Maria Strack

Response of vegetation and net ecosystem carbon dioxide exchange at different peatland microforms following water table drawdown

[1] Northern peatlands are significant stocks of terrestrial soil carbon, and it has been predicted that warmer temperatures and lower water tables resulting from climate change will convert these ecosystems into sources for atmospheric carbon dioxide (CO2). However, these predictions do not consider the potential for hydrologically induced ecological succession or the spatial variability of carbon accumulation rates between different microforms in peatlands. To address these issues, the vegetation community was described, and the rates of gross ecosystem photosynthesis (GEP), ecosystem respiration (Rtot) and net ecosystem CO2 exchange were determined along poor fen microtopographic gradients at a control site and at a site which experienced a water table drawdown of � 20 cm 8 years prior to the study (drained). Sampling plots within these sites were classified as microforms of hummocks, lawns, or hollows. The coverage of Sphagnum moss declined on drained hummocks, drained lawns were invaded by sedges, and hollows shifted from open water plots at the control site to Sphagnum-dominated plots with sparse vascular plant cover at the drained site. As a result, Rtot was significantly greater at the drained site at all microforms while maximum rates of GEP declined at drained hummocks and were enhanced at drained lawns and hollows compared to similar control microforms. These results suggest that predictions about the response of northern peatland carbon exchange to climate change must consider the interaction between ecology and hydrology and the differential responses of microforms related to their initial ecohydrological conditions.

Sedge Succession and Peatland Methane Dynamics: A Potential Feedback to Climate Change

Under the warmer climate, predicted for the future, northern peatlands are expected to become drier. This drying will lower the water table and likely result in reduced emissions of methane (CH4) from these ecosystems. However, the prediction of declining CH4 fluxes does not consider the potential effects of ecological succession, particularly the invasion of sedges into currently wet sites (open water pools, low lawns). The goal of this study was to characterize the relationship between the presence of sedges in peatlands and CH4 efflux under natural conditions and under a climate change simulation (drained peatland). Methane fluxes, gross ecosystem production, and dissolved pore water CH4 concentrations were measured and a vegetation survey was conducted in a natural and drained peatland near St. Charles-de-Bellechasse, Quebec, Canada, in the summer of 2003. Each peatland also had plots where the sedges had been removed by clipping. Sedges were larger, more dominant, and more productive at the drained peatland site. The natural peatland had higher CH4 fluxes than the drained peatland, indicating that drainage was a significant control on CH4 flux. Methane flux was higher from plots with sedges than from plots where sedges had been removed at the natural peatland site, whereas the opposite case was observed at the drained peatland site. These results suggest that CH4 flux was enhanced by sedges at the natural peatland site and attenuated by sedges at the drained peatland site. However, the attenuation of CH4 flux due to sedges at the drained site was reduced in wetter periods. This finding suggests that CH4 flux could be decreased in the event of climate warming due to the greater depth to the water table, and that sedges colonizing these areas could further attenuate CH4 fluxes during dry periods. However, during wet periods, the sedges may cause CH4 fluxes to be higher than is currently predicted for climate change scenarios.

Reducing the Carbon Footprint of Canadian Peat Extraction and Restoration

Abstract The Canadian horticultural peat industry generates carbon emissions through various methods of peat extraction, processing, and land-use changes. This study provides a carbon emissions analysis comparing the traditional vacuum harvest (VH) and block-cut (BC) extraction techniques to a new acrotelm transplant (AT) method that restores natural peatland function by preserving and replacing the surface layer vegetation as part of the extraction process. The relative global warming potential for each extraction method was determined by estimating carbon dioxide (CO2) and methane exchange for each phase of peat extraction, including emissions from land-use change and machinery fuel consumption. Preliminary findings, based on 1 y of measurements, indicate that the AT technique has the lowest annual carbon emissions compared to the VH and BC methods. Projected total carbon emissions from a 75-ha peatland after 50 y of extraction using the AT technique produced a sink of approximately 3300 t CO2 equivalents (CO2-e). This represents a marked reduction in total carbon emissions estimated for the VH (19 000 t CO2-e) and BC (29 000 t CO2-e) extraction techniques. This analysis suggests that the AT method reestablishes peat accumulation and peatland carbon storage function more effectively than the VH and BC methods, which are associated with delayed restoration efforts. Consequently, the AT technique has the potential to greatly reduce the carbon footprint of the Canadian horticultural peat industry.

