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13C-DEPLETED MICROBIAL LIPIDS INDICATE SEASONAL METHANOTROPHIC ACTIVITY IN SHALLOW ESTUARINE SEDIMENTS
Citation:
Molina, M AND R A. Burke Jr. 13C-DEPLETED MICROBIAL LIPIDS INDICATE SEASONAL METHANOTROPHIC ACTIVITY IN SHALLOW ESTUARINE SEDIMENTS. Presented at American Society of Limnology and Oceanography Conference, Victoria, Canada, June 10-14, 2002.
Impact/Purpose:
This research project sets out to design and conduct an assessment of the long-term ecological consequences of alternative management choices. As the first project to be done at this scale using predictive ecological endpoints, we will seek to identify the appropriate components of such an analysis. We will use experience gained in the conduct of this BASE analysis to identify key research and data needs for address, to estimate timing, resource needs, etc., for future analyses. We will extend this analysis beyond previous and ongoing studies in two ways: by incorporating biological endpoints, primarily properties of fish communities, and by introducing the concept of sustainability of ecological state under future scenarios contrasted with the present state of those same ecological resources. Requirements that are identified during the course of this study will permit the recommendation of specific capabilities that should be incorporated in a general modeling system currently under development to support BASE and other environmental assessments. Finally, the analysis is intended to be of value for establishing environmental management choices that will be beneficial and those that would be detrimental to the sustainability of ecological resources of the Albemarle-Pamlico Basin.
Description:
Compound specific isotope analysis was combined with phospholipid fatty acid (PLFA) analysis to identify methanotrophic activity in members of the sedimentary microbial community in the Altamaha and Savannah River estuaries in Georgia. 13C-depleted PLFAs indicate methane utilization because methane is the only C source with a depleted isotopic signal (-45 to -72 per mil) in these ecosystems. Three PLFAs (16:1w7, 16:1w5, and 10Me16:0) had 13C-depleted values (-52.37 to -39.2 per mil) during winter and spring when the salinity was less than 5 ppt. No depleted signal was observed during summer when the salinity was higher (4 to 30 ppt). 10Me16:0, an indicator of sulfate reducing bacteria (SRB), showed 13C-depleted values only in the Altamaha, indicating a discrepancy in the activity of specific functional groups depending on location. Methane production was higher in the Altamaha River than in the Savannah and its production did not correlate with the detection of 13C-depleted PLFAs. Our results suggest that methane oxidation occurs on a seasonal basis in highly dynamic estuaries and is the result of more than one microbial functional group (methanotrophs and SRB) in shallow estuarine sediments.