Study On Phytoplankton Ecology And Limiting Factors To Eutrophication

Over-exploitation of natural resources and great change of land use pattern in the world, with development and expansion of human society, have great influence not only on terrestrial ecosystems but also on aquatic ecosystems, which lead to continuous deterioration of natural environment. Eutrophication is one of the most attracted environmental problems in aquatic ecosystem. Intensive anthropogenic influence on natural nitrogen-phosphorus cycle is fundamental cause of eutrophication. Therefore, studies on the relations between human activities and algal bloom are the most urgent and important.In present paper, water quality and phytoplankton community of water bodies affected by different pollution sources were investigated to reveal anthropogenic influence on surface water pollution and ecological distribution of phytoplankton community. Difference of nutritional physiological ecology between cyanobacteria and green algae were studied to explore mechanism of algal bloom from the angle of nutrition. Laboratory study of algal growth potential (AGP) was conducted to reveal mechanism of algal bloom and limiting factor of primary productivity of water bodies. The results are summarized as below:1) The physico-chemical parameters of surface water quality directly affected by different pollution sources were monitored over one year term. The parameters were analyzed by principal component analysis (PCA). From the results, three factors were responsible for surface water pollution in Taihu Lake area. The first was pollution of NH4+-N and PO43+-P, which was the most serious in rivers of urban residential region and livestock farming region. The second was N03--N pollution, which was the major pollution source in Taihu Lake and rivers of farmland region. The third was the pollution derived from transparency and pH, illustrating a serious negative feedback. The lowest transparency and highest pH were recorded mainly in Taihu Lake and fish ponds. Further analyses showed that farmlands contributed greatly to nitrogen pollution of Taihu Lake, while urban domestic sewage and livestock farming wastewater also polluted lake water in rainy season.2) Phytoplankton community in rivers and lake affected by different pollution sources sources was investigated over one year term. The results showed that phytoplankton community had positive response to water pollution and evolved from clean species to polluted species along the direction of reservoir, farmland region, rural residential region, livestock farming region and urban residential region. The blue-green algae bloom appeared in monitored rivers was relatively lesser.Comparative studies on phytoplankton community were carried out in four lakes with different trophic levels in same water system.The results showed that blue-green algae bloom occurred not only in Xuanwu Lake with high concentrations of nitrogen and phosphorus but also in Pipa Lake with low concentrations of nitrogen and phosphorus. So it is difficult to explain why blue-green algae bloom will outbreak only based on concentrations of nitrogen and phosphorus in water bodies.3) The effects of nitrogen and phosphorus on the growth of M. aeruginosa and S. obliquus were studied with bulk culture.The maximum special growth rate (μmax) and semi-saturation constant (Ks) of them to nitrogen and phosphorus were calculated using the Monod equation.The results showed that special growth rate (μ) of M. aeruginosa and S. obliquus increased with TN or TP, and there exists a point of inflection. The special growth rate of M. aeruginosa and S. obliquus increased rapidly when the concentrations of TN ranged from 0.00 to 2.00 mg·L-1 and 0.00 to 4.00 mg·L-1 respectively. It was also true when the concentrations of TP ranged from 0.00 to 0.20 mg·L-1 and 0.002 to 0.50 mg·L-1 respectively. When TN is not limited,μmax of M. aeruginosa and S. obliquus are 0.230/d and 0.410/d, and Ks are 0.14 mg·L-1 and 0.24 mg·L-1. When TP is not limited,μmax of M. aeruginosa and S. obliquus are 0.250/d and 0.395/d, and Ks are 0..15mg·L-1 and 0.031 mg·L-1.The batch culture experiments were conducted to study the effect of N/P ratio on the growth of M. aeruginosa and S. obliquus under different phosphorus level. The results showed that optimal N/P rate of M. aeruginosa and S. obliquus was 64:1 when phosphorus concentration is 0.02 mg·L-1; optimal N/P rate were respectly 64:1 and 32:1 when phosphorus concentration is 0.20 mg·L-1. However when phosphorus concentration is 2.00 mg·L-1, optimal N/P rate were 4:1 and 8:1. The effect of N/P ratio on the growth of M. aeruginosa and S. obliquus depends on both the concentrations of N and P as well as the N/ P ratio in water bodies.The effects of sources of nitrogen and phosphorus on the growth of M. aeruginosa and S. obliquus were also studied. The results showed that addition of NH4Cl, NaN03 and urea after N depletion all could promote the growth of M. aeruginosa and S. obliquus; however high concentration of NH4Cl (8 mg·L-1) showed toxicity on M. aeruginosa. Addition of KH2PO4, glycerophosphate, ATP could promote the growth of M. aeruginosa and S. obliquus under phosphorus deplete condition. For M. aeruginosa, glycerophosphate and ATP are better phosphorus sources than KH2PO4.The study on the tolerance of M. aeruginosa and S. obliquus to nitrogen and phosphorus starvation was studied. The results indicated that M. aeruginosa was more tolerant to phosphorus than S. obliquus, but it was inverse to nitrogen.4) The algal growth potential experiments were conducted using water from rivers and lakes with different trophic state. The results showed that the water from Qianhu lake, Yueya Lake, Pipa Lake did not stimulate growth of M. aeruginosa and S. obliquus; but the water from Xuanwu Lake only stimulated growth of M. aeruginosa; Both M. aeruginosa and S. obliquus grew well in Hucheng river and Qingxi river. Water from Hucheng river, however, was more beneficial to the growth of M. aeruginosa, and water from Qingxi river was more beneficial to the growth of S. obliquus. After addition of high concentrations of nitrogen and phosphorus, four kinds of lake water all could stimulate growth of M. aeruginosa and S. obliquus, indicating that nitrogen and phosphorus were the limiting factors of algal growth of four lakes. Further experiment revealed that nitrogen was the limiting factor of algal growth in summer.The addition of three different wastewaters to water of Taihu Lake could stimulate the growth of S. obliquus; however, optimal concentrations were different. There were no significant difference on the growth rate and maximum extant biomass of S. obliquus when cultured in lake water after addition of three kinds of wasteter and inonganic nutrients with equal concentrations of nitrogen and phosphorus. Addition of single nitrogen had no effect on algae growth; howeve, addition of phosphorus or phosphorus together with nitrogen greatly stimulated the algae growth, indicating phosphorus.was a limiting factor of algal growth in Taihu Lake.