Water table regulation and biochar amendments govern peat oxidation and greenhouse gas emissions in agricultural peatlands

Peat soils store a disproportionate share of terrestrial carbon, yet agricultural drainage accelerates peat oxidation, converting long-term carbon sinks into substantial sources of greenhouse gases (GHGs). We conducted a two-year mesocosm experiment to quantify how water table level (WTL) and organic amendment type interactively regulate peat oxidation and emissions of CO₂, CH₄, and N₂O under agricultural management. Three hydrological regimes were applied over 730 days: permanently saturated conditions (WTL 0 cm) during the first year, moderate drainage (WTL 20 cm) during the second year, and a continuously deeply drained business-as-usual control (WTL 40 cm). Each regime was combined with five amendments such as Miscanthus biochar, Miscanthus chips, paper waste, biosolids, and cereal straw and an unamended control.

Moderate drainage (WTL 20 cm) emerged as a critical threshold that constrained peat oxidation while strongly suppressing methanogenesis. Although CO₂ emissions increased relative to saturated conditions, CH₄ fluxes declined by more than 90% compared with WTL 0 cm, where CH₄ dominated total GHG output. This shift resulted in a 27-35% reduction in net CO₂ -equivalent emissions, demonstrating a clear climate benefit of maintaining a moderately lowered water table. Labile, low C:N amendments (biosolids and straw) intensified CO₂ and N₂O emissions under WTL 20 cm, reflecting rapid microbial activation following oxygen exposure and enhanced peat decomposition. In contrast, Miscanthus biochar consistently reduced GHG emissions across hydrological conditions, lowering cumulative CO₂-equivalent emissions by up to 52% relative to the deeply drained control after 730 days. chemical recalcitrance of biochar, high microporosity, and redox-buffering capacity promoted CH₄ oxidation, limited N₂O production, and stabilized native peat carbon against oxidative loss.

Our findings demonstrate that peat oxidation and associated GHG emissions can be substantially mitigated through the combined application of moderate water table regulation and stable, recalcitrant organic amendments. Integrating WTL management at -20 cm with biochar addition represents a robust, climate smart strategy for reducing emissions from agricultural peatlands while preserving long-term soil carbon stocks.