Capacities of shallow waters of Sagami Bay for oxidation and reduction of inorganic nitrogen

Abstract

The distribution of nitrite, nitrate and ammonia in Sagami Bay, Japan, was investigated on Cruises KT-70-5 and KT-70-13 of the R.V. Tansei Maru. In summer, the maximum concentration of nitrite (about 0·3 μg atoms N/1. in central Sagami Bay) occurred at 20–30 m depth and was associated with a seasonal thermocline. In winter, the concentrations of nitrite were nearly constant (about 0·3 μg atoms N/1.) from the surface down to about 100 m; below that depth they decreased. The potential activities for nitrite production from nitrate ammonia were measured, using a 15N-tracer method. The activity for nitrite production from nitrate was of the same order of magnitude as that from ammonia (1·4 ng atoms N/1./hour, on an average), irrespective of the season. The capacities for assimilation of inorganic nitrogen in the upper layers (0–50 m) were several times higher than those for the oxidation of ammonia and the reduction of nitrate, but a reverse relation was observed below the euphotic zone. The residence time of nitrite in the upper layers was 7–16 days.