Origin and transport of n-alkane-2-ones in a subtropical estuary: potential biomarkers for seagrass-derived organic matter

n-Alkane-2-ones are lipids commonly found in sediments and soils. This group of compounds, frequently reported in the literature, usually occurs in the form of a homologous series ranging from about C19 to C33 characterized by a strong odd over even carbon number predominance. In this paper we report a different molecular distribution, centered about the C25 homologue as the dominant ketone. The relative abundance of the C25 compared to the C27 homologue in a sediment transect increased from the upper to the lower end of a South Florida estuary, and was found to correlate with surface water salinity in extracts from suspended solids. Analyses of different varieties of seagrasses showed these to be the most likely source of the C25 n-alkane-2-ones, while the C27+ homologues were mainly derived from mangroves and freshwater marsh vegetation. Compound-specific stable isotope measurements and statistical analyses support this finding, suggesting that molecular distributions of n-alkane-2-ones can be used to identify seagrass-derived organic matter in coastal environments.