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Peatlands are found on all continents, covering 3% of the global land area. However, the spatial extent and causes of metal enrichment in peatlands is understudied and no attempt has been made to evaluate global patterns of metal enrichment in bog and fen peatlands, despite that certain metals and rare earth elements (REE) arise from anthropogenic sources. We analyzed 368 peat cores sampled in 16 countries across five continents and measured metal and other element concentrations at three depths down to 70 cm as well as estimated cumulative atmospheric S deposition (1850–2009) for each site. Sites were assigned to one of three distinct broadly recognized peatland categories (bog, poor fen, and intermediate-to-moderately rich fen) that varied primarily along a pH gradient. Metal concentrations differed among peatland types, with intermediate-to-moderately rich fens demonstrating the highest concentrations of most metals. Median enrichment factors (EFs; a metric comparing natural and anthropogenic metal deposition) for individual metals were similar among bogs and fens (all groups), with metals likely to be influenced by anthropogenic sources (As, Cd, Co, Cu, Hg, Pb, and Sb) demonstrating median enrichment factors (EFs) > 1.5. Additionally, mean EFs were substantially higher than median values, and the positive correlation (< 0.40) with estimated cumulative atmospheric S deposition, confirmed some level of anthropogenic influence of all pollutant metals except for Hg that was unrelated to S deposition. Contrary to expectations, high EFs were not restricted to pollutant metals, with Mn, K and Rb all exhibiting elevated median EFs that were in the same range as pollutant metals likely due to peatland biogeochemical processes leading to enrichment of these nutrients in surface soil horizons. The global patterns of metal enrichment in bogs and fens identified in this study underscore the importance of these peatlands as environmental archives of metal deposition, but also illustrates that biogeochemical processes can enrich metals in surface peat and EFs alone do not necessarily indicate atmospheric contamination. [ABSTRACT FROM AUTHOR]

Microtopography is a common attribute of wetlands, particularly boreal bog and fen peatlands. This self-organized patterning is primarily an autogenic process; however, the role of allogenic forces such as disturbance in the maintenance of microtopography is poorly understood. In this study, we quantify the effect of fire on the distribution of the microtopographic gradient in boreal bogs using a before-after wildfire natural experiment. We also quantify the change in spatial abundance of microforms in boreal treed peatlands over a 100-year successional chronosequence. Wildfire nearly doubled the range of the microtopographic gradient, increasing the relative abundance of low-elevation microforms (hollows), although the distribution of elevations was influenced by peatland ontogeny at the time of wildfire. Through succession, raised microforms (hummocks) became more abundant, presumably due to autogenic surface drying facilitating hummock species expansion into adjacent hollows. Although autogenic processes may be responsible for the development of self-organized spatial patterning in wetlands, disturbances such as wildfire are necessary for maintaining boreal peatland microtopography over extended time scales. Because of the tight linkage between microtopography, species diversity, and ecosystem function, these feedbacks between wildfire and microtopography are critical for understanding peatland dynamics and the potential impact of a changing environment. Key words: self-organized patterning, succession, diversity, carbon, ecosystem resilience. La microtopographie est un attribut commun des milieux humides, plus particulierement des tourbieres ombrotrophes et des tourbieres minerotrophes en zone boreale. Cette structuration auto-organisee est un processus principalement autogenique mais le role des forces allogeniques, comme une perturbation, dans le maintien de la microtopographie est mal compris. Dans cette etude, nous avons quantifie l'effet du feu sur la distribution du gradient microtopographique dans les tourbieres boreales a l'aide d'une experience naturelle avant et apres feu. Nous avons aussi quantifie le changement dans l'abondance spatiale des microformes dans des tourbieres boreales boisees au cours d'une chronosequence successionnelle de plus de 100 ans. Le feu a plus que double l'etendue du gradient microtopographique, augmentant ainsi l'abondance relative des microformes basses (depressions), bien que la distribution des hauteurs ait ete influencee par l'ontogenese de la tourbiere lorsque le feu est survenu. Au cours de la succession, les microformes surelevees (buttes) sont devenues plus abondantes, vraisemblablement a cause de l'assechement autogenique en surface qui a facilite l'expansion des especes associees aux buttes dans les depressions adjacentes. Meme si les processus autogeniques peuvent etre responsables du developpement de la structuration spatiale auto-organisee dans les milieux humides, les perturbations telles que les feux sont necessaires pour maintenir la microtopographie des tourbieres boreales a long terme. A cause du lien etroit entre la microtopographie, la diversite des especes et la fonction de l'ecosysteme, ces retroactions entre les feux et la microtopographie sont essentielles pour comprendre la dynamique des tourbieres et l'impact potentiel d'un environnement en mutation. [Traduit par la Redaction] Mots-cles : structuration auto-organisee, succession, diversite, carbone, resilience des ecosystemes., Introduction Self-organized spatial patterning is a common phenomenon in a variety of ecosystems and can play a key role in ecosystem stability (Rietkerk and van de Koppel 2008). Positive feedbacks [...]

