Natural Fen Research Articles

A Concept for a Consolidated Humus Form Description—An Updated Version of German Humus Form Systematics

In Germany, the systematics of humus forms has been developed, which is mainly based on morphological characteristics and has been proven via detailed long-term observation. The humus form systematics presented here is an update based on a new approach, clarifying the hierarchical structure into divisions, classes, types, and subtypes. New diagnostic horizons and transition horizons are introduced, uniquely characterising types and subtypes. This paper holds that the humus form is not only a product of decomposition, humification, and bioturbation but also serves as habitat for soil organisms. The processes and the habitat are shaped by soil-forming factors with the main factor being soil water conditions. Thus, on the first level of systematics, aeromorphic and aero-hydromorphic as well as hydromorphic humus forms are differentiated. Many different features of the organic layers and the mineral topsoil can be observed in forests, open grasslands, the mountain zone above the tree line, and natural fens and bogs, as well as degraded peatlands. Features shaping the humus form, such as the proportion of organic fine material and packing of the organic matter as well as the structure of the mineral soil, have now been unambiguously described. However, site-specific soil-forming factors result in typical organic matter characteristics of individual horizons and typical combinations of different horizons. This relationship is illustrated using descriptions of distinct humus forms.

Microbial communities and biogeochemical functioning across peatlands in the Athabasca Oil Sands region of Canada: Implications for reclamation and management

AbstractPeatlands play an important role in global biogeochemical cycles and are essential for multiple ecosystem functions. Understanding the environmental drivers of microbial functioning and community structure can provide insights to enable effective and evidence‐based management. However, it remains largely unknown how microbial diversity contributes to the functioning of belowground processes. Addressing this gap in knowledge will provide a better understanding of microbial‐mediated processes in peatlands that are undergoing restoration or reclamation. This study assessed the changes in microbial community diversity and structure as well as soil function by measuring microbial respiration on a range of substrates from three natural fen types found in the Athabasca Oil Sands region of Alberta, Canada (a poor fen, a hypersaline fen, and a tree‐rich fen) and a nearby constructed fen undergoing reclamation following open pit mining. Overall, substrate induced respiration was significantly higher in the constructed fen. Alpha diversity of fungi and prokaryotes was highest in the tree‐rich fen, and the composition of microbial communities was significantly different between fens. Both fungal and prokaryotic communities were strongly related to pore water pH and temperature, with plant richness also contributing to the shape of fungal communities. In summary, microbial community structure reflects the underlying differences in soil condition across different fens but plays essential roles in the ecological functions of soil. These findings provide a new outlook for the management of peatlands undergoing post‐mining reclamation. Future research on peatland reclamation should consider the dynamic interaction between communities and ecosystem functionality, for which this study forms a useful baseline.

Physiological responses of fen mosses along a nitrogen gradient point to competition restricting their fundamental niches

Nutrient availability determines vegetation patterns and ecological functioning of intact groundwater‐fed peatlands (fens). Bryophytes, commonly referred to as ‘brown mosses', dominate calcareous fens (rich fens), are an integral part of their unique biodiversity and contribute significantly to peat formation and carbon sequestration. Brown mosses are replaced by vascular plants as nutrient availability increases. The decline of brown mosses may either be due to their physiological intolerance of high nutrient levels or to them being outcompeted by vascular plants. We aimed to distinguish between these two hypotheses by investigating whether the ecological optima reflect the physiological optima of brown mosses. Eight brown moss species, common in calcareous fens of the northern hemisphere, were grown under a gradient of nitrogen and phosphorus availability. Biomass increment, chlorophyll content and biomass nutrient concentration were measured. All brown moss species studied achieved the highest growth rates and chlorophyll contents when grown under conditions of nitrogen and phosphorus concentrations higher than those where they occur naturally at the highest frequency. Two of the species showed no growth saturation even at the highest levels of nutrient availability, while the others appeared potassium‐limited at the highest N and P levels. Brown mosses dominate natural fens at the lower edge of their physiological optimum in terms of nutrient availability, i.e. their realized niche is much narrower than the fundamental one. Based on the literature, we argue that it is the competition for light with vascular plants which limits the occurrence of brown mosses in nutrient‐rich habitats and prevents them from occupying their entire fundamental niche.

