Denitrifying activity and population growth of denitrifying bacteria in Lake Fukami-Ike.

In the oxygen-depleted layer of Lake Fukami-ike during March to July in 1985, denitrifying activities were measured by the acetylene blockage method, and the denitrifying bacterial population was estimated by the MPN method. Up till 22 March, no detectable denitrifying activity was found. On 6 April at and below 5 m depth, lower but distinct denitrifying activities were found. Thereafter, denitrifying activity became higher with time. Maximum activity (0.64 μg·at N·l-1·day-1) was obtained at 4.5 m depth on 2 July. In accordance with the development of denitrifying activity, the average denitrifying bacterial population increased from 3.9 cells·ml-1 on 22 March to 87 cells·ml-1 on 2 July. From the analysis of the correlation between denitrification and in situ dissolved oxygen content, it was shown that denitrifying activity was initiated at 0.25 ml·l-1 D. O. and increased with the decrease of dissolved oxygen content. It was also shown that the ratio of N2O emission in the total denitrification [N2O/(N2+N2O)] was decreased with decrease of in situ dissolved oxygen content.