The denitrification capacity of sediment from a hypereutrophic lake

SUMMARY. In sediment from Wintergreen Lake, Michigan, denitrification was not detectable by the acetylene inhibition method at in situ nitrate concentrations. When nitrate was added to sediment slurries, denitrification capacities up to 18.8μg N g ‐1 h ‐1 were measured. The denitrification capacities decreased with increasing sediment depth and distance from shore. The high denitrification capacities in these sediments which under natural conditions had no supply of nitrate and oxygen suggested that denitrifies with alternative mechanisms for anaerobic energy conversion were present. Nitrous oxide was a significant portion of the N‐gas produced immediately after the nitrate addition. Small amounts (4–5% of the total N‐gas production) of nitric oxide accumulated in the early phase of nitrate reduction. Presumably after depletion of nitrate and nitrite both N 2 O and NO were further reduced to N 2 . About 70%r of the added nitrate was denitrified, and the remainder was assumed to have been reduced to ammonium.