Reclaiming to Brackish Wetlands in the Alberta Oil Sands: Comparison of Responses to Sodium Concentrations by Carex atherodes and Carex aquatilis.

The variation in sodium concentrations in waters of natural fens and marshes on the western Canadian landscape provides a background for choosing the appropriate plants for wetland reclamation. Broad tolerances to salinity are especially important for reclamation trials on saline-rich ‘in-pits’ that were left from open-pit oil sands mining. One such species, Carex aquatilis, has been identified as a key species in early reclamation attempts; however, at the Sandhill Wetland on the Syncrude Canada oil sands lease, this species has aggressively colonized, dominating parts of the wetland and limiting species diversity. A second species, also widespread on natural lake shores and marshes, is Carex atherodes, with field observations suggesting a broad tolerance to salinity. Here, we examine the responses of this species to a series of sodium concentrations and compare these to those of C. aquatilis. In particular, we addressed three questions: (1) How do structural attributes of C. atherodes respond to a series of Na+ concentration treatments? (2) Are different structural responses related to the functional attributes of photosynthesis, stomatal conductance, and/or transpiration rate? (3) How do these responses compare to those of C. aquatilis? We implemented a phytotron experiment to test the responses of these two species to either five or six concentrations of sodium, ranging from 20 to 3000 mg Na+ L−1. In general, structural responses of C. atherodes did not differ between 50 and 789 mg Na+ L−1, while performances of all attributes were reduced at 1407 mg L−1. Physiological attributes had high variation, but also had reduced performances at similar treatment levels. In comparison, a clear threshold was present for structural attributes in Carex aquatilis between 1650 and 2148 mg Na+ L−1, while physiological attributes were reduced between 1035 to 1650 mg Na+ L−1. These responses from C. aquatilis were similar to those previously reported. Na+ concentrations in porewater at the Sandhill Wetland in 2019 reached as high as 1200 mg Na+ L−1, with natural subsaline and sodic sites ranging much higher. Although all of the plants in the treatments remained viable at the end of the experiment, these results indicate that Na+ concentrations above 1500–2000 mg Na+ L−1 may inhibit the growth of these two species and decrease their competitive abilities.

Cause of decade’s stagnation of plant communities through16-years successional trajectory toward fens at a created wetland in northern Japan

Hiraoka is the created wetland that was constructed in 2000 in an urban park in Sapporo City. We introduced fen and bog plants and monitored the hydrochemical conditions and species assemblage composition four times during the 16 years after construction (YAC). The species richness indices of total, exotics, and annuals resembled those of the target fens within 11 YAC, but the species assemblages did not match the target fens even after 16 YAC, showing that species richness is a less effective way to measure success. The 0.1 m high artificial hummocks enhanced species richness 1.3 to 1.4 times more than the surrounding hollows and increased variety within species assemblages (although these hummocks collapsed before16 YAC). Water level from ground surface (WL) were stable at around 0.00 to +0.05 m, except during several-days floods, when a maximum WL of +0.4 to +0.5 m. Hydrological conditions were, therefore, similar to those natural fens nearby. Mean pH values (min and max) decreased from 6.9 (5.5–9.3) in 1 YAC to 6.2 (5.7–6.9) in 16 YAC and approached those of natural fens. The mean electrical conductivity (166–196 μScm-1) and concentrations of major minerals (Ca2+, Mg2+, and K+) were consistently higher than those of Japanese fens, but dissolved phosphorus (0.00–0.04 mg l−1) and nitrogen (0.12–0.48 mg l−1) were lower. The trajectory of species assemblages quickly approached the target fen at least 5 YAC, but then changed between 5 and 11 YAC, before stagnating. Since mineral content in Hiraoka was near the lower limit of calcareous rich-fens, abundant minerals would be less effective in changing the species assemblage compositions. Due to the dominance of eight initially introduced fen species, the trajectory turned in a different direction. Species assemblages stagnated between initial and target communities before 16 YAC, since the five fen dominants introduced at 8 to 9 YAC had not yet dominated. Accordingly, initial introductions, including species combinations of target fen, can shorten the time required to achieve natural fens. At 16 YAC, large emerged macrophytes did not dominate and did not competitively exclude fen species, probably because the water was oligotrophic and the wetland design did not include open water.