Do peatland microforms move through time? Examining the developmental history of a patterned peatland using ground‐penetrating radar

Using ground-penetrating radar (GPR) to map subsurface patterns in peat physical properties, we investigated the developmental history of meso-scale surface patterning of microforms within a raised bog. Common offset GPR measurements were obtained along a 45-m transect, at frequencies ranging from 100 to 900 MHz. We found that low-frequency (central frequency = 240 MHz) showed a striking pattern of subsurface reflections that dip consistently in a northerly direction. The angle of these dipping reflectors is calculated using a semblance algorithm and was shown to average 3.9 degrees between a depth of 1.0 and 2.5 m. These dipping reflectors may indicate downslope migration of surface microforms during the development of the peatland. Based on the estimated angle and the rate of peat accumulation, the average rate of downslope propagation of these surface microforms is calculated at 9.8 mm per year. Further survey work is required to establish whether the downslope migration is common across the peatland.

Methane emissions dynamics from a constructed fen and reference sites in the Athabasca Oil Sands Region, Alberta

Recently, fen construction projects on surface mines in northeastern Alberta have been attempted as a reclamation strategy to reintroduce peatlands into the region where industry disturbs a substantial amount of wetland ecosystems. Knowledge of carbon cycling and greenhouse gas (GHG) dynamics, including methane (CH4), is one way to understand the biogeochemical function of newly constructed fen ecosystems. In this study we monitored CH4 emissions and CH4 pore water concentration, as well as ecological and soil chemistry controls on CH4 emissions and pore water concentration, from a constructed fen. The same variables were also monitored at two natural reference fens that had similar vascular vegetation to the constructed fen. Methane emissions were lower at the constructed fen compared to the reference poor fen, but similar to the reference saline fen. However, CH4 concentration in pore water at 0.2m and 0.7m depth was lower at the constructed fen than either of the natural reference sites. The supply rate of sulfur (all mobile forms) was the most dominant control on CH4 emission and CH4 pore water concentration. While low CH4 emissions may be beneficial for constructed fens from a GHG perspective, this condition indicates that peat and carbon accumulation at these reclaimed sites may ensue slowly. Therefore, a clear statement of goals is required to determine how CH4 dynamics from constructed fen ecosystems relate to the reclamation outcome.

Dissolved organic carbon in a constructed and natural fens in the Athabasca oil sands region, Alberta, Canada.

In the Athabasca oil sands region near Fort McMurray, Alberta, Canada, peatlands are disturbed extensively in order to recover bitumen below the surface. Hence, following oil sands mining, landscape reclamation is a part of the mine closure process in order to return functioning ecosystems, including peatlands, to the region. This study was conducted at a pilot fen reclamation project and three other diverse natural (poor, rich and saline) fens in the oil sands region during the growing seasons of 2013 and 2014, the first and second year post-construction. Ecosystem functioning of the constructed fen (CF) was evaluated with reference to natural fens based on pore water dissolved organic carbon (DOC) concentration and chemistry. Significant variation of DOC concentration among the reference fens was observed, varying from an average of 42.0mg/L at the rich fen (RF) to 70.8mg/L at the saline fen (SF). Dissolved organic carbon concentration at CF was significantly lower than at all reference fens, but increased significantly over the first two years. Seasonal variation of DOC concentration was also observed in each site with concentration increasing over the growing season. At CF, DOC was comprised of larger, more humic and complex aromatic compounds than reference fens in the first year post-construction based on its spectrophotometric properties; however, these differences were reduced in the second year. Initial DOC concentration and chemistry at CF was indicative of the source being largely the peat placed during fen construction. Changes in chemistry and increasing concentration of DOC in the second growing season likely resulted from increasing inputs from plants established on site. These results suggest that DOC concentration is likely to increase in future at CF as vascular plant productivity increases and in response to salinity sourced from tailing sand used to construct the catchment.

