Effects Of Hydrodynamics On Nutrient Cycling And Algal Growth In Lake Tai

In addition to the effect of lake nutrient input from artificial activity,the current climate change and water dynamics of lake would also have impact on the eutrophication of lake.For the shallow lake,they are more easily affected by the hydrodynamic disturbance.Lake Ta is a typical large shallow lake in Eastern in China,in recent years due to water quality degradation,it is facing a severe threat.After a series of measures to carry out to control the nutrient input to the lake,cyanobacteria bloom phenomenon still occur.Previous research shows that water hydrodynamic has a certain effect on eutrophication in Lake Tai,but the mechanism of hydrodynamic influence on Lake Tai is still not fully understood by researchers.The research carried out by simulating different disturbance intensity anddisturbance time in indoor experiment to explore the effect of disturbance on nutrient and algae growth.Study on the hydrodynamic water algae in water sediment system under the influence of nutrients and algae.In addition,thewind data for 7 years in Lake Tai and corresponding water quality data in 23 sites was explored to analyze the hydrodynamic force on the nutrients and algae in the field condition,which could be supportive for the study for hydrodynamic influence on Eutrophication in Lake Tai.The results show that:(1)The main wind direction in algae bloom season and other seasons had influence on the distribution of nutrients and Chl-a.The ratio of wind speed to water depth had influence on the nutrients and Chl-a concentration in lake,with the increase of ratio,nutrients and Chl-a tended to decrease.There are two critical wind speed,the average wind speed of 2.1 and 3.2 m s-1.When the wind speed is between the two critical speed,the corresponding nutrient and chlorophyll-a concentration was significantly higher than that of nutrient and chlorophyll-a in lower wind speed group and higher wind speed group.The wind speed in Lake Tai region began to exist the downward trend after 1990,it would increase the frequency of wind speed between wind the two critical wind speed,the decreasing wind speed in combination with the ongoing anthropogenic activities is of major concern because it may increase the challenge for dealing with the problem of eutrophication in Lake Tai.The anthropogenic activities should be addressed by policy makers.(2)Disturbance will promote the increment of nutrients in the water in the early time of the experiment.But with the time goes by,the nitrogen concentration in the water will be less disturbed.The effects of disturbance on phosphorus concentration in the water wasmore obvious than the nitrogen.When the disturbance intensity increases,the content of TP(Total Phosphorus)in the water body would increase with the time.And the water content of TDP(Total Dissolved Phosphorus)is relatively low,and decreased with the increase of time.Moderate disturbance intensity is conducive to the growth of algae,when in 200rad/min and 300rad/min disturbance intensity,chlorophyll-a concentration was significantly higher than that in other conditions.The moderate disturbance,under the condition of coexistence of two species of algae,Microcystis aeruginosa had a higher growth rate,which showed a growth superiority than Scenedesmus quadricauda.(3)Under the moderate disturbance intensity(200rad/min),disturbance will affect the content of nitrogen and phosphorus in water,and with the increase of disturbance time,the content of TN,TP,TDN and TDP in the water will increase slightly.Under different disturbance time(same disturbance intensity),Microcystis Scenedesmus still have growth advantage on the Scenedesmus quadricauda.The content of chlorophyll-a had a similar trend comparing to the growth of Microcystis aeruginosa.But the Chl-a had no obvious difference in different disturbance time groups,disturbance time chosen in this study had no significant influence on the algae growth.