Unraveling the Importance of Polyphenols for Microbial Carbon Mineralization in Rewetted Riparian Peatlands

There have been widespread attempts to rewet peatlands in Europe and elsewhere in the world to restore their unique biodiversity as well as their important function as nutrient and carbon sinks. However, changes in hydrological regime and therefore oxygen availability likely alter the abundance of enzyme-inhibiting polyphenolic compounds, which have been suggested as a preventing large amounts of carbon from being released into the atmosphere by microbial mineralization. In recent years, a variety of factors have been identified that appear to weaken that latch including not only oxygen, but also pH. In minerotrophic fens, it is unknown if long-term peat mineralization during decades of drainage and intense agricultural use causes an enrichment or a decline of enzyme-inhibiting polyphenols. To address this, we collected peat samples and fresh roots of dominating plants (i.e., the peat parent material) from the upper 20 cm peat layer in 5 rewetted and 6 natural fens and quantified total phenolic content as well as hydrolysable and condensed tannins. Polyphenols from less decomposed peat and living roots served partly as an internal standard for polyphenol analysis and to run enzyme inhibition tests. As hypothesized, we found the polyphenol content in highly decomposed peat to be 8 times lower than in less decomposed peat, while condensed tannin content was 50 times lower in highly degraded peat. In addition, plant tissue polyphenol contents differed strongly between peat-forming plant species, with the highest amount found in roots of Carex appropinquata at 450 mg g-1 dry mass, and lowest in Sphagnum spp. at 39 mg g-1 dry mass: a 10-fold difference. Despite large and clear differences in peat and porewater chemistry between natural and rewetted sites, enzyme activities determined with Fluorescein diacetate (FDA) hydrolysis and peat degradation were not significantly correlated, indicating no simple linear relationship between polyphenol content and microbial activity. Still, samples with low contents of polyphenols and condensed tannins showed the highest microbial activities as measured with FDA.

Spontaneous revegetation of a peatland in Manitoba after peat extraction: diversity of plant assemblages and restoration perspectives

There are very few studies on the spontaneous revegetation of cutover fens or bogs from which peat has been extracted to the minerotrophic layers. Most peatlands with fen-type residual peat have problems regenerating a plant cover satisfactorily from a restoration point of view. We nevertheless found a site (Moss Spur, Manitoba, Canada) presenting a substantial and diversified spontaneous plant cover. We estimated that the site would provide insights about natural revegetation processes operating in peatlands. Vegetation assemblages and environmental conditions were surveyed 19 years after extraction activities ceased. Moss Spur has densely revegetated (163 plant species, vegetation cover of 94%) with minimal human assistance. However, the composition of plant assemblages varies considerably across the site, depending on certain abiotic variables, particularly water pH, water table level, and the thickness of the residual peat layer. Moss Spur was remarkably wet considering the past peat extraction activities and the absence of active rewetting procedures. The high water table level may in part explain the successful revegetation. However, plant assemblages were not of equal quality from a restoration perspective. Some assemblages were highly diversified, and especially those dominated by Scirpus cyperinus, a species that should be further considered in peatland restoration projects to direct the recovery of the peatland towards a natural fen species composition.

Stable carbon isotopic composition of peat columns, subsoil and vegetation on natural and forestry-drained boreal peatlands

ABSTRACTWe studied natural and forestry-drained peatlands to examine the effect of over 34 years lowered water table on the δ13C values of vegetation, bulk peat and subsoil. In the seven studied sites, δ13C in the basal peat layer was 1.1 and 1.2 ‰ lower than that of the middle-layer and surface layer, respectively. Furthermore, there was a positive correlation between the δ13C values of the basal and surface peat layers, possibly due to carbon (C) recycling within the peat column. In the same mire complex, natural fen peat δ13C values were lower than those of the nearby bog, possibly due to the dominance of vascular plants on fen and the generally larger share of recycled C in the fens than in the bogs. Furthermore, natural and 51 years previously drained fen and bog, on the opposite sides of a ditch on the same mire complex, showed no significant differences in δ13C values. Plant δ13C values were lower, while δ13C values of subsoil were higher in the drained than in the natural site of the fen.

