|Other Abstract||Nowadays, eutrophication and massive accumulations of planktonic microalgae as algal blooms in waterbodies have caused serious environmental problems. So it is very important to find effective methods to controll the growth of the bloom-forming algae.
This paper focuses on: the effect of copper sulphate treatment, which is widely used as a global and empirical method to remove or control phytoplankton blooms, on different bloom-forming alga and on water ecosystem especially on the constructure of phytoplankton; effect of environmental factors, such as temperature, pH, and nutrition level, on the grazing speed of golden algae Poterioochromonas sp. to unicellular Microcystis, the species selectivity of Poterioochromonas sp. to Microcystis; and effect of Poterioochromonas sp. during the occurrence of Microcystis bloom. Main results are summarized as follows:
1. According to algal growth inhibition tests, effect of copper on five species of Microcystis aeruginosa （PCC7806）, Anabaena flos-aquae （FACHB245）, Chlamydomonas reinhardii （FACHB 479）, Scenedesmus obliquus （FACHB 416）, Cyclotella sp. （FACHB 986）were illustrated. The EC50. of Cu2+ were in the increasing order for: M.aeruginosa (46 µg/l), A. flos-aquae (75 µg/l), Cyclotella sp. (186 µg/l), Chlamydomonas reinhardii (403 µg/l) and S. obliquus (515 µg/l).
2. In two eutrophic urban lakes, CuSO4•5H2O was used as algicide to control water
bloom caused by cyanobacterial. The copper concentration applied was 102µg l-1 (as copper). Upon treatment, the transparence was increased and the algal biomass were decreased in the first 10-15 days, meanwhile, the dominant species were marked from cyanobacteria to diatom and green algae, but cyanobacteria re-emerged as dominant species after 10-15 days treatment. The short-term succession in species dominance seemed well correlated with the results of EC50 of species sensitiveity to copper. It was also found that, after treatment, the microcystins concetntration increased but soon droped to the level lower than that of before-treatment in 3-5 days.
3. Golden alga Poterioochromonas sp. itself was responsible for the sudden disappearances of cultured Microcystis sp., but not bacteria or secretion of Poterioochromonas sp.. Temperature, pH and nutrition level would not affect the grazing speed of Poterioochromonas sp to unicellular Microcystis. Poterioochromonas sp. feeding on different strains of algae showed feeding selectivity on algae. Poterioochromonas sp. fed with nontoxic strains of algae would show lower selectivity and last longer time.
4. In 10 L cuture system, lake water without zooplankton was used to simulate the occurrence of Microcystis bloom. It showed that Poterioochromonas sp. was able to grow in the lake water and play an active role in controlling the occurrence of unicellular Microcystis bloom in the system.|