Mulching during boreal resource development increases potential methane
emissions and alters near surface hydrophysical structure in peatland
soils
Abstract
Linear disturbances within boreal Canada (e.g., seismic lines) have the
potential to significantly alter carbon cycling in Canada’s northern
peatlands, creating the potential to switch these significant carbon
stocks from long term carbon sinks to carbon sources. While efforts have
been made to quantify the impacts of linear disturbance on ecosystem,
vegetation, soil composition and GHG emissions, little is currently
known about the specific interactions between the disturbance to peat
hydrophysical structure and composition and the resulting alterations to
CO 2 and CH 4 dynamics. To this end, 16
poor fen peat cores representing the top 10 cm of the peat profile were
collected on and adjacent to a seismic line reflecting four degrees of
disturbance complete mulch covering, partial mulch covering, mechanical
roughing only, and undisturbed. In controlled laboratory conditions
cores were then subjected to two subsequent static water table
conditions (3 and 8 cm below core surface) for a period of
~30 days each with GHG flux measurements occurring 2-3
days. Cores were then subdivided into 5 cm segments and underwent
detailed hydro physical (i.e., bulk density, porosity, water retention)
and compositional (i.e., C:N, vegetational assemblage) analysis. Results
show that both peat composition and hydrophysical structure were strong
predictors of greenhouse gas emissions. Higher CO 2
emissions were related to both 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 CH 4 emissions occurred in
disturbed cores characterized by a reduction in macropores and effective
porosity near the surface; these emissions were episodic in nature and
occurred where trapped gas was released during pore desaturation when
water tables were lowered. Additional work should therefore be conducted
at field scale to further assess the interrelationships between direct
changes to hydrophysical structure and these other impacts, to better
determine the long-term changes to carbon cycling in systems disturbed
by seismic line creation.