A Comparison of Five Wetland Communities in a North Dakota Fen Complex

Fens are rare and not well-studied within the Prairie Pothole Region (PPR) of North Dakota. PPR wetlands (including fens) are vulnerable to land use alterations, particularly conversion to agricultural production. In this study, we described a 48-ha natural fen complex with five distinct wetland plant communities (denoted cattail [Typha L. spp.], floating mat [areas at higher elevation with an upward groundwater gradient], herbaceous, tree, and wet meadow). Our goal was to describe the wetland plant communities and determine possible factors driving the formation of several distinct wetland plant communities in close proximity to one another. We identified 148 plant species, six of which are considered priorities for conservation by the North Dakota Natural Heritage Program. We compared the composition of wetland plant communities using multi-response permutation procedure (MRPP) and examined individual attributes (e.g., species richness, evenness, diversity, Floristic Quality Index, percent introduced species, percent soil organic matter, pH, and electrical conductivity) of the wetland plant communities using ANOVA and Tukey's (HSD) test. We found the highest species richness, evenness, and diversity in herbaceous and tree communities and the lowest percent introduced species in floating mat communities. There were no significant differences in the soil properties tested among the five plant communities.

Wind dispersal of alien plant species into remnant natural vegetation from adjacent agricultural fields

Knowledge regarding the seed dispersal of alien species is crucial to manage invasion risk in fragmented natural habitats. Focusing on wind dispersal, this study assessed the spatial and quantitative extents to which a remnant natural fen receives the seeds of alien species dispersed from adjacent hay meadows in Hokkaido, northern Japan. I established a total of 80 funnel seed traps in the fen at distances of 1, 2, 5, 10, 20, 30, 50, and 100 m from the meadows. The proportion of alien species in the seed rain at each distance was quantified, and the 99th-percentile dispersal distance from the meadows was estimated for each alien species by constructing dispersal kernels. Despite the presence of a marginal ditch and an elevational difference between the fen and the meadows, five alien species, including four grasses that do not have modified seed structures for wind dispersal, dispersed their seeds into the fen. These alien species accounted for up to 65.9% of the seed rain in terms of quantity. The 99th-percentile dispersal distances of the alien species ranged from 3.8 m to 309.3 m, and these distances were longer than the values predicted on the basis of their functional traits, such as terminal velocity. The results of this study demonstrated that numerous seeds of farmland-derived alien species were transported into the remnant vegetation via wind dispersal, and that simple predictions of dispersal distance based on functional traits could underestimate the potential area that alien species can reach. Continuous management both in farmland (to reduce seed escape) and in remnant vegetation (to prevent the establishment of alien species) is necessary to protect native vegetation from biological invasion in agricultural landscapes.

Microstructure and property evolution of Fe-N ferrite undergoing early-stages of precipitation

The precipitation-hardening phenomenon is well-known in nitrogen-supersaturated ferrite and its precipitation sequence has received extensive attention. Thus far the α″-Fe16N2 phase has been known as the main hardening precipitates in the alloy upon ageing at low temperatures. Here we report that distinct precursors (pre-α″) of the α″-phase exist and they also play a crucial role in the precipitation-hardened alloy. Using (in-situ) high-resolution transmission electron microscopy, property characterization and first-principle energy calculations in association with varying thermal processes, it is shown that lying on the {001}α planes, the pre-α″ precipitates have a plate-like morphology and are the major hardening precipitates in natural aged Fe-N ferrite. They are stable without much change even after tempering at 60°C for 2h. Furthermore, the plate-like pre-α″ precipitates typically consist of needle-like domains, due to energy minimization. The in-situ observations demonstrate that the precipitation sequence upon ageing is as follows: N-supersaturated α-Fe→N-rich clusters→pre-α″ (GP zones)→α″, where GP zones stands for Guinier-Prestone zones. The pre-α″ precipitates can have even more significant effects on properties of the alloy, as compared with the well-known α″ precipitates.

