Transportation of Suspended Sediment Slowly Settling in a Caldera Lake.

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Dynamic behaviors of suspended sediment settling in volcanic Lake Kuttara, Hokkaido were examined by measuring the amount of trapped deposits and analyzing their particle size, biology, chemistry and mineralogy during a period from 14 September to 14 October 1989. The lake then was thermally stratified under conditions of the autumnal epilimnion cooling. The mean daily settling flux (g⋅m-2⋅d-1) of suspended sediment was numerically obtained from the amount of deposits trapped at five stations, and its horizontal distribution was successively described at depths of 15 m, 60 m and 100 m or 2 m above the bottom. About 50 to 60 vol.% of trapped sediment was occupied by endogenic phytoplankton (diatoms and dinoflagellates) and zooplankton (mainly, Bosmina longirostris), ranging over 11-125 μm in size. Its representative settling velocity is given as 1.26×10-5 m⋅sec-1, using the mean size of 32.6 μm and the mean particle density of 1, 034 kg⋅m-3. The spatial distributions of settling flux of sediment and a scale analysis of the sediment transport equation suggest that from the water surface to near the thermocline (15 m depth), the transport of settling sediment is controlled by vertically circulating flows due to a wind-forced surface wave, while below the thermocline (depths more than 15 m), it is decided by a secondary, vertically circulating flow due to rotating internal waves.
日本陸水学会の論文