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

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 δ 15 N 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 Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 280: [55][56][57][58][59][60][61][62][63][64][65][66][67][68][69][70][71][72] 2004 1999, Cahoon & Safi 2002), but this may shift seasonally to chlorophytes and cyanobacteria (Barranguet et al. 1997). In some areas, intertidal sediments may be dominated by cyanobacteria where high rates of nitrogen fixation may supply a significant amount of nitrogen to the benthic community (Stal et al. 1984, Bautista & Paerl 1985, Stal 1995.A number of approaches have been used to estimate the contributions of organic matter from various sources to sediments. Isotope ratios of 13 C/ 12 C have been used to estimate the relative contribution of terrestrial and marine sources to sedimentary organic matter (Fry & Sherr 1984). While this approach is relatively simple and gives an integrated estimate of sources for the total carbon in the sample, it will only provide useful information when there are 2 welldefined end-members. Furthermore, this technique gives little information about the type of marine or terrestrial organic matter in question.The use of lipid and pigment biomarkers such as fatty acids and sterols can allow the sources of various subfractions of organic matter to be identified much more specifically than any of the above approaches. However, unambiguously assigning sources to biomarkers is difficult, as they are rarely produced by a single class of organism. The advent of compound-specific stableisotope analysis has provided a powerful new tool for the differentiation between 2 sources of the same biomarker, provided the isotopic sign...

Carbon and nitrogen cycling on intertidal mudflats of a temperate Australian estuary. IV. Inverse model analysis and synthesis

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Continental and marine sources of organic matter and nitrogen for rías of northern Galicia (Spain)

“…The high excess of organic C, as found in other coastal inlets (e.g. Cook et al 2004, Silva et al 2011, suggest the presence of either hydrocarbons or, more likely, remains of terrestrial plants. Microbial respiration of labile C (i.e.…”

Monitoring the influence of marine aquaculture on wild fish communities: benefits and limitations of fatty acid profiles

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