SIMULTANEOUS MEASUREMENT OF BENTHIC DENITRIFICATION, WITH THE ISOTOPEPAIRING TECHNIQUE AND THE N-2 FLUX METHOD IN A CONTINUOUS FLOW-THROUGH SYSTEM

Denitrification rates in a freshwater sediment were measured simultane ously with the N-2 flux method and the N-15 isotope pairing technique, using a continuous flow-through system designed for direct applicatio n of both techniques. With the N-2 flux method, denitrification was 15 1 +/- 4 mu mol N m(-2 h-1) and with the isotope pairing technique denj trification was 149 +/- 4 mu mol N m(-2) h(-1). These identical result s strongly suggested that both methods measured the true denitrificati on activity in the system. Using the conventional batch modes, the N-2 flux method has shown much larger denitrification rates than N-15 iso tope pairing. This discrepancy could be explained by the much longer i ncubation time and smaller water column, required by the N-2 flux meth od. Model simulations of a N-2 flux batch incubation showed how NO3- a nd NH4+ accumulated in the water column and in turn increased nitrific ation and denitrification activity much above the initial level. as in cubation proceeded. (C) 1998 Elsevier Science Ltd. All rights reserved .