Mulching During Boreal Resource Development Alters Near-Surface Hydrophysical Properties and Triggers Episodic Methane Emissions in Peatland Soils

Linear disturbances within boreal Canada (e.g. seismic lines) can significantly disrupt carbon cycling in northern peatlands, potentially transforming these significant carbon stocks from long-term carbon sinks into net carbon sources. Recent efforts have been made to quantify the impacts of linear disturbance on vegetation, soil composition and greenhouse gas (GHG) emissions. However, little is known about the specific interactions between disturbances to peat hydrophysical structure and composition and the resulting alterations to CO₂ and CH₄ dynamics. To this end, eight poor fen peat cores were collected on, and eight cores collected adjacent to a seismic line representing the top 10 cm of the peat profile. These cores reflected four degrees of disturbance, with four cores per treatment: complete mulch covering, partial mulch covering, mechanical roughing only and undisturbed. In controlled laboratory conditions, cores were subjected to two subsequent static water table conditions (3 and 8 cm below the core surface) for ~30 days each with GHG flux measurements occurring every 2–3 days. Cores were then subdivided into 5 cm segments and underwent hydrophysical (i.e., bulk density, porosity and water retention) and compositional (i.e., C:N and vegetational assemblage) analysis. Results show that peat composition and hydrophysical structure were both strong predictors of GHG emissions. Higher CO₂ emissions were related to peat with high bulk density, low total and effective porosity and low C:N ratios, which occurred at depth in the undisturbed cores and at the surface where mechanical mulching and mixing occurred. Increased CH₄ emissions occurred in a subset of disturbed cores characterized by a reduction in macropores and effective porosity near the surface; these emissions were episodic and occurred where trapped gas was released. Further field-scale research is needed to evaluate the interrelationships between the direct impacts of seismic line creation on hydrophysical structure and composition and the long-term changes in carbon cycling within disturbed systems.