Controls on plot-scale evapotranspiration from a constructed fen in the Athabasca Oil Sands Region, Alberta

In the Athabasca Oil Sands Region of the Western Boreal Plain mining companies now recognize the importance of reclaiming peatlands, as they cover >50% of the pre-mined regional landscape. To date, reclamation efforts have focused on marsh and open water wetlands. However, these wetland systems are not abundant in the sub-humid climate of the WBP because of their excessive evapotranspiration (ET) losses, compared to peatland wetlands. The experimental Nikanotee Fen was constructed as part of the landscape reclamation, engineered with the intent to support natural fen vegetation and hydrologic processes. The influences of vegetation and treatment types on plot-scale energy fluxes and ET demands were examined over the 2014 growing season, one year post-construction. Actual ET and environmental variables, such as water table, soil moisture, temperature and relative humidity, were monitored in thirty-one study plots comprising control, moss and seedling plots (with and without wood-strand mulch), as well as three ponds. Actual ET was measured with weighing lysimeters and used to correct equilibrium ET, calculated using the Priestley-Taylor combination method. A roaming meteorological station was instrumented to quantify and compare available energy over different cover types. Modeled plot-scale ET was validated against continuously measured eddy covariance ET values. Cumulative ET exceeded precipitation in all plot types with average rates of 4.4, 3.2, 3.9 and 2.8mm/day from open water, control, seedling and moss plots, respectively. Mulch reduced ET rates in both seedling and moss plots, where moss-mulch plots showed the lowest rates (2.4mm/day). The presence of mulch lowered the near-surface vapour pressure deficit, thus providing a more favorable microclimate for moss establishment by elevating near-surface relative humidity and reducing air and soil temperature by ∼2°C. Although vapour pressure deficit did not significantly control ET (p>0.05), mulch appeared to have a greater influence on ET in moss plots than seedling plots. Water table position displayed a weak yet significant (p<0.05) control on ET in seedling plots. As these reclamation practices have not yet been well tested in the Alberta oil sands region; this study provides recommendations to reduce evaporative stress and aid in the establishment of functioning constructed peatland ecosystems.

Net nitrogen mineralization in boreal fens: a potential performance indicator for peatland reclamation

The Sandhill Fen reclamation watershed, commissioned by Syncrude Canada Ltd., is the first attempt to reclaim a self-sustaining peat-forming wetland on a previously mined area. Here, we quantified net nitrogen mineralization rates at Sandhill Fen in the first and second years since initiation (2013–2014). Our main objective was to determine whether nitrogen production potentials at Sandhill Fen were similar to six regional fens sampled across an ombrotrophic–minerotrophic peatland gradient. In the second year, net nitrogen mineralization rates across Sandhill Fen (2014 mean = 20.2 mg N·m−2·day−1; 0.9 mg N·kg−1·day−1) were quite comparable with the benchmark fen sites (2013–2014 pooled means = 20.6 mg N·m−2·day−1; 5.9 mg N·kg−1·day−1). However, in areas exhibiting low gravimetric soil moisture content at Sandhill Fen, net nitrification contributed more than 50% to the net N mineralization total, an uncommon observation in natural fen type wetlands. These findings highlight the importance of managing soil moisture levels during the early stages of reclamation to (1) maintain relatively anaerobic soil conditions, and (2) facilitate microbial-mediated processes to fall within an acceptable range of variation comparable to undisturbed Albertan fens.

Preliminary assessment of greenhouse gas emissions from a constructed fen on post-mining landscape in the Athabasca oil sands region, Alberta, Canada

The ongoing reclamation of boreal forest areas that are impacted by oil sands mining involves the construction of wetlands as desirable land uses. Constructed wetlands receiving peat-mining runoff are known to be major sources of greenhouse gas (GHG) emissions to the atmosphere. However, the GHG fluxes of a fen that is constructed with drained peat substrate and receives runoff containing effluents of salt and naphthenic acids is not known. Using a fen constructed in the post-mining landscape of the Athabasca oil sands region, a study was conducted to quantify the fluxes of carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) during the peak growing seasons over the first two years following revegetation. The specific objective of this study was to evaluate the effect of revegetation strategies and other environmental characteristics on the fen GHG emissions over the growing season. Relative to a natural fen, our results show significantly lower fluxes of CH4 (p<0.001), which correlate with higher bulk density, lower organic matter content, and higher pH and SO42− concentration in the constructed fen. Revegetation did not stimulate CH4 production, but increased CO2 uptake and reduced N2O emissions relative to the non-vegetated control. These results suggest that revegetation strategies and water chemistry might be more important controls on GHG fluxes than substrate quality in a constructed fen. Although the current edaphic conditions in the constructed fen support the potential for a net uptake of GHGs over the growing season, additional monitoring is required to evaluate if these conditions will persist in the long-term. We recommend that future reclamation projects should consider the potential effects of construction materials on water chemistry prior to use in fen reclamation.

