The Number of Nitrifying Bacteria in the North Basin of Lake Biwa

Abstract

To obtain clues for the elucidation of the mechanism of nitrate accumulation in the hypolimnion of the north basin of Lake Biwa during summer stratification, the numbers of nitrifying bacteria and concentrations of nitrate plus nitrite and ammonium in the water body and bottom sediments were determined during the stagnation period of 1982.
The numbers of nitrifying bacteria were small (below one cell per ml) in the water body, but fairly large (9 × 10¹- 4 × 10³ cells per ml) in the surface sediments. Concentrations of nitrate plus nitrite were about two times higher in the surface sediments than those in the deepest layer of the water body. In addition, ammonium was not detected in the water body, but rather in high concentrations (8-26 mg N per l) in the surface sediments.
The above results suggest that the nitrate accumulation in the hypolimnion of Lake Biwa during summer stratification is mainly due to the active nitrification in the bottom sediments and subsequent liberation of nitrate to the hypolimnion.