Verification of the direct uptake of atmospheric CO2 by coastal macrophyte using carbon isotopes and chamber method

• Project/Area Number: 19K20500
• Research Category: Grant-in-Aid for Early-Career Scientists
• Allocation Type: Multi-year Fund
• Review Section: Basic Section 64050:Sound material-cycle social systems-related
• Research Institution: National Institute of Maritime, Port and Aviation Technology
• Principal Investigator: Watanabe Kenta 国立研究開発法人海上・港湾・航空技術研究所, 港湾空港技術研究所, 主任研究官 (20725618)
• Project Period (FY): 2019-04-01 – 2023-03-31
• Project Status: Completed (Fiscal Year 2022)
• Budget Amount: ¥4,290,000 (Direct Cost: ¥3,300,000、Indirect Cost: ¥990,000); Fiscal Year 2020: ¥1,690,000 (Direct Cost: ¥1,300,000、Indirect Cost: ¥390,000); Fiscal Year 2019: ¥2,600,000 (Direct Cost: ¥2,000,000、Indirect Cost: ¥600,000)
• Keywords: 海草藻場 / 大気CO2吸収 / ブルーカーボン / CO2フラックス / アマモ / 沿岸域 / 二酸化炭素吸収 / 気候変動 / 藻場 / 生態系機能 / 環境計測

Outline of Research at the Start

本研究の目標は，沿岸沈水植物による水塊を介さない直接的CO2吸収について，以下の3点を明らかにすることである．１）普遍性：構成種（海草・大型海藻から複数種を選定）や気候帯（亜寒帯~亜熱帯）の異なる植物群落において一般性を検証する．２）規模：沿岸沈水植物の直接的CO2吸収による大気中CO2吸収フラックスを定量化し，大気－水塊間CO2交換フラックスと比較する．３）規定要因：生息深度，季節変化，日周期変動等の環境要因が直接的CO2吸収に与える影響を明らかにする．本研究では，現地調査を主体として放射性炭素同位体法およびフローティングチャンバー法により，沿岸沈水植物による直接的CO2吸収の定量化を行う．

Outline of Final Research Achievements

Recent studies have found that vegetated coastal habitats such as seagrass meadows can be a net sink for atmospheric CO2. This study aims to measure the direct CO2 uptake from seagrass leaves exposed to the atmosphere in seagrass meadows. I developed a transparent floating chamber that does not inhibit photosynthesis of seagrasses, and measured CO2 gas exchange rates in seagrass beds. The measurement results showed that seagrass meadows in the subarctic and temperate sites acted as CO2 sinks on a daily scale during summer. On the other hand, direct CO2 uptake was not detected as CO2 exchange rates. This study suggested that whether direct CO2 uptake by seagrasses contributes significantly to CO2 exchange rates or not may depend on the characteristics of the seagrass meadows (e.g., exposure time and length of exposed leaf).

Academic Significance and Societal Importance of the Research Achievements

海草等が大気に露出した際の直接的CO2吸収という未知の炭素フローの実測を行ったことは，学術的・社会的に意義のある成果と考えている．沿岸植生による大気CO2除去機能は気候変動緩和策への活用が期待されているが，大気CO2除去の過程には未だ評価できていない未知の炭素フローも残されている．ブルーカーボン生態系とも呼ばれる沿岸植生を大気CO2除去の目的で社会的に活用していく上では，こうした過程の解明を進めていく必要がある．

Research Products

• [Journal Article] Drivers of inorganic carbon dynamics and air-water CO2 fluxes in two large tropical estuaries: insights from coupled radon (222Rn) and pCO2 surveys (2022)
  • Author(s): Akhand, A., A. Chanda, K. Watanabe, S. Das, T. Tokoro, S. Hazra, T. Kuwae
  • Journal Title: Limnology and Oceanography Volume: 67 Issue: S2
  • DOI: 10.1002/lno.12075
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] An unintended ecological benefit from human intervention: The enhancement of carbon storage in seagrass meadows (2021)
  • Author(s): Watanabe, K., and T. Kuwae
  • Journal Title: Applied Ecology Volume: 58 Issue: 11 Pages: 2441-2452
  • DOI: 10.1111/1365-2664.13977
  • Peer Reviewed / Open Access
• [Journal Article] Seagrass contributes substantially to the sedimentary lignin pool in an estuarine seagrass meadow (2021)
  • Author(s): Nakakuni Masatoshi、Watanabe Kenta、Kaminaka Khoki、Mizuno Yukiko、Takehara Keiko、Kuwae Tomohiro、Yamamoto Shuichi
  • Journal Title: Science of The Total Environment Volume: 793 Pages: 148488-148488
  • DOI: 10.1016/j.scitotenv.2021.148488
  • Peer Reviewed
• [Journal Article] Low CO2 evasion rate from the mangrove-surrounding waters of the Sundarbans (2021)
  • Author(s): Akhand Anirban、Chanda Abhra、Watanabe Kenta、Das Sourav、Tokoro Tatsuki、Chakraborty Kunal、Hazra Sugata、Kuwae Tomohiro
  • Journal Title: Biogeochemistry Volume: 153 Issue: 1 Pages: 95-114
  • DOI: 10.1007/s10533-021-00769-9
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Lateral carbon fluxes and CO2 evasion from a subtropical mangrove-seagrass-coral continuum (2021)
  • Author(s): Akhand Anirban、Watanabe Kenta、Chanda Abhra、Tokoro Tatsuki、Chakraborty Kunal、Moki Hirotada、Tanaya Toko、Ghosh Jayashree、Kuwae Tomohiro
  • Journal Title: Science of The Total Environment Volume: 752 Pages: 142190-142190
  • DOI: 10.1016/j.scitotenv.2020.142190
  • Peer Reviewed / Open Access / Int'l Joint Research
• [Journal Article] Macroalgal metabolism and lateral carbon flows can create significant carbon sinks (2020)
  • Author(s): Watanabe, K., Yoshida, G., Hori, M., Umezawa, Y., Moki, H. and Kuwae, T.
  • Journal Title: Biogeosciences, Volume: 17 Issue: 9 Pages: 2425-2440
  • DOI: 10.5194/bg-17-2425-2020
  • Peer Reviewed / Open Access
• [Presentation] 温帯ガラモ場の代謝と炭素収支が大気中CO2吸収に与える影響 (2020)
  • Author(s): 渡辺謙太、吉田吾郎、堀正和、梅澤有、茂木博匡、桑江朝比呂
  • Organizer: 日本地球惑星科学連合2020年大会
• [Remarks] 主任研究官:渡辺 謙太
  • URL: https://www.pari.go.jp/unit/ekanky/member/watanabe/
• [Remarks] Kenta WATANABE
  • URL: https://www.pari.go.jp/unit/ekanky/en/member/watanabe/index.html
• [Remarks] 主任研究官:渡辺 謙太 | 港湾空港技術研究所 沿岸環境研究グループ
  • URL: http://www.pari.go.jp/unit/ekanky/member/watanabe/