Distribution And Composition Of Dissolved Amino Acids In The South Yellow Sea And Jiaozhou Bay

Amino acids are the major forms of organic nitrogen (ON) and importantcomponents of organic carbon (OC) in most marine organisms. Dissolved amino acidsare the major forms of dissolved organic nitrogen (DON), which exist in the forms ofdissolved combined amino acids (DCAA) and dissolved free amino acids (DFAA).The majority of dissolved amino acids are in the form of DCAA, while DFAA areminor components. DFAA are utilized as an important source of N by autotroph, andare also important sources of C and N by heterotroph. Studies on dissolved aminoacids will help us know the sources, transformation, circulation and biologicalavailability of marine organisms, so as to provide a scientific proof for understandingthe level of marine primary productivity.In the present dissertation, systematic study on the distribution and compositionof the dissolved amino acids in the South Yellow Sea and the Jiaozhou Bay werecarried out. The study was conducted to reveal the seasonal variations of the aminoacids, the enrichment extent in the surface microlayer and the correlation betweenenvironmental factors and dissolved amino acids. The main findings are shown asfollows:(1) Distribution and composition of dissolved amino acids were determined in theSouth Yellow Sea during autumn. The average concentrations of THAA, DFAA,DCAA in the surface water were2.08μmol/L,0.39μmol/L and1.69μmol/L,respectively. The concentrations of THAA decreased from inshore to offshore sites,while the regularity of distribution of DFAA was poor, which was higher in theeastern offshore part. Serine, glycine, glutamic acid, alanine, aspartic acid were themajor constituents of dissolved amino acids. Cluster analysis showed that an obviousregional characteristic was revealed in the composition of individual amino acidsbetween the north and south area of the South Yellow Sea demarcated by34°N. High similarity was found among individual amino acids with similar chemical propertiesin the cluster analysis of molar percentages of individual amino acids. No significantcorrelation was found between dissolved amino acids and environmental factors suchas chlorophyll a (Chl-a), dissolved organic carbon (DOC), dissolved inorganicnitrogen (DIN), bacterial abundance, temperature and salinity.(2) Seasonal variations of distribution and composition of dissolved amino acidswere determined during surveys from June2010to May2011in the subsurface waterand surface microlayer of Jiaozhou Bay. The average concentrations of THAA, DFAA,DCAA in the subsurface water were2.08μmol/L,0.39μmol/L and1.69μmol/L,respectively, while those in the surface microlayer were2.07μmol/L,0.56μmol/L and1.51μmol/L. Bimodal characteristic (in summer and winter) was found in theseasonal variations of the concentrations of THAA, while the concentrations of DFAAin autumn and winter were higher than those in summer and spring. The annualenrichment probability of DFAA and DCAA in surface microlayer water was65.3%and56.3%, with an average enrichment factor of1.60and1.73, respectively.Although the concentrations of THAA and DFAA varied during difference cruises,higher concentrations occurred in the east and west coast regions, decreasinggradually from the coast to the central region. Serine, glycine, glutamic acid, alanine,aspartic acid were the major constituents of dissolved amino acids. Correlation matrixof amino acids indicated that correlation among individual amino acids in summerand winter was significant than that in autumn and spring. High similarity was foundamong individual amino acids with similar chemical properties by the cluster analysisof molar percentages of individual amino acids. Analysis also revealed that DCAAhad significant correlations with DOC and Chl-a while DFAA was related withbacterial abundance and salinity in subsurface water, in contrast to correlations ofDFAA with DOC, DIN and salinity in surface microlayer.