Treed Fen Research Articles

The Integration of Multi-Source Remotely Sensed Data with Hierarchically Based Classification Approaches in Support of the Classification of Wetlands

Methodologies were developed to classify wetlands (Open Bog, Treed Bog, Open Fen, Treed Fen, and Swamps) from remotely sensed data using advanced classification algorithms through two hierarchical approaches. The data utilized included multispectral optical and thermal data (Landsat-5, and Landsat-8), radar imagery (Sentinel-1), and a digital elevation model. Goals were to determine the best way to combine imagery to classify wetlands through hierarchically based classification approaches to produce more accurate and efficient maps compared to standard classification. Algorithms used were Random Forest (RF), and Naïve Bayes. A hierarchically based RF classification methodology produced the most accurate classification result (91.94%). The hierarchically based approaches also improved classification accuracies for low-quality data, as defined through feature analysis, when compared to a nonhierarchical classifier. The hierarchical approaches also produced a significant increase in classification accuracy for the Naïve Bayes classifier versus the standard approach (∼12% increase) while not significantly increasing computation time – comparable in accuracy to the RF tests for around 20% the computational effort. Preselection of spectral bands, polarizations and other input parameters (Normalized Difference Vegetation Index, Normalized Difference Water Index, albedo, slope, etc.) using log-normal or RF variable importance analysis was very effective at identifying low-quality features and features which were of higher quality.

Deeper burning in a boreal fen peatland 1‐year post‐wildfire accelerates recovery trajectory of carbon dioxide uptake

AbstractPeatlands contain a globally significant store (30%) of soil carbon (C). Within the Canadian Western Boreal Plains, where peatlands are a dominant feature, the climate is becoming warmer and drier, coupled with an increase in forest fire incidence. The response of peatlands to forest fire is likely to be a key determinant in the future of C storage of Boreal peatlands. This study examined the impacts of fire on key environmental controls on CO2 fluxes at the plot‐scale (using static chambers) between burned and unburned understory vegetation throughout the growing season of 2017 in a treed fen impacted by the Horse River wildfire (2016) in Fort McMurray, Alberta, Canada. Both gross ecosystem productivity (GEP) and total respiration (Rtot) were less at burned plots compared with unburned. Temporal patterns varied between the plots, where both component of CO2 fluxes at the unburned plots were largest in June, whereas at the burned plots, CO2 fluxes peaked in the late growing season. GEP and net ecosystem exchange (NEE) showed a positive relationship with depth of burn, with the deepest burned areas showing significantly greater CO2 uptake, coinciding with both increased bioavailable phosphorus and greater moss recolonization. At the unburned plots, soil temperature was a dominant control on CO2 fluxes. This work demonstrates the importance of the depth of burn to post‐fire carbon fluxes and how a knowledge of burn severity and depth can inform understanding of the recovery trajectory of northern peatlands following fire disturbance.

Seismic Line Disturbance Alters Soil Physical and Chemical Properties Across Boreal Forest and Peatland Soils

Industrial activities for resource extraction have led to a network of seismic lines across Canada’s boreal regions where peatlands often make up over 50% of the landscape. These clearings can have a significant influence on ecosystem functioning through vegetation removal, flattening of microtopography, altering hydrological pathways and impacting biogeochemical processes. Recently, there has been a concerted effort to restore seismic lines to bring back the localized microtopography and encourage ecosystem recovery. A common restoration approach on seismic lines is mounding, which involves using machinery to recreate natural microtopography. Research is scarce on the impact on soil properties following both these disturbances and subsequent restoration on organic soils. The objectives of this study were to 1) identify differences in soil physical and chemical characteristics between areas disturbed by seismic lines and adjacent natural areas, and 2) to determine changes to soil physical and chemical properties following the mounding restoration technique. Research was undertaken at two contrasting boreal ecosites (a poor mesic and a treed fen) near Fort McMurray, Alberta, Canada. In July 2018, we collected soil samples at 34 seismic line locations, both on the line and 20 m into the adjacent undisturbed area. Samples were analyzed for bulk density, volumetric water content (VWC), organic matter content (OM), C:N ratios and δ13C/δ15N isotope analysis. Seismic line disturbances had a significant impact on soil properties, with increased bulk density and VWC on the line at both ecosites. We found an almost 40% reduction in OM on the line compared to natural areas at the poor mesic site, implying changes to carbon cycling, increased mineralization rates and carbon loss from the system. There was also δ13C/δ15N enrichment and narrower C:N ratios on the line, indicating increased decomposition. We found evidence of increased decomposition on the mounds created after restoration at the treed fen. Our results highlight a trade-off between restoration activities that may encourage recovery but also cause increased carbon losses from the system. This research is a first step in gaining a better understanding of these impacts in light of current restoration practices to ensure best management practices for improving ecosystem functioning.

