Analysis And Distribution Of Dissolved Free Amino Acids In The East China Sea And Yellow Sea

Amino acids are important depositories of organic nitrogen of the ocean, and nitrogen in most organisms exsist in the form of amino acids. Amino acids in the ocean derive from products during the process of degradation of marine biology, hydrolyzation of proteins, excretion outside the cell, as well as the food chain. Studies on dissolved protein and their amino acid components will help us know the sources, transformation, circulation and biological availability of marine organisms, so as to provide a scientific proof for the level of marine primary productivity.In the present dissertation, analysis and distribution of dissolved free amino acid (DFAA) in the Yellow Sea(YS), the East China Sea(ECS) and Qingdao coastal sea were detailedly studied . The main research results are obtained as follows:1. A reversed-phase high performance liquid chromatography coupled with fluorescence detection(RP-HPLC-FLD)was developed for the determination of DFAA in seawater. The filtered water samples without being desalted or concentrated were derivatized with O-phthalaldehyde/3-mercaptopropionic acid (OPA/3–MPA), and then the derivatives were seperated on an XDB-C18 column at 35℃, with methanol-acetonitrile-sodium acetate served as the mobile phases by gradient elution. The wavelengths of fluorescent detection were set at 337nm (λex) and 454 nm (λem). OPA/3-MPA was used as derivatization reagent, and the mole ratios of OPA:3-MPA:amino aicd were 20:60:1. Most kinds of amino acids could be completely separated using this method. The precisions were 1.62～3.80%, the detection limits were1.4～69.7ng L-1,and the recoveries were 92～110% for different amino acids. 2. The distributions of DFAA were determined in the YS in April and July 2006. The results showed that the concentrations of TDFAA in the surface water varied from 0.15 to 1.63μmolL-1 in spring and from 0.054 to 1.12μmolL-1 in summer, respectively, with the average concentrations of 0.682±0.190μmolL-1 in spring and in 0.29±0.19μmolL-1 in summer, respectively. The most abundant DFAA in the surface water were Serine (Ser), Glycine (Gly), Glutamic acid (Glu), Ornithine (Orn) and Leucine (Leu). The concentration of TDFAA was higher in spring than in summer, and this seasonal variation was obviously related with variation of the plankton community. The horizontal distribution of TDFAA in the surface water displayed a decreasing trend from inshore to offshore. The concentrations of DFAA were higher in the microlayer (ML) than in the subsurface water (SS), indicating that DFAA was enriched in the ML, with an average enrichment factor (EF) of 1.77. Mean DFAA compositions in the ML were not significantly different between ML and SS water. Linear regression analysis showed a poor relationship between concentrations of DFAA and Chl-a, suggesting that microorganisms might have a more important effect on the distribution of DFAA.3. The distribution of DFAA were determined in the ECS during June-July 2006. Horizontal distribution of TDFAA was mostly influenced by the Yangtze River effluent and the YS coastal water. Due to the Yangtze River effluent , the highest concentration of TDFAA occurred off the Yangtze River Estuary,. The concentrations of TDFAA in the surface water of the ECS in summer were 0.062～0.58μmolL-1,with a mean of 0.24±0.13μmolL-1.The distribution of TDFAA was related with biology and environment factors. As a consequence, the vertical distribution of TDFAA along different sections in the ECS were quite variable. The diel variation of TDFAA in the upper water was coincidental with related biological processes. In the evening, an increase in both basic amino acids and TDFAA was offset partly by a corresponding decrease in acidic amino acids.4. The distributions of DFAA in the ML and SS in offshore sea of Qingdao were measured in May 2006. The concentrations of TDFAA were 0.05～2.14μmolL-1 in the SS (mean: 0.94±0.62μmolL-1) and 0.11～3.12μmolL-1 in the ML (mean: 1.25±0.84μmolL-1), respectively. DFAA was enriched in the ML, with an average EFof 1.89. The concentration of TDFAA in the SS decreased from Jiaozhou mouth to offshore sea, due to the effect of terrestrial input, which was different from that in the ML.