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No.43 (1996/12) >

 
Title :マングローブ群落の表層堆積泥における理化学性と鉱物性(生産環境学科)
Title alternative :Physicochemical and mineralogical properties of surface sediment on the mangrove swamp (Department of Enviromental Sciences and Technology)
Authors :渡嘉敷, 義浩
金城, 民明
佐藤, 一紘
志茂, 守孝
Authors alternative :Tokashiki, Yoshihiro
Kinjo, Tamiaki
Sato, Kazuhiro
Shimo, Moritaka
Issue Date :1-Dec-1996
Abstract :マングローブ群落の生態系は生物生産や陸地化や環境浄化の面だけでなく,水産資源の涵養,環境保全や国土保全等に大きな機能的役割を果たすと考えられる。マングローブ群落中における表層堆積泥の内容や陸地化の形成過程の他,上げ潮および下げ潮時に流入・流出・移動する浮遊物粒子の特性や動態等については不明なことが多い。ここでは,マングローブ群落の表層堆積泥の内容や特性を明らかにし,さらに群落内における陸地化の形成過程を検討する目的で,石垣島の吹通川流域のマングローブ群落を選定し,周辺の陸地側の表層土壌の他,河口に近い海中や群落中や河川中の表層堆積泥について調べた。河口に近い海中の表層堆積泥はほとんど粗砂画分で,pHは8.4以上,ECは4ms/cm,CECは1me/100g以下,交換性Ca含量は62me/100gで,Na,Mg, Kの順に交換性塩基含量が低くなり,海水中のイオン組成の順とは異なった。一次鉱物は石英が主体で方解石と長石が随伴し,二次鉱物はカオリナイトが主体でイライト,バーミキュライト,バーミキュライト-クロライト中間種鉱物,イライト/クロライト混合層鉱物が随伴した。陸地側の表層土壌は32& acd;57%の粘土画分を含み,pHは6.5前後,ECは0mS/cm以下,CECは19me/100g前後,交換性塩基類の含量は全般に低かった。そして,海中の鉱物組成に比べて一次鉱物は方解石の代わりにクリストバル石を随伴し,二次鉱物はほぼ類似した。河川中や群落中の表層堆積泥ではpHが8.4 以上を示すのも多く,ECが表層土壌に比べて著しく高く,海水の影響の大きいことが示唆された。CECは河川中の上流側と群落中で高い傾向を示し,交換性塩基含量は海浜由来のサンゴ砂等の溶出を示唆した。両堆積泥の一次鉱物は石英が主体で,長石の随伴には有無が見られた。河口に近い河川中の堆積泥には方解石も含まれた。また,河川中や群落中のにはクリストバル石や角閃石も含まれた。二次鉱物はカオリナイトが主体で,河川中の堆積泥に比べて群落中にかなり高く,イライトが近似し,バーミキュライトが約半分程低く,中間種鉱物が若干低い特徴を示した。そして,各支流の合流地点付近では,河川中の堆積泥にカオリナイトやイライトに加えて,他の鉱物種も多く含まれる特徴が認められた。これらのことから,マングローブ群落内の表層堆積泥では,陸地側や海域側から流入する土砂粒子や有機物等が,群落内で潮の干満や波浪の影響を受けて攪拌・混合・拡散されて集積し,海水や河川水によるその流去量が,群落内の植生や根群の他に干潮時の生物活動等の影響によって制限を受け,群落内に次第に集積されて陸地化の形成過程に関わることが推察された。
It is considered that a community of mangrove not only play an important role in the protection of living things, the formation of terrestrial parts and the purification of natural environment, but also play in the cultivation of fisheries resources, the conservation of national land and the preservation of environment. It was purpose of the present investigation to study on the substances of surface material sedimenting on the mudflat area in mangrove swamp around Fukito river at Ishigaki island. As for sediment in sea bottom near by the river mouth, there were coarse sand in particle size fraction, more than 8.4 in pH, 4mS/cm in EC, less than 1me/100g in CEC and 62me/100g in exchangeable Ca content which was different from the order of concentration of ion in sea water. The main primary mineral was quartz accompanied with calcite and feldspar. Secondary mineral mainly was kaolinite accompanied with illite, vermiculite, vermiculite-chlorite intergrade mineral, vermiculite/chlorite mixed layer mineral. The other hand, as for surface soils of land side, there were 32∿57% clay content in particle size fraction, about 6.5 in pH, less than 0mS/cm in EC, about 19me/100g in CEC and low in exchangeable base content in general. Compared with sediment in sea bottom, there mainly was quartz in primary mineral constituent of surface soils accompanied with cristobalite instead of calcite and almost resembled in secondary mineral constituent of them. It was suggested that sea water have a great influence on both sediment in river and community of mangrove indicating mostly more than 8.4 in pH and remarkable height in EC than surface soils. CEC tended to be high in both sediment in the upper side of river and community of mangrove. The high value of their exchangeable base content suggested dissolution of something like coral sand derived from the seacoast. Both sediment mainly was quartz in primary mineral but differed in accompaniment of feldspar. Calcite also was contained in sediment in river near by the river mouth. And amphibole or cristobalite rarely were contained in both sediment in river and community of mangroves. In comparison with sediment in river, secondary mineral mainly was kaolinite indicating considerable high content in community of mangroves and was similar in illite while it was approximately half in vermiculite and a little low in vermiculite-chlorite intergrade mineral. As for neighborhood of the junction of each tributary river, there were contained much varieties of mineral in addition to kaolinite and illite in the sediment in river.
Type Local :紀要論文
ISSN :0370-4246
Publisher :琉球大学農学部
URI :http://hdl.handle.net/20.500.12000/3732
Citation :琉球大学農学部学術報告 = The Science Bulletin of the Faculty of Agriculture. University of the Ryukyus no.43 p.89 -98
Appears in Collections:No.43 (1996/12)

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