Alternative TitleEvaluation technology of environmental improvement in the marine area where artificial reefs are submerged
Note (General)Osaka Bay has long been called the "Naniwa no Umi," and has a series of environments that are favorable for the growth of seafood, and is rich in marine resources, and various fisheries have been actively carried out. However, due to various developments in the coastal areas during the period of high economic growth, landfill and water pollution progressed mainly in the inner part of the bay, red tides occurred, and shallow areas and seaweed beds that served as spawning grounds and breeding grounds for fish and shellfish disappeared. The seawater flow is stagnant due to the pockmarks formed by dredging, etc., and oxygen-deficient water masses are generated in the summer. In addition, due to the sophistication of water treatment technology, the inflow pollution load has decreased, and as a result, the shortage of nutrients such as nitrogen and phosphorus in the southern waters of Osaka Bay has become remarkable, and the catch of Osaka Bay was in 1982. In recent years, there have been about 230 species, which have peaked at 114,000 tons, and have been around 20,000 tons per year, and the decline in resource productivity is becoming more serious.
Therefore, as a new fishery promotion measure, Osaka Prefecture will use the constant current flow that exists in Osaka Bay to install artificial fish reefs with a stirring function in the waters from the northern part to the central part of the bay to promote vertical mixing of seawater. By reducing the generation of oxygen-deficient water masses and allowing abundant nutrients from rivers to flow down to the southern part of the bay, fishery resources and catches are increased, and the marine environment is being improved.
In the past research, the artificial reef used in this project has been verified for its flow control function by hydraulic experiments and quantitatively evaluated for the range of influence of the flow control effect. Demonstration has been attempted, and its usefulness has been confirmed in the biological collection effect survey, but the research results linking the flow control function after installation with changes in the surrounding environment are scarce, and a fishing ground using artificial reefs is created. Quantitative evaluation of both parties in the project is required.
Therefore, the purpose of this study was to quantitatively evaluate the environmental improvement function of artificial reefs constructed in the actual sea area by various field survey methods.
大阪湾は，古くから「魚庭（なにわ）の海」と呼ばれ，魚介類の生育に好ましい一連の環境が揃い，水産資源が豊富で様々な漁業が盛んに行われてきた．しかしながら，高度経済成長期の沿岸域の各種開発等により，湾奥部を中心に埋立や水質汚濁が進行し，赤潮の発生，魚介類の産卵場や育成の場となる浅場や藻場の消失，浚渫等に伴い形成された海底窪地により海水の流れに停滞が生じ，夏季には貧酸素水塊の発生している．また，水処理技術の高度化により流入汚濁負荷量の減少し，これにより大阪湾南部海域での窒素，リン等の栄養塩類の不足が顕著となっており，大阪湾の漁獲量は，1982年の114,000tをピークに近年では概ね230種，年間20,000t前後で推移しており，資源生産力の低下が深刻化している．
そこで，大阪府は，新たな漁業振興策として，大阪湾に存在する恒流の流れを利用して，湾北部から中部の海域に撹拌機能を有する人工魚礁を設置し，海水の鉛直混合を促進させ，貧酸素水塊の発生軽減，河川からの豊富な栄養塩を湾南部に流下させることで，水産資源，漁獲量の増大を図るとともに，海域環境の改善を図っている．
この事業に用いられている人工魚礁は，既往の研究の中で，水理実験による流動制御機能の検証，流動制御効果の影響範囲の定量的評価がなされており，実海域でも流動制御機能の実証が試みられており，生物蝟集効果調査においても，その有用性が確認されているが，設置後の流動制御機能と周辺環境の変化を関連付けた研究成果は乏しく，人工魚礁を用いた漁場造成事業における両者の定量的評価が求められている．
そこで，本研究では，実海域に施工されている人工魚礁による環境改善機能について，各種現地調査手法により定量的に評価することを目的とした．
Collection (particular)国立国会図書館デジタルコレクション > デジタル化資料 > 博士論文
Date Accepted (W3CDTF)2021-06-07T02:06:26+09:00
Data Provider (Database)国立国会図書館 : 国立国会図書館デジタルコレクション