Study On The Distribution And Composition Of Dissolved Free Amino Acids In The North Yellow Sea And Jiaozhou Bay

Amino acids are the major forms of organic nitrogen (ON) and important components of organic carbon (OC) in most marine organisms. In seawater, dissolved amino acids exist in the forms of dissolved free amino acids (DFAA) and dissolved combined amino acids (DCAA). The majority of dissolved amino acids are in the form of DCAA, while DFAA are minor components. Although concentrations of DFAA are usually low, their fluxes are high enough to support a large fraction of autotrophic or heterotrophic bacterial growth. Studies on dissolved amino acids 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, distribution and composition of DFAA in the North Yellow Sea and Jiaozhou Bay were detailedly studied. The study was conducted to seek the possible relationships between DFAA and environment factors such as chlorophyll a and DOC. The main research work is showed as follows:1. Distributions of DFAA were determined during surveys in the North Yellow Sea in spring, autumn and winter. The results show that the average concentrations of DFAA in the surface water of the North Yellow Sea were 0.52μmol·L-1, 0.49μmol·L-1 and 0.36μmol·L-1 respectively. The mean concentrations of chlorophyll a in the surface water of the North Yellow Sea were 1.02μg·L-1, 1.91μg·L-1 and 0.52μmol·L-1, respectively. The horizontal distribution of DFAA in the surface water displayed a decreasing trend from inshore to offshore, indicating the influence by river effluent and anthropogenic activity. The vertical distributions of DFAA varied at different stations, but the high value appeared in the bottom. There exist significant seasonal variations of DFAA concentrations in the surface seawater. Major constituents of DFAA were serine, aspartic acid, glycine, alanine, threonine, phenylalanine, and leucine. One-way ANOVA showed no significant difference in average mol fractions of DFAA among three seasons. Correlation matrix of amino acids indicate that 11 pairs of amino acids in spring, 4 pairs of amino acids in autumn and 20 pairs of amino acids in winter showed significant positive correlations, suggesting these pairs of amino acids were subject as a whole to similar mechanisms of biogeochemical alteration in seawater. In the present study a correlation was found between DFAA and chlorophyll a (R=0.344, n=42, P<0.05) during spring, but no correlation was obtained in autumn and winter.2. Distributions and compositions of DFAA were determined during surveys in the Jiaozhou Bay in summer and autumn. The results show that concentrations of DFAA in summer ranged from 0.34 to 2.58μmol·L-1, with an average of 0.97μmol·L-1, while those in autumn varied between 0.54 to 4.87μmol·L-1, with an average of 1.32μmol·L-1. The horizontal distribution of DFAA in the surface water displayed a decreasing trend from inshore to offshore. The distributions of chlorophyll a and DOC are influenced by river effluent and anthropogenic activity. Major constituents of DFAA were glycine, glutamic acid, aspartic acid, threonine and arginine in Jiaozhou Bay. Correlation matrix of amino acids indicate that 6 pairs of amino acids in spring and 18 pairs of amino acids in autumn showed significant positive correlations. A negative correlation was obtained between aspartic acid and valine. No correlation was found among DFAA, chlorophyll a and DOC.