AME 09:289-294 (1995)  -  DOI: https://doi.org/10.3354/ame009289

Sediment cores containing different densities of Tubifex tubifex, ranging from 0 to 70000 ind. m^-2, were incubated in the laboratory. Rates of O₂ and NO₃^- uptake, NH₄⁺ production, nitrification and denitrification were determined from sediment-water fluxes. Pore water NH₄⁺ was measured at the end of the experiment. At natural densities, ~50000 ind. m^-2, there were increased rates of O₂ consumption (x2), denitrification of water phase NO₃^- (x3) and NH₄⁺ efflux (x26). Nitrification was stimulated at low worm densities, but inhibited at higher worm densities. The transport of reduced compounds and organic matter, with the fecal pellets, to the sediment surface stimulated anoxic conditions in the inhabited microcosms. These anoxic conditions led to increased rates of denitrification and were responsible for the decrease in nitrification at higher worm densities. Approximately 25% of the NO₃^- produced by nitrification within the sediment was subsequently denitrified. Denitrification was responsible for 25% of the NO₃^- disappearance from the system. The higher rates of denitrification were counterbalanced by higher rates of NH₄⁺ flux from the sediment. It is likely, however, that the presence of T. tubifex resulted in a net loss of nitrogen that could otherwise have been used by the primary producers.

Bioturbation . Nitrification . Denitrification . Sediments