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.

Total and methyl mercury concentrations in sediment and water of a constructed wetland in the Athabasca Oil Sands Region

In the Athabasca Oil Sands Region in northeastern Alberta, Canada, oil sands operators are testing the feasibility of peatland construction on the post-mining landscape. In 2009, Syncrude Canada Ltd. began construction of the 52 ha Sandhill Fen pilot watershed, including a 15 ha, hydrologically managed fen peatland built on sand-capped soft oil sands tailings. An integral component of fen reclamation is post-construction monitoring of water quality, including salinity, fluvial carbon, and priority pollutant elements. In this study, the effects of fen reclamation and elevated sulfate levels on mercury (Hg) fate and transport in the constructed system were assessed. Total mercury (THg) and methylmercury (MeHg) concentrations in the fen sediment were lower than in two nearby natural fens, which may be due to the higher mineral content of the Sandhill Fen peat mix and/or a loss of Hg through evasion during the peat harvesting, stockpiling and placement processes. Porewater MeHg concentrations in the Sandhill Fen typically did not exceed 1.0 ng L−1. The low MeHg concentrations may be a result of elevated porewater sulfate concentrations (mean 346 mg L−1) and an increase in sulphide concentrations with depth in the peat, which are known to suppress MeHg production. Total Hg and MeHg concentrations increased during a controlled mid-summer flooding event where the water table rose above the ground surface in most of the fen. The Hg dynamics during this event showed that hydrologic fluctuations in this system exacerbate the release of THg and MeHg downstream. In addition, the elevated SO42− concentrations in the peat porewaters may become a problem with respect to downstream MeHg production once the fen is hydrologically connected to a larger wetland network that is currently being constructed.

Topsoil removal to minimize internal eutrophication in rewetted peatlands and to protect downstream systems against phosphorus pollution: A case study from NE Germany

This study was conducted in the course of a fen rewetting project in NE Germany aiming to restore a heavily drained spring-percolation mire used as pasture land for more than 100 years. Shallow top soil removal (TSR) up to 40cm was applied to remove the upper degraded peat layer in order to eliminate accumulated nutrients and unwanted seed banks as well as generating material for infilling drain ditches and building dams. This measure has well known positive effects on species development, but very little was known about the phosphorus (P) status in the newly exposed peat soils and porewater. Therefore, we investigated (i) the P mobilisation potential of surface peat soils, (ii) net P release rates in intact soil cores with different degree of peat decomposition, and (iii) P concentrations in porewater of rewetted fen areas with TSR compared to areas without removal and refilled drain ditches. We highlighted that TSR strongly reduced the P mobilisation potential and thereby also the concentration of dissolved P in the porewater at the peat surface. Furthermore, we found low net P release rates close to 0mgPm−2d−1 (median, n=9) in the cut-over areas with less degraded peat similar to those documented for natural fens. Despite of high P concentrations up to 2.6mgL−1 in rewetted areas without TSR (about 50% of total peatland area) there was no evidence of elevated P export to other low-nutrient areas of the fen or in a close-by lake due to high P retention capacity of the iron-rich degraded peat (molar Fe:P ratios >10). It can be concluded that TSR is a suitable measure to recover nutrient poor conditions in rewetted fens in a relatively short timeframe instead of decades to centuries compared to rewetting measures without TSR. This measure is highly recommended if degraded peatlands are characterised by a low P retention capacity or low molar Fe/P ratios in degraded peat (<10) respectively and above all if downstream areas include nutrient-poor systems highly sensitive regarding slightly increased P inputs.