Methane emissions from fens in Alberta’s boreal region: reference data for functional evaluation of restoration outcomes

The aim of the study was to document methane (CH4) dynamics from fen ecosystems in the Athabasca Oil Sands Region (AOSR) in northern Alberta to create a reference database for evaluation of peatland restoration and reclamation projects in the region. The study included three types of fens commonly occurring in this region: poor fen (open and treed), moderately-rich treed fen, and open saline fen (SF). We quantified CH4 fluxes, pore water concentration (PW[CH4]), and production potential together with ecohydrological variables that may influence CH4 dynamics over four growing seasons. Mean (standard deviation) fluxes for open and treed poor fen [99.8 (269.7) and 68.3 (118.8) mg CH4 m−2 day−1, respectively] were higher than for treed rich [32.8 (63.7) mg CH4 m−2 day−1] and open SFs [34.6 (91.3) mg CH4 m−2 day−1]. The total growing season CH4 emissions from these fens ranged between 3.7 and 11.3 g CH4 m−2. Methane production potential varied from 0.1 (0.1) µmol CH4 g peat−1 day−1 at the SF to 4.6 (0.8) µmol CH4 g peat−1 day−1 at the treed rich fen. The variability of CH4 fluxes and pore water concentration between study sites and years was mostly controlled water table (WT) and soil temperature indicating that these variables should be used to assess the expected CH4 flux in peatland reclamation projects. Large inter-annual variability in CH4 flux illustrates the importance of multi-year records for data used in functional evaluation of restoration outcomes.

The Integration of Multi-source Remotely-Sensed Data in Support of the Classification of Wetlands

Wetlands play a key role in regional and global environments, and are critically linked to major issues such as climate change, wildlife habitat, biodiversity, water quality protection, and global carbon and methane cycles. Remotely-sensed imagery provides a means to detect and monitor wetlands on large scales and with regular frequency. In this project, methodologies were developed to classify wetlands (Open Bog, Treed Bog, Open Fen, Treed Fen, and Swamps) from multi-source remotely sensed data using advanced classification algorithms. The data utilized included multispectral optical and thermal data (Landsat-5) and Radar imagery from RADARSAT-2 and Sentinel-1. The goals were to determine the best way to combine the aforementioned imagery to classify wetlands, and determine the most significant image features. Classification algorithms investigated in this study were Naive Bayes, K-Nearest Neighbor (K-NN), Support Vector Machine (SVM), and Random Forest (RF). Based on the test results in the study area in Northern Ontario, Canada (49°31′.34N, 80°43′37.04W), a RF based classification methodology produced the most accurate classification result (87.51%). SVM, in some cases, produced results of comparable or better accuracy than RF. Our work also showed that the use of surface temperature (an untraditional feature choice) could aid in the classification process if the image is from an abnormally warm spring. This study found that wetlands were best classified using the NDVI (Normalized Difference Vegetative Index) calculated from optical imagery obtained in the spring months, radar backscatter coefficients, surface temperature, and ancillary data such as surface slope, computed through either an RF or SVM classifier. It was also found that preselection of features using Log-normal or RF variable importance analysis was an effective way of identifying low quality features and to a lesser extent features which were of higher quality.

The effect of long-term drying associated with experimental drainage and road construction on vegetation composition and productivity in boreal fens

Land-use and climate change are expected to cause drying of vegetation and surface soils in continental boreal peatlands. We examined the effects of multi-decadal drying and drainage on plant community structure and productivity in four fens located in Alberta, Canada. Long-term drying resulted in a two to fourfold increase in total biomass in three of the four fen sites, with a similar large increase in NPP in Treed Fen 1. The treed poor fens consistently had decreased moss cover and productivity with drainage. Across all sites, changes in understory community composition were related to the change in water table position as well as overstory canopy development that occurred post-drainage. Overall, drainage induced a shift toward a drier peatland regime, favoring increased canopy and vascular plant density at the expense of ground-layer mosses or the understory. Within the ground layer communities, drainage favored dry-adapted hummock moss and lichen species over those wet-adapted but dessication-prone species typical of low-lying lawns and hollows. Alteration of fen vegetation due to ecosystem drying will not only influence carbon sequestration but also will increase the vulnerability of peatlands to wildfire, increasing the risk of further ecosystem degradation and possible loss of resilience.

