Phytoplankton Community Composition And Its Phosphorus Stress In The Jiulong River-Reservoir System, Fujian

Significant changes had occurred in watershed ecosystems because of the multiple influence from the global climate change and human activities. Water samplings were conducted in the Jiulong River Watershed to research the spatial and temporal distributions of phytoplankton composition structure, associated the interaction with environmental factors during2012and2013. Water samplings were also conducted in a key regions-Xipi Reservoir throughout the year (May2012-April2013). Meanwhile, as significant impacts of phosphate in fresh waters, bulk alkaline phosphatase activity (bulk-APA) were measured to explore the temporal and spatial variations of phytoplankton phosphorus stress in the research area. The major findings of the present study were as follows:1:Phytoplankton community composition and its phosphorus stress in Beixi, Jiulong River, FujianThe seasonal succession of phytoplankton community composition showed Bacillariophyta (spring)-Cyanophyta (summer)-Cryptophyta (winter). Melosira, Synedra, Cryptomonas and Scenedesmus were the major dominant phytoplankton genera in Beixi. Bacillariophyta, Chlorophyta and Cryptophyta were the main contributors to phytoplankton biomass. Biomass were high in spring and winter (2.80mg/L and2.73mg/L, respectively), while in summer (0.81mg/L) the biomass observed to be low. On the spatial distribution, the biomass was increasing rapidly in the downstream stations. Water temperature was suggested to be the major influence factor to the spatial and temporal distributions of phytoplankton community. Besides, soluble reactive phosphorus (SRP) was also important for the variations of phytoplankton community composition, while the influence of dissolved inorganic nitrogen nutrient was not obvious as SRP.The average APAcwa performed its highest value in summer, followed by those in winter, and was the lowest in spring. Soluble APACh1a always were the main contributor to total APAch1a in three periods and the phytoplankton might suffer from severe phosphorus stress in a long time.2:Phytoplankton community composition and its phosphorus stress in Xixi, Jiulong River, FujianThe seasonal succession characteristic of phytoplankton community composition showed Chlorophyta (spring)-Cyanophyta (summer)-Cryptophyta (winter). Melosira, Synedra, Crucigenia, Cryptomonas, Scenedesmus and Anabaena were the common phytoplankton in Xixi. The average phytoplankton biomass was:winter> spring> summer. Overall, the spatial distributions of biomass characterized higher values in downstream during three periods. NHT-N and water temperature were suggested to be important factors in the phytoplankton biomass and community composition. Soluble reactive phosphorus and N:P ratios also affected the distributions of phytoplankton.The average APAChla value in summer was the highest, followed by those in spring, and was the lowest in winter. High contributions of soluble APAChla to total APAChla. indicated that phytoplankton community might suffer from a long time phosphorus stress status in Xixi.3:Phytoplankton community composition and its phosphorus stress in Xipi Reservoir, Jiulong River, FujianPhytoplankton species were mainly of Bacillariophyta, Chlorophyta, Cryptophyta and Cyanophyta in Xipi Reservoir. Melosira, Cryptomonas, Merismopedia, Pandorina, Dictyosphaerium were the main dominant phytoplankton genera. Annual distributions of phytoplankton biomass showed bimodal state and the peaks occurred in July and March. Discharge and water temperature might be the important factors affecting phytoplankton biomass. On the spatial distribution, phytoplankton biomass was higher in lacustrine zone than those in riverine zone and transition zone. The proportions of Bacillariophyta were decrease gradually from riverine zone to lacustrine zone, while the proportions of Cryptophyta were observed to be increasing.The APAchio ranged from21.22to508.56nmol/μgChla/hr, with significantly higher values in May and June. Soluble APAChla was the major form of the total APAChla. On the space scale, the variations of APAChla showed contrast trend with the variations of DIN/SRP in most months. APAChla was significantly negative correlated with discharge,DIN, and TN/TP, DIN/SRP, while significantly positive correlation was observed between APAchia and TP.