Spatial Distribution of Hypoxic Water Mass Based on a Monitoring Campaign of Bay Environment at Tokyo Bay, Japan.

Abstract

In 2008, a monitoring campaign of bay environment had been done at Tokyo Bay, Japan. This campaign has been a part of implementation of the bay renaissance plan enacted since 2005. The data was collected by 46 institutions in 568 monitoring points in around 2nd July 2008. Dissolved oxygen, salinity and temperature were monitored in sea area basically from the surface to the bottom with 1.0 m vertical spacing at the monitoring points. We analyzed spatial distribution of hypoxic water mass based on this monitoring campaign data. Following results are obtained that 1) Measurement results showed that the bottom hypoxic water mass dominated in the head of Tokyo bay, while dissolved oxygen concentration was high condition in tidal flat and in shallow water, such as the Tama River estuary, Sanbanze tidal flat area and the Ara River estuary. 2) We proposed new parameters, such as CDZ and VDZ, which showed characteristic of spatial distribution of hypoxic water. The proposed parameters could be related to the temporal and spatial development of hypoxic water. Thus, these parameters will extend the interpretation of conservative bottom dissolved oxygen (DOB) data to understand the dynamics of hypoxic water.