How climate and vegetation type influence evapotranspiration and water use efficiency in Canadian forest, peatland and grassland ecosystems

The effects of climatic factors and vegetation type on evapotranspiration (E) and water use efficiency (WUE) were analyzed using tower-based eddy-covariance (EC) data for nine mature forest sites, two peatland sites and one grassland site across an east–west continental-scale transect in Canada during the period 2003–2006. The seasonal pattern of E was closely linked to growing-season length and rainfall distribution. Although annual precipitation (P) during the observation period was highly variable among sites (250−1450mm), minimum annual E was not less than 200mm and was limited to 400−500mm where annual P exceeded 700mm. Site-specific interannual variability in E could be explained by either changes in total P or variations in solar irradiance. A highly positive linear correlation was found between monthly mean values of E and net radiation (Rn) at the grassland site (AB-GRL), the two peatland sites (AB-WPL and ON-EPL), and only one of the forest sites (coastal Douglas-fir, BC-DF49) whereas a hysteretic relationship at the other forest sites indicated that E lagged behind the typical seasonal progression of Rn. Results of a cross-correlation analysis between daily (24-h) E and Rn revealed that site-specific lag times were between 10 and 40 days depending on the lag of vapour pressure deficit (D) behind Rn and the decoupling coefficient, Ω. There was significant seasonal variation in daytime mean dry-foliage Priestley–Taylor α with maxima occurring in the growing season at all sites except BC-DF49 where it was relatively constant (∼0.55) throughout all years. Annual means of daytime dry-foliage α mostly ranging between 0.5 and 0.7 implied stomatal limitation to transpiration. Increasing D significantly decreased canopy conductance (gc) at the forest sites but had little effect at the peatland and grassland sites, while variation in soil water content caused only minor changes in gc. At all sites, a strong linear correlation between monthly mean values of gross primary production (GPP) and E resulted in water use efficiency being relatively constant. While at most sites, WUE was in the range of 2.6–3.6gCkg−1 H2O, the BC-DF49 site had the highest WUE of the twelve sites with values near 6.0gCkg−1 H2O. Of the two peatland sites, AB-WPL, a western treed fen, had a significantly higher WUE (∼3.0gCkg−1 H2O) than ON-EPL, an eastern ombrotrophic bog (∼1.8gCkg−1 H2O), which was related to peatland productivity and plant functional type.

Peatland dynamics in a complex landscape: Development of a fen-bog complex in the Sporadic Discontinuous Permafrost zone of northern Alberta, Canada

Bauer, I. E. & Vitt, D. H. 2011: Peatland dynamics in a complex landscape: Development of a fen-bog complex in the Sporadic Discontinuous Permafrost zone of northern Alberta, Canada. Boreas, 10.1111/j.1502-3885.2011.00210.x. ISSN 0300-9483. The development of a peatland complex in the Sporadic Discontinuous Permafrost zone of northwestern Alberta, Canada was reconstructed using a series of dated profiles. Peat-forming communities first established c. 10 230 cal. a BP, and by 8000 cal. a BP the site supported monocot fens or marshes in several isolated topographic depressions. Most of the current peatland area initiated between c. 8000 and 4000 cal. a BP, and involved the replacement of upland habitats by shrubby or treed fen and, in some areas, the establishment of Sphagnum on mineral terrain. Ombrotrophic hummock communities had established by c. 7000 cal. a BP, and permafrost was present at 6800 cal. a BP in at least some peat plateau areas. Macrofossil-based reconstructions show considerable local diversity in vegetation succession and permafrost dynamics, with cyclic collapse and aggradation in at least one profile and relative stability in others. Lichen-rich peat is rare in deep-peat plateau cores, and where charcoal was recovered, fire effects on vegetation trajectories varied between cores. Organic matter accumulation was high in the early Holocene and declined after permafrost formation, with low rates especially over the past 4000 years. The site was burned in a wildfire in 1971, and by 1998 permafrost had disappeared from almost all peat plateau areas. In this part of the discontinuous permafrost zone, peat plateaus are likely to be unsustainable under a warming climate. The hydrology and carbon dynamics of former plateau areas following large-scale permafrost degradation require further investigation.

