地震による表層崩壊がもたらす環境変化～北海道胆振東部地震による表層崩壊が河川水質や微生物コミュニティーに与えた影響を明らかに～

2025-08-04 産業技術総合研究所

山地流域における表層崩壊、河川水質、微生物コミュニティーの関係

＜関連情報＞

• https://www.aist.go.jp/aist_j/press_release/pr2025/pr20250804/pr20250804.html
• https://www.sciencedirect.com/science/article/pii/S0022169425012983

浅い地滑りによる地滑り堆積物は、森林流域の酸化還元状態を変化させる：水化学的および微生物学的分析からの知見 Landslide deposits caused by shallow landslides alter the redox regime in forested catchments: insights from hydrochemical and microbial analyses

Naoyuki Yoshihara, Mariko Iijima, Miyuki Nishijima, Akira Iguchi
Journal of Hydrology  Available online 21 July 2025
DOI:https://doi.org/10.1016/j.jhydrol.2025.133960

Highlights

• Earthquake-induced shallow landslides altered the catchment-scale redox regime.
• Redox-sensitive element concentrations in stream covaried with landslide intensity.
• Dimensionality reduction showed the impact of landslide deposits on stream chemistry.
• Microbial communities were linked to hydrochemistry in the landslide-affected area.
• Highly reducing zones within landslide deposits affected the stream chemistry.

Abstract

Redox reactions affect freshwater quality in terrestrial systems. Therefore, identifying the roles of various landscape units in the redox regime is important for managing water resources and ecosystems. However, less is known about the effects of topographic changes caused by shallow landslides on the redox regime. This study analyzed the hydrochemistry and microbial community of streams and seepage discharging from landslide deposits (i.e., landslide seepages) in forested headwater catchments where earthquake-triggered shallow landslides occurred in 2018 in Hokkaido, Japan, to evaluate the impact of the formation of landslide deposits on the catchment-scale redox regime. The results showed that the concentrations of redox-sensitive elements (NO₃⁻, SO₄²⁻, NH₄⁺, Mn²⁺, and Fe²⁺) in stream water correlated with the percentage of shallow landslide area to the catchment area. Compared to stream water, landslide seepage had lower redox potential and concentrations of dissolved O₂, NO₃⁻, and SO₄²⁻ and higher electrical conductivity and concentrations of dissolved NH₄⁺, Mn²⁺, and Fe²⁺. Dimensionality reduction of hydrochemical data using the t-distributed Stochastic Neighbor Embedding (t-SNE) method showed that stream chemistry for catchments with a high prevalence of shallow landslides was affected by the contribution of landslide seepage. These results suggest that the formation of landslide deposits on valley floors led to the expansion of waterlogged O₂-depleted soil zones, facilitating redox reactions accompanied by the reductions of NO₃⁻, SO₄²⁻, Mn⁴⁺, and Fe³⁺ in the landslide deposits, further altering the downstream chemistry. In addition, microbial communities that can drive such biogeochemical reactions were investigated via prokaryotic metabarcoding analysis. For robust water resource management in landslide-prone areas, stakeholders should consider the catchment-scale change in the redox regime and the resulting changes in stream chemistry and aquatic ecosystem due to stochastic landslide events.