CONVECTIVE TRANSPORT OF DISSOLVED OXYGEN INTO THE HYPOLIMNION OF DEEP LAKES

YOSHIKAWA Keiko, OKUBO Kenji

doi:10.2208/jscejb.64.41

According to field results in a dam reservoir for the mechanism of convective circulation due to surface cooling at the water surface, we estimate both the flux profiles of temperature and dissolved oxygen. In the northern basin of Lake Biwa, buoyancy flux is only significant in the epilimnion with exceptions of turbid intrusion into the upper thermocline. Oxygen flux profiles are calculated assuming the zero-flux surface at a certain level in the thermocline. Oxygen capacity decreases during the heating season, however the oxygen does not decrease due to successive algae blooming events and the oxygen release from the epilimnion into the air is observed only in early summer, while oxygen is supplied from the air during cooling months and the inflow becomes moderate showing a linear flux profile in January. In contrast, the oxygen flux in the hypolimnion becomes negative consumed in the sediment, all the year except for full turnover in late winter. However the flux occasionally becomes positive, which is not due to the vertical exchange but the horizontal flux due to convective circulation and its final turnover. The surface process in the heating period is due to photosyntheses and bottom process is also biotic and thus the annual cycle is described.

CONVECTIVE TRANSPORT OF DISSOLVED OXYGEN INTO THE HYPOLIMNION OF DEEP LAKES

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