Boreal Forest Wetland Research Articles

Modelling permafrost distribution using the temperature at top of permafrost model in the boreal forest environment of Whatì, NT

Current permafrost models in Canadian boreal forests are generally of low spatial resolution as they cover regional or continental scales. This study aims to understand the viability of creating a temperature at the top of permafrost (TTOP) model on a local scale in the boreal wetland environment of Whatì, Northwest Territories from short-term field-collected temperature data. The model utilizes independent variables of vegetation, topographic position index, and elevation, with the dependent variables being ground surface temperature collected from 60 ground temperature nodes and 1.5 m air temperature collected from 10 temperature stations. In doing this, the study investigates the relationship vegetation and disturbance have on ground temperature and permafrost distribution. The model predicts that 31% of the ground is underlain by permafrost, based on a mean annual temperature at TTOP of <0 °C. This model shows an accuracy of 62.5% when compared to cryotic assessment sites (CAS). Most inaccuracies, showing the limitations of the TTOP model, came from peat plateaus that had been burned in the most recent forest fire in 2014. These resulted in out-of-equilibrium permafrost and climatic conditions that TTOP cannot handle well. Commonly, permafrost mapping places Whatì in the extensive discontinuous zone, estimating that between 50% and 90% of the ground is underlain by permafrost. The study shows that a climatically driven TTOP model calibrated with CAS can be used to illustrate ground temperature heterogeneity from short-term data in boreal forest wetland environments. However, this approach likely underestimates permafrost extent and is perhaps not the best-suited modelling choice for near-surface permafrost, which is currently out of equilibrium with the current climate.

Modelling, Characterizing, and Monitoring Boreal Forest Wetland Bird Habitat with RADARSAT-2 and Landsat-8 Data

Earth observation technologies have strong potential to help map and monitor wildlife habitats. Yellow Rail, a rare wetland obligate bird species, is a species of concern in Canada and provides an interesting case study for monitoring wetland habitat with Earth observation data. Yellow Rail has highly specific habitat requirements characterized by shallowly flooded graminoid vegetation, the availability of which varies seasonally and year-to-year. Polarimetric Synthetic Aperture Radar (SAR) in combination with optical data should, in theory, be a great resource for mapping and monitoring these habitats. This study evaluates the use of RADARSAT-2 data and Landsat-8 data to characterize, map, and monitor Yellow Rail habitat in a wetland area within the mineable oil sands region. Specifically, we investigate: (1) The relative importance of polarimetric SAR and Landsat-8 data for predicting Yellow Rail habitat; (2) characterization of wetland habitat with polarimetric SAR data; (3) yearly trends in available habitat; and (4) predictions of potentially suitable habitat across northeastern Alberta. Results show that polarimetric SAR using the Freeman–Durden decomposition and polarization ratios were the most important predictors when modeling the Yellow Rail habitat. These parameters also effectively characterize this habitat based on high congruence with existing descriptions of suitable habitat. Applying the prediction model across all wetland areas showed accurate predictions of occurrence (validated on field occurrence data), and high probability habitats were constrained to very specific wetland areas. Using the RADARSAT-2 data to monitor yearly changes to Yellow Rail habitat was inconclusive, likely due to the different image acquisition times of the 2014 and 2016 images, which may have captured seasonal, rather than inter-annual, wetland dynamics. Polarimetric SAR has proved to be very useful for capturing the specific hydrology and vegetation structure of the Yellow Rail habitat, which could be a powerful technology for monitoring and conserving wetland species habitat.

Importance of boreal forested wetlands for epiphytic macrolichen communities

Forested wetlands provide ecosystem services and often support elevated levels of biodiversity and rare species. However, forested wetlands are understudied and face threats such as logging and land conversion. Epiphytic lichens are abundant in forested wetlands and may be useful to help delineate microhabitats across wetland–upland gradients. We investigated epiphytic macrolichen richness, diversity, and community composition in 15 sites in the Avalon Forest Ecoregion, Newfoundland, Canada. Within each site, we set up three parallel 40 m transects in (i) the forested wetland, (ii) the ecotone, and (iii) the upland forest. Along each transect, we selected five balsam fir (Abies balsamea (L.) Mill.) trees 10 m apart and surveyed for macrolichens on the lower bole. We collected data on tree height and tree diameter at breast height, which differed significantly among forest types. We also collected data on tree age and canopy cover, which did not differ significantly among forest types. Contrary to hypotheses suggesting that biodiversity is highest in ecotones, we found that mean macrolichen richness was significantly higher in wetlands, lower in the ecotones, and lowest in upland forests, and macrolichen diversity followed a similar pattern but with no significant difference among groups. Macrolichen community composition significantly differed among wetlands, ecotones, and upland forests. A lichen of conservation concern, Erioderma pedicellatum (Hue) P.M. Jørg., was detected primarily in forested wetlands, highlighting wetlands as key habitats for rare epiphytic macrolichens.

