Distribution And Composition Of Dissolved Amino Acids In The South Yellow Sea And The East China Sea

Amino acids distribute widely in the marine environment，which are the majorconstituents of organic nitrogen. Dissolved amino acids are made up of dissolved freeamino acids (DFAA) and dissolved combined amino acids (DCAA), which comefrom the excretion and catabolism of marine plankton. DCAA are the majorcomponent of THAA and exist mostly in the form of small peptides. DFAA are theminor components in seawater besides they are the important source of nitrogen byautotroph and also the important sources of carbon and nitrogen by heterotroph.DCAA and DFAA can be transformed into each other through the microbiological,physical and chemical effects. The research of dissolved amino acids not only canprovide the basis for the marine primary productivity, but also conducive to reveal thecycle of marine biosphere and the sources, transformation and circulation of marineorganisms.In this essay, concentration of dissolved amino acids and environment factors inthe South Yellow Sea and the East China Sea were determined. By further study thedistribution, composition and enrichment of dissolved amino acids in the surfacenicrolayer and the correlation between environment factors and THAA were analyzed.The main results shown as follows:（1）The distributions of dissolved amino acids in the South Yellow Sea and the EastChina Sea in summer2011were investigated. The average concentrations of THAA,DCAA and DFAA in the subsurface water were0.74μmol/L,0.60μmol/L and0.14μmol/L, respectively. The average concentration of THAA in the surface micro layerwater was1.58μmol/L. Concentrations of THAA and DCAA were decreased frominshore to offshore regions, while the distribution-characteristics of DFAA werecomplex. The concentrations of Chl-a showed significant correlations betweensubsurface water and surface microlayer water, DIN was also. The enrichments ofthem were apparent. The major constituents of THAA and DCAA were glycine, serine, alanine, aspartic and glutamic in the subsurface water.The main components andconcentrations of THAA between sub-surface water and surface micro-layer waterwere basically the same which indicated the enrichment had no selectivity. There were4pairs of amino acids in THAA showed significant positive correlations and3pairsshowed negative correlations in the subsurface water. However, there were3pairs ofamino acids in THAA showed significant positive correlations and3pairs showednegative correlations in the surface micro-layer water.（2）The distributions of dissolved amino acids in the East China Sea in autumn2010were investigated. The average concentrations of THAA, DCAA and DFAA inthe subsurface water were0.95μmol/L,0.80μmol/L and0.20μmol/L, respectively.Concentrations of THAA in the surface water were decreased from inshore tooffshore regions. Fujian and Zhejiang coast offshore was the high value areas ofTHAA and DCAA. This may due to the upwelling in that area. There were nocorrelations found between concentrations of THAA and the environmentalfactors(Chl-a、DOC and DIN), neither DFAA. Levels of THAA were high both in thesurface sea water and the bottom, and decreased with depth in the euphotic layer. Thedominant amino acids of THAA and DCAA were aspartic, glutamic, serine, glycineand alanine. There were9pairs of amino acids in DFAA showed significant positivecorrelations, and2pairs of them in DCAA.（3）The distributions of dissolved amino acids in the South Yellow Sea and the EastChina Sea in winter2011were investigated. The average concentrations of THAAand DFAA in the subsurface water were1.10μmol/L and0.18μmol/L. The averageconcentrations of THAA and DFAA in the surface micro-layer water were1.58μmol/L and1.12μmol/L. Concentrations of THAA decreased from inshore tooffshore regions in winter which was similar to that in summer, and Zhejiang coastoffshore was the high value areas of THAA. There was significant correlation foundbetween concentrations of DFAA in subsurface water and surface microlayer water,which indicated DFAA proceeded frequent exchange between the two water-layers.The dominant amino acids of THAA and DCAA in subsurface water and surfacemicro-layer water were glycine, serine, alanine, glutamic and methionine. The dominant amino acids of DFAA in subsurface water and surface micro-layer waterwere serine, glycine and methionine. There were7pairs of amino acids in THAAshowed significant positive correlations and5pairs showed negative correlations inthe subsurface water. However, there were5pairs of amino acids in THAA showedsignificant positive correlations and9pairs showed negative correlations in thesurface Microlayer water.