Temporal and Spatial Variations in Soil Temperature in Tidal Flat of Ariake Sea, Japan

摘要

The tidal variation of the Ariake Bay, which locates in the western part of Japan, is over 6 m. This bay is a closed water area. Tidal flats stretch in the bay, especially in the inner part. Recently water environment has been become worse, specifically, increase in occurrence of hypoxic condition and decrease in fishery. Some researchers think this might occur due to the reclamation of a tidal flat. Tidal flat is a habitation of livings, and has a function to purify water. The purification is decomposition of organic and inorganic matter originated from the land and the sea. Denitrification is caused by bacteria in soil, and the potential depends mainly on soil temperature. Temperature and the thermal properties of soil in tidal flat were measuredin the inner part of the Ariake Sea. Thermal conductivity decreased with increasing soil moisture. This might occur because of shrinkage-swelling characteristic of soil. The relationship between soil temperature at soil surface and air temperature was among seasons. A numerical simulation model was constructed to investigate the variation in soil temperature related with depth of standing water. The influence of standing water on soil temperature was small during the period in which the depth of standing water decrease with time because soil moisture was high, while the influence was apparent from dry to flood period.