Peatlands of the Athabasca Oil Sands Region (AOSR) within Canada’s Western Boreal Plains are under stress from oil and gas development and associated infrastructure such as road construction. Peatlands are important reservoirs of global terrestrial carbon (C), resulting from organic matter accumulation primarily due to slow soil decomposition under saturated conditions. In the Western Boreal Plains of Alberta, up to 50% of the terrain is covered by peatlands which represent a significant store of C for Canada.
Increasing pressure from oil and gas industries, as well as expansion of timber harvesting on the Western Boreal Plains, brings extensive road construction to the region, much of which bisects peatlands with the potential to impede drainage. Nitrogen (N) and phosphorus (P) are fundamental to vegetation net primary productivity (C fixation) and microbial function, and thus, important to overall peatland C cycling. It is unclear how road development impacts peatland hydrology and nutrient cycling and hence influences vegetation productivity and vegetation/soil respiration of carbon dioxide (CO2). Protection of peatland ecohydrological stability requires an improved understanding of water movement, N and P transformations, and CO2 terrestrial‐atmosphere exchange and how they respond to road disturbances. If critical thresholds for peatland water and nutrient availability can be identified, these may assist in predicting the impacts of industrial expansion on the fate of peatland C storage functioning and guide reclamation strategies across the AOSR.
Although much work on peatland biogeochemical cycling of N, P, and C has evaluated the effects of water table drawdown both in situ and under controlled laboratory settings, minimal work evaluating anthropogenic drainage on CO2 exchange and nutrient dynamics exists for peatlands. Moreover, C and nutrients are often not studied together. Therefore, evaluating the potential for roads constructed through peatlands to modify water movement and influence decomposition, nutrient mineralization, and productivity requires careful consideration of the dynamic interactions between water supply, temperature and vegetation over the growing season. As such, the objectives of this study were to examine how a linear disturbance (semi‐permanent road) may influence peatland. More specifically, how this affects water supply and soil properties (water table position, soil moisture, C : N, bulk density, temperature), and how plant available N and P (soil nutrient pools, supply, and net mineralization rates) influence vegetation structure (biomass and species type) and CO2 exchange (gross ecosystem productivity, total ecosystem respiration, and net ecosystem exchange) in the AOSR of Alberta during the growing season.
Methodology
Research was conducted between May and September, 2012 in a poor fen located 50 km south of Fort McMurray, Alberta (Figure 1). In 2001, a semi‐permanent road constructed of clay fill reinforced with geotextile layers was developed across 450 m of the study site. The road bisected the site, running perpendicular to the natural flow of water, which flows south to northwest (Figure 2). As a result, the study site was divided into two main sections, the south side of the road (up‐flow and U‐side) and the north side of the road (down‐flow and D‐side).
Six study plots were located on each side of the road, each equipped with groundwater monitoring wells and semi‐permanent collars for chamber measurements of CO2 exchange. Data was also collected through the use of data loggers, rain gauges, probes, and from paired peat cores collected from each study plot.
Peat nutrient (N and P) supply, net mineralization, groundwater concentrations, and peatland‐atmosphere CO2 exchange rates were quantified over one growing season and statistically analyzed.
Figure 1. Map of the study site (labelled JACOS) and its proximity to Fort McMurray, Alberta.
Figure 2. Satellite image of study site with road.
Outcomes
The study site exists in a moisture deficit region and thus peatlands here exist in a state of hydrologic risk. The semi‐permanent road impeded groundwater movement at the site, whereby a water table drawdown was observed on the down‐flow side. However, the overall seasonal and spatial differences in water table position were minimal with respect to the road, likely due to the unusually wet 2012 season. As a result, peat moisture conditions did not show strong spatial or temporal differences to impact nutrient mineralization rates or total ecosystem respiration and gross ecosystem productivity, as these were instead largely driven by factors such as temperature. No clear impacts of the road on nutrient dynamics were observed, but subtle differences in productivity and respiration resulted in significantly lower net CO2 sequestration on the down‐flow side of the road.
Vegetation composition differed between sides of the road and likely indicates longer‐term moisture differences at this site. As such, predictions of future CO2 exchange at disturbed peatlands of the Western Boreal Plains should consider the effects of ecological succession along with water supply‐ temperature‐CO2 exchange relationships. In addition, subtle trends in nutrient supply were observed, whereby elevated rates of productivity and respiration coincided with a seasonal change in the relative supplies of N and P (increased N : P ratios), suggesting the relative availability of N versus P may also be related to CO2 exchange at the site.
Conclusions
An improved understanding of nutrient cycling and atmospheric carbon dioxide exchange interactions in peatlands can assist in recommending best management practices to industry to minimize the ecohydrological disturbance footprint of road features.
Collectively, our findings demonstrate the need to capture interactions between hydrology, ecology and nutrient biogeochemistry when evaluating peatland carbon cycling response to road disturbances across this region. Further examination into the cycling and availability of P in boreal peatlands is needed, including plant foliage N : P stoichiometric balances within Western Boreal Plains peatlands as well as potential geochemical links to P cycling within the soil‐groundwater system over a longer period of time.
Plach, J.M., M.E. Wood, M. L. Macrae, T.J. Osko, and R.M. Petrone (2017). Effect of a semi‐permanent road on N, P, and CO2 dynamics in a poor fen on the Western Boreal Plain, Canada. Ecohydrology. 10:e1874.
Contact: Richard Petrone, Department of Geography and Environmental Management; Janina Plach, Department of Geography and Environmental Management; Merrin Macrae, Department of Geography and Environmental Management
For more information about the Water Institute, contact Amy Geddes.
