Investigation on algal water-blooms in the Three Gorges Reservoir and its toxicological study

Field: Environmental Science (Physical Sciences)

The paper represents the phenomenon of water-blooms occurring in Three Gorges Reservoir from July 2003 to April 2005. During this period, algal water-blooms occurred for many times, especially in spring when the water temperature rised gradually and sunlight becomed abundant. The main taxa of water-blooms were Peridiniopsis sp(1), Peridiniopsis sp(2), Stephanodiscus neoastraea, Cyclotella caspia, Rhodomonas lacustris, Pandorina morum, and Eudorina elegans, in which water-bloom of Peridiniopsis sp, was the most serious one. When water-bloom of dominant specie Peridiniopsis sp, emerged, Cyclotella sp., Cryptomonas sp. and Melosira sp. supplied much primary productivity too. The peak values of cell density and biomass of Peridiniopsis sp(1) were noted at 1 meter with cell numbers of 8.71 x 10(6)cells/L and the wet weight of 69.65mg/L. The minimal values of two indexes were both noted at bottom layer with 4.58 x 10(5)cells/L and 3.67mg/L. Other algae also represented their own distribution orderliness. Contrasting cell densities and biomass of different algae, we reduced that primary productivity was supplied by Peridiniopsis sp, due to its great cell volume and huge cell numbers. For proving up whether Peridiniopsis sp(1) water-bloom produced toxin and brought effects on human's drinking water, we made out toxicological experiments on water-bloom water and algal distilled solution. The water sample taken in Tongzhuang River was filtered through Whatman GF/C filters (0.45 mu m) to remove natural particles and other organisms prior to experiment. We prepared seven testing medium, namely original water, original water + N, original water + P, original water + N + P, original water + full nutritional elements in BG11, autoclaved original water and BG11. The tested alga was Scenedesmus obliquus and file original cell density was 7.5 x 10(5) cells/L. The culture vessels was 150mL autoclaved glass flasks containing 100mL water. The flasks were incubated at 20 degrees C with a light intensity of 50-70 mu mol/m(2)/s. Bottom light was supplied at all times. The samples were cultured for sever days and the algal growth was examined everyday by light absorbance values (OD650). The experiment was repeated three times and results were analysed with percentage to contrast. The Peridiniopsis sp(1) for mouce toxic bioassay was also taken in the Tongzhuang River with 25# phytoplankton net. Zooplankton and other impurities were removed by filtering and centrifugating. Algal distilled solution was obtained by freezing and skiving repeatedly, also centrifugating with 10000r/min at 4 degrees C. The experiment was performed in six groups and ead each group has three mice. Different concentration of algal distilled solution 1,1/2,1/4,1/8,1/16) was injected in mice's abdomen. The control group was 0.9% NaCl solution. By observing mice's feedback symptom and it's weight change, we judged whether mice were poisoned. According to the results about the toxic tests, the authors elicited primarily that the water-bloom of Peridiniopsis sp(1) had no obvious bio-toxicity to other aquatic organisms and small white mouse. Analysing many factors affecting water-blooms in Three Gorges Reservoir, we considered that water-blooms were caused by industrial effluents, life sewage export, slow current speed and appropriate temperature and so on. In addition, wind changed distribution state of water-bloom algae; It was that ship and water bird played a accelerated pole in algae movement.And also, temperature change and raining affected kinds of water-bloom algae and time of water-bloom lasting. We put forward primarily two ways to prevent water-bloom in Three Gorges Reservoir, namely reducing nutrients input and increasing water velocity.