Precise indices based on n-alkane distribution for quantifying sources of sedimentary organic matter in coastal systems. (November 2015)

• Record Type: Journal Article
• Authors: Chevalier, Nicolas; Savoye, Nicolas; Dubois, Sophie; Lama, Mathias Lama; David, Valérie; Lecroart, Pascal; le Ménach, Karyn; Budzinski, Hélène
• Is Part Of: Organic geochemistry. Volume 88(2015:Nov.)
• Page Start: 69
• Page End: 77
• Publication Date: 2015-11
• Subjects: n-Alkanes -- Sedimentary organic matter -- Coastal system -- Arcachon Bay; Organic geochemistry -- Periodicals; Biogeochemistry -- Periodicals; Géochimie organique -- Périodiques; 553.205
• DOI: 10.1016/j.orggeochem.2015.07.006
• Languages: English
• ISSNs: 0146-6380

Abstract

Highlights: n -Alkane fingerprints for a set of OM sources in a temperate lagoon determined. New indices based on n -alkane ratios defined. Overall approach for quantifying the SOM composition in coastal systems given. Abstract: Precise indices based on n -alkane signatures were developed in order to determine the sources and composition of sedimentary organic matter (SOM) in coastal systems. The Arcachon Bay (France), a well-studied temperate lagoon, was used as an example of a complex coastal system sheltering a wide diversity of OM sources. Three main groups of sources were well discriminated from their n -alkane signatures: seagrass ( Zostera sp.) produced mainly n -C17, n -C19, n -C21, n -C23 and n -C25 alkanes, algae (Rhodophyta, Chlorophyta) produced n -C15 and n -C17 and the terrigenous input [ Quercus sp., Spartina sp. and river suspended particulate OM (SPOM)] was characterized by n -C25, n -C27, n -C29, n -C31 and n -C33 . From the above and literature n -alkane fingerprints, we developed a set of indices ( n -alkane ratios) to quantify the contribution of these three major sources of the SOM. At the Arcachon Bay scale, they indicated that SOM was composed mainly of seagrass (ca. 53 ± 19%) and terrestrial (ca. 41 ± 17%) material, followed by algae (ca. 6 ± 9%). Moreover, the new n -alkane indices exhibited more relevant spatial patterns than classical ones – the TAR (C27 + C29 + C31 /C15 + C17 + C19 ; terrestrial to aquatic ratio) and the P aq (C23 + C25 /C23 + C25 + C29 + C31 ; aquatic plant %) – with a greater contribution from marine sources in the central part of the lagoon where a high density of Zostera seagrass was observed. Therefore, the development of precise indices adapted to the local diversity of OM sources is needed when using n -alkanes for quantifying the source composition of SOM in complex coastal systems.