Denitrification and N₂O production in Lake Kizaki

Abstract

Nitrogen loss from the hypolimnetic water column of Lake Kizaki as a result of denitrification was calculated as 41–43 kg-at N (574–602 kg N) during autumn 1984. This was estimated by nitrate reduction and denitrification activity measurements. About 10% of the nitrogen gas (as N₂ and N₂O) was emitted as N₂O-N during thermal overturn of the hypolimnion. A correlation between denitrification activities and maximum concentrations of accumulated N₂O-N in the hypolimnion was found among observations in 1981, 1982, 1984 and 1986. Surface sediment denitrification activities were estimated by the acetylene blockage method at four depth locations during four different seasons. Maximum activities of 1.2 mg-at N m⁻² d⁻¹ were observed in late June and July at the center of the lake. However, from comparisons of denitrification activity at different locations, higher denitrification activities were observed at littoral zone sites (1, 10 and 20 m depth) than at the lake center (29 m depth).