Canadian Forest Service Publications
Peat properties and water retention in boreal forested peatlands subject to wildfire. Thompson, D.K.; Waddington, J.M. 2013. Water Resources Research 49(6):3651-3658.
Issued by: Northern Forestry Centre
Catalog ID: 35508
CFS Availability: PDF (request by e-mail)
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Peat cores from a recently burned peatland and one over 75 years since fire in Alberta, Canada were analyzed for physical properties and water retention. Wildfire exposed denser peat at the peat surface, more so in hollow than hummock microforms. Water retention in peat has implications for postfire Sphagnum regeneration, as this more dense peat requires smaller volumes of water loss before a critical growth-inhibiting pore-water pressure of -100 mb is reached. Simulations of water retention after fire showed that hollow microforms are at a higher risk of losing low-density surface peat, which moderates water table (WT) declines via high specific yield. Exposure of dense peat to the surface after fire increases surface moisture under a constant WT. The net effect of decreasing specific yield and increasing water retention at the surface has implications on hydrologic stability and resilience of boreal peatlands to future wildfire risk under a changing climate. Earth system models incorporating wildfire disturbance in boreal peatlands would benefit from the inclusion of these hydrological feedbacks in this globally significant carbon reservoir.
Plain Language Summary
We wanted to find out how well different samples of peat could hold water. We performed laboratory tests on the top 50 cm of peat from burned and unburned bog peatlands near Slave Lake, Alberta. Bog systems like these ones have both high areas, called hummocks, and low areas, called hollows. The peat in the hollows is denser and holds less water than the peat in the hummocks. This means that the low areas of peat are drier and burn better during wildfire. After this denser peat in the hollows has burned away during wildfire, peat from further below the surface, which is even denser, becomes exposed. After a fire, the water table declines faster during periods without rain because the remaining peat is denser. This interaction between increasing peat density and declining water table could reduce the ability of peat-forming sphagnum mosses to recolonize an area after a fire. These mosses regenerate best when the water table is no more than 50 cm below the surface.