MEPS 280:55-72 (2004)  -  doi:10.3354/meps280055

Carbon and nitrogen cycling on intertidal mudflats of a temperate Australian estuary. III. Sources of organic matter

Perran L. M. Cook1,2,3,5,*, Andrew T. Revill2,3,4, Lesley A. Clementson2, John K. Volkman2,4

1University of Tasmania, GPO Box 252-75, Hobart, Tasmania 7001, Australia
2CSIRO Marine Research, GPO Box 1538, Hobart, Tasmania 7001, Australia
3CRC for Coastal Zone, Estuary and Waterway Management, Indooroopilly Sciences Centre, 80 Meiers Road Indooroopilly, Queensland 4068, Australia
4Aquafin CRC, PO Box 120, Henley Beach, South Australia 5022, Australia
5Present address: Max Planck Institute for Marine Microbiology, Celsiusstrasse 1, 28359 Bremen, Germany

ABSTRACT: The sources and cycling of organic matter on 2 mudflats in the Huon Estuary, SE Tasmania, were investigated over 4 seasons using pigment and lipid biomarkers as well as stable isotopes of carbon and nitrogen; 1 site was in the upper estuary,1 site was in a marine side-arm. The organic matter within the sediments at both sites was dominated by terrestrial sources, but most of this was refractory and only slowly remineralised. Significant, but seasonally variable, amounts of organic matter were derived from microphytobenthos (MPB), but this was rapidly remineralised and comprised only a minor fraction of the preserved sediment organic matter pool. Compound specific stable-isotope analysis of bacterial biomarkers suggested that the bacteria within the sediment were consuming microalgae-derived material. Separation of MPB from the sediment at the site in the upper estuary using the lens-tissue technique was found to significantly fractionate the algae community with cyanobacteria being enriched in the separated fraction. Nitrogen fixation probably contributed significantly to the growth requirements of cyanobacteria at the site in the upper estuary, as indicated by the low δ15N value of the cyanobacteria separated from the sediment.

KEY WORDS: Microphytobenthos · Stable isotope · Compound-specific isotope-ratio mass spectrometry · Fatty acids · Sterols · Accessory pigment · Mudflat

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