DENITRIFICATION MEASUREMENTS IN AQUATIC SEDIMENTS - A COMPARISON OF 3 METHODS

Measurements of denitrification using the acetylene inhibition, N-15 isotope tracer, and N-2 flux methods were carried out concurrently using sediment cores from Vilhelmsborg so, Denmark, in an attempt to clarify some of the limitations of each technique. Three experimental treatments of overlying water were used: control, nitrate enriched, and ammonia enriched water. The N-2 flux and N-15 tracer experiments showed high rates of coupled nitrification/denitrification in the sediments. The acetylene inhibition method did not capture any coupled nitrification/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 incomplete and the method, therefore, only measured approximately 50% of the denitrification due to nitrate from the overlying water. Similar rates of denitrification due to nitrate in the overlying water were measured by the N-2 flux method and the acetylene inhibition method, after correcting for the 50% efficiency of acetylene inhibition. Rates of denitrification 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.