南海北部海水中氨基酸的分布及其对溶解有机物降解行为的指示研究

于2015年6月对南海北部海区5个断面共26个站位海水中溶解态氨基酸（THAA）、溶解有机碳（DOC）和叶绿素a（Chl a）的浓度进行了科学调查。结果表明:夏季南海北部海水中THAA的浓度范围为0.40~1.95 μmol/L,平均值为（0.80±0.40） μmol/L,THAA的水平分布总体上体现出近岸高、远海低的特点,表明陆源输入对南海北部海域表层THAA分布有重要影响。THAA在断面上的垂直分布呈现出由近岸至远岸、由表层至底层逐渐降低的趋势。THAA浓度与两种D型氨基酸（D-谷氨酸:D-Glu和D-丙氨酸:D-Ala）含量之间存在显著负相关性,与天门冬氨酸/β-丙氨酸（Asp/β-Ala）和谷氨酸/γ-氨基丁酸（Glu/γ-Aba）比值之间存在显著正相关性,表明细菌的消耗是影响南海海水中THAA浓度的重要因素。D-Ala作为细菌肽聚糖中相对稳定的氨基酸,根据其占DOC的含量估算南海海水中的细菌源有机碳对DOC的贡献率为（29.32±14.32）%,其水平分布显示出近岸低、远岸高的特点;而其垂直分布则呈现出从表层至底层逐渐增加的趋势。THAA占DOC百分比（THAA-C%）的变化范围为1.02%~5.49%,平均值为（2.97±1.38）%。THAA-C%、活性因子和降解因子的高值均出现在珠江口外围区域。随着海水深度增加3种降解因子的数值均显著降低,这表明底层海水中有机物比表层海水中的有机物降解程度更大。

Distributions of amino acids and their indications for the degradation of dissolved organic matter in the northern South China Sea

Concentrations of dissolved amino acid (THAA), dissolved organic carbon (DOC) and chlorophyll a(Chl a) were determined in five transects of the northern South China Sea (NSCS) in June 2015. The results showed that the concentrations of THAA ranged from 0.40 to 1.95 μmol/L, with an average of (0.80±0.40) μmol/L. THAA concentrations exhibited a decreasing trend from the nearshore to offshore stations, indicating that terrestrial input plays an important role in affecting the distributions of THAA. The vertical distribution of THAA concentrations displayed a decreasing trend from the surface layer to the bottom layer. The present study found that the concentrations of THAA were negatively correlated to the D-amino acids (D-Glu and D-Ala), but positively correlated to Asp/β-Ala and Glu/γ-Aba ratios. Our results indicated that the bacterial consumption was an important factor influencing the concentration of THAA in the NSCS. The contribution of bacterial organic carbon to DOC was (29.32 ±14.32)% in the NSCS, exhibiting increasing trends from the nearshore to offshore sites and from the surface waters to the bottom waters. High values of carbon normalized yields of amino acids (THAA-C%), reactivity index and degradation index (DI) were found in the area near the Zhujiang Estuary. With the increasing of the water depth, the values of the degradation factors were significantly decreased, reflecting the higher degradation extent of organic matter in the bottom waters.