Phytoplankton Assemblage And Trophic Status Of Seven Reservoirs In Hainan Province, China

Hainan Province is located in the tropics,and is China's second largest island.Its reservoirs supply most drinking water to the Island.Phytoplankton and trophic status was investigated in the lacustrine space of seven reservoirs during the dry(2006-12) and wet seasons(2007-5),to understand phytoplankton assemblage,diversity and estimated trophic status of the reservoirs combined with physical and chemical indicators.About 203 species belonging to 97 genera were observed in all.In the dry season, 164 species belonging to 82 genera were observed,and,in the wet season,159 species belonging to 82 genera were observed.The phytoplankton species or genera simultaneously observed in each of the reservoirs in both seasons are following: Chlamydomonas,Scenedesmus bijuga,Scenedesmus quadricauda,Ankistrodesmus, Dictyosphaerium,Oocystis,Coelastrum reticulatum,Melosira granulata angustissima.By number of species the reservoirs were ranked as follow:Wanning reservoir with 101 species,Nanfu reservoir with 100 species,Shilu reservoir with 99 species,Chitian reservoir with 98 species,Songtao reservoir with 96 species, Yongzhuang reservoir with 92 species,and Gaopoling reservoir with 90 species.In the investigation 62 species of 10 genera in Desmidiaceae were observed.There were 36 species in Songtao,25 species in Nanfu reservoir,22 species in Chitian and Yongzhuang reservoir each other,13 species in Gaopoling reservoir,12 species in Shilu reservoir,9 species in Wanning reservoir.In all of the reservoirs it is show that the number of species of Desmidiaceae is higher in the dry than in the wet season. The species of Euglenophyta,Dinophyta,Cryptophyta and Chrysophyta were few in the two seasons.By the diversity of phytoplankton,in the dry season,Shilu reservoir＞Songtao reservoir=Nanfu reservoir＞Yongzhuang reservoir＞Wanning reservoir＞Chitian reservoir＞Gaopoling reservoir,and in the wet season,Chitian reservoir＞Songtao reservoir＞Wanning reservoir＞Nanfu reservoir＞Shilu reservoir＞Gaopoling reservoir＞Yongzhuang reservoir.The abundance of phytoplankton was the following:in Songtao reservoir 0.708×10~6cells/L,1.775×10~6cells/L in Nanfu reservoir,4.006×10~6cells/L in Shilu reservoir,12.801×10~6cells/L in Chitian reservoir,24.134×10~6cells/L in Wanning reservoir,93.408×10~6cells/L in Gaopoling reservoir,93.841×10~6cells/L in Yongzhuang reservoir.The abundance of Cyanophyta is:0.239×10~6cells/L in Songtao reservoir,0.675×10~6cells/L in Nanfu reservoir,1.151×10~6cells/L in Shilu reservoir,5.786×10~6cells/L in Chitian reservoir,17.655×10~6cells/L in Wanning reservoir,81.565×10~6cells/L in Yongzhuang reservoir,88.786×10~6cells/L in Gaopoling reservoir.In terms of abundance,the dominant genera of phytoplankton were:Melosira and Microcystis in Songtao reservoir,Melosira and Dictyosphaerium in Nanfu reservoir,Achnanthes and Limnothrix in Yongzhuang reservoir,Melosira and Limnothrix in Wanning reservoir,Pseudanabaena and Scenedesmus in Chitian reservoir,Cylindrospermopsis twice in Gaopoling reservoir,Microcystis and Coelastrum in Shilu reservoir.Major increases in total abundance of phytoplankton and of Cyanophyta were accompanied by a decrease in phytoplankton diversity.Biomass of phytoplankton was:0.838mg/L in Nanfu reservoir,1.089mg/L in Shilu reservoir,1.610mg/L in Songtao reservoir,4.408mg/L in Chitian reservoir, 8.421mg/L in Wanning reservoir,14.166mg/L in Gaopoling reservoir,16.684mg/L in Yongzhuang reservoir.The biomass of Cyanophyta was:0.079mg/L in Nanfu reservoir,0.082mg/L in Songtao reservoir,0.146mg/L in Shilu reservoir,2.095mg/L in Chitian reservoir,2.570mg/L in Wanning reservoir,10.865mg/L in Yongzhuang reservoir,12.520mg/L in Gaopoling reservoir.The dominant genera of phytoplankton in each reservoir were:Cyclotella and Botryococcus in Songtao reservoir,Melosira and Dictyosphaerium in Nanfu reservoir,Achnanthes and Limnothrix in Yongzhuang reservoir,Melosira and Limnothrix in Wanning reservoir,Achnanthes and Limnothrix in Chitian reservoir,Cylindrospermopsis twice in Gaopoling reservoir,Cyclotella and Melosira in Shilu reservoir.The Cyanophyta,Chlorophyta and Bacillariophyta contributed most percent,while Chlorophyta was the main contribution in the Songtao and Shilu reservoir,Bacillariophyta in Nanfu and Wanning reservoir,and Cyanophyta in Yongzhuang,Chitian and Gaopoling reservoir.Major increases in total biomass of phytoplankton and of Cyanophyta were accompanied by a decrease in phytoplankton diversity.On the criterion of trophic status based on phytoplankton,in the dry season,the Songtao and Shilu reservoirs were oligotrophic,the Nanfu and Wanning reservoirs were mesotrophic,Yongzhuang and Chitian reservoirs were mesotrophic -eutrophic, and Gaopoling was eutrophic.In the wet seaon,Songtao,Shilu and Nanfu reservoirs were mesotrophic,Wanning and Chitian reservoirs were mesotrophic-eutrophic,and Yongzhuang and Gaopoling reservoirs were eutrophic.The trophic state index for each reservoir was higher in the wet than in the dry season.The trophic state index was lower in larger(V＞10~8m~3) than in smaller reservoirs.