Peatlands account for 15 to 30% of the world's soil carbon (C) stock and are important controls over global nitrogen (N) cycles. However, C and N concentrations are known to vary among peatlands contributing to the uncertainty of global C inventories, but there are few global studies that relate peatland classification to peat chemistry. We analyzed 436 peat cores sampled in 24 countries across six continents and measured C, N, and organic matter (OM) content at three depths down to 70 cm. Sites were distinguished between northern (387) and tropical (49) peatlands and assigned to one of six distinct broadly recognized peatland categories that vary primarily along a pH gradient. Peat C and N concentrations, OM content, and C:N ratios differed significantly among peatland categories, but few differences in chemistry with depth were found within each category. Across all peatlands C and N concentrations in the 10–20 cm layer, were 440 ± 85.1 g kg-1 and 13.9 ± 7.4 g kg-1, with an average C:N ratio of 30.1 ± 20.8. Among peatland categories, median C concentrations were highest in bogs, poor fens and tropical swamps (446–532 g kg-1) and lowest in intermediate and extremely rich fens (375–414 g kg-1). The C:OM ratio in peat was similar across most peatland categories, except in deeper samples from ombrotrophic tropical peat swamps that were higher than other peatlands categories. Peat N concentrations and C:N ratios varied approximately two-fold among peatland categories and N concentrations tended to be higher (and C:N lower) in intermediate fens compared with other peatland types. This study reports on a unique data set and demonstrates that differences in peat C and OM concentrations among broadly classified peatland categories are predictable, which can aid future studies that use land cover assessments to refine global peatland C and N stocks. [ABSTRACT FROM AUTHOR]

Peatlands contain a significant fraction of global soil carbon, but how these reservoirs will respond to the changing climate is still relatively unknown. A global picture of the variations in peat organic matter chemistry will aid our ability to gauge peatland soil response to climate. The goal of this research is to test the hypotheses that (a) peat carbohydrate content, an indicator of soil organic matter reactivity, will increase with latitude and decrease with mean annual temperatures, (b) while peat aromatic content, an indicator of recalcitrance, will vary inversely, and (c) elevation will have a similar effect to latitude. We used Fourier Transform Infrared Spectroscopy to examine variations in the organic matter functional groups of 1034 peat samples collected from 10 to 20, 30–40, and 60–70 cm depths at 165 individual sites across a latitudinal gradient of 79°N–65°S and from elevations of 0–4,773 m. Carbohydrate contents of high latitude peat were significantly greater than peat originating near the equator, while aromatic content showed the opposite trend. For peat from similar latitudes but different elevations, the carbohydrate content was greater and aromatic content was lower at higher elevations. Higher carbohydrate content at higher latitudes indicates a greater potential for mineralization, whereas the chemical composition of low latitude peat is consistent with their apparent relative stability in the face of warmer temperatures. The combination of low carbohydrates and high aromatics at warmer locations near the equator suggests the mineralization of high latitude peat until reaching recalcitrance under a new temperature regime. Plain Language Summary: Peatlands are a large global soil carbon reservoir, containing a quantity of carbon that is equivalent to about half or more of the carbon dioxide in the atmosphere. What will be their fate on a warming planet? Across a latitudinal gradient from 79°N to 65°S, we measured the fraction of the peat made up of carbohydrates, which are easily decomposed, and of aromatics, which are less easily decomposed. We found that peat from high latitudes and high elevations had greater carbohydrate content, while aromatic content showed the opposite trend. Larger carbohydrate content in organic matter indicates greater decomposability, while greater aromatic content indicates lower decomposability. We suggest that this latitude/elevation difference that we observed predicts how high‐latitude and high‐elevation peats may change under warmer conditions. Our work indicates that while a large portion of the carbohydrate fraction in these peats could be lost upon warming, releasing greenhouse gases, a residual fraction will survive and become more aromatic‐rich, making the remainder more resistant to rapid decomposition. Key Points: Peatland soil organic matter stability can be evaluated through the relative abundances of carbohydrate and aromatic content in peatPeat at higher latitudes and elevations has larger carbohydrate and smaller aromatic content relative lower latitudes and elevationsOur results foreshadow a transition of organic matter from higher latitude peatlands to a more recalcitrant form in response to warming [ABSTRACT FROM AUTHOR]

