| Co-Investigator(Kenkyū-buntansha) |
ANGSUPANICH サオワパ プリンスオブソンクラ大学, 助教授
YAMANAKA Kaoru Tokyo University of Agriculture, 生物産業学部, 助手 (60220422)
NARIOKA Hajime Tokyo University of Agriculture, 農学部, 講師 (70211448)
MASUI Yoshio Tokyo University of Agriculture, 農学部, 助教授 (80078196)
YAMAGUCHI Yukuya Tokyo University of Fisheis, 教養科, 教授 (70114220)
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| Research Abstract |
Lake Songkhla, a lagoonal lake system of southern Thailand at 7*08^<, >-7*50N and 100*07^<, >-100*37^<, >E faced to Gulf of Thailand has a total area of about 1,040km^2, which is devided into almost four parts by existence of three lakes, i.e. Thale Noi, Thale Luang and Lake Somgkhla(Thale Sap or the southern lake), connected by a lot of canals and arranged from north to south in the order.
The southern lake which covered 220km^2 and is having 1-2m mean depth and about 9m maximum depth is filled with almost brackish water in its central part. Seasonal variation of water salinity depends upon seawater from open sea and run off from the upper lake and rivers, consequently, typical division of fresh-, brackish-and seawater gones could be observed in dry season but be disturbed in wet season. The lake is usually exposed to turbidity increase caused by tra sportation of inorganic particles from canals and rivers, and by wind action to agitate bottom sediment in shallower parts.
South Asia hav
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e large scale lagoons which have recently been exposing to alteration by port construction, fisheries, urbaniqation and industrialization. Mangrove forest is much receiving a heavy damage derived from these impacts, especially by conversion from the forest to shrimp culture ponds in outer barrier qone of Lake Songkhla system in Thailand. Economical evaluation on this problem was analyzed and discussed.
The view points on our research in the southern lake is 1)to find difference between dry and wet seasons on water environment, 2)horiqontal and vertical distributions of water quality items, 3)gradients of environ mental and biological items influenced by seawater invade and fresh-water inflow, which were successfully achieved on the results of water quality survey and benthic animal distribution.
Another characteristics of ecosystem and the environment in the lake were 1)division of fresh-, brackish and seawater qones which was clear in dry season but destructive in wet season, 2)turbidty being usually : higher than several ten mg/l in the whole area of the southern lake resulted by inflow of inorganic particles from rivers, 3)photosynthetic speed of phytoplan kton was in a range of highest values in Japanese lakes, 4)amount of organic matter in the lake sediment was lower comparing to that of Japanese eutrophic inmerbay area, 5)obtained macrobenthos species about 100spp., and the individual numbers being 1,000-5.000 ind./m^2 as like as that of Japanese inner-bay area, with far difference of the faunistic feature from Japan and with occurrence of same species as china coast of the South China Sea, Viet Nam, the Indian Ocean and Indo-Pacific region, includig a lot of brackish water speeies.
In addition to these results, geomorphology and formation process of the lake system were discussed with citing of topographic and historical references. Less
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