九龙江口潮滩表层沉积物有机质的分布、来源及沉积环境指示意义

Temporal spatial distribution and source of organic matter in tidal flat surficial sediments and their implications for sedimentary environment identification in the Jiulong River Estuary

本研究旨在揭示九龙江口潮滩有机质含量及其来源的时空分异规律,寻找有效识别潮滩沉积环境的有机碳指标,以便更好地将有机碳应用于河口沉积微相识别和古环境研究。在九龙江口潮滩不同地貌单元,于夏季和冬季采集41个表层沉积物,进行粒度、总有机碳(TOC)、总氮(TN)和稳定碳同位素(δ^(13)C)测试。结果显示:从高潮滩至低潮滩,沉积物粒度逐渐变粗,TOC、TN和C/N变小,δ^(13)C值偏正。高潮滩有机质来源以陆源和红树林贡献为主,中潮滩以海源和互花米草贡献为主,低潮滩以海源贡献为主。九龙江口潮滩有机质的分布和来源受控于河口陆海相互作用的季节变化、潮滩沉积动力分异和潮滩植被分布。高潮滩与中–低潮滩之间,TOC存在显著性差异,TN、δ^(13)C存在极显著性差异,因此参数组合TOC、TN和δ^(13)C可作为高潮滩与中–低潮滩的有效判别指标。

This article is focus on the distribution and source of organic matter in tidal flat in the Jiulong River Estuary,and to seek effective organic geochemistry proxies for recognize sedimentary microfacies,and thus to help that organic carbon is better applied to identify sedimentary microfacies and paleo-environment.Forty one surficial sediment samples were obtained and measured their grain size,total organic carbon(TOC),total nitrogen(TN),and organic carbon stable isotopes(δ^(13)C) in the tidal flat from three sedimentary environments:upper tidal flat,middle tidal flat and lower tidal flat in summer and winter.The results show that,from upper tidal flat to lower tidal flat,the grain size of sediments becomes coarser gradually with decreasing TOC,TN and C/N,and the increase of δ^(13)C.The sources of organic matter in the upper tidal flat are dominated by terrestrial organic matter and mangrove,marine organic matter and Spartina alterniflora in middle tidal,and marine organic matter in lower tidal flat.The distribution and sources of organic carbon in tidal flat from the Jiulong River Estuary are controlled by the seasonal changes of land-ocean interaction,sedimentary hydrodynamic sorting,and plants.There is a significant difference in TOC,and a highly significant difference in TN and δ^(13)C in sediments of the tidal flat.We thus proposed that organic geochemistry properties TOC,TN and δ^(13)C are the effective indicators to identify upper tidal flat and middlelower tidal flat in the Jiulong River Estuary.