Peatland Systems Research Articles

Dimethyl Sulfide Emissions From a Peatland Result More From Organic Matter Degradation Than Sulfate Reduction

AbstractVolatile sulfur compounds (VSCs) contribute to acid rain, cloud formation, and albedo, and thus influence the climate. Their global emissions are quite uncertain, especially contributions from freshwater wetlands. We investigated the processes leading to hydrogen sulfide (H2S), methanethiol (MeSH), and dimethyl sulfide (Me2S) emissions in a slightly acidic peatland and found multiple indications that organic matter degradation rather than sulfate reduction is the main driver for Me2S emissions in this system. Evidence includes: the lack of labeled Me234S production after addition of Na234SO4 despite high emissions of Me34SH and H234S, and increased emission rates when soils were amended with organic substrates containing thiol groups (H2S emissions), methylthiols (MeSH), and dimethyl sulfonio groups (Me2S). VSC precursors were identified from an Untargeted Metabolomics data set from the same soil. The abundance of sulfur cycling microbes like Acidobacteria SD 1 and Desulfosporosinus correlated with VSC emissions. We conclude that organic matter degradation is more important than sulfate reduction as a source of Me2S in our peatland system, and potentially also in other organic and wetland soils.

Mercury deposition and redox transformation processes in peatland constrained by mercury stable isotopes

Peatland vegetation takes up mercury (Hg) from the atmosphere, typically contributing to net production and export of neurotoxic methyl-Hg to downstream ecosystems. Chemical reduction processes can slow down methyl-Hg production by releasing Hg from peat back to the atmosphere. The extent of these processes remains, however, unclear. Here we present results from a comprehensive study covering concentrations and isotopic signatures of Hg in an open boreal peatland system to identify post-depositional Hg redox transformation processes. Isotope mass balances suggest photoreduction of HgII is the predominant process by which 30% of annually deposited Hg is emitted back to the atmosphere. Isotopic analyses indicate that above the water table, dark abiotic oxidation decreases peat soil gaseous Hg0 concentrations. Below the water table, supersaturation of gaseous Hg is likely created more by direct photoreduction of rainfall rather than by reduction and release of Hg from the peat soil. Identification and quantification of these light-driven and dark redox processes advance our understanding of the fate of Hg in peatlands, including the potential for mobilization and methylation of HgII.

Elevated temperature alters microbial communities, but not decomposition rates, during 3 years of in situ peat decomposition.

Peatlands are large carbon sinks with primary production outpacing decomposition of organic matter. Results from the Spruce and Peatland Responses Under Changing Environments (SPRUCE) study show net losses of organic matter and increased greenhouse gas production from peatlands in response to whole-ecosystem warming. Here, we investigated how warming and elevated CO2 impact peat microbial communities and peat soil decomposition rates and characterized microbial communities through amplicon sequencing and compositional changes across four depth increments. Microbial diversity and community composition were significantly impacted by soil depth, temperature, and CO2 treatment. Bacterial/archaeal α-diversity increased significantly with increasing temperature, and fungal α-diversity was lower under elevated CO2 treatments. Trans domain microbial networks showed higher complexity of microbial communities in decomposition ladder depths from the warmed enclosures, and the number of highly connected hub taxa within the networks was positively correlated with temperature. Methanogenic hubs were identified in the networks constructed from the warmest enclosures, indicating increased importance of methanogenesis in response to warming. Microbial community responses were not however reflected in measures of peat soil decomposition, as warming and elevated CO2 had no significant short-term effects on soil mass loss or composition. Regardless of treatment, on average only 4.5% of the original soil mass was lost after 3 years and variation between replicates was high, potentially masking treatment effects. Previous results at the SPRUCE experiment have shown warming is accelerating organic-matter decomposition and CO2 and CH4 production, and our results suggest these changes may be driven by warming-induced shifts in microbial communities. IMPORTANCE Microbial community changes in response to climate change drivers have the potential to alter the trajectory of important ecosystem functions. In this paper, we show that while microbial communities in peatland systems responded to manipulations of temperature and CO2 concentrations, these changes were not associated with similar responses in peat decomposition rates over 3 years. It is unclear however from our current studies whether this functional resiliency over 3 years will continue over the longer time scales relevant to peatland ecosystem functions.

