Effect On Growth Of Two Kinds Of Algae And Releasing Nutrition By UV-B Radiation

An experiment of Microcystis aeruginosa and Scenedesmus obliquus exposed to UV-B radiation was carried out to determine the effect of increased UV-B radiation on the growth of two kinds of algae and releasing nutrition. Through measuring the biomass, physiological, ultrastructural indices and the concentrations of nutrition, the purpose was to know the effect on ecological system in the mountain and plateau lakes, and found a method to kill algae. The results are as follows:(1) The ability of resistant UV-B stress of Microcystis aeruginosa is stronger than that of Scenedesmus obliquus. Under the UV-B radiation, Microcystis aeruginosa can resist 513J radiant energy, but Scenedesmus obliquus only can resist 373J radiant energy.If the radiant energy was low or the radiant time was short, it would promote the algae growth.(2) UV-B radiation can kill algae, because a long time or high radiant energy of UV-B radiation restrain the algae growth. When the concentration of chlorophyll a(Chla) is 245.5μg/ml, it may kill Microcystis aeruginosa needs 4 hours(513J radiant energy), UV-B radiation may kill Scenedesmus obliquus only needs 2.9 hours(373J radiant energy).(3) In the course of dying and decomposing of algae, the pace of releasing inorganic phosphorus was faster than inorganic nitrogen, and inorganic phosphorus exists primarily in the form of the phosphate.(4) In mesotrophic or oligotrophic lakes, with the increased UV-B radiation, the primary productivity of phytoplankton would reduce, and then the energy supply of the ecosystem decreased, at last, it effects the normal growth of zooplankter and fish. In the eutrophication of the lakes, it makes positive contribution to restrain the water bloom in the mountain and plateau lakes.