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 grou p of compounds, frequently reported in the literature, usually occurs in th e form of a homologous series ranging from about C-19 to C-33 characterized by a strong odd over even carbon number predominance. In this paper we rep ort a different molecular distribution, centered about the C-25 homologue a s the dominant ketone. The relative abundance of the C-25 compared to the C -27 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 wat er salinity in extracts from suspended solids. Analyses of different variet ies of seagrasses showed these to be the most likely source of the C-25 n-a lkane-2-ones, while the C-27+ homologues were mainly derived from mangroves and freshwater marsh vegetation. Compound-specific stable isotope measurem ents and statistical analyses support this finding, suggesting that molecul ar distributions of n-alkane-2-ones can be used to identify seagrass-derive d organic matter in coastal environments. (C) 2001 Elsevier Science Ltd. Al l rights reserved.