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

Amino acids are of the most important component of organic nitrogen (ON) andorganic carbon (OC) in the marine environment. In seawater, Amino acids exist in twoforms of dissolved amino acids and particulate amino acids. The contribution ofdissolved amino acids, being made up of dissolved free amino acids (DFAA) anddissolved combined amino acids (DCAA), accounts for about15%of theconcentration of dissolved organic nitrogen (DON). DCAA are the major componentof dissolved amino acids and exist mostly in the form of small peptides. DFAA havethe characteristics of low concentration and fast turnover speed in seawater besidesthey are not only the important source of nitrogen by autotroph but also the importantsources of carbon and nitrogen by heterotroph. Amino acids in the ocean derive fromsome process, such as the degradation of marine biology, the hydrolyzation ofproteins, the excretion from the cell as well as the food chain. The research on narineamino acids can provide the basis for the marine primary productivity, but also revealadvantageously the cycle of marine biosphere and the sources, transformation andcirculation of marine organisms.In this essay, typical shelf sea area in China of the South Yellow Sea and the EastSea as the research object, analyze distribution and composition of dissolved andparticulate amino acids and relevant environment factors. By further study dielvariations and enrichment of dissolved amino acids in the surface microlayer and thecorrelation between individual amino acids are discussed in this paper. The mainresults shown as follows:(1) Based on determining the method of dissolved amino acids, the HPLCanalytical method of particulate amino acids was established in the lab. The bestexperimental conditions had been found out. Most kinds of amino acids could be completely separated using this method. The precisions were0.28～2.87%, thedetection limits were6.16~24.5nmol/L, and the recoveries were80~100%fordifferent amino acids. Meanwhile, this method was used successfully to analyze theYellow Sea and the East China Sea.(2) The distribution and composition of total hydrolyzed amino acids (THAA),dissolved combined amino acids (DCAA) and dissolved free amino acids (DFAA)were analyzed in the East China Sea and the Yellow Sea in spring2011. The averageconcentrations of THAA, DCAA and DFAA in the micro-surface water were3.73±2.17μmol/L,0.57±0.44μmol/L, and3.28±2.08μmol/L, respectively. Theaverage Enrichment Factor of DFAA and THAA were2.94and1.78, respectively. Theaverage concentration of THAA in the surface water was2.98±1.72μmol/L(1.27~8.54μmol/L), while the average concentrations of DCAA and DFAA in thesurface water were2.76±1.63μmol/L (0.91~7.70μmol/L) and0.31±0.21μmol/L(0.11~1.14μmol/L), respectively. In the diel variations, high values of THAA andDFAA appeared in the evening, with the highest concentrations at21:00. Theconcentrations of dissolved amino acids displayed a decreasing trend from inshore tooffshore stations, especially DCAA and THAA. In the vertical distribution, the highvalues of THAA appeared in the subsurface layer and in the bottom layer of the watercolumn. In the study area, major constituents of dissolved amino acids were aspartic,glycine, serine, glutamic acid and alanine acid. Correlation matrix analysis of aminoacids indicated that5pairs of amino acids in DFAA showed significant positivecorrelations. No significant correlations were found between the concentrations ofdissolved amino acids and environmental factors such as chlorophyll a, dissolvedorganic carbon (DOC) and dissolved inorganic nitrogen (DIN).(3) The distribution and composition of DAA and PAA were analyzed in theseawater samples collected at the East China Sea and the Yellow Sea in autumn,2011.The results showed that the average concentrations of DFAA, DCAA, THAA, andPAA were0.42μmol/L,1.40μmol/L,1.70μmol/L, and0.85μmol/L, respectively.The DCAA were the major forms of THAA, comprising the largest component(~82.45%) in the THAA. The concentrations of amino acids displayed a decreasing trend from inshore to offshore stations, with the highest value occurred at the YangtzeEstuary. The concentrations of PAA decreased from inshore to offshore and fromsurface to middle-level, but the concentrations in the bottom layer were higher thanthose in the middle water. The concentration of PAA was higher than the ambientwaters at vertical depth of about50m layer, being consistent with the distributionpattern of POC and PON. The generally bottom ascend in amino acids concentrationswere attributed to sedimentation and resuspension events. Carbon-normalized yield ofPAA (%C-PAA),%C-DCAA, and Nitrogen-normalized yield of PAA (%N-PAA) weregenerally higher at offshore station, reflective of in situ sources. Higher values ofratios between C and N revealed that terrestrial inputs enriched amino acids.Difference between PAA and DAA in seawater were affected by the bottom sedimentof selective adsorption to amino acids and biological function.