The Impacts Research Of The Environmental Factors On The Algae Growth In The Backwater Areas Of The Tributaries In Three Gorges Reservoir

As a fairly complex natural phenomenon, the apparent form of eutrophication is the abnormal increase of algae. There are many factors which affect the growth of algae in eutrophication water. Such as nitrogen and phosphorus nutrient concentration, water temperature, light intensity, pH value, dissolved oxygen and water flow and so on. Base on the special hydrology and eco-environment in the backwater areas of Xiangxi River, a dual-ring hydrodynamic experimental device was designed and environmental factors during the growth of algae in the backwater areas of Xiangxi River were also studied. Orthogonal experiments of algae growth were conducted in the laboratory. Nutrient concentrations, water temperature, light intensity and water flow velocity were selected as environmental factors, and the growth rate of Chla was taken as evaluation index. On the basic of environmental experiment, the effect of velocity on the algae growth was studied under the same condition of other three factors. RBF neural network model was built according to the experimental results. Through the research of experiments and simulation, the conclusions were shown in the following parts.1) Nutrient concentration,water temperature,light intensity and water flow were taking as the environmental factors in orthogonal experiments. The influence of nutrient concentration and temperature (20℃-30℃) on the algae growth were not significant under the high nutrient concentration, light intensity showed significant effect on algae growth, and velocity also had a relatively effect. The degree of impact of four environmental factors on the algal growth was described in the descending order of light intensity>water flow>water temperature>nutrient concentration.2)The optimal conditions for algal growth under the condition of the orthogonal experiments were 3.5mg/L for total nitrogen (TN), 0.3mg/L for total phosphorus (TP), 20℃for water temperature, 4700lx for light intensity and 0.1m/s for flow velocity.3)In the orthogonal experiments, the sensitizing range of N, P concentrations on the algae growth were in a region of low concentration(TN below1.5 mg/L, TP below 0.1 mg/L). The algae growth could be significantly promoted with the increases of N,P concentrations when nutrients were in a range of low concentration. The algae growth would not be promoted obviously after the concentrations of TN, TP reach 3.5 mg/L, 0.3mg/L relatively.4)The trend of algae growth increased at first and then decreased with the increase of velocity within the range(0.0-0.3m/s). Chla had significant correlation at the 0.05 level with TN,TP,DO and pH at different water velocities. Under static conditions, chla with TN,TP,DO and pH correlation coefficient was from 0.668 to 0.877. Under dynamic conditions, the correlation coefficient had been greatly improved, and the higher the chla was, the more obvious the correlation was.5)Neural network can learn well and test at the base of orthogonal experiments data. The trained model has a high accuracy, which has reference meaning to analysis the factors on the algae growth in Xiangxi River, and it also can give new ideas for the next experimental design.