Stable Isotope Compositions Of The Red Tide/green Tide Prone Area In China Coastal Sea

The research consists of three parts.In the first part, under laboratory conditions, the thesis takes three species of microalgae including Platymonas helgolandica var. tsingtaoensis, Amphidinium carterae Hulburt and Prorocentrum micans and Prorocentrum micans as research objects. Through stable isotope technique to make sure that the influence of nutrient salt has made to the content of the algous stable isotopics (δ13C、δ15N). It aims to discuss the relationship between different growing seasons and rate, isotopic fractionation effect and the physiological process where U. pertusa absorbs ammonia, which has an important theoretical and practical significance on understanding the aquatic ecosystem functions and the protection of ocean ecosystems. The main results are as follows:(1) There is no relationship between the change of algous isotopic value and its taxonomic group. The isotopic value of different species are various, even the different species of the same class are distinctive. Generally speaking, the stable isotopic content of the same species at the exponential phase is lower than that at the stable phase. There is relationship between the change of algous stable isotope and its nutrition conditions which the limitation of nitric can bring about the correction of isotopic value and the phossy deficiency has no significance on the isotopic value.(2) In the initial test phase, the assimilation of14NH4+-N and12CO2by Ulva pertusa is undergoing to satisfy their nitrogen demand for growth, which leads to the concentration of ammonia,15N and13C sharp decline in waters. After five to twenty-five hours, there is very little change of concentration of ammonia in water, which15N slowly decreases to moderate phase. After about twenty-five hours, the concentration of ammonia decreases slowly and the substrate concentration in seawater is very low. During that period, Vlva pertusa assimilates a grate quantity of15NH4+-N when14NH4+-N in waters is almost exhausted, however,15N rises. Four hours after that,13C takes on erratic fluctuations. The second part of the research is to sample and investigate the sea area where the red tide and the green tide happen, that is the Pearl River sea area and the Qingdao seacoast. The ecological environment features at the sea area are studied, including the species and quantity of the phytoplankton and the key environment factors which affect the phytoplankton and red tide/greed tide populations like nutrient salt and so on. In addition, the stable isotope technology is firstly adopted to measure the δ13C、δ15N of the phytoplankton and the green tide algae at the sea area where red tide/greed tide happen. It aims to provide with the fundamental parameters for making control measures and the theory about protecting the environment of sea area where red tide/greed tide happen a lot. The main results are as follows:(1) During the red tide period, the distribution scale of the phytoplankton stable isotopic is large. Results demonstrate a significantly positive correlation between δ13C and time. But the δ13C of phytoplankton declines sharply on November6th which returns to the.previous level of the red tide. There is no linear correlation between δ15N and time. With the red tide happening, the number of δ15N declines first (before November1st) and increases later (after October31st). However, the δ15N of phytoplankton keeps increasing on November6th which returns to the previous level of the red tide.(2) With the comparison between the central area and the fringing area of the red tide, the DIP and the DIN at the fringing area are obviously lower than those at the central area, which keeps lower concentration without large fluctuation.δ15N shows a rising trend with the red tide happening wherever it is. And the numbers of δ13C at the central area increases with the red tide happening but that at the fringing area is the opposite.(3) After the bloom of green tide, green tide algae suppresses the growth of the phytoplankton through many ways. But comparing with the historical records, the amount of the species and total cell of phytoplankton decline and it is obvious that the amount of diatom species is smaller after green tide happens. Usually, the decline of the total cellular numbers of phytoplankton can cause the decrease of the planktonic animal which feed on it, which can influence the other links of the food chain. Its influence to the planktonic animal needs further investigation.(4) The δ13C of collected Entemorpha has no obvious rules to follow and its δ13N shows a slight decline. It might because the growth rate of the algae is not only related to the nutrient concentration of the external environment, but also related to the accumulation of the nutrition inside the cell. The existent state itself might be another reason.In the third part, the thesis firstly adopted the stable isotope technique in China to investigate the δ13C and δ15N of the phytoplankton and6species of marine organism. Moreover, the thesis studies the food chain organization and the nutrition relationship of the ecological systems of the sea area around the drain outlet. The main results are as follows:Significant differences were found among stable isotope (δ13C and δ15N) of some species. Nitrogen isotope ratios (δ15N) of biota can be influenced by sewage inputs, and found that the δ15N ratios in the food webs decreased with distance from the sewage inputs. The δ15N of biota decreased significantly with distance down the sewage treatment plant, however only minor and on consistent were observed in the813C of the biota with the distance of the sewage treatment plant. Nitrogen isotope ratios (δ15N) can be used to monitor future trends in nitrogen to this estuary.