Microclimatic Effects of Forest to Peatland Transitions Within the Boreal Plains
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Date
2019-04-30
Authors
Green, Adam
Journal Title
Journal ISSN
Volume Title
Publisher
University of Waterloo
Abstract
Peatlands cover approximately 50% of the total landscape of the Western Boreal Forest, which
includes the sub-humid Boreal Plains (BP) ecozone. The BP experiences persistent water deficit
conditions, promoting anaerobic conditions, which has the potential to increase decomposition,
transforming the peatlands from carbon sinks to carbon sources. With evapotranspiration (ET)
being the dominant source of water loss in the BP, peatland persistence is hydrologically
precarious, and as such, it is necessary to understand the dynamics and controls on ET within these
systems. Due to the heterogeneity of the landscape, surrounding upland forests often shelter
peatlands from wind. This results in spatially varying evaporative rates, which can influence
surface moisture and vegetation regimes across a peatlands surface. High-resolution turbulent
models allow for such flow scenarios to be resolved as they resolve flow in a 3D domain.
Therefore, high-resolution turbulent models are essential in assessing the spatial variability of
stresses placed on surface scalars such as ET, by displacement height transition.
This study uses a canopy resolving large-eddy simulation (RAFLES) to study the impact
of displacement height transitions on surface-atmosphere exchanges of moisture within peatlands
of the BP. The dimensions, vegetation structure and energy dynamics of the modeled peatlands
were generated from observations of natural peatlands of the BP. Within the sheltered region
leeward of a backward-facing step transition, the simulated peatlands experienced higher
resistances to surface-atmosphere exchanges of moisture when compared to the reattachment and
recovery regions. However, this trend was muted when the surface roughness of the peatland was
increased as the roughness lowered the overall resistance of the surface. This study also found that
the length of the peatland did not influence the flow reattachment dynamics within the peatland.
However, it was observed that the peatlands with a narrow shape and a curved front-facing step
geometry resulted in faster regional wind velocities. Understanding the turbulent dynamics within
heterogeneous landscapes can help to control the rate and variability of surface to atmosphere
exchanges of moisture within disrupted and reclaimed landscapes which can increase the
predictability of moisture demands within future landscapes.
Description
Keywords
peatland, flow separation, hydrometeorology