Biochar mitigates the peatland GHG dilemma under contrasting water table regimes: phase-dependent responses of CO₂ and CH₄ over a two-year study

Abstract

Peat soils are major terrestrial carbon stores, yet drainage alters redox conditions that stimulate CO₂, CH₄, and N₂O emissions. We conducted a two-year mesocosm experiment to quantify how water table level (0, 20, and 40 cm) interacts with organic amendments to regulate gaseous C and N fluxes from lowland peat. Amendments included Miscanthus biochar, Miscanthus chip, paper waste, biosolids, and cereal straw. Results revealed that moderate drainage (WTL₂₀) provided the optimal balance between carbon loss and CH₄ suppression compared to saturated (WTL₀). Although CO₂ emissions increased under WTL₂₀, CH₄ fluxes declined by over 90% relative to WTL₀, where methanogenesis dominated. This shift in the Control (from WTL₀ toWTL₂₀), reduced overall CO₂-equivalent emissions by 17 t CO₂eq ha⁻¹ yr⁻¹, highlighting the critical GHG balance of maintaining a WTL₂₀ in lowland peatlands. Among the amendments, labile, low C:N amendments (cereal straw, biosolids) increased CO₂ and N₂O emissions under WTL₂₀, indicating enhanced aerobic mineralization following oxygen exposure. In contrast, biochar consistently outperformed all treatments, reducing cumulative CO₂ emissions by up to 52% compared with the Control-WTL₄₀ when assessed over the full 730-day experimental period. The consistent reduction in GHG emissions indicates constrained peat carbon mineralization under biochar amendment across contrasting hydrological conditions (WTL₀ and WTL₂₀) in two consecutive years. Overall, this study demonstrates that integrating WTL₀ and WTL₂₀ water table manipulations alternatively with stable, recalcitrant amendments such as biochar substantially altered greenhouse gas fluxes, offering a promising strategy to mitigate emissions while adding to and maintaining peat carbon stocks and fluxes from lowland bare peat.

Graphical Abstract

Keywords

Climate change / Greenhouse gas removal / Biochar / Nature-based solutions / Water table level

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Funding

Biotechnology and Biological Sciences Research Council(BB/V011561/1)

RIGHTS & PERMISSIONS

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