Stimulation of both photosynthesis and respiration in response to warmer and drier conditions in a boreal peatland ecosystem

Peatland ecosystems have been consistent carbon (C) sinks for millennia, but it has been predicted that exposure to warmer temperatures and drier conditions associated with climate change will shift the balance between ecosystem photosynthesis and respiration providing a positive feedback to atmospheric CO2 concentration. Our main objective was to determine the sensitivity of ecosystem photosynthesis, respiration and net ecosystem production (NEP) measured by eddy covariance, to variation in temperature and water table depth associated with interannual shifts in weather during 2004–2009. Our study was conducted in a moderately rich treed fen, the most abundant peatland type in western Canada, in a region (northern Alberta) where peatland ecosystems are a significant landscape component. During the study, the average growing season (May–October) water depth declined approximately 38 cm, and temperature [expressed as cumulative growing degree days (GDD, March–October)] varied approximately 370 GDD. Contrary to previous predictions, both ecosystem photosynthesis and respiration showed similar increases in response to warmer and drier conditions. The ecosystem remained a strong net sink for CO2 with an average NEP (± SD) of 189 ± 47 g C m−2 yr−1. The current net CO2 uptake rates were much higher than C accumulation in peat determined from analyses of the relationship between peat age and cumulative C stock. The balance between C addition to, and total loss from, the top 0–30 cm depth (peat age range 0–70 years) of shallow peat cores averaged 43 ± 12 g C m−2 yr−1. The apparent long-term average rate of net C accumulation in basal peat samples was 19–24 g C m−2 yr−1. The difference between current rates of net C uptake and historical rates of peat accumulation is likely a result of vegetation succession and recent increases in tree establishment and productivity.

Warmer and drier conditions stimulate respiration more than photosynthesis in a boreal peatland ecosystem: Analysis of automatic chambers and eddy covariance measurements

Continuous half-hourly net CO(2) exchange measurements were made using nine automatic chambers in a treed fen in northern Alberta, Canada from June-October in 2005 and from May-October in 2006. The 2006 growing season was warmer and drier than in 2005. The average chamber respiration rates normalized to 10 degrees C were much higher in 2006 than in 2005, while calculations of the temperature sensitivity (Q(10)) values were similar in the two years. Daytime average respiration values were lower than the corresponding, temperature-corrected respiration rates calculated from night-time chamber measurements. From June to September, the season-integrated estimates of chamber photosynthesis and respiration were 384 and 590 g C m(-2), respectively in 2006, an increase of 100 and 203 g C m(-2) over the corresponding values in 2005. The season-integrated photosynthesis and respiration rates obtained using the eddy covariance technique, which included trees and a tall shrub not present in the chambers, were 720 and 513 g C m(-2), respectively, in 2006, an increase of 50 and 125 g C m(-2) over the corresponding values in 2005. While both photosynthesis and respiration rates were higher in the warmer and drier conditions of 2006, the increase in respiration was more than twice the increase in photosynthesis.

Environmental control of net ecosystem CO 2 exchange in a treed, moderately rich fen in northern Alberta

Peatlands cover about 21% of the landscape and contain about 80% of the soil carbon stock in western Canada. However, the current rates of carbon accumulation and the environmental controls on ecosystem photosynthesis and respiration in peatland ecosystems are poorly understood. As part of Fluxnet-Canada, we continuously measured net ecosystem carbon dioxide exchange (NEE) using the eddy covariance technique in a treed fen dominated by stunted Picea mariana and Larix laricina trees during August 2003–December 2004. The total carbon stock in the ecosystem was approximately 51,000 g C m −2, with only 540 g C m −2 contributed by live above ground vegetation. The NEE measurements were used to parameterize simple physiological models to assess temporal variation in maximum ecosystem photosynthesis ( A max) and ecosystem respiration rate at 10 °C ( R 10). During mid-summer the ecosystem had a relatively high A max (approx. 30 μmol m −2 s −1) with relatively low R 10 (approx. 4 μmol m −2 s −1). The peak mid-day NEE uptake rate during July and August was 10 μmol m −2 s −1. The ecosystem showed large seasonal variation in photosynthetic and respiratory activity that was correlated with shifts in temperature, with both spring increases and fall decreases in A max well predicted by the mean daily air temperature averaged over the preceding 21 days. Leaf-level gas exchange and spectral reflectance measurements also suggested that seasonal changes in photosynthetic activity were primarily controlled by shifts in temperature. Ecosystem respiration was strongly correlated with changes in ecosystem photosynthesis during the growing season, suggesting important links between plant activity and mycorrhizae and microbial activity in the shallow layers of the peat. Only very low rates of respiration were observed during the winter months. During 2004, the peatland recorded a net annual gain of 144 g C m −2 year −1, the result of a difference between gross photosynthesis of 713 and total ecosystem respiration of 569 g C m −2 year −1.

