Abstract
The nitrification capacity of riffles in a natural river was discussed. The bacteria density in the river bank subsurface layer was estimated together with the seepage flow direction and speed, the porosity of the sand gravel layer and the nitrogen concentrations in the river and seepage waters. On the basis of the exponential growth model for nitrogen oxidation bacteria, the nitrification rate of the seepage layer on the river bank was obtained. The spatial variety of bacteria density due to the inhomogeneity of gradation structure, porosity and the input of ammonium and nitrite nitrogen was observed. Without the considerable load of substrate, the density of the ammonia oxidation bacteria per unit volume of the seepage layer was 0.5-1.5mg/L and that of nitrite oxidation bacteria was 0.05-0.2mg/L. The nitrification capacity in the subsurface layer of a riffle was estimated more than ten times as large as that of a pool in the same longitudinal length. The maximum density of the ammonium and nitrite oxidation bacteria was 5.35mg/L and 1.46mg/L respectively in the subsurface layer adjacent to the wastewater effluent, in which approximately 20% of the inorganic nitrogen load was thoroughly oxidized.
