| The South-to-North Water Diversion Project(SNWDP)which is divided into the eastern,central and western lines is of great significance to alleviate the water supply crisis in the northern China.Especially,the implementation of the eastern route plays an important role on ensuring the water safety in Jiaodong region.Donghu Reservoir,as an important reservoir in Jiaodong line of the eastern route of the SNWDP,is responsible for receiving water from Dongping Lake and supplying water to Jinan city,Zibo city and other places.Therefore,it is necessary to clarify the changes of water quality and phytoplankton community in Donghu Reservoir.Studies have been conducted on the phytoplankton in Donghu Reservoir from 2014 to 2017,however,due to the large water leakage,it was reconstructed in 2020 leading to the fragile phytoplankton community in the reservoir.Small environmental changes may have significant impacts on the structure of phytoplankton community.Therefore,it is of great scientific significance to explore the community characteristics of phytoplankton community after the reservoir reconstruction and to analyze the differences of water quality and phytoplankton before and after reconstruction,which not only provides reference for water management and safety in the process of water transfer,but also benefits to understand the variation traits of phytoplankton community in a new environment.From March 2021 to December 2022,the variation of phytoplankton community and water quality in Donghu Reservoir was studied systematically in this paper.By analyzing of the density,species composition,dominant species,evenness and diversity of phytoplankton community,the variation characteristics of phytoplankton community were clarified.Besides,the main environmental driving factors affecting the phytoplankton community in the reservoir were point out using redundancy analysis.Moreover,the similarities and differences of phytoplankton community were revealed based on comparative analysis.Finally,more attention was paid on the changing trait of Cyanobacteria community.The main conclusions were as follows:(1)During the studying period,a total of 151 species belonging to 81 genera and 8 phyla were detected in Donghu Reservoir,where the species of Chlorophyta were the most,followed by Bacillariophyta and Cyanobacteria,and the phytoplankton community showed obvious seasonal variation trend.Besides,Donghu Reservoir experienced mesotrophic stages,the concentration of total nitrogen(1.05-3.33 mg/L)was high,while the concentration of total phosphorus was low,with the average value of 0.02 mg/L.Water depth,temperature and turbidity were the mainly environmental factors affecting the changes of phytoplankton community in Donghu Reservoir,and their interpretation rates were 24.4%,21.6%and 13.5%respectively.(2)The water quality of Donghu Reservoir had great difference before and after reconstruction.The concentration of total phosphorus decreased significantly after reconstruction,with the average value reduced from 0.05 mg/L to 0.02 mg/L,while the water depth and the concentration of total nitrogen increased significantly,with the average values increased from 3.93 m to 11.23 m and 0.88 mg/L to 1.91 mg/L,respectively.In addition,before and after the reconstruction the similarity of phytoplankton community was low,and the dominant species were different.After reconstruction,the dominance of the dominant species Synedra acus was reduced from 0.19 to 0.01,and new dominant species appeared,such as Cocconeis placentula,Navicula dicephala and Oocystis lacustris.Water depth had an important influence on the phytoplankton community in the reservoir before and after the reconstruction.(3)There were large differences in Cyanobacteria community before and after the reconstruction of Donghu Reservoir.The Cyanobacteria density in the reservoir before reconstruction(0.43×104-3015.67×104 individuals/L)was obviously higher than that after reconstruction(0-101.10×104 individuals/L).The dominant species of Cyanobacteria in the reservoir was changed from Pseudanabaena limnetica to Microcystis aeruginosa after reconstruction.Water depth and total nitrogen were the main environmental driving factors of Cyanobacteria community before and after the reconstruction.Water depth was positively correlated with Microcystis aeruginosa and Chroococcus minutus,negatively correlated with Pseudanabaena limnetica.Total nitrogen was positively correlated with Pseudanabaena limnetica and negatively correlated with Microcystis aeruginosa. |
