Comparison of Carbon Production and Decomposition, Benthic Nutrient Fluxes and Denitrification in Seagrass, Phytoplankton, Benthic Microalgae-And Macroalgae-Dominated Warm-Temperate
MARINE ECOLOGY PROGRESS SERIES Vol. 229: 43–59, 2002 Published March 20 Mar Ecol Prog Ser Comparison of carbon production and decomposition, benthic nutrient fluxes and denitrification in seagrass, phytoplankton, benthic microalgae- and macroalgae- dominated warm-temperate Australian lagoons Bradley D. Eyre*, Angus J. P. Ferguson Centre for Coastal Management, Southern Cross University, Lismore , New South Wales 2480, Australia ABSTRACT: The influence of marine plants representing different stages of eutrophication on carbon decomposition and production, benthic nutrient fluxes and denitrification was examined in 4 shallow warm-temperate Australian lagoons. Differences in carbon production and decomposition across the lagoons were the main regulators of the quantity and quality of benthic nutrient fluxes and the rela- tive proportion of nitrogen lost through denitrification. For example, the efficiency with which the lagoon sediments recycled nitrogen as N2, (i.e. denitrification efficiency: N2-N/(N2-N + DIN), decreased as carbon decomposition rates increased. C:N ratios of the remineralised organic matter in some of the plant-sediment systems were much higher than expected from the stoichiometry of the dominant carbon supply. Dark DON fluxes were also very high in all the plant-sediment systems (30 to 80% of the total nitrogen flux). We offer 2 alternative explanations for the observed sediment and benthic flux characteristics: (1) The low dark C:N ratios of the remineralised organic matter may have been due to dark uptake by benthic microalgae and possibly other plants. The large DON effluxes were either the hydrolysis product of freshly produced in situ organic material or/and associated with the grazing of benthic microalgae.
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