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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
Citation:
Shi, W., M. Y. Sun, M Molina, AND R. E. Hodson. 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. ORGANIC GEOCHEMISTRY 32(4):453-467, (2001).
Impact/Purpose:
The overall objective of this task is to develop quantitative relationships for assessing the vulnerability of aquatic resources to global change. The task will contribute experimental and modeling tools for assessments of the interactions of global climate and UV changes with coral reefs and selected watersheds and estuaries in the U.S. These activities are contributing primarily to two APGs in the ecosystems component of the Global Change Research Multiyear Plan: the 2006 APG (APG 3) on building the capacity to assess global change impacts on coastal aquatic ecosystems, including coral reefs and estuaries and the 2004 APG (APG 2) on building capacity to assess and respond to global change impacts on selected watersheds. One major task objective is to assess interactions of global warming and UV exposure that are contributing to the observed coral bleaching and disease. Our lab is working with scientists at the NHEERL Gulf Ecology Lab to characterize UV exposure and effects at several coral reef sites. Other research in this task is examining the interactions between UV-induced breakdown of refractory organic matter in estuaries and coastal areas that enhance UV penetration into the water and concurrently form biologically-labile nitrogen-, phosphorus- and carbon-containing substances that stimulate productivity and microbial activity. This task also involves research in central Brazil that is part of the Large Scale Biosphere Atmosphere Experiment (LBA). The objectives of this project are to assess the impacts of land use and climatic changes on soil nutrient cycles and microbiota, trace gas exchange and water quality in the Brazilian cerrado. This work involves a close collaboration between EPA and a group of scientists from the Department of Ecology, University of Brasilia, Brazil. Other objectives of this task are to assess the interactions of land use and climate changes with the ecological functioning of streams in watersheds of the Piedmont region of the southestern U.S.
Description:
The estuarine mixing zone is an effective trap for particulate and dissolved organic matter From many sources, and thus greatly affects transport and deposition of organic matter between the land and ocean. This study examined 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 lipids (phytol, C-14-C-32 fatty alcohols, and two sterols) were also determined as supplementary biomarkers from various sources. Results suggest that POM from terrestrial plant material was dominant at an initial, upper estuary mixing zone (salinity in the water column is near zero but porewater in
the sediment is saline) while POM from marine sources was mainly deposited at a more intensive mixing zone (whenin salinity in surface and bottom waters was identical) in the Altamaha. Much less particulate lipid was deposited in Altamaha River mouth sediments even during the high discharge season, suggesting that terrestrial plant-derived POM may not be significantly transported across the mixing zone. Analyses of fatty acid isotopic composition further verify the differential deposition pattern of POM from different sources.