Ref ID : 1916
Silvia P. Pelegri and T. Henry Blackburn; Effects of Tubifex tubifex (Oligochaeta: Tubificidae) on N-mineralization in freshwater sediments, measured with 15N isotopes. Aquatic Microbial Ecology 9:289-294, 1995
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Sediment cores containing different densities of Tubifex tubifex, ranging from 0 to 70,000 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, ~50,000 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 NO3- produced by nitrification within the sediment was subsequently denitrifed. 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.