INFLUENCE OF CHIRONOMUS-PLUMOSUS LARVAE ON AMMONIUM FLUX AND DENITRIFICATION (MEASURED BY THE ACETYLENE BLOCKAGE-TECHNIQUE AND THE ISOTOPE PAIRING-TECHNIQUE) IN EUTROPHIC LAKE SEDIMENT
Jm. Svensson, INFLUENCE OF CHIRONOMUS-PLUMOSUS LARVAE ON AMMONIUM FLUX AND DENITRIFICATION (MEASURED BY THE ACETYLENE BLOCKAGE-TECHNIQUE AND THE ISOTOPE PAIRING-TECHNIQUE) IN EUTROPHIC LAKE SEDIMENT, Hydrobiologia, 346, 1997, pp. 157-168
Oxygen uptake, ammonium flux and denitrification were determined in se
diment from a eutrophic lake in southern Sweden. Part of the sediment
was bioturbated by incubation in a laboratory mesocosm by incubation c
ontaining 2000 tube-dwelling larvae of Chironomus plumosus L. m(-2). O
xygen consumption was increased 2-fold in the bioturbated compared wit
h the nonbioturbated sediment, some 20% of the increase could be expla
ined by chironomid respiration. There was a net release of ammonium fr
om the bioturbated sediment to the overlying water. Only 11-45% of thi
s could be explained on the basis of larval excretion. With increasing
nitrate concentration, denitrification of the nitrate coming from the
water (d(w)) increased to a greater extent in the bioturbated than in
the non-bioturbated sediment, whereas denitrification of the nitrate
from the coupled nitrification-denitrification (d(n)) was unaffected.
The acetylene blockage technique underestimated denitrification by 63-
88% compared with the nitrogen isotope pairing technique. The results
indicate that bioturbation by tube-dwelling chironomid larvae can have
a major impact on the nitrogen turnover in lake sediment, mobilising
the ammonium to the water and stimulating denitrification by reducing
the diffusive barrier blocking nitrate from reaching anoxic zones in t
he sediment. Under the aerobic conditions under which the experiments
were conducted, the bioturbated eutrophic sediment acted as a more pro
nounced sink for inorganic nitrogen compared with the non-bioturbated
sediment.