| This research used field investigation and indoor experiment for analyzing, focused on the survey of waters in the northeast of Waihai, where located between Eastern Bay and the central of Dianchi Lake in the direction of Guanyin Mountain. During the whole year, we observed the temporal and spatial variation of cyanobacteria bloom in Dianchi Lake, surveyed the temporal and spatial variation characteristics of microcystin. and analyzed the relationship between the former and the later, and the relationship between the two and environmental factors. Moreover, because microbial degradation is one of the reasons that lead to microcystins degradation, the microcystins removal ability of3highly active algicidal bacteria strains (W7,N1,N4) was studied.The result indicated that:(1) The temporal and spatial variation characteristics of cyanobacteria bloom in Dianchi Lake:The maximum phytoplankton total appeared in June, the annual average concentration was2.82×108cell/L. The fastigium of cyanobacteria bioom in Dianchi Lake lasted from April to December. In this period, dominant population was Microcystis with a dominance of over93.73%. Compared with historical data, the peak of phytoplankton total in2001still appeared in June. The annual average concentration was4.63×108cell/L, dominance of Microcystis was just72.98%.(2) The temporal and spatial variation characteristics of microcystin in Dianchi Lake: The detection rate of the soluble microcystin was low. No microcystin could be detected in the water during the whole year except May and December. The peak content was0.195μg/L in December. The temporal and spatial variation characteristics of the inner microcystin in vivo were consistent with cyanobacteria bloom, the level of microcystin was higher from April to December, which had the maximum of7.19μg/L in June. Whereas, it was lower from January to March. The fastigium of cyanobacteria bloom in Dianchi Lake lasted from April to December, which had the mean of1.61μg/L Compeared with data of ten years ago, the average level of microcystin from May to November was6.28μg/L in2001, and the maximum of soluble microcystin in the water was0.42μg/L appeared in January2002.(3) Correlations between cyanobacteria, microcystin (MC) and various ecological factors in Dianchi Lake:Based on the evidences from the analysis results of the density of cyanophytes and microcystin in Dianchi Lake, the appearance of microcystin and cyanobacteria water bloom were synchronous and they were very significantly correlating with each other, and the correlation coefficient was0.944. The ecological factors including water temperature, air temperature, TN, TP, and chlorophylla, had a positive correlation with the amount of cyanophytes and the concentration of microcystin in Dianchi Lake. However, transparence had a negative correlation with them.(4) The influence of microcystin on bacteria and the removal of microcystin by bacteria: All the3bacterial strains were restrained in high density enviroment of microcystin, among which the biomass of N4strain that belonged to Aeromonas declined by0.07(OD600) when cultured for48h in an environment where the concentration of microcystin was1.0mg/L.3algicidal bacteria strains were effective for the removal of microcystin, among which N4strain had the strongest function. It could decompose23.67%of microcystin when cultured for72h in an enviroment where the concentration of microcystin was1.0mg/L(5) The correlation between the temporal and spatial variation of phytoplankton and microcystin and environmental factors was analyzed. The model of the forming of cyanobacteria bloom and influencing factors were given after compared with those data recorded before. Based on the study of microbial removal of microcystin. this work provides basic data for researches on the forming of cyanobacteria bloom and environmental behavior of microcystin in water. |
PDF Full Text Request