DENITRIFICATION MEASUREMENTS IN AQUATIC SEDIMENTS - A COMPARISON OF 3METHODS

Measurements of denitrification using the acetylene inhibition, N-15 i sotope tracer, and N-2 flux methods were carried out concurrently usin g sediment cores from Vilhelmsborg so, Denmark, in an attempt to clari fy some of the limitations of each technique. Three experimental treat ments of overlying water were used: control, nitrate enriched, and amm onia enriched water. The N-2 flux and N-15 tracer experiments showed h igh rates of coupled nitrification/denitrification in the sediments. T he acetylene inhibition method did not capture any coupled nitrificati on/denitrification. This could be explained by acetylene inhibition of nitrification. A combined N-15 tracer/acetylene inhibition experiment demonstrated that acetylene inhibition of N2O reduction was incomplet e and the method, therefore, only measured approximately 50% of the de nitrification due to nitrate from the overlying water. Similar rates o f denitrification due to nitrate in the overlying water were measured by the N-2 flux method and the acetylene inhibition method, after corr ecting for the 50% efficiency of acetylene inhibition. Rates of denitr ification due to nitrate from the overlying water measured by the N-15 tracer method, however, were only approximately 35% or less of those measured by the acetylene inhibition or N-2 flux methods.