ESTIMATION OF HYPOXIA VOLUME IN OSAKA BAY BY EXPERIMENT OF SEDIMENT OXYGEN CONSUMPTION WITH AIRTIGHT CORES AND DATA ASSMILATION

Abstract

 This paper presents the results of a field survey and laboratory experiments to evaluate sediment oxygen demand in Osaka Bay, where Total Pollutant Load Control has been conducted in recent years. The measured sediment consumption rates were used to estimate the volume of hypoxic water by a three-dimensional biogeochemical model with data assimilation. The survey results showed that the oxygen consumption rates in 2019 were smaller than the results in 1999. The biogeochemical model simulated seasonal change in the distribution of hypoxia in the head of the bay. Dissolved oxygen was underestimated near the mouth of the Yamato River compared with observations. Estimaed hypoxia volume was 1.75 km³ in mid-summer of 2018, resulting in 27% reduction of the volume by the assimilation.