珠江口沉积物有机质特征、来源及其对碳存储的意义

Characteristics and sources of organic matter in sediments of the Pearl River Estuary: Carbon storage implications

河口沉积物作为承接陆海过程的重要载体,是有机质赋存的主要形式之一。本文研究了珠江口沉积物总有机碳、总氮含量和沉积物可溶性有机物三维荧光特征,以及其在口内区、混合区和口外区空间差异和影响因素,并结合碳稳定同位素(δ^(13)C)估算了珠江口各区域沉积物中不同来源有机质的贡献。结果显示:(1)沉积物总有机碳和总氮含量空间变化相似,口内区和混合区域沉积有机质含量显著高于口外区;主成分分析发现,口内区沉积有机质含量主要受径流输入的影响,口外区主要受Fe^(3+)的影响;(2)MixSIAR稳定同位素混合模型结果显示,口内区和混合区沉积有机质以陆源为主,口外区则以海源为主;(3)珠江口沉积物新生有机质较多,可快速被利用,总体上不利于有机碳存储;而陆源输入导致口内区和混合区沉积有机质腐殖化程度较高,有机碳可存储性相对较高,口外受海源有机质和铁氧化物—有机质复合体的影响,有机碳可存储性相对较低。本研究可为深入认知河口区沉积有机质的生物地球化学过程及有机碳存储提供参考。

Estuarine sediment, as an important carrier of terrestrial and marine ecosystems, is one of the main forms of organic matter occurrence. In this study, we analyzed total organic carbon(TOC) concentration, total nitrogen(TN) concentration,soluble organic matter excitation emission matrix spectroscopy(EEMs), spatial differences and influencing factors in different areas. Carbon stable isotope(δ^(13)C) was applied to estimate the contribution of sediment organic matter(SOM) in different regions of the Pearl River Estuary(PRE). The results are as follows.(1) Spatial variations of TOC and TN concentrations are similar. The concentrations of SOM in the inner estuary and mixed areas are significantly higher than those in the estuary mouth. Principal component analysis results show that SOM concentrations in the inner estuary and the mixed area are mainly affected by river flow input, and those in the estuary mouth, by ferric iron.(2) MixSIAR results show that SOM in the inner estuary and the mixed zone is still mainly from terrestrial sources, and that in the estuary mouth is primarily from marine sources.(3) Newly produced organic matter in the sediments, which can be quickly utilized, is highly enriched in the PRE.Terrestrial input induced the higher humification degree of SOM in the inner estuary and mixed areas, which is conducive to organic carbon storage processes. In contrast, low storage capability was implicated in the estuary mouth, due to the influence of marine sources and iron oxide-organic matter complex. This makes it unfavorable for the storage of organic carbon in the PRE. This study provides a supplementary reference for further understanding the biogeochemical process of SOM and carbon storage in estuaries.