The Effect Of Macroalgae On Removing Eutrophication Of Seawater In Engineering And Inhibiting Pathogeny Germ

The rapid development of industry and agriculture and human activities had caused great effect on marine ecosystem. Abuse of chemical fertilizer and the drainage of sewage polluted the seawater and made it eutrophicated, so the red tide occurred frequently. Recently, marine aquacultures develop too fast but without scientific management. This affects seriously the coastal marine ecosystem. The eutrophication becomes more and more serious and diseases of cultural animals often happen. How to deal with eutrophication and marine animals'diseases in coastal areas is an urgent issue for sustaining a healthy coastal ecosystem.Macroalgae is an important primary producer with a long life and fast growing speed. It can absorb many nutrients such as C, N, and P etc. in the seawater through photosynthesis and increase the concentration of dissolved O2 in the water body. Therefore, macroalgae is regarded as a bio-filter in marine ecosystem. In addition, macroalgae has direct or indirect effect on the plankton and microorganisms in the seawater.There exist two serious problems (eutrophication and pathogeny germ control) in now marine environment, especially in the marine aquaculture seawater. Some researches were carried out in this study according to the two problems. Because of different climate and condition between North China and South China, two typical macroalgae Kappaphycus alvarezzi and Ulva clathrata were selected as experimental materials. The nutrients removing experiments were done in the laboratory, in the algae cultural system and under the natural condition respectively. N and P uptake rates of K. alvarezii at different conditions were detected and the ecological value of K. alvarezii was evaluated.An eutrophication removing model was designed in a semi-closed bay. The abilitiy of K. alvarezii in removing N and P of eutrophicated seawater was studied and the results were as follows:1) In the laboratory, N and P uptake rates of K. alvarezii increased with the increase of N and P concentration. At the N concentration 50μmol·L-1, N and P uptake rates reaches the maximums in 28℃with the N/P ratio 10. The N and P maximal uptake rates were 0.93μmol·g-1(FW)·h-1 and 0.072μmol·g-1(FW)·h-1.2) The algae culture system was constructed in a big pool outdoor near the sea. The semi-continuous experiment of nutrients removing by algae was conducted. The results showed that K. alvarezii could removing N and P continuously from seawater. The N and P uptake rates by the alga always stayed a highest level 0.3μmol·g-1(FW)·h-1 and 0.03μmol·g-1(FW)·h-1 if the substrate concentration was enough.3) Under natural condition, the N and P removing by K. alvarezii was inspected yearly in Li'an Bay, Hainan province. K. alvarezii contributed a lot to the purification of the seawater. In this bay, K. alvarezii was a dominant alga. Every year, about 33t nitrogen and 7.5t phosphorus was removed from the bay by harvesting the alga body. The water quality of Li'an Bay now stayed at 1 or 2 grade of national standard. Therefore, culturing K. alvarezii had great contribution to marine environment protection.The effect of Ulva clathrata on inhibiting Vibrio anguillarum was primarily studied. The results showed that Ulva clathrata not only could remove large amount of N and P from the culture system, but also had striking suppressive effect on Vibrio anguillarum without reduce of the total amount of bacteria. The suppressive effect was disturbed by the concentration of nitrogen and phosphorus in the culture seawater. In the experiments, with the algae density 10 g·L-1 and the initial inoculation concentration of vibrio 105~107 cfu·mL-1, the vibrio density dropped under the level of 10 cfu·mL-1 after 2 days whether the external N and P were added or not. The algae Ulva clathrata removed almost all of the vibrio in the culture medium.The results also indicated that adding N and P could enhance the repressive effect the algae had on the vibrio, but did not reduce the amount of bacteria cluster. The total amount of bacteria in the cultural system was in a high level at all the time.