Trophic Status And Phytoplankton Assemblages Of Typical Reservoirs In Guangdong Province In A Dry Season

Guangdong Province,located in a transition from tropics to subtropics,is rich in reservoirs and the reservoirs play an important role in drining water supply.Trophic status,phytoplankton and filamentous cyanobacteria of 42 reservoirs in six main sub-watersheds were investigated from October to December 2016,to understand the distribution of phytoplankton assemblages,and the risk of filamentous cyanobacteria blooms in a dry season.The main results were summarized as follows:1)Among the 42 investigated reservoirs,two reservoirs were hypereutrophic,twenty-two reservoirs were eutrophic,and eighteen reservoirs were mesotrophic.In the six sub-watersheds,reservoirs in Pearl delta area,the west coastlal area,Beijiang river sub-watershed,and Hanjiang river sub-watershed were eutrophic,while reservoirs in Dongjiang river sub-watershed,and the east coastal area were mesotrophic.small-sized and medium-sized reservoirs were eutrophic,while large-sized reservoirs were mesotrophic.2)In total,144 species(genus)in seven phylum were observed,85 species from Chlorophyta.Besides,26 species of Bacillariophyta,19 species of Cyanophyta,6 species of Dinophyta,4 species of Euglenophyta,3 species of Cryptophyta and 1 species of Chrysophyta.The phytoplankton communities in the surveyed reservoirs were dominated by species in Chorophyta,Bacillariophyta and Cyanobacteria.According to abundance,the common dominant species of phytoplankton were: Cylindrospermopsis rackiborskii,Pseudanabaena sp.,Limnothrix redekei,Chroococcus sp.,Scenedesmus bijuga,Cyclotella sp.,Synedra sp.and Cryptomonas erosa.In terms of biomass,the common dominant species of phytoplankton were:Cylindrospermopsis rackiborskii,Pseudanabaena sp.,Cyclotella sp.,Synedra sp.,Melosira granulate,Cryptomonas erosa,Chroomonas acuta and Peridinium sp..3)Filamentous cyanobacteria was frequently observed in the investigated reservoirs.Cylindrospermopsis rackiborskii occurred in 40 reservoirs,it was the dominant species in all the six sub-watersheds.Pseudanabaena sp.occurred in 37 of the investigated reservoirs,it was the dominant species in sub-watersheds except Hanjiang river sub-watershed.Limnothrix redekei appearred in 26 reservoirs.It was the dominant species in sub-watersheds except Hanjiang river sub-watershed and Dongjiang river sub-watershed.Dolichospermum sp.occurred in 27 reservoirs.It was the dominant species in the reservoirs in the Pearl delta area,the western coastal area.Oscillatoria sp.is distributed in 8 reservoirs,Spirulina sp.is distributed in 6 reservoirs.Aphanizomenon sp.occurred in one reservoir.Cylindrospermopsis rackiborskii,Pseudanabaena sp.and Limnothrix redekei were dominant species in large-sized,medium-sized and small-sized reservoirs.4)Reservoirs in all the six sub-watersheds had high relative abundance of cyanobacteria.Reservoirs in Dongjiang river sub-watershed had the highest relative biomass of Dinophyta,while the relative biomass of the cyanobacteria was highest in the reservoirs in the other five sub-watersheds.There were no significant differences in abundance,biomass of phytoplankton,filamentous cyanobacteria between the reservoirs in the six sub-watersheds.Vertical variation of abundance and biomass of phytoplankton,filamentous cyanobacteria was not significantly different in the six sub-watersheds.Large-sized,medium-sized,and small-sized reservoirs all had the high abundance of cyanobacteria.large-sized,medium-sized reservoirs had the high biomass of cyanobacteria,small-sized reservoirs had the high biomass of chlorophyta.There were no significant differences in both abundance and biomass of phytoplankton,filamentous cyanobacteria between the three sized reservoirs.5)Linear regression and redundancy analysis showed that nutrients,water temperature and water transparency were the main environmental variables explaining the variation of phytoplankton community,while nutrients and water transparency were the main environmental variables explaining the variaition of abundance and biomass of filamentous cyanobacteria.