Mapping Fractional Vegetation Coverage across Wetland Classes of Sub-Arctic Peatlands Using Combined Partial Least Squares Regression and Multiple Endmember Spectral Unmixing

Vegetation communities play a key role in governing the atmospheric-terrestrial fluxes of water, carbon, nutrients, and energy. The expanse and heterogeneity of vegetation in sub-arctic peatland systems makes monitoring change at meaningful spatial resolutions and extents challenging. We use a field-collected spectral endmember reference library to unmix hyperspectral imagery and map vegetation coverage at the level of plant functional type (PFT), across three wetland sites in sub-arctic Alaska. This study explores the optimization and parametrization of multiple endmember spectral mixture analysis (MESMA) models to estimate coverage of PFTs across wetland classes. We use partial least squares regression (PLSR) to identify a parsimonious set of critical bands for unmixing and compare the reference and modeled coverage. Unmixing, using a full set of 110-bands and a smaller set of 4-bands, results in maps that effectively discriminate between PFTs, indicating a small investment in fieldwork results in maps mirroring the true ground cover. Both sets of spectral bands differentiate between PFTs, but the 4-band unmixing library results in more accurate predictive mapping with lower computational cost. Reducing the unmixing reference dataset by constraining the PFT endmembers to those identified in the field-site produces only a small advantage for mapping, suggesting extensive fieldwork may not be necessary for MESMA to have a high explanatory value in these remote environments.

Historical anthropogenic disturbances explain long-term moorland vegetation dynamics.

Upland moorlands are important landscapes, but many are considered degraded as a result of human activities. Consequently, their protection and restoration are of substantial concern. In Europe, restoration activities are often aimed at reversing the effects of 19th and 20th century "agricultural improvements," which often involved major drainage schemes. However, the ecological effects and long-term ecological context of "agricultural improvement" are not yet fully understood. To develop this understanding, we analyze paleoecological data (pollen, coprophilous fungal spores, microcharcoal) from five upland peatland sites using a range of analytical approaches: cluster analysis, principal component analysis, rate-of-change analysis, and regression analyses incorporating documentary historical data. The sites are located on Exmoor (South West England, UK), a landscape that typifies historic upland degradation. We demonstrate that in this landscape, 19th century drainage is associated with declines in Sphagnum and non-arboreal taxon richness; over longer timescales burning is associated with enhanced graminoid monocot abundance and grazing with lower taxon richness. We also show that rate-of-change in moorland vegetation communities during the 19th century is not distinctive in a long-term context: change has been a constant in this landscape, rather than an exception during the 19th century. Our findings indicate that the aims of "restoration" interventions intended to increase Sphagnum abundances, increase taxon richness and reduce graminoid dominance are consistent with the long-term dynamics of peatland systems, such as those on Exmoor. "Restoration" deemed successful in these terms may or may not resemble pre-drainage conditions, which were themselves a function of millennia of successive moorland management regimes.

A Multifunctional ‘Scape Approach for Sustainable Management of Intact Ecosystems—A Review of Tropical Peatlands

