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Aquatic Microbial Ecology

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AME 14:289-299 (1998)  -  doi:10.3354/ame014289

Emission of N2O, nitrification and denitrification in a eutrophic lake sediment bioturbated by Chironomus plumosus

Jonas M. Svensson*

Department of Ecology/Limnology, Ecology Building, University of Lund, S-223 62 Lund, Sweden

Emission of nitrous oxide and rates of nitrification and denitrification were determined in sediment from a eutrophic lake in southern Sweden. Effects of bioturbation on nitrogen transformation were investigated by incubating sediment at 10 and 15°C in a continuous flow-through system containing ca 2000 tube-dwelling larvae of Chironomus plumosus L. (Chironomidae, Diptera) m-2. N2O emission was found to be independent of nitrate concentration (33 to 267 μM) in the overlying water at both 10 and 15°C. It is shown that C. plumosus larvae significantly enhanced the emission of N2O from the sediment at 15°C, the highest emission recorded under these conditions was 0.45 ± 0.2 μmol N m-2 h-1. Since released N2O was proportional to the rate of nitrification, it is suggested to originate mainly from this process. Bioturbation stimulated the rate of nitrification by a factor of 1.8 at 15°C. However, no enhancement of nitrification by chironomids was observed at 10°C. In contrast to N2O emission and nitrification, denitrification in both bioturbated and non-bioturbated cores was significantly correlated to the concentration of nitrate in the overlying water. The stimulation of denitrification by bioturbation at 10 and 15°C was 3.5- and 4.3-fold respectively. Denitrification rates were mainly accounted for (98%) by changes in the concentration of nitrate in the water, the water temperature and the biomass of C. plumosus larvae. C. plumosus larvae were found to decrease the N2O:N2 ratio at both temperatures. This was explained by the water pumping activity of the animals, mobilizing released N2O to denitrifiers in or close to the animal burrows. The ratio of N2O:N2 did not exceed 0.5% in any of the treatments.

Nitrous oxide · Nitrification · Denitrification · Lake · Sediment · Bioturbation · Chironomus plumosus

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