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

Abstract

Western Boreal Canada could experience drier hydrometeorological conditions under future climatic changes, and the drying of nonpermafrost peatlands can lead to higher frequency and extent of wildfires. Despite increasing pressures, our understanding of the impact of fire on dissolved organic carbon (DOC) concentration and quality across boreal peatlands is not consistent. This study capitalizes on the rare opportunity of having 3 years of prefire and 3 years of postfire DOC data at a treed, moderate‐rich fen in the Western Boreal Plain, northern Alberta, to investigate wildfire effects on peatland DOC dynamics. We investigated whether a wildfire facilitated any changes in the pore water DOC concentration and quality. There was very little impact of the fire directly, with no significant changes in DOC concentrations postfire. We highlight that DOC patterns are more likely to be controlled by local hydrogeological factors than any effect of fire. Fall hydrological conditions and subsequent winter storage processes impose a strong control on DOC concentrations the following year. We suggest that the presence or absence of concrete ground frost in the fen (determined by fall water table position) influences overwinter storage changes, controlling the effect that DOC‐poor snowmelt may have on pore water concentrations. However, an increase in SUVA254 was found 2 years postfire, indicating an increase in aromaticity. These results highlight the need for careful consideration of the local hydrogeologic setting and hydrological regime when predicting and analysing trends in DOC concentrations and quality.

Effects of Prescribed Burn on Nutrient and Dissolved Organic Matter Characteristics in Peatland Shallow Groundwater

“…DOC concentrations in shallow groundwater were similar (except for well B1) in the burned and unburned sections. The result of no change in DOC concentrations after the prescribed burn is similar to other studies that reported no clear effect on DOC concentrations as a result of wildfires [26,27]. While it is unclear what caused the DOC concentration to decrease at well B1, it could have been caused by wetter conditions at this location (Figure 4).…”

“…The changes in the optical parameters for wells in the burned section were inconsistent, suggesting that other factors such as hydrology and topography may have influenced the concentration and composition of DOM in shallow groundwater. For example, Davidson et al (2019) found the antecedent hydrological conditions to be the dominant control on DOC concentration along a burn severity gradient in Northern Alberta [26]. found that in a region affected by wildfires, microtopography influenced soil leachate DOM composition based on SUVA and HIX results; samples from hollows exhibited higher aromaticity and degree of humification of DOM [8].…”

The influence of burn severity on dissolved organic carbon concentrations across a stream network differs based on seasonal wetness conditions post-fire

“…Additionally, spatial studies in Sweden and Japan measured significant negative relationships between the percentage of groundwater and DOC concentrations (Egusa et al, 2021;Peralta-Tapia et al, 2015). The importance of groundwater on DOC concentrations after wildfire was also noted following in Alberta, CAN, where there was no measurable impact of wildfire on DOC concentrations in fens (Davidson et al, 2019) or boreal lakes (Olefeldt et al, 2013). Both attributed this lack of wildfire effect to the regulation of DOC concentrations due to the processes of selective adsorption, degradation, and desorption as water and DOC moves slowly downwards through mineral soils to groundwater tables (Kaiser and Kalbitz, 2012).…”

Response of dissolved organic carbon dynamics to salinity in a Constructed Fen Peatland in the Athabasca Oil Sands region

“…It is likely that multiple compounding factors contributed to the observed result. With many conflicting studies on the influence of water table on DOC dynamics and further debate on the mechanism (Clark et al, 2005(Clark et al, , 2012Davidson et al, 2019;Dieleman et al, 2016;Fenner et al, 2011;Khadka et al, 2015;Strack et al, 2015), this study suggests water table variability should be studied to better understand the relationship between DOC and water table.…”