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Raised peatlands, or bogs, are gently mounded landforms that are composed entirely of organic matter1–4 and store the most carbon per area of any terrestrial ecosystem5. The shapes of bogs are critically important because their domed morphology4,6,7 accounts for much of the carbon that bogs store and determines how they will respond to interventions8,9 to stop greenhouse gas emissions and fires after anthropogenic drainage10–13. However, a general theory to infer the morphology of bogs is still lacking4,6,7. Here we show that an equation based on the processes universal to bogs explains their morphology across biomes, from Alaska, through the tropics, to New Zealand. In contrast to earlier models of bog morphology that attempted to describe only long-term equilibrium shapes4,6,7 and were, therefore, inapplicable to most bogs14–16, our approach makes no such assumption and makes it possible to infer full shapes of bogs from a sample of elevations, such as a single elevation transect. Our findings provide a foundation for quantitative inference about the morphology, hydrology and carbon storage of bogs through Earth’s history, as well as a basis for planning natural climate solutions by rewetting damaged bogs around the world.Physical analysis of processes universal to raised peatlands produces an equation that explains their morphology and carbon storage across biomes, from Alaska to New Zealand. [ABSTRACT FROM AUTHOR]

The tropical peat swamp forests of South‐East Asia are being rapidly converted to agricultural plantations of oil palm and Acacia creating a significant global "hot‐spot" for CO2 emissions. However, the effect of this major perturbation has yet to be quantified in terms of global warming potential (GWP) and the Earth's radiative budget. We used a GWP analysis and an impulse‐response model of radiative forcing to quantify the climate forcing of this shift from a long‐term carbon sink to a net source of greenhouse gases (CO2 and CH4). In the GWP analysis, five tropical peatlands were sinks in terms of their CO2 equivalent fluxes while they remained undisturbed. However, their drainage and conversion to oil palm and Acacia plantations produced a dramatic shift to very strong net CO2‐equivalent sources. The induced losses of peat carbon are ~20× greater than the natural CO2 sequestration rates. In contrast, a radiative forcing model indicates that the magnitude of this shift from a net cooling to warming effect is ultimately related to the size of an individual peatland's carbon pool. The continuous accumulation of carbon in pristine tropical peatlands produced a progressively negative radiative forcing (i.e., cooling) that ranged from −2.1 to −6.7 nW/m2 per hectare peatland by 2010 CE, referenced to zero at the time of peat initiation. Peatland conversion to plantations leads to an immediate shift from negative to positive trend in radiative forcing (i.e., warming). If drainage persists, peak warming ranges from +3.3 to +8.7 nW/m2 per hectare of drained peatland. More importantly, this net warming impact on the Earth's radiation budget will persist for centuries to millennia after all the peat has been oxidized to CO2. This previously unreported and undesirable impact on the Earth's radiative balance provides a scientific rationale for conserving tropical peatlands in their pristine state. Tropical peatlands in South‐East Asia store large amounts of carbon in their peat soils. Widespread conversion of tropical peatlands to agricultural oil palm and pulp plantations entails draining water from the peat soils. These drier soil conditions lead to peat carbon being rapidly released to the atmosphere as carbon dioxide. We calculated the effect of these significant greenhouse gas emissions on the global climate and found that they will contribute to climate warming for several centuries. Reducing drainage of tropical peatlands and restoring drained peatlands will reduce this climate warming impact. [ABSTRACT FROM AUTHOR]

Northern peatlands are an important source for greenhouse gases, but their capacity to produce methane remains uncertain under changing climatic conditions. We therefore analyzed a 43 year time series of the pore-water chemistry to determine if long-term shifts in precipitation altered the vertical transport of solutes within a large peat basin in northern Minnesota. These data suggest that rates of methane production can be finely tuned to multidecadal shifts in precipitation that drive the vertical penetration of labile carbon substrates within the Glacial Lake Agassiz Peatlands. Tritium and cation profiles demonstrate that only the upper meter of these peat deposits was flushed by downwardly moving recharge from 1965 to 1983 during a Transitional Dry-to-Moist Period. However, a shift to a moister climate after 1984 drove surface waters much deeper, largely flushing the pore waters of all bogs and fens to depths of 2 m. Labile carbon compounds were transported downward from the rhizosphere to the basal peat at this time producing a substantial enrichment of methane in Δ14C with respect to the solid-phase peat from 1991 to 2008. These data indicate that labile carbon substrates can fuel deep production zones of methanogenesis that more than doubled in thickness across this large peat basin after 1984. Moreover, the entire peat profile apparently has the capacity to produce methane from labile carbon substrates depending on climate-driven modes of solute transport. Future changes in precipitation may therefore play a central role in determining the source strength of peatlands in the global methane cycle. [ABSTRACT FROM AUTHOR]

