気仙沼湾における貝毒原因プランクトンの移流に関する観測とシミュレーション検討  [in Japanese] OBSERVATION AND SIMULATION STUDY OF TRANSPORT MECHANISM OF PLANKTON CAUSING SHELLFISH POISONING IN KESENNUMA BAY  [in Japanese]

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Abstract

気仙沼湾を対象として,貝毒原因プランクトン<i>Alexandrium tamarense</i>の分布と流動の関係を,現地観測と三次元流動シミュレーションから検討した.2013年は<i>A. tamarense</i>が気仙沼港の奥部で発生して大島瀬戸へ移流したと推測された.2014年の計数データから<i>A. tamarense</i>の移動指数を作成し,大島瀬戸における平均流速との関係を調べたところ,正の相関が認められた.以上から,<i>A. tamarense</i>は1週間程度かけて湾奥から湾内全域に拡散すると推測された.三次元流動シミュレーションにより,中立浮遊粒子を気仙沼港奥部の底層に配置して,その挙動を調べた.粒子は気仙沼港内で鉛直循環流により表層に巻き上げられてから南部に移流し,2日後には西湾を下るものが33 %,大島瀬戸へ移動するものが12 %になった.渦鞭毛藻類の日周鉛直移動を考慮することで,移動メカニズムを把握できる可能性が示唆された.

 We investigated the transport characteristics of toxic plankton <i>Alexandrium tamarense</i>, in the Kesennuma Bay. We conducted the field survey for <i>A. tamarnese</i> distribution during the bloom in 2013 and 15 month-long velocity monitoring at the Oshima-seto together with plankton monitoring in 2014. The survey indicated the trend in the plankton transport from the innermost part to the south and east areas of the bay. The velocity monitoring also showed positive correlation between the <i>A. tamarense</i> density and the velocity measured at the Oshima-seto. To support these results, 3D numerical simulation was carried out with the particle tracking simulation assuming the planktons as gravitationally neutral particles. The 10,000 particles were initially placed inside the innermost part where the origin of <i>A. tamarense</i> was highly suspected. The particles mainly drifted in the surface layer and 33% of these were transported to south through the west bay and 12% to the Oshima-seto within 3 days. Although the simulated result revealed the transport as expected, the speed of the transport might get slower by considering diurnal vertical migration of the plankton.

Journal

  • Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering)

    Journal of Japan Society of Civil Engineers, Ser. B2 (Coastal Engineering) 74(2), I_1159-I_1164, 2018

    Japan Society of Civil Engineers

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