Analysis And Study On Cause Of Algal-bloom In Eutrophic Aqueous Environment

The water-bloom has been recognized as one of the environmental hazards worldwide. As the significant indication of water pollution, it further intensifies the pollution of water bodies. This thesis systematically analyzed and discussed the various causes of algal-bloom in eutrophic aqueous environment, including the mechanism of algal-bloom, the relationship between water bloom and nutrition elements, weather conditions, water physical characteristics, biological factors. On the basis of the analysis above, the growing characteristics of three commonly represented blue-green algae of Microcystis aeruginosa, Anabaena spiroides and Aphanizomeno flos-aquae in cyanobacteria bloom and their response to the concentration of nitrate and phosphate were investigated by pure culture and multi-culture. The results provided the experimental basis for explaining the alternation of dominant species in phytoplankton community in water bloom.The growth characteristics of three blue-green algae were studied in medium of BG11 by culture experiments. The results indicated that Aphanizomeno flos-aquae had the greatest maximum biomass and maximum specific growth rate but poorly adapted to environment and hardly formed water bloom with great presence of Microcystis aeruginosa and Anabaena spiroides, Anabaena spiroides had good adaptation, greater maximum biomass and specific growth rate forming algae bloom in a very short term, and with greatest adaptation Microcystis aeruginosa would become dominant species and water bloom along with the accumulation of biomass in spite of the least maximum biomass and specific growth rate.The experiment on nitrogen and phosphorus contents showed that all three algae in tests excreted or released chemicals containing nitrogen with varied but declining trend. The phosphorus contents in three samples significantly linearly declined with culture time, for Anabaena spiroides quickest while for Microcystis aeruginosa slowest. Further analysis showed that the ratio of nitrogen to phosphorus absorbed by Microcystis aeruginosa, Anabaena spiroides and Aphanizomeno flos-aquae were 12.1, 14.8 and 12.5, which was speculated as the optimistic rates for their respective growth. Through the investigation of the relationship between the alternation of dominant species and variation of phosphorus contents, it was found that Anabaena spiroides reproduced rapidly but suppressed the growth of Microcystis aeruginosa with high phosphorus contents; while Microcystis aeruginosa increased explosively and ultimately become dominant, inhibiting the growth of Anabaena spiroides with low phosphorous concentration.