Nature is declining globally at unprecedented rates with adverse consequences for both ecological and human systems. This paper argues that only transformative change—a fundamental, system-wide reorganization—will be sufficient to arrest and reverse this loss and to meet globally agreed development goals, including the post-2020 Global Biodiversity Framework. In search for a credible platform to help facilitate such transformative change, this paper explores the potential of multifunctional ‘scape approaches to improve sustainable management outcomes at scale. Beyond a current international focus on nature restoration, this paper emphasizes the urgency and criticality of confirming approaches for sustainably preserving large ‘intact’ natural areas. Through a semi-systematic review of contemporary academic and gray literature and derivation of a theory of change, the authors consider tropical peatland systems—which can interconnect multiple ecosystem types and be of global biodiversity and carbon sequestration significance—to help derive potentially broader sustainable ecosystem management lessons. Beyond identifying key considerations for implementing multifunctional ‘scape approaches, the paper recommends further work to deepen understanding of the multidimensional ‘value’ of nature; strengthen governance frameworks; empower indigenous peoples and their knowledge sharing and community management; align nature-positive and climate-positive goals; andmobilize commensurate business and financial support.

System responses to Holocene relative sea-level rise and sediment supply in a macrotidal estuary

Estuaries are at the interface of marine and terrestrial systems and as such, are subject to environmental change arising from multiple driving mechanisms, with the interplay between the dominant controls varying spatially and temporally. Relative sea-level (RSL) change and sediment supply can play a significant role in driving environmental change. This study examines the relative influence of these drivers during the Holocene. Biostratigraphic records and RSL data are presented from two locations in the inner portion and upper reaches of the macrotidal Humber Estuary, eastern England. The results provide a new terrestrial limiting point and six sea-level index points, two of which at c. 1500 cal years BP provide the youngest sea-level index points for the inner estuary. An early-mid Holocene tidal lagoon system, that lacks modern equivalent, is recorded at one site. The results indicate a shift in the dominance of RSL rise driving the early Holocene creation of wetlands, to sediment supply dominating changes in the mid-late Holocene against the backdrop of a reduced rate of RSL rise, with a submergence of wetlands evident after c. 4000 cal years BP. The persistence of fen carr evident between c. 6800 and 5500 cal years BP suggests stability and resilience of the peatland system to continuing RSL rise. As rates of contemporary RSL rise increase, combined with climate and human impacts on the landscape, the drivers of change in these type of estuary systems will shift, with the records providing analogues of potential system responses that can help inform coastal management strategies.

Effects of Clearcutting and Residual Biomass Harvesting on Hillslope Mercury Mobilization and Downgradient Mercury Accumulation

AbstractMercury (Hg) in forest runoff varies geographically and in relation to silvicultural practices. There is also considerable uncertainty about how forest management practices, such as residual biomass removal, affect Hg mobilization, and downgradient cumulative effects. In this study, total Hg, dissolved organic carbon (DOC), and sulfate (SO42−) mobilization in runoff were compared among unharvested and harvested hillslopes with and without residual biomass removal, and peat soil and invertebrate methylmercury (MeHg) concentrations were assessed in a down‐gradient peatland. Using a before‐after‐control‐impact design, runoff from three adjacent hillslopes was monitored pre‐harvest (2010–2011) and post‐harvest (2012–2013) from snowmelt to freeze‐up at the USDA Forest Service’s Marcell Experimental Forest in northern Minnesota. Dilution, due to increased available hillslope soil water, led to decreased THg and DOC concentrations after harvest at both harvested hillslopes. Sulfate concentrations did not statistically change following harvest. Compared to its removal, leaving residual biomass significantly increased yields of all solutes but only DOC yields significantly increased when the residual biomass was removed. In the adjacent down‐gradient peatland, peat MeHg concentrations decreased, whereas no change was observed in peat below the unharvested hillslope. There was no discernible change post‐harvest in MeHg levels among several peatland macroinvertebrate taxa. This study provides a much‐needed hillslope‐scale understanding of Hg response to forest management practices, highlighting that increased solute yields from hillslopes do not necessarily stimulate Hg methylation or invertebrate bioaccumulation in down‐gradient peatland systems.

