Stability in hypolimnion of Deep Rift Lakes, East Africa
Grant-in-Aid for international Scientific Research
|Allocation Type||Single-year Grants|
|Research Institution||Hokkaido University|
NAKAO Kinshiro Professor, Faculty of Science, Hokkaido University, 理学部, 教授 (40000830)
MENGA Kiluki ザイール自然科学研究所, ウビラセンター, センター長
NDONTONI Zan ザイール自然科学研究所, 所長
TANOUE Ryuichi Associate Professor, Asahikawa National College of Technology, 制御情報工学科, 助教授 (50042081)
TOMINAGA Hiroyuki Instructor, Water Research Institute, Nagoya University, 水圏科学研究所, 助手 (10022625)
CHIKITA Kazuhisa Lecturer, Faculty of Science, Hokkaido University, 理学部, 講師 (70142685)
ZANA Ndontoni General Director, Research Center of Natural Science, Zaire
KWETUENDA Menga Kuluki President, Uvira Station, Research Center of Natural Science, Zaire
MENGA kuluki ザイール自然科学研究所, ウビラセンター, センター長
|Project Period (FY)
1991 – 1992
Completed(Fiscal Year 1992)
|Budget Amount *help
¥17,500,000 (Direct Cost : ¥17,500,000)
Fiscal Year 1992 : ¥8,000,000 (Direct Cost : ¥8,000,000)
Fiscal Year 1991 : ¥9,500,000 (Direct Cost : ¥9,500,000)
|Keywords||Rift lake / Meromictic lake / Dissolved gases of Carbon dioxide / Stable stagnant layer / Last glaciation / Equatorial climate / Trade-wind climate / Climatic change / 深水層 / メロミクティック構造 / 溶存メタン / 熱帯湖 / 熱塩対流 / リフトバレ-|
Lake Kive is situated in the equatorial region of the Rift Valley, East Africa, at latitude 2ﾟS and longitude 29ﾟE ; It discharges from the south end of the lake by the Ruzizi River into Lake Tanganyika located 150km downstream.
The lake basin was formed by the tectonic activity in 50X10^4yr.B.P. or 100X10^4yr.B.P., newer than the Tanganyika Lake in about 2000X10^4yr.B.P., The lake-level had been fell down to 300 meters lower than present one, during the last glaciation from 7X10^4yr.B.P. to 1X10^4yr.B.P., then the Kivu Lake was a closed lake in this time,
Its morphometric features are : 2,300km^2 in area of lake surface, 7,300km^2 in basin area including the lake surface, 485m in maximum depth and 240m in mean depth. The sounding results of water temperature indicate significant tendency of increasing from the depth of 90m to the bottom at all sites, it is characterized that the density of lake water is increased by a dissolved matter and is meromictic. The water of lake Kivu has been stabilized by the increase on the amounts of dissolved gases of carbon dioxide and methane and the salinity contents of CaCO_3, K and Na discharged from the bottom floor through a thin sediments cover.
On the other hand, the Tanganyika Lake is oldest rift lake, covered by thick sediments of 2,000m and then is not meromictic and the morphonetric features are : 32,000km^2 in area of lake surface, 238,700km^2 in basin area including the lake surface.
From the results of water budget for the both lakes, it became clear that the annual precipitation in the Kivu basin of equatorial climate incleased from 790mm to 1,500mm after the last glaciation, but was not changeable in the Tanganyika basin of trade-water climate. During the last glaciation, the both lakes became a closed lake and the zone of trade-wind climate spread over the several hundreds kilometer to the north.
Research Output (5results)