δ13C and δD identification of sources of lipid biomarkers in sediments of Lake Haruna (Japan)

Organic materials in lacustrine sediments are from multiple terrestrial and aquatic sources. In this study, carbon (delta C-13) and hydrogen isotopic compositions (delta D) of phytol, various sterols, and major n-fatty acids in sediments at Lake Haruna, Japan, were determined in their solvent-extractable (free) and saponification-released forms (bound). The delta C-13-delta D distributions of these lipid molecules in sediments are compared with those of terrestrial C3 and C4 plants, aquatic C3 plants, and plankton to evaluate their relative contributions. delta C-13-delta D of free-phytol in sediments is very close to that of phytol in plankton samples, whereas delta C-13-delta D of bound phytol in sediments is on a mixing line between terrestrial C3 plant and plankton material. Unlike phytol, no significant delta C-13-delta D difference between free and bound forms was found in sterols and n-fatty acids. delta C-13-delta D values of algal sterols such as 24-methylcholesta-5,22-dien-3 beta-ol in sediments are close to those of plankton, whereas delta C-13-delta D of multiple-source sterols such as 24-ethylcholest-5-en-3 beta-ol and of major n-fatty acids such as n-hexadecanoic acid in sediments are between those of terrestrial C3 plants and plankton samples. Thus, delta C-13-delta D distributions clearly indicate the specific source contributions of biomarkers preserved in a lacustrine environment. Free phytol and algal sterols can be attributed to phytoplankton, and bound phytol, multiple source sterols, and major n-fatty acids are contributed by both terrestrial C3 plants and phytoplankton. Copyright (C) 2005 Elsevier Ltd.