崇明东滩潮沟系统水体溶解有机物光化学特性及来源解析

Photochemical Characteristics and Source Analysis of Dissolved Organic Matter in TidalCreek System of Chongming Dongtan

2018年7月大潮期间于崇明东滩典型潮沟采集表层水体测定溶解有机碳(DOC)浓度、有色溶解有机质(CDOM)紫外-可见光吸收特性和三维荧光光谱特性,结合平行因子分析与统计分析,探讨涨落潮期间盐沼湿地水体溶解有机质来源、组成及影响因素。结果表明,潮汐过程中355 nm处的紫外吸收系数a(355)与DOC浓度表现出显著相关性,一定程度上可表征DOC浓度与行为;表征芳香性的光谱斜率Sg及比紫外吸光度SUVA254均表明盐沼水体芳香性强于河口水体,暗示了陆源输入的重要作用。CDOM的三维荧光光谱揭示了其中含有陆源类腐殖质、类蛋白及海源类腐殖质,且均与潮汐变化显著相关,其中来源于陆地高等植被的C2成分与潮汐高度变化一致。受河口水域潮汐作用影响,采样水体荧光指数(FI)1.19~1.40,腐殖化指数(HIX)1.71~2.75,生物源指数(BIX)<1,水体中溶解有机质多为陆源输入,但腐殖化程度相对较低。综合主成分分析结果与荧光特征分析可知,来自高等植物或土壤有机物的陆源有机质在CDOM来源上占主导地位。盐沼溶解有机质受局地再悬浮、孔隙水释放及潮汐横向输运的共同作用,成分复杂多变,后续需拓展时间与空间对比,以探明CDOM的产生、消亡与运动轨迹。

The concentration of dissolved organic carbon(DOC),UV-visible light absorption characteristics and three-dimensional fluorescence spectrum characteristics of chromophoric dissolved organic matter(CDOM)were measured in surface water collected from typical tidal creeks of Chongming Dongtan during the spring tide in July 2018.Combined with parallel factor analysis and statistical analysis,the sources,composition and influencing factors of dissolved organic matter in salt marsh wetland during the flood and ebb tides were discussed.The results showed that the UV absorption coefficient at 355 nm,a(355),during the tidal process was significantly correlated with DOC concentration,which characterized DOC concentration and behavior to a certain extent.The spectral slope Sg and specific ultraviolet absorbance SUVA254 indicated that the aromaticity of salt marsh water was stronger than that of estuarine water,suggesting the important role of terrestrial input.The three-dimensional fluorescence spectrum of CDOM revealed that it contained terrestrial humic-like substances,protein-like substances and marine humic-like substances,which were significantly correlated with tidal changes,in which C2 components from terrestrial higher vegetation were consistent with tidal height changes.The fluorescence index(FI)and humification index(HIX)of the sampling water were 1.19~1.40 and 1.71~2.75,respectively,and biological index(BIX)<1.The dissolved organic matter in the water was mostly terrestrial input,but the humification degree was relatively low.Based on the results of principal component analysis and fluorescence characteristics analysis,the terrestrial organic matter from higher plants or soil organic matter dominated the source of CDOM.The composition of dissolved organic matter in salt marshes was complex and changeable due to the combined effects of local resuspension,pore water release and tidal lateral transport.In the future,it is necessary to expand the time and space comparison to explore the generation,demise and trajectory of CDOM.