In this study, we contrast the fluorescent properties of dissolved organic matter ( DOM) in fens and bogs in a Northern Minnesota peatland using excitation emission matrix fluorescence spectroscopy with parallel factor analysis ( EEM- PARAFAC). EEM- PARAFAC identified four humic-like components and one protein-like component and the dynamics of each were evaluated based on their distribution with depth as well as across sites differing in hydrology and major biological species. The PARAFAC- EEM experiments were supported by dissolved organic carbon measurements ( DOC), optical spectroscopy ( UV-Vis), and compositional characterization by ultrahigh resolution Fourier transform ion cyclotron resonance mass spectroscopy ( FT- ICR MS). The FT- ICR MS data indicate that metabolism in peatlands reduces the molecular weights of individual components of DOM, and oxygen-rich less aromatic molecules are selectively biodegraded. Our data suggest that different hydrologic and biological conditions within the larger peat ecosystem drive molecular changes in DOM, resulting in distinctly different chemical compositions and unique fluorescent fingerprints. PARAFAC modeling of EEM data coupled with ultrahigh resolution FT- ICR MS has the potential to provide significant molecular-based information on DOM composition that will support efforts to better understand the composition, sources, and diagenetic status of DOM from different terrestrial and aquatic systems. [ABSTRACT FROM AUTHOR]

Ground water recharge is assumed to occur primarily at raised bog crests in northern peatlands, which are globally significant terrestrial carbon reservoirs. We synoptically surveyed vertical profiles of peat pore water δ18O and δ2H from a range of bog and fen landforms across the Glacial Lake Agassiz Peatlands, northern Minnesota. Contrary to our expectations, we find that local-scale recharge penetrates to not only the basal peat at topographically high bog crests but also transitional Sphagnum lawns and low-lying fen water tracks. Surface landscape characteristics appear to control the isotopic composition of the deeper pore waters (depths ≥0.5 m), which are partitioned into discrete ranges of δ18O on the basis of landform type (mean ± standard deviation for bog crests = −11.9 ± 0.4‰, lawns = −10.6 ± 0.1‰, fen water tracks = −8.8 ± 1.0‰). Fen water tracks have a shallow free-water surface that is seasonally enriched by isotope fractionating evaporation, fingerprinting recharge to underlying pore waters at depths ≥3 m. Isotope mass balance calculations indicate on average 12% of the waters we sampled from the basal peat of the fen water tracks was lost to surface evaporation, which occurred prior to advection and dispersion into the underlying formation. These new data provide direct support for the hypothesis that methane production in deeper peat strata is fuelled by the downward transport of labile carbon substrates from the surface of northern peat basins. Copyright © 2013 John Wiley & Sons, Ltd. [ABSTRACT FROM AUTHOR]

Multiple analyses of dissolved organic carbon (DOC) from pore waters were conducted to define the processes that govern carbon balance in peatlands: (1) source, reactivity, and transport of DOC with respect to vegetation, peat, and age of carbon substrate, (2) reactivity of DOC with respect to molecular size, and (3) lability to photoxidation of surficial DOC. We found that surface organic production fuels heterotrophic respiration at depth in advection-dominated peatlands, especially in fens. Fen DOC was Δ14C enriched relative to the surrounding fen peat, and fen respiration products were similar to this enriched DOC indicating that DOC was the main microbial substrate. Bog DOC was more variable showing either enrichment in ∆14C at depth or ∆14C values that follow peat values. This variability in bogs is probably controlled by the relative importance of vertical transport of labile carbon substrates within the peat profile versus DOC production from bog peat. These results extended our set of observations to 10 years at one bog-fen pair and add two additional bog-fen pairs to our series of observations. Anaerobic incubations of peat, rinsed free of residual DOC, produced DOC and respiration products that were strikingly similar to the peat values in a bog and two fens. This result demonstrated conclusively that downward advection is the process responsible for the presence of modern DOC found at depth in the peat column. Fen DOC has lower C/N values and up to twice as much LMW (<1 kDa) DOC as bogs due to differences in organic inputs and greater microbial processing. Fluorescence irradiation experiments showed that fen DOC is more photolabile than bog DOC. [ABSTRACT FROM AUTHOR]