Identification of typical ecohydrological behaviours using InSAR allows landscape-scale mapping of peatland condition

Abstract. Better tools for rapid and reliable assessment of global peatland extent and condition are urgently needed to support action to prevent further decline of peatlands. Peatland surface motion is a response to changes in the water and gas content of a peat body regulated by the ecology and hydrology of a peatland system. Surface motion is therefore a sensitive measure of ecohydrological condition but has traditionally been impossible to measure at the landscape scale. Here we examine the potential of surface motion metrics derived from satellite interferometric synthetic aperture radar (InSAR) to map peatland condition in a blanket bog landscape. We show that the timing of maximum seasonal swelling of the peat is characterised by a bimodal distribution. The first maximum, usually in autumn, is typical of “stiffer” peat associated with steeper topographic gradients, peatland margins, and degraded peatland and more often associated with “shrub”-dominated vegetation communities. The second maximum, usually in winter, is typically associated with “softer” peat typically found in low topographic gradients often featuring pool systems and Sphagnum-dominated vegetation communities. Specific conditions of “soft” and “stiff” peats are also determined by the amplitude of swelling and multi-annual average motion. Peatland restoration currently follows a re-wetting strategy; however, our approach highlights that landscape setting appears to determine the optimal endpoint for restoration. Aligning the expectation for restoration outcomes with landscape setting might optimise peatland stability and carbon storage. Importantly, deployment of this approach, based on surface motion dynamics, could support peatland mapping and management on a global scale.

Peatland drainage alters soil structure and water retention properties: Implications for ecosystem function and management

AbstractPeatland functions (e.g., carbon sequestration and flora diversity) are largely driven by soil moisture dynamics and thus dependent on interactions between hydrologic regimes and organic soil properties. Understanding these interactions is particularly important in drained peatlands, where drier conditions may alter soil properties with feedbacks to soil water retention and associated ecosystem functions. In this work, we focused on the Great Dismal Swamp (GDS) in Virginia, USA, a historically drained, temperate peatland with ongoing hydrologic restoration efforts. Two distinct soil layers varying in thickness exist at GDS: an upper layer with subangular blocky structure thought to be a result of past drainage, and a sapric lower layer with a massive structure more representative of an undisturbed state. To understand the occurrence and consequences of these distinct layers, we used continuous water table data and analysed soil physical and hydraulic properties to characterize soil profiles at 16 locations. We found significant differences between layer properties, where upper layers had lower fibre and organic matter contents and higher bulk densities. Further, moisture release curves demonstrated lower water retention in upper layers compared with lower layers and key differences in pore structure, with upper layers having higher macroporosity. Upper layers varied in thickness across sampling locations (~0.30 to 1.0 m) with a transition to lower soil layers typically occurring at depths below contemporary water level observations, suggesting that the upper layer may be a result of historical drainage and deeper water table conditions. Yet, upper layers with more frequent saturation exhibited higher water retention and lower macroporosity compared with drier upper layers, thus indicating potential recovery following re‐wetting efforts. These findings highlight how past drainage influences soil properties and water retention, with important implications for current management objectives at GDS and other drained peatland systems.

Role of Ester Sulfate and Organic Disulfide in Mercury Methylation in Peatland Soils.

We examined the composition and spatial correlation of sulfur and mercury pools in peatland soil profiles by measuring sulfur speciation by 1s X-ray absorption near-edge structure spectrocopy and mercury concentrations by cold vapor atomic fluorescence spectroscopy. Also investigated were the methylation/demethylation rate constants and the presence of hgcAB genes with depth. Methylmercury (MeHg) concentration and organic disulfide were spatially correlated and had a significant positive correlation (p < 0.05). This finding is consistent with these species being products of dissimilatory sulfate reduction. Conversely, a significant negative correlation between organic monosulfides and MeHg was observed, which is consistent with a reduction in Hg(II) bioavailability via complexation reactions. Finally, a significant positive correlation between ester sulfate and instantaneous methylation rate constants was observed, which is consistent with ester sulfate being a substrate for mercury methylation via dissimilatory sulfate reduction. Our findings point to the importance of organic sulfur species in mercury methylation processes, as substrates and products, as well as potential inhibitors of Hg(II) bioavailability. For a peatland system with sub-μmol L-1 porewater concentrations of sulfate and hydrogen sulfide, our findings indicate that the solid-phase sulfur pools, which have a much larger sulfur concentration range, may be accessible to microbial activity or exchanging with the porewater.

