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Title: 栄養塩濃度が大幅に減少した洞海湾の貧酸素水塊と低次生産過程について(シンポジウム:沿岸海域の貧酸素化)
Other Titles: Oxygen-deficient Water Volume and Marine Lower Trophic Processes in Dokai Bay after Large Decreases in Nutrient Concentrations(Symposium: Hypoxic Water in Coastal Seas)
Authors: 濱田, 建一郎1 Browse this author
上田, 直子2 Browse this author
山田, 真知子3 Browse this author
多田, 邦尚4 Browse this author →KAKEN DB
門谷, 茂5 Browse this author →KAKEN DB
Authors(alt): Hamada, Kenichiro1
Ueda, Naoko2
Yamada, Machiko3
Tada, Kuninao4
Montani, Shigeru5
Keywords: 貧酸素水塊
Issue Date: 30-Aug-2010
Publisher: 日本海洋学会沿岸海洋研究会
Journal Title: 沿岸海洋研究
Volume: 48
Issue: 1
Start Page: 29
End Page: 36
Abstract: 九州北部に位置する閉鎖性の強い洞海湾は,窒素・リンが過剰に存在する過栄養状態であったが,1997年に全窒素・全リンの環境基準IV類型が適用され,2001年には窒素負荷量の削減により基準をクリアした.本研究では環境基準の達成前後における栄養塩濃度の減少と貧酸素水塊や植物プランクトン量の変化について報告する.窒素負荷量の削減によりNH_4-Nは0.97〜1,590μMから0.120〜63.0μMへ大幅に減少した.しかしChl a濃度は環境基準の達成前1.5〜146μg L^<-1>,達成後1.4〜218μg L^<-1>で変化していなかった.また,粒子状有機物の質や量にも変化は見られなかった.この結果から栄養塩濃度の減少が植物プランクトンの成長を抑制していないことが判った.貧酸素水塊の規模は達成前521×10^4m^3,達成後508×10^4m^3で変化していないが,形成期間は短くなっていると考えられた.また,洞海湾における貧酸素水塊の形成要因としては海底堆積物の影響が大きいと考えられた.これらの結果から,環境基準の達成前後で湾内の貧酸素水塊の規模や低次生産過程は大きく変化していないことが判った.
Dokai Bay is a small enclosed bay, located in the northern part of Kyushu Island, Japan. This bay is hypertrophic, as evidenced by extraordinarily high total N and P concentrations (TN & TP). TN and TP environmental quality standards (EQSs, TN : less than 1.0 mg L^<-1>, TP : less than 0.09 mg L^<-1>) were applied to Dokai Bay in 1997. Through reductions in nitrogen loading, TN and TP concentrations had declined to below the EQSs by 2001. In this study, we report the decrease of nutrients and change in phytoplankton biomass in an oxygen-deficient water mass in Dokai Bay. After the reduction of nitrogen loading, the annual range of NH_4-N concentrations remarkably decreased from 4.97-1,590μM to 0.120-63.0μM. However, Chl a concentrations remained relatively unchanged, from 1.5-146μg L^<-1> before the implementation of EQSs to 1.4-218μg L^<-1> afterward. Furthermore, the quality and quantity of particulate organic matter did not change. This result shows that even such a remarkable decrease in nutrient concentrations did not inhibit phytoplankton growth in a hypertrophic bay. The oxygen-deficient water mass volume was approximately the same : 521×10^4 m^3 before the implementation of EQSs and 508×10^4 m^3 after. However, we presume that the duration of the oxygen-deficient water mass was shorter after EQS-implementation. Moreover, we think that the oxygen-deficient water mass in Dokai Bay was affected by the bay sediment. These findings show that the oxygendeficient water mass volume and marine lower trophic process did not change after the implementation of EQSs.
Type: article
Appears in Collections:水産科学院・水産科学研究院 (Graduate School of Fisheries Sciences / Faculty of Fisheries Sciences) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)

Submitter: 門谷 茂

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