Distribution And Composition Of Dissolved Amino Acids In The Coastal Waters Of China

The major forms of dissolved organic nitrogen are dissolved amino acids, which exist in the forms of dissolved combined amino acids (DCAA) and dissolved free amino acids (DFAA). DCAA comprise the major components of dissolved amino acids, while DFAA are the minor components (1%~35%). Although concentrations of DFAA are usually low in seawater, DFAA are utilized as an important source of N by autotroph, also are important sources of C and N by heterotroph. As the most easily recognizable components of dissolved organic matter, dissolved amino acids participate in and affect a large number of biogeochemical processes. Studies on dissolved amino acids are important to know the sources, circulation, transformation and biological availability of marine organisms, also important to know the level of marine primary productivity.In this paper, composition and distribution of dissolved amino acids in the coastal waters of China were detailedly studied. The possible relationships between dissolved amino acids and chlorophyllα, DOC and bacteria biomass were studied. The main results are showed as follows:1. Distributions of dissolved amino acids in the northern South China Sea in winter were determined. The average concentrations of THAA, DFAA, DCAA in the surface water were 2.59μmol/L, 0.42μmol/L and 2.17μmol/L, respectively. The concentrations of THAA were decreased from inshore to offshore sites, however, there is no obvious regularity of the horizontal distribution of DFAA, further studies are needed to study the characters of DFAA. Glycine, glutamic acid, alanine, serine, aspartic acid were the major constituents of dissolved amino acids. Correlation matrix of amino acids indicate that 5 pairs of amino acids in THAA, 4 pairs of amino acids in DCAA and 9 pairs of amino acids in DFAA showed significant positive correlations. No correlation was found between concentrations of THAA and environmental factor (chlorophyllα, DOC), neither DCAA nor DFAA.2. Distributions of dissolved amino acids in the Yellow Sea in winter and spring were determined. The results show that the average concentrations of THAA, DFAA, DCAA in the surface water in winter were 6.13μmol/L, 1.10μmol/L and 5.03μmol/L, respectively, and in spring were 2.47μmol/L, 0.90μmol/L and 1.57μmol/L, respectively. Levels of DFAA were low in the surface layer and increased with depth, in this study the levels of DFAA were the highest in the mid-depth water, high value of DFAA also appeared at the bottom of the Yellow Sea. Major constituents of DFAA and DCAA were alanine, serine, glycine, glutamic acid and aspartic acid. Correlation matrix of amino acids indicate that 18 pairs of amino acids in THAA, 14 pairs of amino acids in DCAA and 12 pairs of amino acids in DFAA showed significant positive correlations. No correlation was found between concentrations of THAA and environmental factor (chlorophyllα, DOC), neither DCAA nor DFAA.3. Distributions of dissolved amino acids in the Bohai Sea in spring were determined. The results show that the average concentrations of THAA, DFAA, DCAA in the surface water were 3.81μmol/L, 0.46μmol/L and 3.35μmol/L, respectively, while the concentrations of DFAA and DCAA in the surface microlayer were 0.80μmol/L and 3.41μmol/L. In the microlayer DFAA was enriched with an average enrichment factor of 1.81±0.07. Major constituents of dissolved amino acids were glutamic acid alanine, glycine, serine and aspartic acid both in surface water and in surface microlayer, suggesting that all individual amino acids have the same enrichment in surface microlayer. Correlation matrix of amino acids indicate that 10 pairs of amino acids in THAA, 5 pairs of amino acids in DCAA and 7 pairs of amino acids in DFAA showed significant positive correlations. No correlation was found between concentrations of THAA and environmental factor (chlorophyllα, DOC, bacteria biomass), neither DCAA nor DFAA.4. Distributions of DFAA in the East China Sea in winter were determined. The results show that concentrations of DFAA ranged from 0.29μmol/L to 0.87 μmol/L, with an average of 0.51μmol/L. The concentrations of DFAA were decreased from inshore to offshore sites. Major constituents of DFAA were serine, glycine, alanine, glutamic acid and aspartic acid. No correlation was found between concentrations of DFAA and environmental factor (chlorophyllα, DOC).