Study On Effect Of Disturbance To Colonial Microcystis On Nutrient Absorption And Its Biological Response

Microcystis bloom is the most common type of bloom in cyanobacterial bloom,it is difficult to govern and its harmfulness has caused serious effect to people's production and life.Nitrogen and phosphorus nutrients are the main factors that trigger Microcystis bloom.In the shallow lake,many studies have also shown that cyanobacterial bloom often occur after large winds.Lake Taihu is a typical shallow lake,wind-wave disturbance is offen happened.Study show that the disturbance of wind-wave plays an important role in the outbreak of Microcystis bloom.The studies on Microcystis are mostly based on single-cell and double-celled Microcystis,and the studies of effects of disturbance on colony size,growth,nutrient absorption and related physiological characteristics of colonial Microcystis have been very few reports.In this study,field disturbance experiments were performed in Lake Taihu,while simulating the effect indoor disturbance on the Microcystis of colony size and nutrient absorption,and the effects of disturbance on related physiological characteristics of purebred and colonial Microcystis were further studied.The main research contents and results are as follows:?1?The effect of different disturbance intensity on the nutrient absorption of Microcystis.The laboratory simulation experiment of different disturbance intensity?0 r/min,50 r/min,100r/min,200 r/min and 400 r/min?on the nutrient absorption of colonial Microcystis flos-aquae and Microcystis aeruginosa in the Lake Taihu was conducted.The study found that,after 24 h of disturbance,the average diameters of the colonies of 50 r/min and 100 r/min of the colonial M.flos-aquae increased to 17.92?m and 39.50?m,which was significantly greater than the control group colony size of 10.88?m?P<0.01?;The mean diameters of the colonies of the 100r/min and 200 r/min groups of M.aeruginosa increased to 92.85?m and 67.84?m respectively,which was significantly greater than the colony size of the control group 23.60?m?P<0.01?.During the experiment,the algal densities of the experimental group of M.flos-aquae and M.aeruginosa at 100 r/min were significantly higher than those of the control group?P<0.05?;the algal density in the 400 r/min experimental group was significantly lower than that in the control and other experimental groups during the experimental period?P<0.05?.The absorption efficiencies of colonial M.flos-aquae and M.aeruginosa 100 r/min for total dissolved nitrogen?TDN?,nitrate nitrogen?NO₃^--N?,total soluble phosphorus?TDP?and orthophosphate(PO₄^3--P)were 22.59%,26.59%,28.22%,53.95%and 20.46%,21.28%,34.43%,and 40.91%,respectively,which were significantly higher than the control and 400 r/min experiment groups.The results of this study indicate that appropriate disturbance intensity is favorable for the growth of colonial Microcystis and the formation of larger colonies,and excessive disturbance is not conducive to the aggregation and growth of colonial Microcystis,and the appropriate disturbance intensity is favorable for the colonial Microcystis on absorption and utilization of nitrogen and phosphorus nutrients.?2?The effect of situ wind-wave disturbance in Lake Taihu on nutrient absorption of colonial Microcystis.In this study situ colonial Microcystis of Lake Taihu was the object,we studied the effects of in situ wind-wind disturbance on the nutrient absorption of Microcystis in the wild colony in Lake Taihu Meiliang Bay.The study found that,on the third day of the experiment,the colony size of the experimental group increased significantly from 19.07?m to 31.42?m?P<0.05?;excessive wind-wave disturbances are detrimental to the growth of algae density At the end of the experiment,the consumption of TDN,NO₃^--N,and NH₄⁺-N in the control and experimental groups was 17.00%,15.78%,25.00%and 17.00%,15.99%,26.00%,respectively,the experimental group TDP and PO₄^3--P decreased from the initial 0.41 mg/L and0.35 mg/L to 0.21 mg/L and 0.19 mg/L.The results of the study showed that the situ wind-wave disturbance in the Taihu Lake had no significant effect on the nutrient absorption of the field colony of Microcystis,but short-term disturbances favored the colony of Microcystis.?3?The effect of situ wind-wave disturbance in Taihu Lake on nutrient absorption of Microcystis.In this study,the objects were colonial M.flos-aquae and M.aeruginosa in Taihu Lake,we studied the effect of situ wind-wave disturbance on the nutrient absorption of colonial Microcystis in Meiliang Bay of LakeTaihu.The study found that,on the third day of the experiment,the colony size of the experimental group of M.flos-aquae and M.aeruginosa increased to 59.01?m and 40.78?m,significantly higher than the control group size 31.51?m and 26.90?m?P<0.01?.Excessive wind-wave disturbance is not conducive to the growth of Microcystis.At the end of the experiment,the TDN concentrations in the experimental group of M.flos-aquae and M.aeruginosa decreased from initial values of 9.45 mg/L and 9.43 mg/L to 6.64 mg/L and 6.88 mg/L,respectively;and the concentrations of NO₃^--N from the initial values of 9.19 mg/L and 9.18 mg/L were reduced to 5.33 mg/L and 5.85 mg/L;the utilization rates of TDP and PO₄^3--P by the colonial M.flos-aquae and M.aeruginosa were respectively53.00%,51.00%and 55.00%,53.00%;except for the TDP concentration of the colonial M.flos-aquae,there was no significant difference between the other experimental groups and the control group?P>0.05?.The results of the study showed that,the situ wind-wave disturbance in the Lake Taihu had no significant effect on the nutrient absorption of the field colonial Microcystis basically,but short-term disturbances favored the colonial Microcystis.?4?Effects of different disturbance intensity on nutrient absorption and physiological and biochemical changes of Microcystis.Simulating the effects of different wind-wave disturbance intensity?0 r/min,50 r/min,100 r/min,200 r/min,and 400 r/min?on the nutrient absorption and physiological and biochemical characteristics of the colonial Microcystis in Lake Taihu.The study found that,after 24 h of disturbance,the membrane permeability of the algae cells increased by 9.77%and 24.36%at 200 r/min and 400 r/min experimental groups,respectively,which was significantly greater than that of the control and other experimental groups?P<0.05?;malondialdehyde?MDA?content increased significantly from 5.23 nmol/10⁸cells to 5.55nmol/10⁸cells and 6.21 nmol/10⁸cells,respectively?P<0.05?;superoxide dismutase?SOD?activity increased significantly after disturbance?P<0.05?,were 1.07 and 1.22 times higher than that before disturbance;Ca²⁺/Mg²⁺-ATPase activity was significantly increased to 2.85?mol/h/10⁸cells and 3.24?mol/h/10⁸cells?P<0.05?.At the end of the experiment,the utilization rates of Ca²⁺and Mg²⁺in the 0 r/min-400 r/min group of colonial M.flos-aquae respectively was 45.54%,50.44%,53.30%,51.89%,44.45%and 65.31%,68.87%,74.11%,68.51%,60.65%,400 r/min experimental group and control group and were significantly lower than those in other experimental groups?P<0.05?.The results of this study indicate that,low-intensity disturbances?50 r/min and 100 r/min?are beneficial to the growth and absorption and utilization of nitrogen and phosphorus of the colonial M.flos-aquae,and have no significant effect on the physiological and biochemical characteristics of the cells?P>0.05?.High intensity disturbances?200 r/min and 400 r/min?significantly affected the physiological characteristics of the colonial Microcystis algae cells and caused some damage to the algal cells.