Clarifying Forest-Water Interactions using environmental isotope tracers and development of element cycling analysis method

2022 Fiscal Year Final Research Report

• Project/Area Number: 20K06140
• Research Category: Grant-in-Aid for Scientific Research (C)
• Allocation Type: Multi-year Fund
• Section: 一般
• Review Section: Basic Section 40010:Forest science-related
• Research Institution: University of Tsukuba
• Principal Investigator: Kato Hiroaki 筑波大学, 生命環境系, 准教授 (90732636)
• Project Period (FY): 2020-04-01 – 2023-03-31
• Keywords: 森林 / 水循環 / 降下放射性核種 / 放射性セシウム / Pb-210 / トレーサー

Outline of Final Research Achievements

In this research project, to investigate the possibility of using atmospheric fallout radionuclides as tracers of material cycles in forest ecosystems, the canopy water balance and litterfall deposition rate were calculated and the radionuclide fluxes transferred with them in the experimental forests were clarified. By comparing radionuclide concentrations in rainwater that passed through the canopy (throughfall and stemflow) and tree components (e.g., branch and foliage), it was found that the transfer coefficient from tree body to rainwater changed with time. Field data were also obtained to suggest that deposition fluxes to the soil vary depending on the transfer pathway from the tree canopy to the forest floor, and that canopy density and preferential infiltration flow can explain the heterogeneous distribution of atmospheric fallout radionuclides and materials on the forest floor.

Free Research Field

環境動態解析

Academic Significance and Societal Importance of the Research Achievements

森林の水・物質循環研究において，従来から水の安定同位体や溶存イオン等がトレーサーとして用いられており、近年では森林を含むクリティカルゾーンの環境動態解析に広く応用されている。一方で，福島原発事故後に放射性セシウムの環境動態研究が飛躍的に増加したものの，森林での物質循環トレーサとしての利用可能性は未だ調査されていない。本研究課題においては，福島事故由来の放射性セシウムと天然放射性核種の森林環境動態を通じて，大気-森林-雨水-土壌間のシームレスな水・物質循環を定量的に解析できる可能性が示され，森林物質循環解析のツールとして国内外の森林水文・生態学のさらなる発展に寄与することが期待される。