Arboreal macrolichen community composition and habitat associations in boreal forested wetlands of Newfoundland, Canada

Forested wetlands are ecologically and economically important, but many are poorly understood. A robust inventory of species is important for sound management in these ecosystems, particularly ones that include cryptogams such as arboreal lichens, which are rich and abundant in forested wetlands. On the island of Newfoundland, Canada, little is known about what lichens are found in forested wetlands, how lichen communities interact with different forested wetlands, or whether there are lichens unique to forested wetlands. Therefore, we investigated the potential for macrolichens to act as indicators of forested bog, fen and swamp wetland classes in four regions. We counted macrolichen thalli, by species, on the lower bole of black spruce (Picea mariana) trees within plots from each forested wetland class in each region. We also collected data on habitat characteristics in each wetland: soil pH, canopy closure, and ground and shrub cover, all of which differed significantly among forested wetland classes. Macrolichen communities differed among regions and forested wetland classes but the greatest differences were among regions. We also attempted to identify reliable macrolichen indicator species for forested wetland classes and regions but were unsuccessful. A lichen of conservation concern, Erioderma pedicellatum (Hue) P.M.Jørg., was detected in some of our forested wetland sites, highlighting the importance of proper management of these unique habitats.

Direct and indirect climate change effects on carbon dioxide fluxes in a thawing boreal forest-wetland landscape.

In the sporadic permafrost zone of northwestern Canada, boreal forest carbon dioxide (CO2 ) fluxes will be altered directly by climate change through changing meteorological forcing and indirectly through changes in landscape functioning associated with thaw-induced collapse-scar bog ('wetland') expansion. However, their combined effect on landscape-scale net ecosystem CO2 exchange (NEELAND ), resulting from changing gross primary productivity (GPP) and ecosystem respiration (ER), remains unknown. Here, we quantify indirect land cover change impacts on NEELAND and direct climate change impacts on modeled temperature- and light-limited NEELAND of a boreal forest-wetland landscape. Using nested eddy covariance flux towers, we find both GPP and ER to be larger at the landscape compared to the wetland level. However, annual NEELAND (-20gCm-2 ) and wetland NEE (-24gCm-2 ) were similar, suggesting negligible wetland expansion effects on NEELAND . In contrast, we find non-negligible direct climate change impacts when modeling NEELAND using projected air temperature and incoming shortwave radiation. At the end of the 21st century, modeled GPP mainly increases in spring and fall due to reduced temperature limitation, but becomes more frequently light-limited in fall. In a warmer climate, ER increases year-round in the absence of moisture stress resulting in net CO2 uptake increases in the shoulder seasons and decreases during the summer. Annually, landscape net CO2 uptake is projected to decline by 25±14gCm-2 for a moderate and 103±38gCm-2 for a high warming scenario, potentially reversing recently observed positive net CO2 uptake trends across the boreal biome. Thus, even without moisture stress, net CO2 uptake of boreal forest-wetland landscapes may decline, and ultimately, these landscapes may turn into net CO2 sources under continued anthropogenic CO2 emissions. We conclude that NEELAND changes are more likely to be driven by direct climate change rather than by indirect land cover change impacts.

