The Distribution Of Microcystin In Reservoirs And Lakes In Guangdong Province And The Characteristic Of Microcystin Production Of Microcystis Flos-aquae

To study the distribution of microcystin in fresh waters especially water supply reservoirs in Guangdong Province, water samples were collected in 12 reservoirs and 4 urban lakes in July, September and December in 2003. In 2004, 7 reservoirs and one lake (Xinghu Lake) were sampled biomonthly for analysis of microcystin dynamic. The microcystin concentration was detected by HPLC (High-Performance Liquid Chromatograph) and ELISA (Enzyme-Linked Immunosorbent Assay) . In most of the sampled water bodies, the microcystin was dominated by MC-RR. Though the microcystin concentrations in 2004 increase a lot in most reservoirs, the MC levels were below the critical value for drinking water.A series of experiments were designed for physiological and ecological study and toxin-produced characteristics of a stain of Microcystis flos-aquae, which was separated from the Shenzhen Reservoir. M. flos-aquae was cultured under photosynthetically active radiation(PAR) intensity between 10 and 450 umol of photons m^-2·s^-1. The growth rate was highest when the light intensity was 250μmol of photons m^-2·s^-1. The microcystin concentration maintained in higher level while the light intensities were more than 170 umol of photons m^-2·s^-1 while the cellular microcystin were high when the light intensities between 50 and 100μmol of photons m^-2·s^-1. The growth rate was highest when N:P ratio was near 16. Phosphorus had more effect than nitrogen on MC production. When the phosphorus concentration was below 5.76 mg L^-1, the MC concentration increased with the phosphorus concentration. The growth rate negatively correlated to the cellular microcystin content. The highly significant relationship between the microcystin content and the chlorophyll-a content suggested that the ligh intensities may be the primary factor to affect the synthesizing of microcystin.A group of experiments were carried to study the effects of the rapid change of the environmental factors including temperature, light intensity and nutrients on the growth and toxin production of M. flos-aquae. The results showed that the rapid increase of light intensity and temperature can stimulated cell growth. The rapid change of light intensity or the rapid decrease of nutrient would result in the increase of the cellular MC while therapid change of temperature or the rapid increase of nutrient would result in the decrease of the cellular MC. Although the rapid change of temperature would reduce the synthesizing of microcystin, the ratio of microcystin to chlorophyll-a was higher in low temperature than that in high temperature.