Content area
Abstract
Oxygen uptake, ammonium flux and denitrification were determined insediment from a eutrophic lake in southern Sweden. Part of the sediment wasbioturbated by incubation in a laboratory mesocosm by incubation containing2000 tube-dwelling larvae of Chironomus plumosus L. m^sup -2^.Oxygen consumption was increased 2-fold in the bioturbated compared with thenonbioturbated sediment, some 20% of the increase could be explainedby chironomid respiration. There was a net release of ammonium from thebioturbated sediment to the overlying water. Only 11-45% ofthis could be explained on the basis of larval excretion. With increasingnitrate concentration, denitrification of the nitrate coming from the water(dw) increased to a greater extent in the bioturbated than in thenon-bioturbated sediment, whereas denitrification of the nitrate from thecoupled nitrification-denitrification (dn) was unaffected. The acetyleneblockage technique underestimated denitrification by 63-88%compared with the nitrogen isotope pairing technique. The results indicatethat bioturbation by tube-dwelling chironomid larvae can have a major impacton the nitrogen turnover in lake sediment, mobilising the ammonium to thewater and stimulating denitrification by reducing the diffusive barrierblocking nitrate from reaching anoxic zones in the sediment. Under theaerobic conditions under which the experiments were conducted, thebioturbated eutrophic sediment acted as a more pronounced sink for inorganicnitrogen compared with the non-bioturbated sediment.[PUBLICATION ABSTRACT]