Nitrogen metabolism in the brackish lake Nakanoumi. II. - Characterization of epilimnetic sediment denitrification in summer.

Abstract

Factors controlling denitrification were investigated by the acetylene inhibition technique using epilimnetic sediment sample collected from the brackish lake Nakanoumi. Temperature and substrate concentrations (nitrite and nitrate) were important factors for controlling denitrification in sediments. Denitrification rate estimated from temperature and substrate concentration was about 12.0mg N·m-2 d-1 (August 1981). The decrease of total inorganic nitrogen concentration in hypolimnion from July to August 1981 was principally caused by nitrification denitrification. The capacity for the reductions of NO3- to N2 (N2O), NH4+, and organic nitrogen was also measured in 15NO3--amended epilimnetic sediment by the acetylene inhibition technique and the 15N-label tracer method. 15NH4+ and org.15N accounted for about 30% of the three products. The result suggested that the pathway of nitrate reduction to NH4+ and PON was important as well as denitrification in sediments of the brackish lake Nakanoumi.