Diversity Of Algae And Physiological Characteristics Of Dominant Algal Strains In Danjiangkou Reservoir

Danjiangkou Reservoir,the source of water for the South-North Water Transfer Project,is a drinking water source,and the safety of water supply is crucial.In order to prevent the occurrence of eutrophication in Danjiangkou Reservoir,it is necessary to study the diversity of phytoplankton community and the growth characteristics of dominant algae in Danjiangkou Reservoir.Phytoplankton are important primary producers of aquatic ecosystems.Their abundance and species composition vary with nutrient salts,temperature,light and hydrological conditions,and they are indicator organisms of water health.This study was conducted from May 2021 to July 2022 to monitor the phytoplankton diversity and nutrients in Danjiangkou Reservoir,analyze the phytoplankton community diversity and spatial and temporal changes in Danjiangkou Reservoir,and use the dominant species of common freshwater green algae isolated from Danjiangkou Reservoir:Tetrahymena and Deba algae as research objects to grasp the biological characteristics of common dominant algae in Danjiangkou Reservoir,and provide theoretical basis for the study of phytoplankton community dynamics,water quality monitoring,water quality evaluation and protection in Danjiangkou Reservoir.In this study,use the dominant species of common freshwater green algae isolated from Danjiangkou Reservoir:Chlamydomonas debaryana and Scenedesmus quadricauda as research objects to grasp the biological characteristics of common dominant algae in Danjiangkou Reservoir,and provide theoretical basis for the study of phytoplankton community dynamics,water quality monitoring,water quality evaluation and protection in Danjiangkou Reservoir.The main results were as follows:First,on the temporal scale,there were differences between seasons in other environmental factors except Cond,NH₃-N,TN and SD,which showed significant patterns of variation.In terms of spatial scale,except WT,TN,TP and COD,there was no significant difference in other environmental factors.Second,a total of 136 taxonomic units of phytoplankton were identified during the study,belonging to 88 genera,41 families,8 phyla.The Phytoplankton in Danjiangkou Reservoir are mainly composed of Chlorophyta,Bacillariophyta and Cyanobacteria.The abundance of phytoplankton in Danjiangkou Reservoir was the highest in summer and the lowest in winter.Spatially,the abundance of phytoplankton in Han Reservoir was higher than that in Dan Reservoir.The diversity index showed that community structure of the phytoplankton was stable and the water quality was good in summer and spring,but poor in autumn and winter.In this study,the dominant phytoplankton species in Danjiangkou Reservoir were identified as 7 phyla,33 genera and 44 species.Pearson correlation analysis showed that WT,pH,DO,COD and Chl a were the main driving factors of phytoplankton community structure changes in Danjiangkou Reservoir.Third,a total of four species of green algae were isolated and purified from Danjiangkou Reservoir.Two dominant algae species,Chlamydomonas debaryana and Scenedesmus quadricauda,were selected as the research objects to study their growth conditions under different temperature,light,nitrogen and phosphorus concentrations.The experiments showed that the suitable growth temperature of Chlamydomonas debaryana was 20～25℃,and it could grow normally at low temperature,while its growth was inhibited at high temperature.The optimum temperature range of Scenedesmus quadricauda was25～30℃,and it could grow normally at both low and high temperature.The low light condition was not conducive to the growth and propagation of Chlamydomonas debaryana.The suitable light range was 90～120μmol/（m²·s）.The adaptability of Scenedesmus quadricauda to light intensity was stronger,and the growth was normal at 10～120μmol/（m²·s）.When the light intensity was 30μmol/（m²·s）,the growth of Scenedesmus quadricauda was the best.Fourth,Chlamydomonas debaryana had a high demand for nitrogen concentration,and could not grow normally under low nitrogen concentration.In the range of 0～2.4 mg/L nitrogen concentration,the higher the nitrogen concentration was,the better the growth of Chlamydomonas debaryana was.In the low concentration of 0～0.25 mg/L phosphorus concentration,the higher the P concentration was,the better the growth of Chlamydomonas debaryana was.In the range of 0～0.25 mg/L P concentration,the growth trend of Scenedesmus quadricauda was the same.The growth rate of 0.25 mg/L P concentration group was significantly higher than that of 0～0.05 mg/L P concentration group,and Scenedesmus quadricauda could grow normally under low P concentration.