Capacity for Denitrification and Reduction of Nitrate to Ammonia in a Coastal Marine Sediment

The capacity for dissimilatory reduction of NO(3) to N(2) (N(2)O) and NH(4) was measured in NO(3)-amended marine sediment. Incubation with acetylene (7 x 10 atmospheres [normal]) caused accumulation of N(2)O in the sediment. The rate of N(2)O production equaled the rate of N(2) production in samples without acetylene. Complete inhibition of the reduction of N(2)O to N(2) suggests that the "acetylene blockage technique" is applicable to assays for denitrification in marine sediments. The capacity for reduction of NO(3) by denitrification decreased rapidly with depth in the sediment, whereas the capacity for reduction of NO(3) to NH(4) was significant also in deeper layers. The data suggested that the latter process may be equally as significant as denitrification in the turnover of NO(3) in marine sediments.