Abstract
Effect of the physical and chemical conditions of the seepage flow on the bacterial nitrification were discussed in order to determine the nitrification within the hyporheric zone in a natural river. Several kinds of liquid medium were supplied into the cylindrical columns filled with the river sand gravel at different velocities, and the characteristics of the nitrifying capacity varying with both the flow velocity and the inorganic nitrogen concentration were clarified in detail.
In batch incubation experiments, more bacterial growth and nitrification were observed in the unidirectional, less turbulent seepage flow condition such as usually seen in the hyporheic zone than in the well-mixed condition generated by the bubble aeration. The nitrified nitrogen within the sand gravel column in unit time was strongly affected by the flow velocity. In the rich nitrogen conditions, the high nitrification was observed which was several times as large as the maximum values estimated by the logarithmic growth model using the corresponding bacterial density. Furthermore, in low concentration conditions, wherelittle bacterial growth was expected by the model, nearly the maximum oxidation, approximately 70% of that, was achieved under the seepage flow speed 3 meters/hour.
