Effects Of Turbulent Fluctuation On The Growth Of Algae And Water Environment

The growth of algae is close to nutrient concentrations, environmental factors andhydrodynamic conditions. After the formation of Three Gorges Reservoir (TGR),subject to the influence of flow backward and backwater by the main stream, thehydrological environment conditions had significantly changed at the backwater area ofthe branch rivers in the TGR area, which lead to the flow rate slow down, water updatecycle becomes longer, the capacity of self-purification declines, the phenomenon ofeutrophication occurs frequently, algae bloom exploded continuously in the spring andsummer, the above factors caused great harm to the environmental safety in reservoirwater. Analyze the hydraulic conditions of this kind of water, we found that although theflow rate is lower, but due to its hydraulic radius is large, the flow is still in a turbulentstate, and the turbulence fluctuation is the most important hydrodynamic factor.Through a self-designed vertically oscillating grid experiment device, the experimentwas carried out to research the effects of the turbulence fluctuation intensity on thegrowth of algae and water environment in the water with adequate nutrients by changethe vibration frequency under a certain light and temperature conditions. To explore therelationship between temperature and the growth of algae, further simulationexperiments carried out at different temperatures in the turbulent water on the basis ofturbulence fluctuation experiments. Through the simulation experiments and analysis,the following conclusions were shown as following:1) The turbulent fluctuation in the range of experimental level will affect the processof the growth about the algae, the peak biomass, the changes of nutrients and otherenvironment factors in water obviously.2) The turbulent fluctuation has significant effects on algae growing that weakturbulence fluctuation can promote the growth of algae and strong turbulencefluctuation will inhibit the growth of algae, algae grow best when the vibrationfrequency of grid was0.5Hz. With the increase of the turbulent fluctuation intensity, thepeak of algal biomass gradually delayed. Chl-a had significant negative correlation withTN and TP when the vibration frequency was at the range of0-1.5Hz, the correlation ofChl-a with TP was most significant, and the higher the peak of chl-a, the more obviousthe correlation was.3) The changes of nitrogen and phosphorus in the experimental process had significant differences, and phosphorus was most significant. When the vibrationfrequency up to2.0Hz, the maximum reduction of TN and TP lower55.2%and69.0%compared with0.5Hz. Turbulent fluctuation can promote the pH adjusted to the level ofalgae growing required quickly, and the most appropriate value was maintained at8.40with small range, changes of temperature impact a little on the value.4) The process of algae growth and changes of the nutrients showed the sameregularity at different temperatures of15℃，20℃，25℃and30℃, but the peak of algaebiomass and the maximum reduction of TN and TP changed obviously as thetemperature changed. Algae grow best and the reductions of TN and TP were biggest at25℃. The maximum rate of decrease of nitrogen and phosphorus concentrationsoccurred at30℃.5) The higher the temperature, adaptation period is shorter and the peak of algaebiomass reached sooner at the temperatures set in experiments. The specific increase rate ofChl-a was biggest at30℃, and the growth of algae reached the maximum rate.