Characterization of Photobleaching of Chromophoric Dissolved Organic Matter in Xiamen Bay by Excitation Emission Matrix Spectroscopy
CHENG Yuan-yue, GUO Wei-dong*
State Key Laboratory of Marine Environmental Science (Xiamen University)，College of Oceanography and Environmental Science, Xiamen University, Xiamen 361005, China
摘要： 利用荧光激发-发射矩阵光谱(excitation-emission matrix spectroscopy，EEMs)研究了厦门湾九龙江河口中、低盐度区表层水样中有色溶解有机物在秋季天然太阳辐照下的光化学漂白。结果表明，光漂白未引起水样中类腐殖质(C, A, M)和类蛋白质(T，B)荧光峰位置的移动。5个峰的荧光强度均随辐照时间的增加而减少，其中低盐度水样的降低幅度更大，并以指示陆源河流输入的特征荧光峰C的光漂白程度最大。根据漂白速率可将各荧光团区分出易漂白和难漂白两类组分。光漂白导致T、C峰及A、C峰之间的荧光强度比值增加，说明光漂白可引起海水中溶解有机物性质的明显改变，并且也是近海类蛋白质荧光相对类腐殖质荧光占优势的一个重要控制因素。研究结果对于探究陆源有机物在近海的转化及去除过程以及海洋光学有一定的参考价值。
关键词：有色溶解有机物;光漂白;三维荧光光谱;厦门湾
Abstract：Fluorescence excitation-emission matrix spectroscopy (EEMs) was applied to study the photobleaching of chromophoric dissolved organic matter (CDOM) in two surface water samples from Xiamen Bay exposed to natural sunlight between 10:00-16:00 during September 12-18, 2007. Both samples were collected from the lower and middle salinity areas in Jiulong Estuary of Xiamen Bay, and then filtered by 0.2 μm polycarbonate filters before the photobleaching incubation experiment. The results showed that three humic-like (C, A, M) and two protein-like (T, B) fluorescence peaks were observed in both samples, and the photobleaching didn’t cause obvious shift of the positions of these fluorescence peaks. The fluorescence intensities of the five peaks decreased with the increase in irradiation time and peak C demonstrated the fastest photobleaching rate. The photobleaching rate of low salinity sample was higher than that of middle salinity sample, consistent with its higher content of chromophores. All the five fluorophores could be distinguished into labile and refractory components based on their photobleaching dynamics. The increase in the intensity ratios of peak T and C (IT/IC) and peak T and C (IA/IC) after irradiation suggested that photobleaching can cause obvious change of the properties of dissolved organic matter in seawater, and it may partly account for the dominance of the protein-like fluorescence relative to the humic-like fluorescence in coastal area. The results suggest that EEMs was a useful tool to trace the transformation and removal processes of terrestrial CDOM entering the coastal regions.
Key words：Chromophoric dissolved organic matter (CDOM);Photobleaching;Excitation-emission matrix spectroscopy (EEMs);Xiamen bay
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