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In order to quantify the spatial and seasonal variations of sediment oxygen consumption and nutrient fluxes, we performed a spatial survey in the south west lagoon of New Caledonia during the two major seasons (dry and wet) based on a network of 11 sampling stations. Stations were selected along two barrier reef to land transects representing most types of sediments encountered in the lagoon. Fluxes were measured using ex-situ sediment incubations and compared to sediment characteristics. Sediment oxygen consumption (SOC) varied between 500 and 2000 micromol m(-2)h(-1), depending on season and stations. Nutrient effluxes from sediment were highly variable with highest fluxes measured in muddy sediments near the coast. Inter-sample variability was as high as seasonal differences so that no seasonally driven temperature effect could be observed on benthic nutrient fluxes in our temperature range. Nutrient fluxes, generally directed from the sediment to the water column, varied between -5.0 and 70.0 micromol m(-2)h(-1) for ammonia and between -2.5 and+12.5 micromol m(-2)h(-1) for PO(4) and NO(2+3). SOC and nutrient fluxes were compared to pelagic primary production rates in order to highlight the tight coupling existing between the benthic and pelagic compartments in this shallow tropical lagoon. Under specific occasions of low pelagic productivity, oxygen sediment consumption and related carbon and nutrient fluxes could balance nearly all net primary production in the lagoon. These biogeochemical estimates point to the functional importance of sediment biogeochemistry in the lagoon of New Caledonia., (Copyright (c) 2010 Elsevier Ltd. All rights reserved.)

A study coupling core incubation and a large number of in situ microelectrode measurements (n=18) was performed at a single station in the Golfe de Fos, a semi-enclosed estuarine system in the South of France on the Mediterranean Sea. Total and diffusive oxygen fluxes were determined for two different seasons (October 2000 and May 2001). The average total and diffusive oxygen fluxes were 21.5 and 12.7 mmol m−2 day−1, respectively, in October and 18.5 and 16.5 mmol m−2 day−1, respectively, in May. The average total oxygen demand does not vary significantly between the two periods (21.5±5 to 18.5±4 mmol m−2 day−1). The spread of the values obtained by microelectrode measurements reveals the variability at the decimeter scale indicating a control by small-scale processes. Little difference was found in May between the total and diffusive oxygen fluxes when the number of microelectrode profiles (n=18) and core incubation (n=9) was sufficient to catch larger fluxes linked to “organic hot spots”. Although present at a population density of 5700 individuals for 0.1 m2, macrofauna is mostly composed of surface deposit feeders. The little difference found between total and diffusive oxygen demand points towards not only the population density but also the faunal assemblage as a determining factor for sediment irrigation. [Copyright &y& Elsevier]