Factors influencing analysis of chromophoric dissolved organic matter in estuarine waters by excitation emission matrix spectroscopy (EEMS)
- 海洋环境－已发表论文 
结合在厦门湾九龙江口的现场调查与实验室分析,对目前河口区CDOM三维荧光光谱(excitation-emission matrix spectroscopy,EEMS)分析的一些影响因素(主要是离子强度、浓度效应、不同孔径滤膜过滤)进行了探讨.结果表明,CDOM的EEMS与样品中离子强度关系不大,说明在河口区河海水混合过程中,仅仅由于水体盐度的变化不会造成CDOM光学特征的明显变化.河端CDOM的荧光强度随物理稀释倍数的增大成相应比例的减小,稀释对EEMS的影响仅仅体现在荧光强度上,显示河口区的CDOM样品不存在荧光淬灭效应.九龙江口河流端样品中共含有类腐殖质(C、A)及类蛋白质(T1、T2)4种荧光团,随着混合样品中海水体积分数的增大,样品荧光强度逐渐降低,代表海洋来源的类腐殖质荧光峰M逐渐显露,T1峰逐渐高于A峰.这说明从河端至外海CDOM的组成结构发生了一系列的变化,来源上逐渐完成了以陆源为主到海源为主的转变;性质上逐渐完成了以类腐殖质荧光团为主到类蛋白质荧光团为主的转变.在中、高盐度区,0.2μm的Millipore聚碳酸酯滤膜可以很好地去除水体散射对EEMS的干扰,EEMS(0.2μm)比EEMS(0.7μm)更为规则,各峰的显示更加清晰,不同荧光基团的划分更加容易.无论高、中、低盐度站位,0.7μm滤膜过滤的样品,其CDOM荧光强度都要略高于0.2μm滤膜过滤的样品,2种不同孔径滤膜过滤对CDOM荧光测定带来的差异不可忽略.Excitation emission matrix spectroscopy (EEMS) was used to analyze chromophoric dissolved organic matter (CDOM) from field samples from the Jiulong estuary,Xiamen Bay. The effects of various factors including ionic strength,concentration and filter pore size were investigated. The results indicate that increasing ionic strength did not affect the EEMS of CDOM,suggesting that salinity changes do not influence the optical properties of CDOM during estuarine mixing. Dilution of the river end member sample only caused a proportional decrease of CDOM fluorescence intensity,while the position of the fluorescence peaks remained unchanged. No fluorescence quenching effect was observed for relatively high concentrations of terrestrial CDOM sources. Four fluorophores (including humic-like peaks C and A,and protein-like peaks T1 and T2) were found in river end member samples of the Jiulong estuary. As the volume proportion of seawater in the mixture increased during the mixing experiment between river and seawater end members,the fluorescence intensity of these peaks decreased,while peak M,representing marine humic-like material,gradually appeared. The intensity of peak T1 was eventually stronger than peak A,suggesting that a change of CDOM composition occurred from the river end member to the seawater end member. The dominant sources of CDOM gradually changed from terrestrial fluorophores to marine fluorophores and the dominant fluorescence components gradually changed from humic-like fluorophores to protein-like fluorophores. In the middle and high salinity area of the Jiulong estuary,a 0.2 μm Millipore polycarbonate filter can be used to remove the disturbance of water scattering to CDOM EEMS. EEMS of samples pre-filtered with 0.2 μm filters were more regular than those pre-filtered with 0.7 μm GF/F filters,making the division of different fluorescence peaks much easier and clearer. Additionally,the fluorescence intensities of different salinity samples pre-filtered with 0.7 μm filters were a little higher than those pre-filtered with 0.2 μm filters,indicating that the difference of CDOM fluorescence intensity due to the use of different filter pore sizes cannot be ignored.