Late-summer carbon fluxes from Canadian forests and peatlands along an east–west continental transect

Net ecosystem productivity (NEP) during August 2003 was measured by using eddy covariance above 17 forest and 3 peatland sites along an east–west continental-scale transect in Canada. Measured sites included recently disturbed stands, young forest stands, intermediate-aged conifer stands, mature deciduous stands, mature conifer stands, fens, and an open shrub bog. Diurnal courses of NEP showed strong coherence within the different ecosystem categories. Recently disturbed sites showed the weakest diurnal cycle; and intermediate-aged conifers, the strongest. The western treed fen had a more pronounced diurnal pattern than the eastern shrub bog or the Saskatchewan patterned fen. All but three sites were clearly afternoon C sinks. Ecosystem respiration was highest for the young fire sites. The intermediate-aged conifer sites had the highest maximum NEP (NEPmax) and gross ecosystem productivity (GEPmax), attaining rates that would be consistent with the presence of a strong terrestrial C sink in regions where these types of forest are common. These results support the idea that large-scale C cycle modeling activities would benefit from information on the age-class distribution and disturbance types within larger grid cells. Light use efficiency followed a pattern similar to that of NEPmax and GEPmax. Four of the five recently disturbed sites and all three of the peatland sites had low water use efficiencies.

Stand structure and vegetation dynamics of a subalpine wooded fen in Rocky Mountain National Park, Colorado

Abstract. The tree population size structure and relationship between tree diameter and age were examined in a subalpine fen and surrounding Picea‐Abies forest in northern Colorado. The fen grades from a sedge fen, through an ecotone, to a treed fen. Tree growth rate varies across the vegetational gradient, with the sedge fen having the slowest growth, and the upland forest having the fastest growth. Differences in growth rate are related to the average size of peat hummocks, with areas containing tall hummocks exhibiting the highest tree growth rates. Size structures display the characteristic reverse‐J distribution generally indicative of stable populations, but forest vegetation is expanding into the open regions of the fen, and within the treed fen an increase in Abies lasiocarpa is occurring. These changes are primarily attributed to a positive feedback situation wherein the fen's surface is built up by peat accumulation. Distinct hummocks form first on the open fen but then coalesce to form raised peat islands in the treed fen. This new substrate provides habitat with a comparatively low water table and allows the growth of mesophytic forest vegetation. A pathway for this vegetational development is proposed.

Methane flux from drained northern peatlands: Effect of a persistent water table lowering on flux

Measurements of CH4 flux from drained and undrained sites in three northern Ontario peatlands (a treed fen, a forested bog, and a treed bog) were made from the beginning of May to the end of October 1991. In the drained portions, the water table had been lowered between 0.1 and 0.5 m, compared to the water table of the undrained portion of the peatlands. The mean seasonal CH4 flux from the undrained portions of three peatlands was small, ranging from 0 to 8 mg m−2d−1, but similar to the CH4 flux from other treed and forested northern peatlands. The mean seasonal CH4 flux from the drained portion of the peatlands was either near zero or slightly negative (i.e.,uptake): fluxes ranged from 0.1 to −0.4 mg m−2 d−1. Profiles of CH4 in the air‐filled pores in the unsaturated zone, and the water‐filled pores of the saturated zone of the peat at the undrained sites, showed that all the CH4 produced at depth was consumed within 0.2 m of the water table and that atmospheric CH4 was consumed in the upper 0.15 m of the peatland. On the basis of laboratory incubations of peat slurries to determine CH4 production and consumption potentials, the lowering of the water table eliminated the near‐surface zone of CH4 production that existed in the undrained peatland. However, drainage did not alter significantly the potential for CH4 oxidation between the water table and peatland surface but increased the thickness of the layer over which CH4 oxidation could take place. These changes occurred with a drop in the mean summer water table of only 0.1 m (from −0.2 to −0.3 m) suggesting that only a small negative change in soil moisture would be required to significantly reduce CH4 flux from northern peatlands.