Short-term effects of harvesting on carbon storage of boreal Larix gmelinii–Carex schmidtii forested wetlands in Daxing’anling, northeast China

Forested wetlands are recognized as long-term terrestrial C sinks, so they are very important in global C accounting. Daxing’anling is the main area of Chinese forested wetlands, however, effects of harvesting on ecosystem C storage for boreal forested wetlands are still poorly understood. The aim of this study was to evaluate the short-term effects of selective harvest on ecosystem C storage and C sequestration for Larix gmelinii–Carex schmidtii forested wetlands in Daxing’anling, northeast China, by measuring and comparing changes in its total ecosystem C storage (biomass, litter, and soil C pools) and annual C sequestration under four harvest treatments (0.0% – uncut, 25% – low, 35% – moderate and 50% – high of total volume) after 5years, so as to provide references for managing wetland resources. We found that: (1) the vegetation C storage of harvested plots decreased significantly by 15.5–38.6% of that 99.61tCha−1 in the uncut stand and showed a decreasing trend with increasing harvest intensity; (2) low intensity harvest increased the soil C storage by 19.4%, however, both moderate- and high-intensity harvest caused significant reductions (30.1–48.5%) relative to 174.93tCha−1 in the uncut stand; (3) low intensity harvest led to a mild increase in the total ecosystem C storage while moderate- and high-intensity harvest resulted in significant reductions (33.2–41.6%) compared with the uncut stand (274.54tCha−1); (4) significantly greater total NPP (69.1–83.2%) and annual C sequestration (52.0–78.7%) were in the low- and moderate-intensity harvest stands compared to the high intensity harvest and uncut stands (8.28tha−1yr−1, 5.08tCha−1yr−1 and 6.48tha−1yr−1, 3.52tCha−1yr−1). Finally, it appears that low intensity harvest may not only be capable of sustaining the ecosystem C sink for this forested wetland type, but restore its C sequestration capacity more efficiently.

Ten‐year water table recovery after clearcutting and draining boreal forested wetlands of eastern Canada

AbstractIn boreal forested wetlands, the observed increase in the water table level after clearcutting (watering‐up) is often a threat to sustained ecosystem productivity. Hydrologic recovery refers to the processes by which a water table progressively drops back to its initial level after the cut. In eastern Canada, drainage is used operationally after clearcutting wet sites in order to lower the water table level and accelerate hydrologic recovery. The objective of this study was to evaluate the duration of the watering‐up caused by timber harvesting and the extent to which drainage affected the water table recovery on five peatlands and three hydromorphic mineral sites located in the St. Lawrence Lowlands of Québec (Canada). The mixed wood stands studied are dominated by balsam fir (Abies balsamea (L.) Mill.), eastern white cedar (Thuja occidentalis L.), and red maple (Acer rubrum L). Results indicate that, 10 years after clearcutting, water table levels in undrained plots are still 5 to 7 cm higher than the pre‐cut levels. The slight recovery in water table level plateaued after the third year. Rainfall interception by vegetation was also monitored, and after 10 years had reached nearly 50% of the pre‐cut rate. The immediate water table drawdown following drainage mitigated watering‐up within 40 m of a ditch. The persistent watering‐up observed in this study should encourage using sylvicultural systems adapted to boreal forested wetlands in order to prevent productivity loss and stand conversion. Copyright © 2008 John Wiley & Sons, Ltd.

Speciation and transport of newly deposited mercury in a boreal forest wetland: A stable mercury isotope approach

As part of the Mercury Experiment to Assess Atmospheric Loadings in Canada and the United States (METAALICUS) the fate and transport of contemporary mercury (Hg) deposition in a boreal wetland was investigated using an experimentally applied stable mercury isotope. We applied high purity (99.2% ± 0.1) 202Hg(II) to a wetland plot to determine if (1) the 202Hg was detectable above the pool of native Hg, (2) the 202Hg migrated vertically and/or horizontally in peat and pore waters, and (3) the 202Hg was converted to methylmercury (MeHg) in situ. The 202Hg was easily detected by ICP/MS in both solid peat and pore waters. Over 3 months, the 202Hg migrated vertically downward in excess of 15 cm below the water table and traveled several meters horizontally beyond the experimental plot to the lake margin along the dominant vector of groundwater flow. Importantly, at one location, 6% of aqueous 202Hg was detected as Me202Hg after only 1 day. These results indicate that new inorganic Hg in atmospheric deposition can be readily methylated and transported lakeward by shallow groundwater flow, confirming the important role of wetlands as contributors of Hg to aquatic ecosystems.