Comparing GHG Emissions from Drained Oil Palm and Recovering Tropical Peatland Forests in Malaysia

For agricultural purposes, the drainage and deforestation of Southeast Asian peatland resulted in high greenhouse gases’ (GHGs, e.g., CO2, N2O and CH4) emission. A peatland regenerating initiative, by rewetting and vegetation restoration, reflects evidence of subsequent forest recovery. In this study, we compared GHG emissions from three Malaysian tropical peatland systems under the following different land-use conditions: (i) drained oil palm plantation (OP), (ii) rewetting-restored forest (RF) and (iii) undrained natural forest (NF). Biweekly temporal measurements of CO2, CH4 and N2O fluxes were conducted using a closed-chamber method from July 2017 to December 2018, along with the continuous measurement of environmental variables and a one-time measurement of the soil physicochemical properties. The biweekly emission data were integrated to provide cumulative fluxes using the trapezoidal rule. Our results indicated that the changes in environmental conditions resulting from draining (OP) or rewetting historically drained peatland (RF) affected CH4 and N2O emissions more than CO2 emissions. The cumulative CH4 emission was significantly higher in the forested sites (RF and NF), which was linked to their significantly higher water table (WT) level (p &lt; 0.05). Similarly, the high cumulative CO2 emission trends at the RF and OP sites indicated that the RF rewetting-restored peatland system continued to have high decomposition rates despite having a significantly higher WT than the OP (p &lt; 0.05). The highest cumulative N2O emission at the drained-fertilized OP and rewetting-restored RF sites was linked to the available substrates for high decomposition (low C/N ratio) together with soil organic matter mineralization that provided inorganic nitrogen (N), enabling ideal conditions for microbial mediated N2O emissions. Overall, the measured peat properties did not vary significantly among the different land uses. However, the lower C/N ratio at the OP and the RF sites indicated higher decomposition rates in the drained and historically drained peat than the undrained natural peat (NF), which was associated with high cumulative CO2 and N2O emissions in our study.

Responses of oribatid mites to warming in boreal peatlands depend on fen type

Climate warming is expected to disproportionately affect high latitude and alpine systems such as boreal peatlands. Previous studies observing changes in both plant and microbial communities suggest boreal peatlands may shift from carbon sinks to sources under warming. But few studies have investigated oribatid mites (Acari: Oribatida) under climate change scenarios in peatland systems, despite oribatid mites being well represented in terms of diversity in boreal peatlands. We performed a large-scale experimental field manipulation of warming in two contrasting peatland sites in Northern Ontario, Canada, and sampled oribatid mites over four years following three years of passive warming and one full growing season of active warming. We found that warming had contrasting effects on the oribatid mite community at both peatland sites, and depended on the peatland type. Specifically, we observed an increase in species richness at the drier, Sphagnum-dominated site and a reduction in species richness at the wetter, Carex-dominated site. That said, we suggest that these outcomes arise from the same mechanism, namely warming-induced reductions in soil moisture that impacted semi-aquatic species and facilitated the establishment of new species, likely from surrounding forests. We also observed increases in small-bodied species suggesting direct metabolic effects from warming. As such, we show that peatland oribatid mite community composition is driven to an extent by interactions between temperature and moisture but dependant on peatland type. As oribatid mite communities are responsive to multiple environmental changes, and play important mid-trophic level roles in soil food webs, changes in oribatid mite community composition may have consequences for carbon flux in peatland systems.

