Comparative Analysis Of Phytoplankton Communities And Their Succession In Two Large Reservoirs, South China

To understand the succession of phytoplankton communities in reservoir in southern China, phytoplankton assemblages and environmental factors were investigated from January,2008 to December,2010 in Liuxihe reservoir and August,2008 to December,2010 in Dashahe reservoir. Limnological features, phytoplankton biomass and community structure and phytoplankton functional groups structure in the two reservoirs were comparatively explored. Multivariate analysis (CCA and RDA) was used to analyze the correlations between phytoplankton assemblages and environmental factors. Correlation and regression analysis were used to identify critical factors regulating the population dynamics of Microcystis and Anabaena circinalis.Both the intensive monsoon rains and artificial drawdown lead to the seasonality of water level and water retention time. Basin morphology influences hydrodynamics, temperature structure in water column and the effect of water level, water retention time and mixing regime on the availability of nutrients and light in the two reservoirs. Water level was the primary factor regulating nutrient and light availability in Liuxihe reservoir, while mixing regime was the primary factor that influenced nutrients and light availability in Dashahe reservoir.Availability of light, phosphorus and water retention time were the primary factors determining the phytoplankton standing biomass, but their roles significantly different between the riverine, transition, and lacustrine zones. Liuxihe reservoir was oligo-mesotrophic, and phosphorus concentration and availability of light were the most important factors for phytoplankton standing biomass. Dashahe reservoir was meso-eutrophic, and phosphorus concentration, availability of light and water retention time were all important for phytoplankton standing biomass.One hundred and twenty four species and 27 phytoplankton functional groups were identified in Liuxihe reservoir. The phytoplankton with smaller biovolume was predominant from July to September. The assemblage was dominated by Dinophyta and Bacillariophyta and showed a spatial difference in structure. Cyclotella spp., Peridinium pusillum, Peridinium bipes, Ceratium hirundinella were the primary predominant species. Multiple analyses indicated that euphotic depth, dissolved phosphorus concentration and light availability were the first important factors for structuring phytoplankton assemblage and functional groups. Water level controlled by monsoon rains and artificial drawdown and nutrient and light availability regulated by water stratification were the primary driven factors for phytoplankton community seasonal succession in Liuxihe reservoir.One hundred and seventy five species and 25 phytoplankton functional groups were identified in Dashahe reservoir. A phytoplankton with larger biovolume was predominant from July to September. The assemblage was dominated by Cyanophyta and Chlorophyta without markedly spatial difference in structure. Microcystis spp., Anabaena circinalis, Staurastrum muticum, Staurastrum gracile became the predominant species. Multiple analyses showed that total nitrogen, water level, ammonium, pH and water retention time were important for structuring phytoplankton assemblage, but euphotic depth was the critical factor for structuring phytoplankton functional groups. Water retention time was mainly controlled by monsoon rains and artificial drawdown, it affected phytoplankton growth rate. Water stratification altered nutrient availability. Water retention time and water stratification were the primary driven factors for seasonal succession of phytoplankton community in Dashahe reservoir.5) Microcystis and Anabaena circinalis were the prevailing cyanobacteria in Dashahe reservoir, and their biomass peaks separate seasonally. Microcystis with S-life strategy has a broader niche than Anabaena circinalis. Microcystis biomass significantly negatively correlated with water temperature, euphotic depth, the ratio of euphotic depth and mixing depth but positively correlated with total nitrogen, total phosphorus, ammonium, nitrate and water retention time. Anabaena circinalis has a life strategy in the intergradation zone of a S-C strategy and its biomass was significantly positively correlated with water retention time.