Experimental Study on the Influence of pH Value, Illumination, Nutrient, and Temperature Factors on Cyanobacteria Growth

Using dominant algae, Microcystis aeruginosa, during cyanobacteria bloom period in Lake Taihu as a study object, the influences of various factors including pH value, illumination, water temperature, and nutrients condition, on the growth of Microcystis aeruginosa were studied through indoor experiments under the nutrient condition resemblance to that of Wuli bay of Lake Taihu. Certain phenomena are revealed from experimental results that there did not exist a single optimal pH value favorable to growth of Microcystis aeruginosa, the optimal pH value was different in the different growth phases, During the process of Microcystis aeruginosa growth Microcystis aeruginosa also affected the water environment inversely, it changes the pH value of the water towards the value favorable to the growth of Microcystis aeruginosa, The Microcystis aeruginosa was sensitive to the water temperature and illumination, abrupt change of illumination and temperature affects the growth of Microcystis aeruginosa enormously, the influence degree of the intensity of illumination ranked as 18 µmol m-2 s-1, 24 µmol m-2 s-1and 36 µmol m-2 s-1from large to small, the rate of both growth and death of Microcystis aeruginosa increased with increasing the intensity of illumination in the range of 18~36 µmol m-2 s-1of the illumination intensity, The higher the temperature was, the fast the rate of both growth and death of Microcystis aeruginosa was in the range of 20~28°C of the temperature, The ratio of TN and TP affected the increasing rate and peak value of the concentration of the Microcystis aeruginosa, low ratio of TN and TP (10:1 in present experiment the TP concentration was 0.1 mg/L) was favorable to fast growth of Microcystis aeruginosa, which indicated that the growth of the Microcystis aeruginosa in Lake Taihu was restrained by the concentration of phosphorous, high concentration of phosphorous made for Microcystis aeruginosa to obtain dominant position in the population competition. The results provide the basis for further investigation of the possibility of occurrence of cyanobacteria bloom in the Lake Taihu in the natural condition.