Radiocarbon Data Reveal Contrasting Sources for Carbon Fractions in Thermokarst Lakes and Rivers of Eastern Canada (Nunavik, Quebec)

AbstractGreenhouse gas emissions from permafrost organic carbon decomposition in lakes and rivers can accelerate global warming. We used radiocarbon (14C) measurements to determine the predominant sources of dissolved organic carbon (DOC), particulate organic carbon (POC), dissolved inorganic carbon (DIC), and methane (CH4) in five thermokarst lakes and three rivers in an area of widespread permafrost degradation in Northern Quebec to assess contributions from thawing permafrost and other old carbon (fixed before CE 1950) reservoirs. We compared emission pathways (dissolved gas and ebullition), seasons (summer and winter), and surface soil type (mineral and peat soils). Modern carbon (fixed after CE 1950) was the dominant source of DOC, DIC, and CH4 of non‐peatland aquatic systems, while POC and sediment carbon were predominantly fixed in the last millennia. In the peatland systems, modern and permafrost carbon were important sources of DOC, lake DIC, lake ebullition CO2, and lake dissolved CH4. In contrast, POC, lake ebullition CH4, and river DIC were dominated by millennial‐old carbon. In winter, the 14C age of DOC, DIC, and POC in the peatland lakes increased, but the 14C age of dissolved CH4 did not change. Our results point to a clearly older overall carbon source for ebullition CH4 relative to dissolved CH4 in the peatland lakes but not the non‐peatland lakes. The younger ages of dissolved CH4 and DIC relative to DOC and POC in all lakes suggest that recent primary productivity strongly influences the large total lake CH4 and CO2 emissions in this area, as diffusion fluxes greatly exceed ebullition fluxes.

Effects of snow and climate on soil temperature and frost development in forested peatlands in minnesota, USA

Black spruce (Picea mariana) peatlands play important ecologic and economic roles in the temperate-boreal region of North America, providing a valuable timber resource while also performing important ecosystem functions. Climate models project decreases in the amount of snowfall received throughout the temperate-boreal region by 2100, as average wintertime temperatures increase. We used a paired-plot experimental design to assess the effect of snow removal on soil temperature and frost development at six forested peatland sites in northern Minnesota, USA, during the three winters from 2017 to 2020. Treatments consisted of 1) removal of snow throughout the winter, or 2) ambient snow cover conditions. During the three years of the study, there was a significant effect of snow removal by mid-winter that continued into late winter and spring, where removal of snow increased soil frost depth compared to plots with ambient snow cover treatment. Soil temperatures in the removal plots were highly responsive to air temperature fluctuations to depths of 20 cm or more, whereas the ambient snow cover soils exhibited little fluctuation and maintained temperatures near or above 0° C for much of the winter season. We found that each cumulative freezing degree day resulted in an average of 0.36 cm of soil frost development in snow removal plots, as compared to 0.07 cm depth in the ambient treatment plots. Soils were significantly colder through much of the summer growing season in the removal treatment compared to the ambient treatment, with detectable soil frost in the soil profile as late as mid- to late-June. These results indicate that predicted changes in wintertime precipitation may result in increased development of soil frost in forested peatland systems, although some of this effect may be offset by predicted concurrent increases in air temperature. We did not measure indicators of biological activity, but the large and prolonged reduction in soil temperature with snow removal is likely to depress biological activity throughout the growing season and the many ecosystem functions it influences. Because of the role that soil temperature and frost play on the hydrologic and ecological processes of peatlands, as well as the crucial role of soil frost in peatland forest management, findings of this study provide important insight into the potential effects of altered winter conditions on these expansive and ecologically important ecosystems.

