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Aquatic Microbial Ecology

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AME 21:59-71 (2000)  -  doi:10.3354/ame021059

Marine meiofauna, carbon and nitrogen mineralization in sandy and soft sediments of Disko Bay, West Greenland

Søren Rysgaard1,*, Peter Bondo Christensen1, Martin V. Sørensen2, Peter Funch3, Peter Berg4

1Dept. of Lake and Estuarine Ecology, National Environmental Research Institute, Vejlsøvej 25, 8600 Silkeborg, Denmark
2Zoological Museum, Dept. 2, University of Copenhagen, Universitetsparken 15, 2100 Copenhagen Ø, Denmark
3Dept. of Zoology, Institute of Biological Sciences, University of Aarhus, 8000 Århus C, Denmark
4Dept. of Environmental Sciences, University of Virginia, Charlottesville, Virginia 22903, USA

ABSTRACT: Organic carbon mineralization was studied in a shallow-water (4 m), sandy sediment and 2 comparatively deep-water (150 and 300 m), soft sediments in Disko Bay, West Greenland. Benthic microalgae inhabiting the shallow-water locality significantly affected diurnal O2 conditions within the surface layers of the sediment. Algal photosynthetic activity and nitrogen uptake reduced nitrogen effluxes and denitrification rates. Sulfate reduction was the most important pathway for carbon mineralization in the sediments of the shallow-water station. In contrast, high bottom-water NO3- concentrations and a relatively deep O2 penetration into the sediment at the deep-water stations ensured high denitrification activity, particularly as a result of an efficient coupling between nitrification and denitrification. Denitrification accounted for up to 33% of total carbon mineralization in the deep-water sediment and was, together with organotrophic O2 respiration, the most important pathway for carbon mineralization within these sediments. The obtained process rates were comparable to mineralization rates from much warmer localities, suggesting that benthic mineralization in arctic marine environments is regulated primarily by the availability of organic matter and not by temperature. The shallow-water sediment contained a larger meiofauna population than the deep-water muddy sediments. Crustacean nauplia dominated the upper 9 mm while nematodes dominated below. A typical interstitial fauna of species belonging to Platyhelminthes, Rotifera, Gastrotricha, and Protodriloidae (Polychaeta) occurred only at the sandy locality, whereas Kinorhyncha, Foraminifera, and Cumacea (Crustacea) occurred only at the muddy stations. The larger number of meiofauna individuals at the sandy locality may in part be explained by higher food availability, as living diatoms served as food for the meiofauna. Based on interpretation of the vertical O2 concentration profiles compared with intact-core O2 flux measurements, it was shown that the bioturbation coefficient was approximately 3 times higher in the sandy sediment, corresponding to the 3 times higher number of meiofauna found in the upper 2 cm of this sediment. Thus, meiofauna increased the transport of solutes as compared to molecular diffusion by a factor of 1.5 to 3.1, thereby stimulating microbial mineralization.

KEY WORDS: Arctic · Sediment · Mineralization · Meiofauna · Carbon cycling · Denitrification

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