ABSTRACT: 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 larvaesignificantly 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.

KEY WORDS: Nitrous oxide · Nitrification · Denitrification · Lake · Sediment · Bioturbation · Chironomus plumosus

Published in AME Vol. 14, No. 3 (1998) on April 6
Print ISSN: 0948-3055; Online ISSN: 1616-1564. Copyright © Inter-Research, Oldendorf/Luhe, 1998