Seasonal variation in albedo and radiation exchange between a burned and unburned forested peatland: implications for peatland evaporation

Abstract

Forested boreal peatlands represent a precipitation‐dependent ecosystem that is prone to wildfire disturbance. Solar radiation exchange in forested peatlands is modified by the growth of a heterogeneous, open‐crown tree canopy, as well as by likely disturbance from wildfire. Radiation exchange at the peat surface is important in peatlands, as evaporation from the peat surface is the dominant pathway of water loss in peatlands of continental western North America. We examined shortwave and longwave radiation exchange in two forested ombrotrophic peatlands of central Alberta, Canada: one with (>75 years since wildfire; unburned) and another without a living spruce canopy (1–4 years since wildfire; burned) between the autumn of 2007 and 2010. Above‐canopy winter albedo was nearly two times greater in the recently burned peatland than the unburned peatland. Incoming shortwave radiation at the peat surface was much higher at the burned peatland, which increases the amount of energy available for evaporation. This is especially true for hollow microforms that are generally shaded by the tree canopy in unburned peatlands. Snow‐free albedo was similar between peatlands, although an increase in longwave losses at the burned site resulted in slightly greater net radiation at the unburned site. Copyright © 2015 John Wiley & Sons, Ltd.

Ecosystem scale evapotranspiration and CO2 exchange in burned and unburned peatlands: Implications for the ecohydrological resilience of carbon stocks to wildfire

“…This difference in energy partitioning persisted across the study period, despite greater total available energy at the unburned site. The effects on wildfire on changes to peatland ecosystem scale net radiation in this region have been previously examined by Thompson, Baisley, and Waddington (), who found that snow‐free albedo between burned and unburned areas were similar, but increased outgoing longwave radiation from burned sites decreased the total available energy relative to unburned sites. These findings are consistent with our results, particularly in that the diurnal pattern of energy availability diverges between sites during periods of maximum outgoing longwave radiation, that is, during mid‐late afternoons when surface temperatures are at their daily maximum (Figure ).…”

“…In agreement with their findings at the plot scale, we found a significant difference in paired halfhourly ET across two years between the unburned and burned peatlands at the ecosystem scale. Further, the sites differed in the F I G U R E 3 Relationship between half-hourly ET and available energy, as well as vapour pressure deficit, between the burned (red) and unburned (black) sites Thompson, Baisley, and Waddington (2015), who found that snow-free albedo between burned and unburned areas were similar, but increased outgoing longwave radiation from burned sites decreased the total available energy relative to unburned sites. These findings are consistent with our results, particularly in that the diurnal pattern of energy availability diverges between sites during periods of maximum outgoing longwave radiation, that is, during mid-late afternoons when surface temperatures are at their daily maximum (Figure 4).…”

Low Evapotranspiration Enhances the Resilience of Peatland Carbon Stocks to Fire

“…The water repellent layer may accordingly act as a figurative one‐way valve, permitting rainfall to percolate down through preferential flow pathways to the water table beneath because of the high porosity of the peat and the abundance of macropores (Holden, ) but restricting its loss via evaporation at local and regional scales (Rye & Smettem , ). Such a feedback response would limit peatland evaporation during periods of high solar radiation resulting from the burning of the shrub and canopy cover (Thompson et al, ). While water repellency in the studied peatland persisted for at least 2 years, depending upon site conditions, water repellency can remain for several years (Doerr et al, ).…”

“…Further, within Sphagnum-dominated boreal peatlands, postfire ET can exceed prefire ET (Thompson et al, 2014). Canopy removal increases both the energy availability (Kettridge et al, 2012;Thompson et al, 2015) and the potential ET within the subcanopy (Plach et al, 2016). Within Sphagnum-dominated peatlands the subcanopy can account for up to 80% of prefire ET (Gabrielli, 2016;Lafleur & Schreader, 1994).…”

Vegetation and location of water inflow affect evaporation in a subtropical wetland as indicated by the deuterium excess method

“…This explanation is supported by the high precipitation and water levels during the same time period (Figure 2b,c), and the precipitation is characterized by depleted water isotope ratios (Price et al, 2008). Moreover, the high water input from (Biederman et al, 2014;Mengistu, Everson, & Clulow, 2014;Thompson, Baisley, & Waddington, 2015) and wind reduction on the water surface (Helfer, Zhang, & Lemckert, 2009;Sugita, 2018). Importantly, if the evaporation differences caused by these factors persist, the water isotopic difference will persist and can be used to indicate the evaporation difference.…”