諫早湾締め切り後の堤内の干陸地におけるカキ床の分布と小江沖カキ床での雑草の定着

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  • イサハヤワン シメキリゴ ノ テイナイ ノ カンリクチ ニ オケル カキショ
  • A distribution of Oyster Beds on Dried Land after and Inner Part of Isahaya Bay was Closed and an Establishment of Weeds at these Beds beyond Oe

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Inner part of Isahaya Bay was closed for the reclamation on April 14,1997,and the water level in the regulating pond was kept at -1m of sea level standardized at Tokyo Bay. Therefore, a broad salty mud flat dried up and a wide area of an oyster bed emerged at the area beyond Oe. It consisted of many oyster beds and they were about 2×3～5×10m^2 and their heights were 30～50cm. After the closing, these oysters at beds were dead after a while. Many kinds of weeds were confirmed on the soil among shells of these beds from June after the death of these oyster. A field survey was done on Aug., Nov. 1997 and on Feb. 1998,at seven same oyster beds set beyond Oe. Dominat species were Bidens frondosa and Eclipta prostrata on Aug. 1997,Eclipta prostrata and Sonchus oleraceus on Nov. 1997,sonchus oleraceus, on Feb. 1998,from the survey at these oyster beds. Moreover, 45 species were confirmed at the whole area of oyster heds on left bank of R. Honmyo on Feb. 1998. However, plants did not grow at clayey soils around the oyster bed at the survey on Aug. 1997. Buds of a Chenopodium glaucum and a halophytic plant, Chenopodium stenophyllum were scarcely confirmed around oyster beds on Nov. 1997 and on Feb. 1988,respectively. Soils at oyster beds were weathered and were found to be desalinized. While, soils around oyster beds were found to be salty and were reduced state. Soil salinity and soil oxidative-reductive state were found to be limiting factors for the invasion and establishment of weeds into the reclaming land.

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