Above and below-ground nutrient cycling: a criteria for assessing the biogeochemical functioning of a constructed fen

Recent peatland restoration studies have highlighted the need to modify the conventional approach of monitoring the recovery of biogeochemical functions through above-ground processes by integrating below-ground components, which are potentially sensitive indicators of reclamation trajectory in long-term monitoring programs. In this study, the recovery of nutrient cycling processes were assessed from both above and below-ground perspectives in a fen constructed on a post-mining landscape in the Athabasca oil sands region, Canada. The goal of this study was to understand if and how different revegetation strategies (seedlings (SDL); moss layer transfers (MLT); seedlings with moss transfer (SMLT) and a control treatment (CTRL)) influence the evolution of biogeochemical functions in the constructed fen relative to a natural reference (REF). The treatments were replicated 6 times and monitored over 2 growing seasons. Our results showed that revegetation facilitated both above-ground productivity and the cycling of below-ground nutrients, especially in the species-rich SMLT plots. Supply of labile substrates in the re-vegetated plots increased microbial potential activity. This was reflected in higher rates of respiration (c.7.8g CO2m−2day−2), nutrient acquisition (net immobilization) and productivity (c. −16.3g CO2m−2day−2) among revegetated plots relative to the CTRL. Nutrient dynamics within the constructed fen suggest that phosphorus limitation (N:P ratio>20) could hamper the establishment of a diverse plant community, whereas the build-up of microbial biomass appears to be NO3− limited. Our results also emphasize the need to track the evolution of nutrients cycling processes through long-term monitoring programs, and identify the potential use of ammonification, nitrogen mineralization and phosphorus availability as functional indicators of a fen’s recovery trajectory towards conditions present in natural fens.

Effect of environmental factors on production and bioavailability of dissolved organic carbon from substrates available in a constructed and reference fens in the Athabasca oil sands development region

Fen peatlands cover a large proportion of the landscape in boreal Alberta and thus these ecosystems are likely to be constructed as part of mine closure following oil sands mining. Peatlands are large sources of dissolved organic carbon (DOC); however, little is known about DOC dynamics in constructed peatlands. We investigated DOC production and its bioavailability from substrates collected from a constructed fen and natural fens (reference ecosystems) in the Athabasca oil sands region near Fort McMurray, Alberta. Dominant vegetation and other substrates used in fen construction, like peat, petroleum coke, tailings sand and upland soil, were collected for the study. The effect of substrate type, salinity and temperature on DOC production and bioavailability were analyzed in a laboratory incubation study. Sedges and trees produced the largest amount of DOC, followed by peat and moss in all the fens, whereas the substrates from the constructed fen such as petroleum coke, tailings sand and upland soil produced very little DOC per unit dry mass. In addition, temperature and salinity were also significant explanatory variables for both initial (30 day) and final (60 day) net DOC production rates. It was also observed that greater production of DOC resulted in lower pH and higher electrical conductivity (EC) in incubation jar water. In addition, the quality of DOC depended upon the type of substrate. Specific ultraviolet absorbance at 254nm wavelength (SUVA254) indicated that sedges produced DOC having less aromatic humic substances than peat, tailings sand, upland soil and petroleum coke. Substrate, salinity and temperature at which DOC was produced, and interactions among these factors were all found to significantly explain variation in DOC bioavailability. Aromatic content of DOC produced, based on SUVA254, had an effect on its bioavailability. As various substrates produced different amounts and quality of DOC, and since construction material like petroleum coke and tailings sand produce very little DOC, it is likely that establishment of the vegetation community and its composition will play an important role in DOC dynamics at the constructed fen in the future.

The influence of the aeration status (ODR, Eh) of peat soils on their ability to produce methane

Methane is a greenhouse gas having well-known impacts on global radiative forcing. However, understanding the dynamics and thresholds of methane formation in peatlands, which undergo cyclic aeration and anoxia, is currently limited even though it is crucial for reliable estimation of methane emission to the atmosphere. The purpose of this study was to estimate the optimal range and thresholds of aeration conditions, which impact methane formation in upper layers of peat originating from a natural fen (East Poland). The experiment was conducted under laboratory conditions on two groups of differently treated soils which were incubated at field water capacity. One group was incubated in air and another in helium, both at temperatures of 5, 10 and 20 °C. Direct soil aeration estimation included measurements of redox potential and oxygen diffusion rate. The latter was used for the first time as an indicator of methane formation in soil. Both the aerated and anoxic groups showed that methane formation took place at ODR of below 20 μg O2 m−2 s−1 and Eh of below +240 mV which are the higher threshold levels for methanogenesis than previously reported. Maximum methanogenic activity amounted up to 71.86 mg CH4 kgDW−1 d−1. Aeration was capable of reducing this methanogenic activity by 28–100 %. Decreasing temperatures and aeration increased the time until the initiation of CH4 production (p < 0.05, n = 72).