Dynamic Study And Influence Of Nutrients To The Growth Of Phytoplankton In Mesocosm Experiments Of East China Sea

In recent years, influence by the activity of human beings, eutrophication of the marine environment became more serious and enlarge in level and the scale as well, in the East China Sea, especially in the adjacent area of Changjiang estuary and Hangzhou Bay. Thus serious problems in marine environment were induced, such as the worsen of sea water, unbalance of marine ecosystem and the high frequency of Red Tide. All of these do harm to the economic development of marine, even the health of human beings.Aimed at the characteristic of Red Tide in East China Sea, the influence of nutrients to the growth of phytoplankton which mainly includes Prorocentrum dentatum and Skeletonema costatum was conducted in this thesis, according to the mesocosm experiment that combined with the batch culture experiment in the laboratory . Variations of uptake and using to nutrients by phytoplankton were described by the dynamic model. At the same time, the constants of uptake /release rates to PO4-P and NO3-N by phytoplankton were calculated as well. The research would give some necessary scientific foundation to the research work for mechanism of the Red Tide in East China Sea. The main research work and conclusions listed as follows:1 Influence of nutrients in different concentrations to the growth of HAB algae(Prorocentrum dentatum and Skeletonema costatum) was studied in the mesocosm experiment.The variation of nutrient concentration and structure has a closely relationship with the growth of phytoplankton in the mesocosm experiments. Increasing the contents of phosphate in the sea water has visible effects on the growth of both phytoplankton .In particular, the influence to the growth of phytoplankton is moreobvious by increasing of the nitrate concentration in the sea water with richer phosphate. However, there is a limited concentration value to nutrients uptake by phytoplankton. Nitrate is the mainly uptake shape by phytoplankton in the culture experiments in which nitrate was added as the nitrogen resource.Prorocentrum dentatum grows better in the condition with smaller nutrients because of its strong endurance for "starvation". On the contrary, the growth of Skeletonema costatum is more fit for higher nutrients conentration. In the other word, it has stronger competition than Prorocentrum dentatum in the eutrophication of the marine environment. Simultaneously, the biomass and the replace of domination species can be changed to the ratio of nitrate and phosphate. It is no use for the growth of phytoplankton when this ratio is more higher or more lower. Although, the ratio of nitrate and phosphate in the cells of phytoplankton is more stable relatively.2 Influence of nutrients in different concentrations to the growths of Prorocentrum dentatum and Skeletonema costatum was studied in the batch culture experiment in the laboratory.It is consistent that the results got form the experiment in the laboratory and in the mesocosm. That is to say, Prorocentrum dentatum needs smaller nutrients in its growing than Skeletonema costatum. On one hand, They have different growing statues in different phosphate concentrations, and the biomass of phytoplankton will be increasing with the adding of phosphate content; on the other hand, they show the same growing statues in the same condition of phosphate concentration but different nitrate concentrations.3 Variations of uptake and using the nutrients by phytoplankton were described by the dynamic model of nutrients uptake and release by phytoplankton, and the constants of uptake /release rates to PO4-P and NO3-N by phytoplankton in the mesocosm , Prorocentrum dentatum and Skeletonema costatum were calculated as well.The variation of nutrients concentration in the cells of phytoplankton in the mesocosm experiments are described by the kinetics model of nutrients uptake and release by phytoplankton. The constants of uptake /release rates (ki &k2) to PO4-P andNO3-N by phytoplankton are also calculated by using nonlinear drawing up. And do the same to Prorocentrum dentatum and Skeletonema costatum. The results show that the constant of uptake (ki) is always bigger than that of release (k2), which represents the net absorption process during the growing of phytoplankton. Comparing kj and k2 of different algae for phosphate and nitrate, the content of phosphate is more important than that of nitrate as the limited factor of the phytoplankton growth. What is more, the growth of Skeletonema costatum is limited more easily by the content of nitrate than that of Prorocentrum dentatum.