Factors influencing methane flux from a boreal forest wetland in Saskatchewan, Canada

Methane flux in a boreal wetland in central Saskatchewan, Canada was measured by a static chamber technique. The northern ribbed fen site was part of the Boreal Ecosystem and Atmospheric Study. The results indicated temperature, water level relative to the peat surface, vegetative type and P concentrations in interstitial water all had an influence on CH 4 emission rates. Methane fluxes from peat at the site ranged from 176 to 2250 mmol CH 4 m −2 yr −1, exceeding those commonly reported for other freshwater wetlands around the world. The CH 4 flux rates increased from 1.08 at the edge of the fen to 13.80 mmol CH 4 m −2 d −1 near the center. Methane flux was directly correlated with water levels and temperature at all measurement locations except two in the central part of the fen where fluxes became lower. The lower correlation of water levels and temperature with CH 4 flux in sites located at the fen center may be attributed to other more restricting variables created by the water flow through the center of the fen. Methane flux rates in sites with limited water flow were also positively correlated with P concentrations in interstitial water at 50 cm, the depth where CH 4 is likely to be produced.

The importance of floating peat to methane fluxes from flooded peatlands

The effect of flooding on methane (CH4) fluxes was studied through the construction of an experimental reservoir in a boreal forest wetland at the Experimental Lakes Area in northwestern Ontario. Prior to flooding, the peatland surface was a small source of CH4 to the atmosphere (1.0 ± SD of 2.3 mg CH4 m−2 d−1). After flooding, CH4 fluxes from the submerged peat surface increased to 64±68 mg CH4 m−2 d−1. CH4 bubbles within the submerged peat caused about 1/3 of the peat to float. Fluxes from these floating peat islands were much higher (440±350 mg CH4 m−2 d−1) than from both the pre-flood (undisturbed) and the post-flood (submerged) peat surfaces.

Effect of temperature on production of CH4 and CO2 from Peat in a Natural and Flooded Boreal Forest Wetland

Flooding of a small boreal forest wetland (979) in northwestern Ontario, caused the formation of peat islands, which resulted in an approximate 10 °C increase in peat temperatures at a depth of 50 cm. Peat collected from the flooded wetland and a natural unflooded wetland was incubated anaerobically at temperatures of 4 °C, 15 °C, and 20 to 25 °C. Flooding of the wetland greatly increased CH4 production rates by increasing the ratio of CH4:CO2 produced from 979 peat (40% : 60%) compared to 632 peat (20% : 80%), at both preflood and postflood temperatures, likely due to the altered hydrological and geochemical conditions within the peat mats due to flooding. CH4 and CO2 production rates approximately tripled for every 10 °C temperature increase and may have been linked to to the metabolic rate of the methanogens or the fermentors independent of the substrate quality. Methane production rates from deep peat deposits within the islands were also significant and responded well to temperature increases despite peat 14C ages of 1000 years. Due to the large quantity of carbon stored within natural wetlands, artificial reservoirs may act as a significant and long term source of CH4 to the atmosphere.

Increases in Fluxes of Greenhouse Gases and Methyl Mercury following Flooding of an Experimental Reservoir

Experimental flooding of a boreal forest wetland caused the wetland to change from being a small, natural carbon sink, with respect to the atmosphere, of −6.6 g of C m-2 yr-1 to a large source of +130 g of C m-2 yr-1. This change was caused by the death of the vegetation, which eliminated the photosynthetic CO2 sink and stimulated the microbial production of CO2 and CH4 from decomposition of plant tissues and peat. Another type of microbial activity that increased was the methylation of inorganic mercury to the much more toxic methyl mercury (MeHg) form. The wetland was a source of MeHg prior to flooding and became an even larger source (39 fold) after flooding. MeHg concentrations in the water sometimes exceeded 2 ng L-1, with the average being 0.9 ng L-1 in the first 2 years after flooding. MeHg also increased in the flooded vegetation and peat, in lower food chain organisms, and in fish. Two recommendations, which should minimize both greenhouse gas production and MeHg production in reservoirs, can be made: (1) minimize the total area of land flooded (i.e., avoid flooding areas of low relief) and (2) minimize the flooding of wetlands, which contain larger quantities of organic carbon than uplands and are sites of intense production of MeHg.

Use of boreal forested wetlands by Pacific loons (Gavia pacifica Lawrence) and horned grebes (Podiceps auritus L.): relations with limnological characteristics

Use of boreal forested wetlands by Pacific loons (Gavia pacifica Lawrence) and horned grebes (Podiceps auritus L.): relations with limnological characteristics