近岸沉积物再悬浮期间所释放溶解有机物的荧光特征

对采自厦门湾九龙江人海河口的4个沉积物样品进行了室内再悬浮模拟实验,利用荧光激发-发射矩阵光谱(EEMs)研究了再悬浮过程中从沉积物中释放出的有色溶解有机物(CDOM)的荧光特征,同时通过与相应站位沉积物间隙水和底层水的对比分析,探讨了河口近岸海域的沉积物再悬浮作用作为水体中溶解有机物来源之一的可能性.结果表明,对给定站位,CDOM相对荧光强度和溶解有机碳(DOC)含量分布变化非常一致,均为间隙水最高,再悬浮次之,底层水最低;站位之间,底层水和再悬浮水样中CDOM相对荧光强度随盐度的降低而增加,从海端向河端增加的趋势明显.EEMs分析表明,各样品中均存在类腐殖质荧光与类蛋白质荧光团,且模拟实验也表明再悬浮作用可释放类腐殖质与类蛋白质荧光物质到底层水中,表明底质再悬浮将是近岸水体中CDOM的一个重要来源.与相应的底层水相比,间隙水的荧光峰(如峰A/C)的位置发生红移.再悬浮样品中EEMs的荧光团同时表现出相应底层水和间隙水的特征,但是荧光峰(峰A和峰C)的最大激发和发射波长更接近底层水中相应荧光团,与间隙水相比,则发生谱峰位置的蓝移.近海端样品中荧光峰M明显,随着盐度的降低,底层水和再悬浮水样的γ(M/C)值逐渐降低,且海源的峰M由海端向河端逐渐消失,表明峰M属于海洋自生来源.本研究区域DOM的荧光指数在1.61～1.93之间,表明近海端样品DOM主要为生物来源,而近河端样品DOM主要为陆源输入,或者为陆源与生物活动共同作用的结果.

Fluorescence characteristics of dissolved organic matter released from estuarine sediments during resuspension

Excitation-Emission Matrix Fluorescence Spectroscopy (EEMs) was employed to study fluorescence characteristics of chromophoric dissolved organic matter (CDOM) readily released from sediment particles during episodes of resuspension,and bottom waters and surface sediment pore waters were compared in all corresponding sites. The results show that,for a given site,both relative intensities of CDOM fluorescence and concentrations of dissolved organic carbon (DOC) have the same variation trend with the maxima in the pore waters and the lowest in the bottom waters. Relative intensities of CDOM fluorescence increased with decreasing salinity from marine to riverine environments in bottom waters and resuspended samples. EEMs showed several types of fluorescence signals observed,including humic-like and protein-like fluorescences for all samples,and simulated experimentation also showed humic-like and protein-like materials were released to bottom waters by resuspension,indicating sediment resuspension would be an important source of CDOM from coastal waters. For a given site,positions of fluorescence peaks (e.g. peak A and peak C) in pore waters were red-shifted,compared to their respective bottom waters. EEMs for all resuspended samples exhibited mixed characteristics between corresponding bottom and pore waters,but Ex/Em-max of peak A and peak C was very close to that in bottom waters,and observed blue-shift of peak positions in comparison with pore water samples. Peak M was strong in marine environment,and gradually disappeared with decreasing salinity from marine to riverine environments,and peak M and peak C ratios also lowered in bottom waters and resuspended samples,indicating peak M was derived from marine origin. The fluorescence index values of DOM varied from 1.61 to 1.93,suggesting DOM in marine environment was dominating biological origin,and DOM in riverine environment was controlled by terrestrial input,or was associated with terrestrial substances and microbial activities.