Nitrogen loss process in hypoxic seawater based on the culture experiment

Abstract

The oxygen minimum zones (OMZs) and other hypoxic seawaters are considered as the main areas of oceanic nitrogen loss. The laboratory simulation culture was conducted to study the main reactions, rates and proportions of dissolved inorganic nitrogen (DIN) in different dissolved oxygen concentrations seawater, with aim of clarifying the process of nitrogen loss in hypoxic seawater. The results showed that the change of DIN in hypoxic water could be divided into three stages. In the first stage, the main reactions were the dissimilatory nitrate reduction to ammonium (DNRA) and denitrification. In the second stage, anammox and denitrification were main reactions. In the last stage, anammox was the most important nitrogen loss reaction; nitrogen loss eventually reached a relative balance with the input from sediment mineralization. Based on the data obtained from the last stage, the annual nitrogen loss could be estimated to be about 240–260 Tg in the global OMZs.