Study Of Effect Of Nitrogen And Phosphorous On Colony Of Microcystis

The eutrophication is a very serious water problem all around the world, so people paymore attention to the algae bloom which was often broke out in a eutrophication lake. TheMicrocystis blooms are the most common alage bloom. The formation and accumulation ofmassive Microcystis colonies was the important condition of Microcystis blooms outbreak.Many researches indicated that the nutrient concentration is critical factors which restrict themassive Microcystis colonies formation and accumulation. Microcystis flos-aquae is one ofthe domestic species in Lake Taihu. The research was focused on the effectof different nitrogen and phosphorus concentration to the Microcystis flos-aquae coloniesincreasing. Then observed the Microcystis flos-aquae colonies increasing trend after reducingthe concentration of nitrogen and phosphorous.The results of the study showed thatappropriate concentration of nitrogen and phosphorous can promote the the Microcystiscolonies increasing. Too high or low concentration of nutrient may restrict the increasing. Theresult indicated that we can suppress the Microcystis blooms by controlling the nutrientconcentration to some extent. And maybe can supply theoretical basic for controllingMicrocystis blooms in Lake Taihu. It is helpful for revealing the mechanism of thecyanobacteria bloom formation. Also, it has practical significance to control blue algae bloomand control cyanobacteria bloom more effectively. The main contents and results are asfollows:(1) Effect of nitrogen and phosphorus concentration on colony growth of Microcystisflos-aquae: Observed the increasing tendency of Microcystis flos-aquae under differentconcentration of nitrogen and phosphorous. The results showed that different concentration ofnutrient have effect on accumulation of Microcystis flos-aquae colonies. The cells number ofthe biggest colonies was437cells/colony in the treatment of T3(TN=10mg/L, TP=5mg/L).Allof the treatments T1(TN=0.1mg/L, TP=0.005mg/L), T2(TN=1mg/L, TP=0.05mg/L), T3(TN=10mg/L, TP=0.5mg/L), T4(TN=100mg/L, TP=5mg/L), we could find100+cellscolonies. But the concentration of nutrient increased to TN=250mg/L, TP=5.44mg/L(whichwas equal to the concentration of nutrient in BG-11), there wasn’t100+cells colonies in thetreatment. And the number of the colonies was increased first and then decreased in thetreatment.With the concentration of the nitrogen and phosphorous increasing, the Microcystisgrowth rate increased first and then decreased. And the growth rate was the biggest (μ=0.212d-1) in the treatment of T3(TN=10mg/L, TP=5mg/L).(2) Effect of TN/TP on colony increasing of Microcystis flos-aquae: Observed theincreasing of Microcystis flos-aquae under different ratio of nitrogen and phosphorous. Andour study compared with the concentration of nitrogen and phosphorous in BG-11as a control.It turned out that the Microcystis flos-aquae colonies were grew very well when TN/TP=0.18.When TN/TP>50, the density of Microcystis flos-aquae cells was higher than other treatmentsapparently. But the percentage of100+cells colonies was very low, in the upper course ofexperiments, the100+cells colonies were disappeared in all of the treatments. WhenTN/TP<50, the density of Microcystis flos-aquae cells was lower, but the density of100+cellscolonies was greater than the high TN/TP treatment. There’s no significant difference in mean sizes of colonies in all treatment, but there’s significant difference in the density of colonies inall treatment mostly. In the high rate of TN/TP treatment, with the concentration of thephosphorous increasing, the Microcystis increasing rate increased first and then decreased,and in the low rate of TN/TP treatment, the growth rate was showed a linear increasing trend.And the growth rate was the biggest (μ=0.212d-1) when TN/TP=18.(3) Effect on colony increasing of Microcystis flos-aquae after decreasing concentrationof nitrogen and phosphorous: Researched the increasing of Microcystis flos-aquae coloniesafter decreasing the concentration of nutrient. And our research compared with the average ofnutrient concentration in Meiliang Bay in2013. The result showed that the sizes of coloniesand the density of10-100cells colonies was descended when decreased the phosphorous andkeep the concentration of nitrogen remain unchanged, and the growth rate was lineardescended. Decreased the concentration of nitrogen and phosphorous can inhibit theincreasing of Microcystis flos-aquae colonies. But there’s no obvious effect on the increasingof Microcystisflos-aquae colonies when decreased the nitrogen and keep the concentration ofphosphorous unchanged. When decreased the concentration of phosphorous from0.025mg/Lto0.0125mg/L, the percentage of10-100cells colonies was just descended3%. There wassignificant difference between the control groups from all of the treatments of colonies density.There’s significant difference of sizes of colonies between the control group from T1-T3treatments, and no significant difference with T4-T6treatments.（4）Effect of nitrogen and phosphorus on Microcystis in Gonghu Bay in Lake Taihu.We selected six points in Gonghu Bay and monitored the nitrogen, phosphorous concentrationand Microcystis biomass for a year. In May and October, the nitrogen concentration,phosphorous concentration, biomass of single-cell Microcystis and Microcystis coloniesreached the highest point. Correlation analysis of various indexes showed that biomass ofMicrocystis colonies was significantly positive correlated to the TN and TP. There wassignificant positive correlation between biomass of single-cell Microcystis with TN.