秋季南海珠江口和北部湾溶解有机物的光降解

利用三维荧光光谱分析手段,结合吸收光谱测定,分析了2007年10月中国珠江口及北部湾水体中4个典型有色溶解有机物(CDOM)样在太阳光辐照下的光降解特性.结果表明,珠江口及广西沿海CDOM样受陆源输入影响较大,而北部湾中部的HX样具有典型海洋CDOM特征,80m水深的HN样则受到北部湾环流的主要影响.这些CDOM样品中均观测到类腐殖质荧光峰A、C、M以及类色氨酸荧光峰R、T,它们的荧光峰强度及吸收系数a(280)在秋季短期日光辐照下发生了较明显的光化学降解,受陆源输入影响较大的珠江口及广西沿海样品的光降解程度高于北部湾的远岸样品,反映出它们含有更多的发色团.光降解未引起CDOM荧光峰位置的显著变化,类腐殖质荧光峰M和A、类蛋白质荧光峰R和T的强度变化趋势一致,表明这两对峰具有相似的性质.A峰区存在的双峰现象表明其为多个荧光组分的叠加.CDOM吸收光谱的光谱斜率S(270～350)随光辐射而逐渐增加,可用于指示光降解引起的CDOM分子量的减小趋势.研究表明,光降解在南海生源要素的生物地球化学循环中起重要作用.

Photodegradation of DOM in the Pearl River Estuary and the Beibu Gulf of the South China Sea in Autumn

Fluorescence excitation emission matrix spectroscopy (EEMs) analysis combined with absorption spectroscopy measurement was used to investigate the photodegradation of four typical chromophoric dissolved organic matter (CDOM) samples from the Pearl River Estuary and the Beibu Gulf under natural solar irradiation.CDOM samples from the Pearl River Estuary and Guangxi coastal waters were more influenced by terrestrial input,while a sample from the middle of the Beibu Gulf has typical characteristics of marine CDOM,and another sample from a depth of 80 m in the south of the Beibu Gulf was somewhat influenced by the Beibu Gulf circulation.Humic-like (A,C and M) and tryptophan-like (R and T) fluorescence peaks were observed in all of the CDOM samples.Obvious photochemical degradation of their fluorescence peak intensity and absorption coefficient occurred under five day's solar irradiation in the autumn.The photodegradafion degree of samples from the Pearl River Estuary and Guangxi coastal waters was higher than samples from offshore in the Beibu Gulf,suggesting that the two former samples influenced by terrestrial input contained more chromophores.Photadegradation did not cause a significant position variation of CDOM fluorescence peaks.The fluorescence intensity of the humic-like peaks M and A,protein-like peaks R and T have the same variation trend,indicating that each pair of peaks was closely interrelated.Double peaks were found in the fluorescence peak A area,suggesting that peak A was actually a superposition of multiple fluorescence components.The spectrum slope S (270～350) of the CDOM absorption spectra increased gradually with irradiation time,which can be used to indicate the decrease of CDOM molecular weight caused by photochemical degradation.Our results show that photodegradation could play an important role in the biogeochemical cycling of biogenic elements in the South China Sea.