Changes in Physical Properties of Everglades Peat Soils Induced by Increased Salinity at the Laboratory Scale: Implications for Changes in Biogenic Gas Dynamics

AbstractSaltwater intrusion due to sea level rise is a major concern for the Florida Everglades because it may induce shifts in ecosystem productivity and physical soil properties. However, the effects of saline water intrusion into the current carbon gas dynamics of the Everglades (particularly in terms of biogenic gas production and emissions, i.e., CH4 and CO2) are still uncertain. In this work, we present a laboratory‐based study to simulate how sea level rise may alter the physical properties (i.e., hydraulic conductivity) of peat soils from the Everglades and consequently affect the accumulation and release of biogenic gases within the peat matrix. Peat monoliths collected from the Everglades were subjected to progressive increases in salinity from a NaCl solution, and changes to the biogenic gas dynamics regime were simultaneously monitored using a combination of time‐lapse ground‐penetrating radar measurements, manometers, time‐lapse photography, and gas traps. Physical changes to the peat matrix at each salinity interval were assessed using constant head permeameter tests. Consistent with previous research, results show that a progressive increase in salinity (from fresh to saltwater) results in (1) a progressive increase in hydraulic conductivity and (2) a progressive decrease in gas content within the peat matrix (i.e., production) and gas releases. This work has implications for better understanding the potential effects of saltwater intrusion into freshwater peatland systems in the Everglades, particularly in terms of carbon gas dynamics.

Impacts of Groundwater Drainage on Peatland Subsidence and Its Ecological Implications on an Atlantic Raised Bog

AbstractField data of topography, water levels, and peat hydraulic conductivity collected over a 28‐year period have revealed the impacts of marginal drainage on uncut raised bog ecohydrology and its peat properties. Drainage of the regional groundwater body has induced changes in the hydraulic properties of deep peat, with peat compression decreasing hydraulic conductivity and storativity while simultaneously introducing localized secondary porosity and effective storage. Where peat has increased in hydraulic conductivity, there is a corresponding decline in vertical hydraulic gradients and significant localized increases in recharge to the underlying substrate. Repeated topographic surveys show intense localized areas of peat consolidation (&gt;5%) where it is underlain by highly permeable (&gt;10 m/day) glacial till deposits. More widely, continued subsidence (4–6 mm/year) of the bog surface has been measured over 900 m from the bog margin, resulting in the progressive loss of approximately 40% of actively growing raised bog since 1991. This loss has thus been shown to be attributable to changes in the underlying groundwater head due to deep‐cut drainage, rather than near‐surface peatland drainage. However, although reinstating regional hydrostatic pressures in order to restore this ombrotrophic peatland may control the rapid drainage through preferential flow pathways, this may not eliminate the ecological impacts resulting from changed surface morphology arising from subsidence. Hence, this longitudinal study provides new insights into the role that aquifer systems and groundwater bodies play in maintaining hydrogeological processes in ombrotrophic peatland systems, while highlighting the difficulty in ecological restoration where regional groundwater dependencies are significant.

Changes to the hydrophysical properties of upland and riparian soils in a burned fen watershed in the Athabasca Oil Sands Region, northern Alberta, Canada

Hydrogeologic setting strongly influences the hydrologic function of peatland systems. For base–rich fens in the Athabasca Oil Sands Region (AOSR) of the Western Boreal Plain, northern Alberta, local groundwater flow from gently sloping adjacent uplands has been shown to help sustain fen water tables and chemistry. Natural forest disturbance in the AOSR is dominated by wildfire, with peatlands susceptible to combustion and subsequent carbon release. However, few studies have aimed to characterize the degree of change to the hydrophysical properties of upland soils following wildfire. To address this, we measured differences in water repellency and hydrophysical properties of burned and unburned upland organic and mineral soils in a burned moderate–rich fen watershed (Poplar Fen), ~25 km north of Fort McMurray. Samples were taken in the fall of 2017, ~1.5 years after the watershed burned (May 2016). Study locations included burned and unburned jack pine–dominated upland and black spruce–dominated riparian areas. Results illustrated significantly lower water repellency and higher infiltration on burned locations of both land types. Furthermore, no significant differences were detected in organic soil moisture retention in uplands; however, burned organic soil samples had significantly lower water retention in riparian areas. We postulate the lower water retention in riparian areas was due to the greater organic layer thickness there, thus greater fuel load and potential for exceeding the temperature threshold of repellency destruction. Following retention, all soil cores exhibited high hysteresis, with differences in volumetric moisture content averaging 0.38 and 0.34 m3 m−3 at −10 cm pressure for upland and riparian locations, respectively. Our results are contrary to the increased hydrophobicity following burning that is commonly reported in boreal regions. The promoted infiltration, groundwater recharge and subsequent enhanced water supply to fens in the local groundwater system may help in accelerating the moss recovery process.

