MITIGATING PERMAFROST DEGRADATION DUE TO LINEAR DISTURBANCES IN SUB-ARCTIC PEATLANDS

The presence or absence of permafrost significantly influences the hydrology and ecology of northern watersheds. Linear disturbances resulting from tree canopy removal have led to widespread permafrost degradation in sub-arctic peatlands. Seismic lines resulting from petroleum exploration can account for up to five times the natural drainage density of these basins, and affect the region’s water and energy balances. As peatlands represent some of the most sensitive ecosystems to climate and human disturbances, the ability to simulate perturbations to natural systems in a controlled environment is particularly important. A method is presented that is capable of simulating natural freeze-thaw and permafrost conditions on a large variably-saturated soil monolith, housed in a two level climate chamber. The design replicates realistic thermal boundary conditions, which enables field scale rates of active-layer thaw, and presents a path forward for the large-scale experimental study of frozen ground processes.

Mulching over seismic lines, using mulch of the removed tree canopy, has been proposed to reduce their environmental impact. The new set-up enabled field-scale remediation techniques to be tested, and was used to investigate the effects of the mulch on thermally mitigating permafrost thaw. Freeze-thaw cycles with and without the mulch enabled its effects to be tested. The data were assimilated into a coupled heat and water transport numerical model. An analysis was conducted on the combined effects of mulch thickness, antecedent moisture conditions and meteorological interactions. Experimental and numerical simulations show that the application of the mulch insulates the underlying soil, by decoupling the subsurface from meteorological forcing and impeding heat conduction. Net ground heat flux is reduced, which delays thaw initiation by slowing the input of energy to the subsurface. This effect prolongs the period of time the ground remains frozen during positive air temperatures and reduces frost table depths. Results indicate that mulching is an effective technique to reduce permafrost degradation and provides a scientific basis to assess the mitigation measure. This study will provide guidance in ensuring that northern exploration is performed in a more environmentally sustainable manner.