Measurement of denitrification in two freshwater sediments by an in situ acetylene inhibition method.

An acetylene inhibition method was satisfactorily used for the in situ measurement of denitrification in two sediment-water systems incubated for not more than 22 h. In the presence of added nitrate, denitrification acted as a source of nitrous oxide in a drainage pond, but acted as a sink in its absence. The averaged rates of nitrous oxide accumulation with nitrate enrichment in the absence and presence of acetylene were 0.15 and 0.30 mg of N mh, respectively. Acetylene reduction at an average rate of 0.07 mmol of C(2)H(4) formed mh was simultaneously measured in the absence of added nitrate. In a small eutrophic lake where nitrogen was nonlimiting, the in situ rates of sediment denitrification were 0.09 and 0.11 mg of N mh in the presence and absence of macrophytes, respectively, and no acetylene reduction activity was found.