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|Carbon and nitrogen cycling on intertidal mudflats of a temperate Australian estuary: 4. Inverse model analysis and synthesis|
|Cook, P.L.M.; van Oevelen, D.; Soetaert, K.; Middelburg, J.J. (2009). Carbon and nitrogen cycling on intertidal mudflats of a temperate Australian estuary: 4. Inverse model analysis and synthesis. Mar. Ecol. Prog. Ser. 394: 35-48. dx.doi.org/10.3354/meps08270|
|In: Marine Ecology Progress Series. Inter-Research: Oldendorf. ISSN 0171-8630, more|
Carbon cycle; Nitrogen cycle; Nitrogen fixation; Organic matter; Phytobenthos; Sediments; Stoichiometry; Tidal flats; PSE, Australia, Tasmania; Marine; Brackish water
Microphytobenthos (MPB) are recognised as exerting an important controlling influence over C and N flows in euphotic sediments; however, the coupling between these flows remains poorly studied. We undertook an inverse model analysis of C and N fluxes through the microbial compartment on intertidal flats in a temperate estuary. The analysis showed that the trophic balance of the sediment exerted a strong influence on the relative fluxes of C and N through the sediment microbial community. Under increasingly autotrophic conditions (production:respiration >1), the assimilation of C relative to N rose above the cellular C:N ratio of MPB, resulting in increased excretion rates of organic matter by MPB. The C:N ratio of the organic matter excreted was also highly variable, ranging from ~20 (mol:mol) under heterotrophic conditions, and increasing to >50 under autotrophic conditions. The relative fluxes of C and N through bacteria were also significantly affected by the trophic balance of the sediment and the ratio of C:N mineralized by bacteria was significantly higher under autotrophic conditions. Dissolved organic N release by bacteria and uptake by MPB also predominated over inorganic N forms under autotrophic conditions. We conclude that C and N fluxes through shallow euphotic sediments may become significantly decoupled and well above the commonly assumed Redfield ratio and measured cellular C:N ratios of MPB.