BIOLOGICAL MIXING DEPTH USING DISSOLVED OXYGEN AS PHYTOPLANKTON HABITAT

Abstract

 We investigated the estimation mehod for mixing depth from the viewpoint of phytoplankton habitat by using water temperature and dissolved oxygen (DO). An automatic water temperature and water quality monitoring system was installed in Yamashiro Pond on Kume Island, Okinawa Prefecture, to measure the spatiotemporal detailed vertical distributions of water temperature and DO. The data obtained every two hours at a resolution of 1 cm depth were used to determine the depth above a certain Thorpe length (L_T) (zm(L_T)) and the depth within a certain difference range of DO relative to the surface (zm(ΔDO)), respectively, as mixed water depths. The relationship between zm(ΔDO) to zm(L_T) was analysed for a period when convection due to surface cooling was the dominant external mixing force. DO difference values, 2-5% had the highest correlation with zm(L_T). The versatility of zm(ΔDO) and its applicability to dam water quality protection as well as future issues are discussed.