Cyanobacteria Communities And Microcystins In Small And Medium Sized Reservoirs In The Pearl River Delta Region, South China

In recent years, reservoirs have showed a dramatic eutrophic trend with rapid development of economics and heavy pollution in Guangdong province. Cyanobacterial blooms have been observed in a few reservoirs, and seriously threaten to water supply for urban and rural residents. Small and medium sized reservoirs are important direct and indirect water sources for drinking water in the Pearl River Delta. These reserviors are concerned closely to the sustainable development of economics and society. In 2010, we collected water samples from ten typical small and medium sized reservoirs in this region in three seasons:dry season, wet season, and transition season. The characticals of cyanobacteria communities and environmental fators were systematically analysed for assessment of blooming risk and the safty of water qulity.The results showed that Meizhou reservoir, Furongzhang reservoir and Meixi reservoir were oligo-mesotrophic; Sankeng reservoir, Baihualin reservoir, Helong reservoir, Dajingshan reservoir, Fenghuangshan reservoir and Nanping reservoir were meso-eutrophic; and Hongxiuquan reservoir was eutrophic.In our survey,31 species in 21 genera of cyanobacteria were detected. The most common genera were Dactylococcopsis, Microcystis, Pseudanabaena, Cylindrospermopsis, Chroococcus, Limnothrix, Anabaena, Merismopedia and Oscillatoria.22 species were observed in Hongxiuquan reservoir. Filamentous cyanobacteria dominated in seven reserviors except Meizhou reservoir, Furongzhang reservoir and Meixi reservoir. Cylindrospermopsis and Limnothrix in Dajingshan reservoir and Fenghuangshan reservoirs, Limnothrix in Nanping reservoir and Helong reservoirs, Anabaena and Oscillatoria in Hongxiuquan reservoir, Cylindrospermopsis in Sankeng reservoir and Baihualin reservoir were dominant in these reserviors.The cyanobacterial biomass ranged from 0-40.9 mg/L and showed a significantly seasonal variation in ten reservoirs. Cyanobacterial biomass was mainly regulated by phosphorus in nine reservoirs. Rainfall was the main factor affecting cyanobacteria growth in the reservoirs fed by rivers in their natural catchments, but the water residence time was a key factor in pumped storage reservoirs except Hongxiuquan reservoirs.Microcystin concentration ranged from 0-1.42μg/L in the ten reservoirs, the highest concentration was observed in Sankeng reservoir in the dry season. Microcystin was detected in Sankeng reservoir and Hongxiuquan reservoir during the investigated period, while the microcystin concentration was always belowed the detecting limitation in Furongzhang reservoir, Meizhou reservoir, Helong reservoir and Meixi reservoir. The most important factors that correlated with microcystins concentration were the biomass of Microcystis and Anabaena and storage capacity in the reservoirs.Generally, Hongxiuquan reservoir, Sankeng reservoir, Baihualin reservoir, Fenghuangshan reservoir and Dajingshan reservoir have been seriously conolized with cyanobacteria and showed a high risk for cyanobacterial blooming; Nanping reservoir and Helong reservoirs showed a moderate risk; Meixi reservoir, Meizhou reservoir and Fenghuangshan reservoirs were slightly polluted by cyanobacteria with a low risk.