Root Network Impact on Soil Thermal Conductivity and Active Layer Thaw

English Abstract:

A large portion of Canada’s land surface is underlain by permafrost ranging from continuous to isolated and sporadic. Future increases in regional air temperatures are expected to lead to widespread degradation of permafrost, particularly in the zone of discontinuous permafrost where ground temperatures are close to the freezing point. This study examines the impact of black spruce root networks on the thermal conductivity of northern peatland soils and their resultant impact on active layer thaw. Measurements were taken in the Scotty Creek research basin, a wetland dominated area in the zone of discontinuous permafrost located near Fort Simpson, Northwest Territories. Thermal conductivities for black spruce roots and peat soils of various moisture contents were determined and used to model the relative importance the thermal conduction from each material has on the thawing of the active layer. As soil thawing progresses, the frost table and the thawed saturated zone above it descend through the wetted soil profile while the saturated horizontal hydraulic conductivity of peat decreases with depth. The influence of vegetation on soil moisture is an important aspect to consider when understanding permafrost thaw due to the relationship of thermal conductivity of soils and moisture content. Root systems of plants are known to extend vertically into the soil profile for considerable depths and can tap water and nutrients from both deep and shallow layers, black spruce roots reach only approximately 30 cm below ground. The movement of moisture by plant roots is an important component of below ground hydrological processes and is therefore also important in understanding heat movement within soils through 1) the effect of soil moisture on heat conduction, and 2) coupled heat and mass transfer processes. In the context of a peat plateau complex understanding the process of hydraulic redistribution is important because the root networks are an important mechanism of soil moisture movement and as a result the relation between the soil thermal conductivity and moisture content.