Seasonal dynamics of benthic O-2 uptake in a semienclosed bay: Importance of diffusion and faunal activity

Ronnie Glud, JK Gundersen, H Roy, BB Jorgensen

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The benthic O-2 uptake and the O-2 microdistribution in a coastal sediment of Aarhus Bay, Denmark, were investigated during a seasonal study. Measurements were performed in situ by a profiling lander and a flux chamber lander, as well as on recovered sediment cores. The O-2 penetration depth, the diffusive O-2 uptake, and the volume-specific O-2 consumption rate strongly depended on the seasonal changes in bottom water O-2 concentration and the sedimentation of organic carbon. The in situ O-2 penetration depth varied between 0.5 mm in summer and 4.5 turn in winter. The diffusive O-2 uptake varied between 8 and 30 mmol m(-2) d(-1), whereas the volume-specific O-2 consumption rate varied by a factor of 13. The O-2 distribution was very sensitive to environmental controls, and microprofiles obtained in the laboratory tended to overestimate the in situ O-2 penetration depths and underestimate the in situ diffusive O-2 uptake. Three-dimensional O-2 flux calculations based on in situ microtopographic mapping showed that the actual diffusive exchange rate was similar to10% higher than the simple one-dimensional, microprofile-derived diffusive O-2 exchange. The total O-2 Uptake measured in the laboratory showed less distinct seasonal variation, but on the average, it was similar to20% higher than the diffusive O-2 uptake. The difference reflected the microtopography of the sediment surface and the contribution from benthic macrofauna. In situ total O-2 uptake was generally twice as high as laboratory rates, reflecting a higher fauna-related O-2 consumption in the larger enclosures incubated in situ. Annually, the in situ three-dimensional diffusive O-2 consumption was 6.2 mol O-2 m(-2), whereas the additional benthos-mediated O-2 uptake was 3.9 Mol O-2 m(-2). Thus, 40% of the total O-2 uptake was due to faunal activity and respiration. The present study demonstrates the importance of realistic faunal representation during sediment incubations in order to obtain correct benthic mineralization rates.
Original languageEnglish
Pages (from-to)1265-1276
Number of pages12
Issue number3
Publication statusPublished - 2003


  • FLUX
  • Limnology
  • Oceanography


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