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Marine Ecology Progress Series

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MEPS 209:35-42 (2001)  -  doi:10.3354/meps209035

Denitrification in exposed intertidal mud-flats, measured with a new 15N-ammonium spray technique

Lars Ditlev Mørck Ottosen*, Nils Risgaard-Petersen, Lars Peter Nielsen, Tage Dalsgaard**

Institute of Biological Sciences, Department of Microbial Ecology, University of Aarhus, Ny Munkegade, 8000 Aarhus C, Denmark
*E-mail: **Present address: National Environmental Research Institution, Vejlsøvej 25, 8600 Silkeborg, Denmark

ABSTRACT: Denitrification in exposed intertidal sediment was measured for the first time at locations in the Tagus Estuary, using a new ammonium spray method. With this method, 15NH4+ was sprayed on to the sediment surface, and nitrification-denitrification was subsequently estimated from accumulation of 29N2 and 30N2 in gas-tight glass chambers placed on the 15N-labeled sediment. Coupled nitrification-denitrification ranged from 8.5 to 11.5 µmol N m-2 h-1 at night to below 2 µmol N m-2 h-1 during the day. Salt stress, light inhibition and depletion of NH4+ by benthic diatoms could contribute to the low daytime activity. The nighttime rates were confirmed by an independent estimate based on potential nitrification-denitrification and oxygen uptake. Coupled nitrification-denitrification activity at night during exposure was not significantly different from the activity measured when the sediment was inundated, but was 3 times lower than rates measured at a subtidal station in the estuary.

KEY WORDS: Intertidal mud flats · Exposed sediment · 15N · Denitrification

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