SIMULTANEOUS VARIATION PROCESS OF WATER TEMPERATURE AND TURBIDITY IN LAKE BIWA

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  • 琵琶湖における水温・濁度の変動過程
  • ビワコ ニ オケル スイオン ダクド ノ ヘンドウ カテイ

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Abstract

Field and laboratory studies on the interaction between water temperature and turbidity in lakes are presented. In Lake Biwa, during the summer of 1993-1994, curious variations of water temperature were measured in a layer of thermocline under the intrusion of turbid water. The similar phenomena have been observed in the ocean, and called 'thermohaline staircase'. Such staircases usually accompany salt finger forms of double-diffusive convection in oceanography. We considered the phenomena like double-diffusive convection also exist in the thermocline of lake. In order to elucidate this phenomena, we performed nine series of two-layer 'rundown' laboratory experiments by using a circular vertical cylinder. As the initial condition, hotter turbid water was set in the upper layer of the cylinder, colder fresh water in the lower layer. Silt with 10 μm in diameter was used as the turbid materials. Silt-driven fingers showed similar features for the density ratio and the buoyancy flux ratio. Turbid water due to resuspention of bed sediment and river inflow causes an intermediate nepheloid layer with silt-driven fingers, which makes a major contribution to vertical mixing in lakes.

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