KINETIC-PARAMETERS OF DENITRIFICATION IN A RIVER CONTINUUM

Kinetic parameters for nitrate reduction in intact sediment cores were investigated by using the acetylene blockage method at five sites alo ng the Swale-Ouse river system in northeastern England, including a hi ghly polluted tributary, R, Wiske, The denitrification rate in sedimen t containing added nitrate exhibited a Michaelis-Menten-type curve. Th e concentration of nitrate for half-maximal activity (K-map) by denitr ifying bacteria increased on passing downstream from 13.1 to 90.4 mu M in the main river, but it was highest (640 mu M) in the Wiske, The ap parent maximal rate (V-maxap) ranged between 35.8 and 324 mu mol of N m(-2) h(-1) in the Swale-Ouse (increasing upstream to downstream), but it was highest in the Wiske (1,194 mu mol N m(-2) h(-1)). A study of nitrous oxide (N2O) production at the same time showed that rates rang ed from below the detection limit (0.05 mu mol of N2O-N m(-2) h(-1)) a t the headwater site to 27 mu mol of N2O-N m(-2) h(-1) at the downstre am site. In the Wiske the rate was up to 570 mu mol of N2O-N m(-2) h(- 1), accounting for up to 80% of total N gas production.