Postfire Soil Carbon Accumulation Does Not Recover Boreal Peatland Combustion Loss in Some Hydrogeological Settings

Abstract

Deep peat burning at the interface between subhumid Boreal Plains (BP) peatlands and forestlands (margin ecotones) in some hydrogeological settings has brought into question the long-term stability of these peatlands under current and future predicted climate. Small peatlands located at midtopographic positions on coarse sediments have been identified as hot spots for severe burning, as these peatland margins are not regularly connected to regional groundwater flow. The ability of these peatland systems to recover carbon lost from both the interior and margin within the fire return interval, however, has not yet been investigated. Here we examine peatland soil carbon accumulation along a chronosequence of time since fire for 26 BP ombrotrophic bogs located across a range of hydrogeological settings. Soil organic carbon accumulation following wildfire does not appear to be influenced by hydrogeological setting; however, the ability of a peatland to recover the quantity of carbon lost within the fire return interval is dependent on the amount of carbon that was released through smoldering, which is influenced by hydrogeological setting for peatland margins. Based on published measurements of organic soil carbon loss during wildfire and our soil carbon accumulation rates, we suggest that peatlands located at topographic lows on coarse-grained glaciofluvial outwash sediments or on low-relief, fine-grained sediment deposits from glaciolacustrine or subglacial paleoenvironments are currently resilient to wildfire on the BP landscape. Peatlands that experience severe smoldering at the margins, such as ephemerally perched systems on glaciofluvial outwash sediments, will likely undergo permanent loss of legacy carbon stores.

Hydrogeologic setting overrides any influence of wildfire on pore water dissolved organic carbon concentration and quality at a boreal fen

“…Even in ecosystems with predominantly high moisture levels, fire can still impact soil C dynamics, including altering vegetation composition (Mayner et al .,) and reducing microbial activity (Artz, ). This can be especially true in peatlands located in topographical and surficial geological settings that promote deep burning and smouldering at margins (Ingram et al ., ; Mayner et al ., ). There is a strong link between vegetation and DOC concentration and composition (Armstrong, Holden, Luxton, & Quinton, ; Wickland, Neff, & Aiken, ); therefore, a change in vegetation community or an increase in vegetation regrowth after fire could lead to an increase in labile plant‐derived C, potentially increasing DOC concentrations.…”

“…Even in ecosystems with predominantly high moisture levels, fire can still impact soil C dynamics, including altering vegetation composition (Mayner et al,2018) and reducing microbial activity (Artz, 2009). This can be especially true in peatlands located in topographical and surficial geological settings that promote deep burning and smouldering at margins (Ingram et al, 2019;Mayner et al, 2018).…”

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

“…As such, this predicted alteration to the boreal fire regime may exceed the ecohydrological resilience of these carbon stocks (Kettridge et al, ) and tip some boreal peatlands to a net carbon source. Nevertheless, although there is some paleo‐ecological (Pellerin & Lavoie, ) and contemporary carbon balance evidence for such a carbon stock tipping point in some boreal peatlands (Granath, Moore, Lukenbach, & Waddington, ; Ingram, Moore, Wilkinson, Petrone, & Waddington, ), the boreal peatland carbon store is presently generally resilient to wildfire (Wieder et al, ).…”

Wildfire overrides hydrological controls on boreal peatland methane emissions

“…CH 4 dynamics in peatlands results from a combination of various biogeochemical processes (Lai, 2009). Controls on CH 4 production, oxidation, and emissions include microtopography (Cresto Aleina et al, 2016), water table depth (Bubier et al, 1995;Granberg et al, 1997), soil temperature (Granberg et al, 1997;Saarnio et al, 1998), substrate quality and availability (Granberg et al, 1997;Segers, 1998;Joabsson et al, 1999), and vegetation cover (Ström et al, 2005;Strack et al, 2017).…”

“…Fire can alter soil organic matter quality in the soil column (Neff et al, 2005;Olefeldt et al, 2013a) and reduce belowground C stores in peatlands (Wilkinson et al, 2018). Overall, wildfire can lead to a decrease in C accumulation rate through combustion loss, reduction in vegetation productivity, and increased organic matter decomposition post-fire (Ingram et al, 2019;Robinson and Moore, 2000;Wieder et al, 2009). Furthermore, increased ash deposition after wildfire can increase soil pH (Molina et al, 2007;Davies et al, 2013) and change the physical characteristics of the soil, including blocking of peat macropores and altering hydrology (Noble et al, 2017).…”