Seasonal ground ice impacts on spring ecohydrological conditions in a western boreal plains peatland

Abstract

Peatlands in the Western Boreal Plains act as important water sources in the landscape. Their persistence, despite potential evapotranspiration (PET) often exceeding annual precipitation, is attributed to various water storage mechanisms. One storage element that has been understudied is seasonal ground ice (SGI). This study characterized spring SGI conditions and explored its impacts on available energy, actual evapotranspiration, water table, and near surface soil moisture in a western boreal plains peatland. The majority of SGI melt took place over May 2017. Microtopography had limited impact on melt rates due to wet conditions. SGI melt released 139mm in ice water equivalent (IWE) within the top 30cm of the peat, and weak significant relationships with water table and surface moisture suggest that SGI could be important for maintaining vegetation transpiration during dry springs. Melting SGI decreased available energy causing small reductions in PET (<10mm over the melt period) and appeared to reduce actual evapotranspiration variability but not mean rates, likely due to slow melt rates. This suggests that melting SGI supplies water, allowing evapotranspiration to occur at near potential rates, but reduces the overall rate at which evapotranspiration could occur (PET). The role of SGI may help peatlands in headwater catchments act as a conveyor of water to downstream landscapes during the spring while acting as a supply of water for the peatland. Future work should investigate SGI influences on evapotranspiration under differing peatland types, wet and dry spring conditions, and if the spatial variability of SGI melt leads to spatial variability in evapotranspiration. K E Y W O R D Sevapotranspiration, ground heat flux, microtopography, peatlands, seasonal ground ice, western boreal plain

Recent Crown Thinning in a Boreal Black Spruce Forest Does Not Reduce Spread Rate nor Total Fuel Consumption: Results from an Experimental Crown Fire in Alberta, Canada

“…The depth of the concrete layer of seasonally frozen organic soil (depth to ice) varied considerably throughout the stand as a result of differences in surface elevation of peatland microtopography, but was in line with other early season measurements of depth to ice in other non-permafrost boreal peatlands [50]. Although seasonally frozen soil can be an input of water into the upper layers of peat [50] and/or act to limit drainage [51], there is little field observation of the persistence of this added moisture in a sub-humid environment such as the Boreal Plains, especially in periods of high fire weather where evaporation rates are towards their upper limits. In this instance, there is the potential for the layer of frozen soil to act as a barrier to an upward movement of (unfrozen) water from the water table, leading to enhanced drying of the uppermost surface layers.…”

Growing season evapotranspiration in boreal fens in the Athabasca Oil Sands Region: Variability and environmental controls

“…season (May) due to sparse vegetation(Brown et al, 2014;Phillips et al, 2016), relatively high ET rates were measured in May at Pauciflora and Saline Fens in 2017 and 2018. Such elevated ET rates can be related to high water availability caused by inundation over frozen saturated peat; substantial seasonal ground ice can maintain saturated conditions near the surface during the melt season(Van Huizen et al, 2020). From August to September, ET rates gradually decreased as T air , R net , and VPD declined and vegetation began to senesce (c.f Kim & Verma, 1995;Lafleur et al, 1997)…”

The role of snow processes and hillslopes on runoff generation in present and future climates in a recently constructed peatland watershed in the Athabasca oil sands region

“…Variations in blowing snow, sublimation, interception, frozen ground and vegetation communities among landscapes impact snow accumulation and melt regimes (Pomeroy et al, 2006(Pomeroy et al, , 1998Price & Fitzgibbon, 1987;Spence & Woo, 2003;Whittington, Ketcheson, Price, Richardson, & Febo, 2012;Woo & Marsh, 2005;Woo & Winter, 1993). Soil ice formation is another critical component of winter hydrology as frozen water is unavailable in the early growing season for evapotranspiration and is released later into the growing season (Devito et al, 2012;Van Huizen, Petrone, Price, Quinton, & Pomeroy, 2020). Seasonal frost tables can also assist in the transmission of snowmelt water to other landscape units that rely on that annual input of water prior to the growing season (Devito et al, 2012;Van Huizen et al, 2020).…”

“…Soil ice formation is another critical component of winter hydrology as frozen water is unavailable in the early growing season for evapotranspiration and is released later into the growing season (Devito et al, 2012;Van Huizen, Petrone, Price, Quinton, & Pomeroy, 2020). Seasonal frost tables can also assist in the transmission of snowmelt water to other landscape units that rely on that annual input of water prior to the growing season (Devito et al, 2012;Van Huizen et al, 2020).…”