It was concluded from experiments using chloride as tracer that denitrification could be enhanced by the worms at least in part as a result of accelerated movement of nitrate-N into the sediment. The rate of CO 2 evolution from sediment containing worms and overlain with nitrate-N solution was about 21% greater than that of sediment with worms overlain with distilled water. The corresponding rates for denitrification and nitrification in sediment without worms were 50 mg N/m 2∙d −1 and 29 mg N/m 2∙d −1. The denitrification rate over 48 d at 15 ☌ in the sediment that contained the worms was 90 mg N/m 2∙d −1 the simultaneous rate of nitrification was 69 mg N/m 2∙d −1. Denitrification and nitrification occurred simultaneously and were enhanced significantly in the presence of the worms. Labeled nitrate-N in the form of K 15NO 3 was used to determine the effects of the tubificid oligochaetes, Tubifex tubifex and Limnodrilus hoffmeisteri, on the N transformation processes in stream sediment contained in laboratory columns.

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