Variability in the distribution of lipid biomarkers and their molecular isotopic composition in Altamaha estuarine sediments: implications for the relative contribution of organic matter from various sources

The estuarine mixing zone is an effective trap for particulate and dissolve d organic matter From many sources, and thus greatly affects transport and deposition of organic matter between the land and ocean. This study examine d sedimentary distributions of various fatty acids and their stable isotope compositions at three sites which represent different levels of mixing in the Altamaha River estuary, Georgia, USA. Distributions of other neutral li pids (phytol, C-14-C-32 fatty alcohols, and two sterols) were also determin ed as supplementary biomarkers from various sources. Results suggest that P OM from terrestrial plant material was dominant at an initial, upper estuar y mixing zone (salinity in the water column is near zero but porewater in t he sediment is saline) while POM from marine sources was mainly deposited a t a more intensive mixing zone (whenin salinity in surface and bottom water s was identical) in the Altamaha. Much less particulate lipid was deposited in Altamaha River mouth sediments even during the high discharge season, s uggesting that terrestrial plant-derived POM may not be significantly trans ported across the mixing zone. Analyses of fatty acid isotopic composition further verify the differential deposition pattern of POM from different so urces. (C) 2001 Elsevier Science Ltd. All rights reserved.