To purchase or authenticate to the full-text of this article, please visit this link: http://dx.doi.org/10.1111/j.1365-2745.2006.01180.x Byline: BRIAN W. BENSCOTER, DALE H. VITT Keywords: allometry; boreal forest; bryophyte; ground layer production; growth model; growth morphology; modelling; net primary production; Pleurozium schreberi; Ptilium crista-castrensis Abstract: Summary 1 Accurate assessment of net primary production is vital for understanding carbon (C) cycling, both regionally and globally. However, this requires effective methods of measurement that acknowledge the unique characteristics of the subject or area being monitored. 2 Feathermosses dominate the ground layer of boreal upland ecosystems and play a vital role in soil C accumulation, accounting for up to 50% of total photosynthesis. Feathermoss growth is both apical and lateral, with branches of determinate length at maturity produced at consistent frequencies along the stem. 3 Traditional methods of estimating annual production of feathermosses underestimate total plant production because they do not account for lateral growth of the previous year's immature branches. We present a conceptual model of feathermoss growth using Pleurozium schreberi that includes apical and lateral annual growth. From this model, we provide a modified method to more accurately estimate P. schreberi production. The top 3 cm of 10 P. schreberi plants from each of five bog peatlands in Alberta, Canada, were collected. For each plant, distance from the stem apex to branch insertion, branch length and dry mass, and dry mass of 3-mm stem sections were measured and used to define model parameters that, due to lack of significant variability among the sites, can be applied regionally and possibly globally throughout the boreal zone. An additional 20 plants were collected from a sixth site for testing the accuracy of our modified method. 4 Assessment of our method showed an insignificant mean difference between observed and calculated production values. Furthermore, comparison of our method with traditional methods showed a c. 25% underestimation of annual production by the latter. Traditional methods underestimate annual biomass production of P. schreberi by c. 73 g m.sup.-2, accounting for more than 14 Tg C year.sup.-1 across the boreal region. 5 Our study shows that accounting for species-specific growth characteristics when estimating ground layer production has a substantial impact on boreal C budget assessments and therefore the terrestrial C cycle. Article History: Received 22 March 2006 revision accepted 24 August 2006 Handling Editor: Matthew Turnbull Article note: Correspondence: Brian W. Benscoter (tel. +1 618 536 2331; fax +1 618 453 3441; e-mail BBensc01@SIU.edu).

Droughts and other extreme precipitation events are predicted to increase in intensity, duration, and extent, with uncertain implications for terrestrial carbon (C) sequestration. Soil wetting from above (precipitation) results in a characteristically different pattern of pore-filling than wetting from below (groundwater), with larger, well-connected pores filling before finer pore spaces, unlike groundwater rise in which capillary forces saturate the finest pores first. Here we demonstrate that pore-scale wetting patterns interact with antecedent soil moisture conditions to alter pore-scale, core-scale, and field-scale C dynamics. Drought legacy and wetting direction are perhaps more important determinants of short-term C mineralization than current soil moisture content in these soils. Our results highlight that microbial access to C is not solely limited by physical protection, but also by drought or wetting-induced shifts in hydrologic connectivity. We argue that models should treat soil moisture within a three-dimensional framework emphasizing hydrologic conduits for C and resource diffusion. [ABSTRACT FROM AUTHOR]

