| Microcystis is a common dominant population during the outbreak of cyanobacterial blooms in China,The outbreak of Microcystis blooms is very harmful,which greatly affects people’s production and life.Many studies have shown that wind and wave disturbances have a great impact on the outbreak of Microcystis blooms,and nitrogen andPhosphorus is also considered to be the primary cause of Microcystis blooms.However,most of the previous studies focused on single factor analysis of nitrogen and phosphorus or disturbance,and most of them were single-cell,two-cells Microcystis.Studies on the effects of different perturbations and nitrogen and phosphorus and their comprehensive effect on the morphology and growth of Microcystis colonies have rarely been reported at home and abroad.Based on the field investigation of Taihu Lake to understand the annual variation of the number and shape of Microcystis,experiments on the effects of disturbance mode,nitrogen and phosphorus and their combination on the growth and morphology of colonial Microcystis in Taihu Lake were conducted,through in-situ wind and wave disturbance experiment in Taihu,indoor and field simulation experiments.The main research results are as following:(1)Annual survey of the number and colony morphology of Microcystis in Taihu Lake.The survey results showed that the annual average concentration of total nitrogen(TN)in Meiliang Bay and East Taihu Lake was 2.73 and 2.03 mg/L,respectively.The average annual concentration of total phosphorus(TP)in Meiliang Bay and East Taihu Lake was 0.224 and0.118 mg/L,respectively.There were significant differences in TN and TP between Meiliang Bay and East Taihu Lake(P<0.05).The average annual number of Microcystis cells in Meiliang Bay and East Taihu Lake were 4.46×10~7 and 3.66×10~7 cells/mL,respectively,and there was a significant difference between the two lake areas(P<0.01).In most months,the size of colonial Microcystis in the Meiliang Bay was larger than that in the East Taihu Lake.The average annual sizes of colonial Microcystis in the Meiliang Bay and East Taihu Lake were 44.61 and 36.60μm,respectively,and which was significant difference between the two lake areas(P<0.01).Correlation analysis showed that the colony size of Microcystis in Meiliang Bay was significantly correlated to water temperature,total nitrogen and totalPhosphate(P<0.05),indicating that the concentration of nitrogen and phosphorus and water temperature may be important factors affecting the size of colonial Microcystis in Meiliang Bay,while the the colony size of Microcystis in East Taihu Lake was not related to physical and chemical factors such as nitrogen and phosphorus.(2)Effects of in-situ wind disturbance and nitrogen and phosphorus on the morphology and growth of colonial Microcystis flos-aquae in Lake Taihu.The results of in-situ experiments in Taihu Lake showed that the colony size of M.flos-aquae in the no nitrogen and nphosphorus and undisturbed groups,nitrogen and nphosphorus addition and undisturbed groups,the no nitrogen and nphosphorus disturbance groups,the nitrogen and nphosphorus addition disturbance groups during the experimental period were 23.32,26.94,32.38 and36.95μm,respectively.There were significant differences among the four treatment groups(P<0.05).The average algal cell density of the no nitrogen and nphosphorus and undisturbed groups,the nitrogen and nphosphorus addition and undisturbed groups,the no nitrogen and nphosphorus disturbance groups,the nitrogen and nphosphorus addition disturbance groups were 6.85×10~5,9.11×10~5,6.32×10~5 and 8.68×10~5 cells/mL,respectively.There were significant differences among the four treatment groups(P<0.05).The results of this study indicated that the comprehensive effect of in-situ wind disturbance and nitrogen and nphosphorus in Taihu Lake significantly promoted the growth and size increase of colonial M.flos-aquae.(3)Effects of different disturbance modes and nitrogen and phosphorus on the morphology and growth of colonial Microcystis.The experimental results showed that the average colony size of M.flos-aquae in the undisturbed groups,the continuous disturbance groups and the intermittent disturbance groups were 32.22,27.78 and 46.56μm,respectively,without adding nitrogen and phosphorus.There were significant differences among the three treatment groups(P<0.01).The average density of Microcystis cells in the undisturbed groups,continuous disturbance groups and intermittent disturbance groups were 0.92×10~6,0.49×10~6,0.95×10~6 cells/mL,respectively,and there were significant differences among the three treatment groups(P<0.05).Under the condition of adding nitrogen and nphosphorus,the average colony size of M.flos-aquae in the undisturbed groups,the continuous disturbance groups and the intermittent disturbance groups were 34.65,26.78 and 51.66μm,respectively.There were significant differences among the three treatment groups(P<0.01).The average density of Microcystis cells in the undisturbed groups,continuous disturbance groups and intermittent disturbance groups were 1.14×10~6,0.58×10~6,1.32×10~6 cells/mL,respectively,and there were significant differences among the three treatment groups(P<0.05).Under intermittent disturbance conditions,the average colony size and average algal cell density of the nitrogen and phosphorus addition groups were significantly higher than those of the no nitrogen and phosphorus groups(P<0.05).The results of this study indicated that a certain concentration of nitrogen and phosphorus and intermittent disturbance were most beneficial to the colony size and growth of M.flos-aquae,while long-term persistent disturbance(17 days)inhibited the colony size and growth of M.flos-aquae.(4)Effects of simulated wind and wave disturbances and nitrogen and phosphorus on the morphology and growth of colonial Microcystis in Taihu Lake.The experimental results showed that the average colony size of Microcystis in the undisturbed groups,the continuous disturbance groups and the intermittent disturbance groups were 24.05,29.65 and 40.47μm,respectively,without adding nitrogen and phosphorus nutrients.There were significant differences among the three treatment groups(P<0.01).The average density of Microcystis cells in the undisturbed groups,continuous disturbance groups and intermittent disturbance groups were 8.42×10~6,4.17×10~7,4.34×10~7 cells/mL,respectively,and there were significant differences among the different treatment groups(P<0.05).Under the condition of adding nitrogen and phosphorus,the average colony size of Microcystis in the undisturbed groups,the continuous disturbance groups and the intermittent disturbance groups were 26.51,32.57and 40.47μm,respectively.There were significant differences among the three treatment groups(P<0.05).The average density of Microcystis cells in the undisturbed groups,continuous disturbance groups and intermittent disturbance groups were 2.12×10~7,7.10×10~7,8.71×10~7 cells/mL,respectively,and significant differences were found among the three treatment groups(P<0.05).Under intermittent disturbance conditions,the average colony size and average algal cell density of the nitrogen and phosphorus addition groups were significantly higher than those of the no nitrogen and phosphorus groups(P<0.01).At the beginning of the experiment,the percentage of colonial Microcystis in the six different treatment groups was about 78%.By the end of the experiment,under the condition of no added nitrogen and phosphorus,the percentages of Microcystis in the undisturbed groups,continuous disturbance groups and intermittent disturbance groups were 54.80%,29.88%and73.57%,respectively.Under the condition of adding nitrogen and phosphorus,the percentages of undisturbed groups,continuous disturbance groups and intermittent disturbance groups were 4.53%,9.05%and 65.68%,respectively.The results of this study indicated that the comprehensive effect of intermittent wind disturbance and nutrient were beneficial to maintain the dominant position of Microcystis in phytoplankton in Taihu Lake. |
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