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

Groundwater level (GWL) and depth to water (DTW) are related metrics aimed at characterizing groundwater-table positions in peatlands, and two of the most common variables collected by researchers working in these ecosystems. While well-established field techniques exist for measuring GWL and DTW, they are generally difficult to scale. In this study, we present a novel workflow for mapping groundwater using orthophotography and photogrammetric point clouds acquired from unmanned aerial vehicles. Our approach takes advantage of the fact that pockets of surface water are normally abundant in peatlands, which we assume to be reflective of GWL in these porous, gently sloping environments. By first classifying surface water and then extracting a sample of water elevations, we can generate continuous models of GWL through interpolation. Estimates of DTW can then be obtained through additional efforts to characterize terrain. We demonstrate our methodology across a complex, 61-ha treed bog in northern Alberta, Canada. An independent accuracy assessment using 31 temporally coincident water-well measurements revealed accuracies (root mean square error) in the 20-cm range, though errors were concentrated in small upland pockets in the study area, and areas of dense tree covers. Model estimates in the open peatland areas were considerably better.

Mineral nitrogen and phosphorus pools affected by water table lowering and warming in a boreal forested peatland

Changes in atmospheric temperature and lowering in water-table (WT) are expected to affect peatland nutrient dynamics. To understand the response of peatland nitrogen (N) and phosphorus (P) dynamics to warming and drainage in a continental wooded-bog of hummock – hollow microtopography, we compared three sites: 1) control, 2) recently drained (2-3 years; experimental), and 3) older drained (12-13 years; drained), during 2013. The WT was lowered at experimental and drained sites to 74 cm and 120 cm, respectively, while a warming of ~1 °C was created at one half of the microforms using open-top chambers. Responses of peat total-inorganic-nitrogen [TIN = nitrate nitrogen (NO3--N) + ammonium nitrogen (NH4+-N)] and phosphate-P [PO43--P] pools and, vegetation C:N ratio, δ13C and δ15N to the experimental treatments were investigated across sites/microforms and over time. Peat TIN available and extractable pools increased with deepening of WT and over time, and were greater at hummocks relative to hollows. In contrast, the PO4 pools increased with short-term drainage but reverted to very close to their original (control) nutrient values in the longer-term. The WT and warming driven change in the peat TIN pool was strongly reflected in the vascular vegetation C:N ratio and, shrub δ13C and δ15N, while moss nutrient dynamics did not vary between sites. Therefore, we suggest that atmospheric warming combined with WT deepening can increase availability of mineral N and P, which then can be reflected in vascular vegetation and hence modify the productivity and ecosystem functioning of the northern mid-latitude continental wooded bogs in the long-term.

Access roads impact enzyme activities in boreal forested peatlands

We investigated the impacts of resource access roads on soil enzyme activities in contrasting forested boreal peatlands (bog and fen). In August 2016, a total of 72 peat samples were collected from twelve 20 m long transects perpendicular to access roads, with a further six samples collected from undisturbed reference areas. Sampling locations represent a range in three variables associated with roads: 1) side of the road (upstream/downstream), 2) distance to a culvert (longitudinal; <2 and >20 m), and 3) distance from the road (lateral; 2, 6, and 20 m). Phenol oxidase and hydrolase (glucosidase, sulfatase, xylosidase, glucosaminidase, and phosphatase) enzyme activities were determined for each sample, in addition to water table depth, phenolic concentration, pH, and peat temperature. The average hydrolase activities in the fen were ~four times higher than in the bog. At the bog, the water table depth, phenolic concentration, pH and the activities of phenol oxidase, sulfatase, glucosidase, xylosidase and glucosaminidase were all significantly influenced by one or more road associated factors. The highest enzyme activities in the bog occurred on the downstream side of the road at plots located far from the culvert. In contrast, the flow of water in the fen was not perpendicular to the road. Consequently, no significant variations in water table depth, phenolic concentration, pH or enzyme activity were found with respect to road associated factors. Results indicate that road crossings in boreal peatlands can indirectly alter enzyme activities, likely as part of a causal chain following changes to hydrology and redox conditions. Two of six investigated enzymes had significantly higher activities in the road disturbed areas compared to undisturbed areas, suggesting ultimately that roads may enhance organic matter decomposition rates. However, adequate hydrologic connections through culverts and road construction parallel to the water flow can minimize the road-induced impacts.