We examined the water balance of a forested ombrotrophic peatland and adjacent burned peatland in the boreal plain of western Canada over a 3-year period. Complete combustion of foliage and fine branches dramatically increased shortwave radiation inputs to the peat surface while halting all tree transpiration at the burned site. End-of-winter snowpack was 7-25% higher at the burned site likely due to decreased ablation from the tree canopy at the unburned site. Shrub regrowth at the burned site was rapid post-fire, and shading by the shrub canopy in the burned site approached that of the unburned site within 3 years after fire. Site-averaged surface resistance to evaporation was not different between sites, though surface resistance in hollows was lower in the burned site. Water loss at both burned and unburned sites is largely driven by surface evaporative losses. Evaporation at the burned site marginally exceeded the sum of pre-fire transpiration and interception at the unburned site, suggesting that evapotranspiration during the growing season was 20-40 mm greater at the burned peatland. Although the net change in water storage during the growing season was largely unchanged by fire, the lack of low-density surface peat in the burned site appears to have decreased specific yield, leading to greater water table decline at the burned site despite similar net change in storage. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Boreal peatland ecosystems occupy about 3.5 million km2 of the earth's land surface and store between 250 and 455 Pg of carbon (C) as peat. While northern hemisphere boreal peatlands have functioned as net sinks for atmospheric C since the most recent deglaciation, natural and anthropogenic disturbances, and most importantly wildfire, may compromise peatland C sinks. To examine the effects of fire on local and regional C sink strength, we focused on a 12 000 km2 region near Wabasca, AB, Canada, where ombrotrophic Sphagnum-dominated bogs cover 2280 km2 that burn with a fire return interval of 123±26 years. We characterized annual C accumulation along a chronosequence of 10 bog sites, spanning 1–102 years-since-fire (in 2002). Immediately after fire, bogs represent a net C source of 8.9±8.4 mol m−2 yr−1. At about 13 years after fire, bogs switch from net C sources to net C sinks, mainly because of recovery of the moss and shrub layers. Subsequently, black spruce biomass accumulation contributes to the net C sink, with fine root biomass accumulation peaking at 34 years after fire and aboveground biomass and coarse root accumulation peaking at 74 years after fire. The overall C sink strength peaks at 18.4 mol C m−2 yr−1 at 75 years after fire. As the tree biomass accumulation rate declines, the net C sink decreases to about 10 mol C m−2 yr−1 at 100 years-since-fire. We estimate that across the Wabasca study region, bogs currently represent a C sink of 14.7±5.1 Gmol yr−1. A decrease in the fire return interval to 61 years with no change in air temperature would convert the region's bogs to a net C source. An increase in nonwinter air temperature of 2 °C would decrease the regional C sink to 6.8±2.3 Gmol yr−1. Under scenarios of predicted climate change, the current C sink status of Alberta bogs is likely to diminish to the point where these peatlands become net sources of atmospheric CO2-C. [ABSTRACT FROM AUTHOR]

Questions: What is the mechanism of bog ground layer colonization post-fire? Is species colonization stochastic or does facilitation occur? Location: Boreal bog peatland near Crow Lake, Alberta, Canada. Methods: Diaspore-addition treatments were applied in 2003 to autoclaved peat samples from high and low microtopographic positions within a recently burned bog. Colonization was assessed within the plots in 2005 and compared to control plots to determine treatment success and patterns of colonization. Results: A significant degree of ground layer colonization was found two years after fire, with Polytrichum stricture dominating the site. Colonization was greater in low (wet) plots, although only P. stricture and Sphagnum angustifolium had significant colonization. No effect of diaspore addition was observed and Sphagnum was only found in conjunction with P. stricture. Conclusions: Environmental conditions and species life history strategy are more important than diaspore availability for post-fire colonization. True mosses (e.g. P. strictum) appear to facilitate Sphagnum colonization. [ABSTRACT FROM AUTHOR]

Questions: Does post-fire plant succession in boreal bogs vary microtopographically and are successional patterns re- producible among similar microtopographic features? Does succession preserve microtopography post-fire? Location: Boreal bog peatlands near Sinkhole Lake and Athabasca, Alberta, Canada. Methods: We assessed microtopographic variation in post- fire plant community succession through stratigraphic macrofossil analysis of bog soil cores collected from high (hummock) and low (hollow) positions. We conducted vegetation surveys and collected soil cores from ten hummocks and hollows in each bog. Pre-fire microtopographic status was inferred based on floral composition and compared to current microtopography. Results: Hollow vegetation was more variable than hum- mocks, both in present composition and post-fire succession. The successional trajectory of current hummocks was relatively uniform, showing relatively rapid shifts to Sphagnum fuscum dominance, but varied greatly in hollows. Hollows, although compositionally variable, were typically perpetuated following fire, while hummocks had an approximately equal chance of being perpetuated or becoming hollows. Conclusions: Greater compositional variability at lower microtopographic positions, both spatially and temporally, is most likely due to the ability of hollows to support a wider range of species and greater susceptibility to severe disturbance. Likewise, spatial variability in fire severity appears to be responsible for perpetuation or change in microtopographic status, favouring the creation of hollows over maintenance of hummocks. [ABSTRACT FROM AUTHOR]