Denitrifying activities in two freshwater lakes, Lake Kizaki during October to December 1986 and Lake Fukami-ike during July to August 1985 and in July 1986, were estimated by the acetylene blockage method. Relationships between the denitrifying activities and the concentration of denitrifying intermediates such as NO
2- and N
2O in the water column of the two lakes were analyzed. Denitrifying activity in L. Fukami-ike was essentially dependent on NO
2-concentration, in two ways. A positive correlation was found between denitrifying activity and
in situ NO
2- concentration, while in some cases remarkable denitrifying activities were found in the NO
2--depleted layer and correlated with the maximally accumulated NO
2- concentration. On the other hand, a better correlation of denitrifying activity with N
2O concentration was found in L. Kizaki.
Mineralization of
14C-acetate and its coupling with the denitrification were also compared in the two lakes. Mineralized
14CO
2 plotted against the total uptaken
14C-acetate fell in a regression line with the same slope of 0.34 not only even in NO
3--enhanced uptake of the substrate, but also in both L. Fukami-ike (at 4-4.5 m depth on 20 July 1986) and L. Kizaki (at 21-24 m depth on 2 December 1986).
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