 96 genera and 8phyla was identified in the lake during the study period.The phytoplankton community included 156 Chlorophyta species,93 Bacillariophyta species,74 Cyanophyta species.The average phytoplankton biomass varied from0.25 mg/L(spring in April)to 1.01 mg/L(winter in January),and the overall spatial performance was moderately polluted areas>heavy polluted areas>lightly polluted areas;cell density The average value was 1.87×10⁶cells/L,and the cell density time was July>October>April>January,and the overall spatial performance was severely polluted area>moderately polluted area>lightly polluted area.(2)There were 90 zooplankton species in the lake,including 24protozoa species,43 rotifera species,11 cladocera species and 12 copepods species.The average annual cell density of zooplankton was 549.9 cells/L,the highest in autumn and the lowest in summer,the average total biomass of zooplankton was 0.32 mg/L,and the spatial change was manifested by the high content of moderately polluted areas.(3)From winter to spring,the order of stability was chlorophyta>bacillariophyta>dinoflagellate>cyanobacteria;the total phytoplankton species richness has no significant correlation with the community turnover value,and the uniformity has a strong negative impact on the community turnover stability(R=0.606,p<0.05);from spring to summer,the dinoflagellate community has the highest turnover stability,and the species richness of the Cyanophyta was negatively correlated with the community turnover(R=0.671,p<0.05);from summer to autumn,The order of stability was cyanobacteria>bacillariophyta>diaph-ta>chlorophyta.(4)From winter to spring,the stability of various zooplankton groups was as follows:rotifers>protozoa>zooplankton>cladocerans>copepods,the uniformity and stability of rotifers and copepods were shown as follows:Positive correlation and negative correlation(R=0.520,p<0.05;R=0.542,p<0.05);from spring to summer and from summer to autumn,the stability of the copepod community was the highest;the abundance of protozoa There was no significant correlation between uniformity and community turnover stability(p>0.05).(5)Results of CCA revealed that the factors affecting the diversity of phytoplankton species are TP,DO,NO₂^--N and TDS;the diversity of zooplankton was mainly affected by Chl-a,NO₂^--N,TP and DO.The main positive factors affecting the stability of Cyanophyta were DO and TP.The stability of diatoms was mainly affected by NH₄⁺-N.The stability of Chlorophyta and total phytoplankton stability were mainly affected by WD,TEMP,and COD.Protozoan stability has a significant positive correlation with COD,Chl-a,SAL and TDS.The stability of rotifers and total zooplankton were mainly positively correlated with pH,WD,DO and TN,but negatively correlated with NH₄⁺-N and TEMP.