Impact of winter roads on boreal peatland carbon exchange

Abstract

Across Canada's boreal forest, linear disturbances, including cutlines such as seismic lines and roads, crisscross the landscape to facilitate resource exploration and extraction; many of these linear disturbances cross peatland ecosystems. Changes in tree canopy cover and the compression of the peat by heavy equipment alter local thermal, hydrological, and ecological conditions, likely changing carbon exchange on the disturbance, and possibly in the adjacent peatland. We measured bulk density, water table, soil temperature, plant cover, and CO and CH flux along triplicate transects crossing a winter road through a wooded fen near Peace River, Alberta, Canada. Sample plots were located 1, 5, and 10 m from the road on both sides with an additional three plots on the road. Productivity of the overstory trees, when present, was also determined. The winter road had higher bulk density, shallower water table, higher graminoid cover, and thawed earlier than the adjacent peatland. Tree productivity and CO flux varied between the plots, and there was no clear pattern in relation to distance from the road. The plots on the winter road acted as a greater CO sink and greater CH source compared to the adjacent peatland with plots on the winter road emitting on average (standard error) 479 (138) compared to 41 (10) mg CH m day in the adjacent peatland. Considering both gases, global warming potential increased from 70 to 250 g CO e m year in the undisturbed area to 2100 g CO e m year on the winter road. Although carbon fluxes on any given cutline through peatland will vary depending on level of compaction, line width and vegetation community shifts, the large number of linear disturbances in Canada's boreal forest and slow recovery on peatland ecosites suggest they could represent an important anthropogenic greenhouse gas source.

A New Method to Map Groundwater Table in Peatlands Using Unmanned Aerial Vehicles

“…Deep DTW also increases the susceptibility of peatlands to wildfire [42]. The impact of resource development across the boreal has also been shown to alter DTW in the range of 5 cm to > 1 m, with clear impacts on ecosystem vegetation community and carbon exchange [43][44][45]. Across the majority of the open peatland areas of the study site, absolute error in DTW models was less than 20 cm.…”

Road Crossings Increase Methane Emissions From Adjacent Peatland

“…However, only peat temperature 5 cm below the surface was used for this study (Strack et al, 2018). Peat temperatures at the depth of 2, 5, 10, 15, 20, 25, and 30 cm below the surface were also recorded using thermocouple temperature probes, and WT was measured from the well beside each collar.…”

“…After that, the annual CH 4 emissions were estimated by adding 15% of the growing season totals to the interpolated value (Saarnio et al, 2007;Strack et al, 2018) since we did not measure CH 4 fluxes representing early spring, fall or, winter seasons. Also, to calculate total road-related CH 4 flux rates to areas up to 20 m around the road (both upstream and downstream) for each kilometer of the road, in 2016 and 2017, respectively, we calculated the weighted arithmetic mean of interpolated daily CH 4 fluxes at 2, 6, and 20-m plots (equation 2).…”

“…Methane flux from a peatland depends on environmental factors such as water table position (WT), peat temperature, presence or absence of aerenchymatous plant species and vegetation cover, soil moisture content, pH, availability of substrate, and atmospheric nitrogen and sulfur deposition (Bergman, 2000;Chanton et al, 1995;Huttunen et al, 2003;Moore et al, 2011;Turetsky et al, 2008). Therefore, CH 4 emissions from pristine peatlands vary between and within sites in response to variations in local hydrological, biological, and geochemical properties (Juszczak et al, 2013;Mahmood & Strack, 2011;Munir & Strack, 2014;Potter et al, 2001;Strack et al, 2018). For instance, the presence of more labile carbon substrates generally results in higher CH 4 emissions from moderate to rich fens compared to bogs that have less labile forms of organic matter derived from Sphagnum spp.…”

“…Although resource access roads occur in many areas of the boreal forest, they are particularly dense in the province of Alberta, where petroleum deposits are abundant and are being actively extracted (ABMI, 2018). The resulting hydrological perturbation in the peatland surrounding the access road crossing may lead to altered plant community, peat temperature, substrate availability, microbial activity, and soil biogeochemistry (Bocking et., 2017;Campbell & Bergeron, 2012;Plach et al, 2017;Saraswati et al, 2019;Strack et al, 2018) that could ultimately impact CH 4 emissions from peatlands. This compresses the peat underneath the road, acting as a dam and limiting the hydrological connection between fragmented parts of the peatland (Partington & Clayton, 2012;Saraswati et al, 2019).…”