Some hydrological effects of peatland drainage in Alberta's boreal forest

Ninety hectares in a treed fen in north central Alberta were drained to improve growth of stagnant black spruce (Piceamariana (Mill.) B.S.P.) and tamarack (Larixlaricina (Du Roi) K. Koch) stands. Installation of 30-, 40-, 50-, and 60-m ditch spacings resulted in a lowering of the average water table by 79, 66, 56, and 73 cm, respectively. The results and the groundwater level criteria used (drainage norm, 40 cm; flood duration limit, 14 days) indicated that the 50-m ditch spacing was hydrologically the most appropriate one for this area. Given the relatively high hydraulic conductivity of the area, it is believed the 30-m spacing was too narrow and resulted in an excessively low average water table. The 60-m spacing was also overeffective, but in this case, overeffectiveness was attributed more to "edge effects" i.e., to site factors such as the proximity to uplands and the small size of upstream source areas, than to the distance between ditches. The results illustrate the importance, for ditch network design purposes, of taking into account hydrologic conditions both within and well beyond the boundaries of an area proposed to be drained. Peat subsidence after drainage appeared to be related to the average drop in water table level and amounted to about 5 cm•a−1.

Impact of right-of-way construction on vegetation in the Red Lake Peatland, northern Minnesota

During the winters of 1978–79 and 1979–80, a 500-kV electrical transmission right-of-way (r-o-w) was constructed across the Red Lake Peatland in northwestern Minnesota, the largest contiguous peatland in the lower 48 states of the USA. Immediately before, and for two years following construction, vascular vegetation was monitored within the r-o-w and in undisturbed control areas. Monitoring was carried out in five vegetation types: a thicket swamp, a low shrub bog, a graminoid fen, a treed bog, and a treed fen. Evaluation of construction impacts was based on vegetation structure, irrespective of species composition, and on community composition (species data for low shrubs and herbs). Construction eliminated trees from the r-o-w. Vegetation structure, excluding trees, was markedly altered in the two bog types and the treed fen type in the first postconstruction growing season. By the second season, measurable recovery to control levels had begun. The sample plots were placed into a previously developed vegetation classification system for the Red Lake Peatland, on the basis of herbs and low shrubs. There was a shift in composition in the low shrub bog and in the treed vegetation types following construction. Results of both methods of data analysis were consistent. Major vegetation changes following construction occurred in the low shrub bog and treed types. The open, low-stature fen types showed almost no changes related to construction. Even in the affected types, all vegetation strata except trees were returning to their preconstruction status by the second growing season following construction.

IMPACT OF RIGHT-OF-WAY CONSTRUCTION ON ORGANIC SOIL BULK DENSITY IN THE RED LAKE PEATLAND

The objective of this study was to evaluate changes in soil bulk density associated with construction of a 500-kV transmission right-of-way (ROW) across a peatland in northwestern Minnesota. Immediately before (1979), and for 2 yr following construction (1980, 1981), bulk density of the organic soil within the ROW and in undisturbed control areas was monitored. Soils were primarily Typic Mesisols (Borohemists), with some Mesic Fibrisols (Sphagnofibrists). Monitoring was carried out in five vegetation types, ranging from graminoid fen to treed bog. Soil bulk density was determined in 25-cm increments to 1 m. There were no significant differences in density between the ROW and the control before construction. When data for the 2 yr following construction were combined, results showed significantly higher density in the surface of the ROW than in the surface of the controls. Absolute differences were small, however. The density in the ROW was 5% higher and that in the controls 5% lower than the overall mean of 0.052 g∙cm−3. Largest differences were in a vegetation type with a fibric surface, the treed fen, where, in 1981, the surface in the control had a bulk density of 0.033 g∙cm3, and in the ROW, 0.049 g∙cm−3. Because of high hydraulic conductivity at both densities, any present restriction of water flow across the peatland is unlikely. Key words: Transmission lines, water flow, histosols, Minnesota