Aeolian dust is rarely considered an important source for nutrients in large peatlands, which generally develop in moist regions far from the major centers of dust production. As a result, past studies assumed that the Everglades provides a classic example of an originally oligotrophic, P-limited wetland that was subsequently degraded by anthropogenic activities. However, a multiproxy sedimentary record indicates that changes in atmospheric circulation patterns produced an abrupt shift in the hydrology and dust deposition in the Everglades over the past 4,600 y. A wet climatic period with high loadings of aeolian dust prevailed before 2800 cal BP (calibrated years before present) when vegetation typical of a deep slough dominated the principal drainage outlet of the Everglades. This dust was apparently transported from distant source areas, such as the Sahara Desert, by tropical storms according to its elemental chemistry and mineralogy. A drier climatic regime with a steep decline in dustfall persisted after 2800 cal BP maintaining sawgrass vegetation at the coring site as tree islands developed nearby (and pine forests covered adjacent uplands). The marked decline in dustfall was related to corresponding declines in sedimentary phosphorus, organic nitrogen, and organic carbon, suggesting that a close relationship existed between dustfall, primary production, and possibly, vegetation patterning before the 20th century. The climatic change after 2800 cal BP was probably produced by a shift in the Bermuda High to the southeast, shunting tropical storms to the south of Florida into the Gulf of Mexico. [ABSTRACT FROM AUTHOR]

Aim We present a model to account for self-assembly of the slough–ridge–tree island patterned landscape of the central Everglades in southern Florida via feedbacks among landforms, hydrology, vegetation and biogeochemistry. We test aspects of this model by analysing vegetation composition in relation to local and landscape-level drivers. Location We quantified vegetation composition and environmental characteristics in central Water Conservation Area (WCA) 3A, southern WCA-3A and southern WCA-3B in southern Florida, based on their divergence in water management and flow regimes over the past 50 years. Methods In 562 quadrats, we estimated species coverages and quantified maximum, minimum and average water depth, soil depth to bedrock, normalized difference vegetation index (NDVI) and proximity to the nearest tree island. We used non-metric multi-dimensional scaling (NMS) to relate compositional variation to local and landscape-level factors, and evaluated environmental differences among eight a priori vegetation types viaanova. Results Water depth and hydroperiod decreased from sloughs to ridges to tree islands, but regions also differed significantly in the abundance of several community types and the hydroregimes characterizing them. NMS revealed two significant axes of compositional variation, tied to local gradients of water depth and correlated factors, and to a landscape-scale gradient of proximity to tall tree islands. Sawgrass height and soil thickness increased toward higher ridges, and NDVI was greatest on tree islands. Main conclusions This study supports four components of our model: positive feedback of local substrate height on itself, woody plant invasion and subsequent P transport and concentration by top predators nesting on taller tree islands, compositional shifts in sites close to tree islands due to nutrient leakage, and flow-induced feedback against total raised area. Regional divergence in the relationship of community types to current hydroregimes appears to reflect a lag of a few years after shifts in water management; a longer lag would be expected for shifts in landscape patterning. Both local and landscape-level drivers appear to shape vegetation composition and soil thickness in the central Everglades. [ABSTRACT FROM AUTHOR]

We report the results of an investigation on the processes controlling heat transport in peat under a large bog in the Glacial Lake Agassiz Peatlands. For 2 years, starting in July 1998, we recorded temperature at 12 depth intervals from 0 to 400 cm within a vertical peat profile at the crest of the bog at sub-daily intervals. We also recorded air temperature 1 m above the peat surface. We calculate a peat thermal conductivity of 0.5 W m -1 °C-1 and model vertical heat transport through the peat using the SUTRA model. The model was calibrated to the first year of data, and then evaluated against the second year of collected heat data. The model results suggest that advective pore-water flow is not necessary to transport heat within the peat profile and most of the heat is transferred by thermal conduction alone in these waterlogged soils. In the spring season, a zero-curtain effect controls the transport of heat through shallow depths of the peat. Changes in local climate and the resulting changes in thermal transport still may cause non-linear feedbacks in methane emissions related to the generation of methane deeper within the peat profile as regional temperatures increase. [ABSTRACT FROM AUTHOR]