Postfire Soil Carbon Accumulation Does Not Recover Boreal Peatland Combustion Loss in Some Hydrogeological Settings

AbstractDeep peat burning at the interface between subhumid Boreal Plains (BP) peatlands and forestlands (margin ecotones) in some hydrogeological settings has brought into question the long‐term stability of these peatlands under current and future predicted climate. Small peatlands located at midtopographic positions on coarse sediments have been identified as hot spots for severe burning, as these peatland margins are not regularly connected to regional groundwater flow. The ability of these peatland systems to recover carbon lost from both the interior and margin within the fire return interval, however, has not yet been investigated. Here we examine peatland soil carbon accumulation along a chronosequence of time since fire for 26 BP ombrotrophic bogs located across a range of hydrogeological settings. Soil organic carbon accumulation following wildfire does not appear to be influenced by hydrogeological setting; however, the ability of a peatland to recover the quantity of carbon lost within the fire return interval is dependent on the amount of carbon that was released through smoldering, which is influenced by hydrogeological setting for peatland margins. Based on published measurements of organic soil carbon loss during wildfire and our soil carbon accumulation rates, we suggest that peatlands located at topographic lows on coarse‐grained glaciofluvial outwash sediments or on low‐relief, fine‐grained sediment deposits from glaciolacustrine or subglacial paleoenvironments are currently resilient to wildfire on the BP landscape. Peatlands that experience severe smoldering at the margins, such as ephemerally perched systems on glaciofluvial outwash sediments, will likely undergo permanent loss of legacy carbon stores.

Geomorphological controls on fluvial carbon storage in headwater peatlands

AbstractGeomorphological controls and catchment sediment characteristics control the formation of floodplains and affect their capacity to sequester carbon. Organic carbon stored in floodplains is typically a product of pedogenic development between periods of mineral sediment deposition. However, in organically‐dominated upland catchments with a high sediment load, eroded particulate organics may also be fluvially deposited with potential for storage and/or oxidation. Understanding the redistribution of terrestrial carbon laterally, beyond the bounds of river channels is important, especially in eroding peatland systems where fluvial particulate organic carbon exports are often assumed to be oxidised. Floodplains have the potential to be both carbon cycling hotspots and areas of sequestration. Understanding of the interaction of carbon cycling and the sediment cascade through floodplain systems is limited.This paper examines the formation of highly organic floodplains downstream of heavily eroded peatlands in the Peak District, UK. Reconstruction of the history of the floodplains suggests that they have formed in response to periods of erosion of organic soils upstream. We present a novel approach to calculating a carbon stock within a floodplain, using XRF and radiograph data recorded during Itrax core scanning of sediment cores. This carbon stock is extrapolated to the catchment scale, to assess the importance of these floodplains in the storage and cycling of organic carbon in this area. The carbon stock estimate for the floodplains across the contributing catchments is between 3482‐13460 tonnes, equating on an annualised basis to 0.8‐4.5% of the modern‐day POC flux. Radiocarbon analyses of bulk organic matter in floodplain sediments revealed that a substantial proportion of organic carbon was associated with re‐deposited peat and has been used as a tool for organic matter source determination. The average age of these samples (3010 years BP) is substantially older than Infrared Stimulated Luminesence dating which demonstrated that the floodplains formed between 430 and 1060 years ago. Our data suggest that floodplains are an integral part of eroding peatland systems, acting as both significant stores of aged and eroded organic carbon and as hotspots of carbon turnover. © 2019 The Authors. Earth Surface Processes and Landforms published by John Wiley &amp; Sons Ltd.