Effects Of Nitrogen And Phosphorus Nutrients On The Growth Of Microcystis Aeruginosa Of Different Water Sources

As the improvement of people’s living standard, landscape water body has become an important part of urban planning. Because of the serious situation caused by the limitation of the water resource and the water contamination, the quality of the water has been intensively deteriorated, including the eutrophication caused by the overgrowth of the algae which has become a threatening to the quality of the landscape water body. However, many researchers focused on the influence of the N/P ratio on the algae growth, have not looked at the relationship of the combination of N/P ratio and concentration of nitrogen and phosphorus with the reproduction of the algae.The research is supported by the national major water special project “Study of the impact of nitrogen, phosphorus and trace elements on the urban water quality” of the12 th Five-Year Plan, which is working on the influence of the nitrogen, phosphorus and trace element on the quality of the water. The experiment is based on the Microcystis aeruginosa which is a dominant species in the algal bloom and conducted in a particular lab in order to avoid the influence of other species. The water resource used in the research one is reclaimed water and the other is water blended under the lab condition.The goal of this paper is to investigate the increasing pattern of the nitrogen ratio and phosphorus ratio by analyzing the basic indicator of the concentration of the nitrogen and the phosphorus and the growing status of the Microcystis aeruginosa. In addition, to illustrate the influence of nutrients on the reproduction of the Algae growth. The indicator used in the case are the algal cell number, total nitrogen, total phosphorus and the pH value of the water environment.The main results are as follows:(1) The Microcystis aeruginosa showed a higher absorptivity of the phosphorus than the nitrogen in the nutrient solution with a lower phosphorus concentration, while in the nutrient solution with a higher phosphorus concentration, the absorptivity of the nitrogen is better than the phosphorus. In addition, as shown in the experiment, the concentration of both the nitrogen and the phosphorus vibrates during the cultivation process.(2) In different water source experiment, for any specific total nitrogen concentration, by changing the phosphorus concentration, the trends of the algae growth rate would almost keep the same. In other words, with a lower total nitrogen concentration, the algae growth rate has a positive correlation with the total phosphorus concentration. While, with a moderate total nitrogen concentration, the algae growth rate would be increased by increasing the total phosphorus concentration at a lower phosphorus concentration, and it would be decreased if the total phosphorus concentration increased at a higher phosphorus concentration. If the total nitrogen concentration is relatively high, again, the algae growth rate has a positive correlation with the total phosphorus concentration. And under different water sources, when at a higher phosphorus concentration,the algae growth rate has a positive correlation with the total nitrogen concentration.(3) In different water source experiment, the increase of N/P ratio is not conducive to the absorption of nitrogen by algae with a lower phosphorus concentration, the increase of N/P ratio promoted the absorption of nitrogen by algae while with an adequate phosphorus concentration. The absorption of phosphorus by algae has a positive correlation with the N/P ratio,the increase of N/P ratio promoted the absorption of phosphorus. The decrease of N/P ratio to promote the absorption of nitrogen but not conducive to the absorption of phosphorus by algae. At the same time, the algae biomass increased with the incubation time in different N/P ratios, it was found that the algae biomass at low N/P ratio was greater than that of medium and high N/P ratio,which showed the algae was more suitable for the growth at low N/P ratio.(4) In different water source, the N/P ratio in culture medium decreased with the growth of algae. At the meanwhile, the nutrition of the nitrogen and the phosphorus is sufficient, even the ratio is off from the optimum point, the algae growth rate would stillstay at a high level. Under this condition, the ratio of the total nitrogen and the total phosphorus wouldn’t have effect on the algae growth rate.(5) The algae would only reproduce within a specific pH value range, and the pH value would vary during the cultivation process. At the end of the cultivation period, the pH value would be higher than the one at the beginning. That indicates the propagation of algae is the cause of the increase of pH in culture medium.(6) During the cultivation process, by using the water blended in the lab, the algae growth rate has a positive correlation with the total nitrogen concentration when at a lower phosphorus concentration. While in the experiment for the reclaimed water, the algae growth rate would be increased by increasing the total nitrogen concentration at a lower nitrogen concentration, and it would be decreased if the total nitrogen concentration increased at a higher nitrogen concentration under lower phosphorus concentration.(7) When changing the TN concentration while the TP concentration was 0.2mg/L or changing the TP concentration while the TN concentration was 15mg/L, then the algae growth rate would be significantly promoted. In order to inhibit the excessive propagation of algae, the TN concentration should be controlled under 15mg/L and the TP concentration should be controlled under 0.2mg/L.