Recent research indicates that accumulation and release of biogenic gas from northern peatlands may substantially affect future climate. Sudden release of free-phase gas bubbles into the atmosphere may preclude the conversion of methane to carbon dioxide in the uppermost oxic layer of the peat, resulting in greater contribution of methane to the atmosphere than is currently estimated. The hydrology of these peatlands also affects and is affected by this process, especially when gas is released suddenly and episodically. Indirect hydrological evidence indicates that ebullitive gas releases are relatively frequent in some peatlands and time-averaged rates may be significantly greater than diffusive releases. Estimates of free-phase gas contained in peat have ranged from 0 to nearly 20% of the peat volume. Abrupt changes in the volume of gas may alter hydraulic gradients and movement of water and solutes in peat, which in turn could alter composition and fluxes of the gas. Peat surfaces also move vertically and horizontally in response to accumulation and release of free-phase gas. Future research should address the distribution, temporal variability, and relative significance of ebullition in peatlands and the consequent hydrological responses to these gas-emission events. [ABSTRACT FROM AUTHOR]

1 Groundwater–peatland interactions were assessed by a regional survey in the Hudson Bay Lowlands, where the rapid rate of isostatic uplift has perturbed hydrological flow systems across a 6000-year chronosequence.2 A 24 000 km2 study area along the Albany River consists of 55% fen, 35% bog and 10% mineral soil. The peatland vegetation may be further subdivided into 11 noda, which are closely related to different water levels, ranges in water chemistry, and peat landform type. Species richness generally declines with increasing water level and acidity, whereas the gradient from bog to extremely rich fen is marked by the changing abundance and occurrence of fen-indicator species.3 Bog landforms are restricted to physiographic settings where surface waters flow downwards and the bog vegetation is therefore isotated from the influence of geogenous waters. In contrast, fens are located in areas where mineral solutes are transported to the peat surface either by upwelling groundwater or by advective/dispersion along lateral flow paths.4 Peatlands spread across the study area between 6000 and 3000 bp, coinciding with the emergence of new land from the sea. The release of organic acids from the nearly continuous peat cover acidified this calcareous landscape, leading to the convergence of the surface-water chemistry into four discrete groupings of pH vs. calcium.5 Isostatic uplift, however, continues to alter the topography, fluvial geometry and groundwater flow systems of the lowlands, maintaining diverse peatland types on land surfaces of similar age. The formation of water-table mounds under the interfluvial divides and rising moraine system spurred the development of raised bogs, whereas the formation of regional seepage faces for goundwater on the margins of the moraine and rivers of the till plain maintains large areas of fen.6 Although peatland succession seems to follow predictable pathways within a given hydrogeological setting, these pathways are locally altered by tectonic drivers that continually modify surface and groundwater flow systems. In this large peat basin the pace and pathway of peatland succession seems to be driven by tectonic rather than climatic forcing.Journal of Ecology(2004)92, 1054 –1070 [ABSTRACT FROM AUTHOR]

1 The Hudson Bay Lowlands have been rising isostatically for the past 7000 years, creating a regional chronosequence as new land emerges from the sea. Rates of uplift are most rapid in the eastern portion of the lowlands near the lower Albany River study area.2 The stratigraphy of three raised bogs was investigated to determine rates and pathways of peatland development in the Albany River region. The bogs are distributed evenly along the regional chronosequence from the oldest site at Oldman (5980 ± 100 bp) to progressively younger sites at Albany River (4810 ± 70) and Belec Lake (3960 ± 60).3 Each bog had the same stratigraphic sequence, beginning with a basal tidal marsh assemblage that was rapidly replaced by aLarix-dominated swamp forest, followed by aPicea-forested bog, and ultimately a non-forested bog. The bog–fen boundary is marked by the disappearance of fen indicators, dominance of bog-formingSphagna, and a sharp decline in nitrogen. Each of these successional stages was associated with different rates of vertical growth.4 The rate of successional change was more rapid at the younger sites, and their vertical growth curve was more curvilinear. The formation of a raised bog, for example, was 1.3 times more rapid at Albany River and 5.5 times more rapid at Belec Lake than at Oldman. Belec Lake reached its ultimate successional stage first, although it was the last site to emerge from the sea.5 The differential rate of isostatic uplift across this region rather than climate was the principal environmental driver for peatland development. The faster rate of uplift on the lower reaches of the drainage basin continues to reduce the regional slope, impede drainage and shift river channels, continually altering the local hydrogeological setting.6 Groundwater flow simulations based on the Dupuit equation show that the growth of these raised bogs was probably constrained by their local hydrogeological setting. Bog formation was first induced by the creation of interfluvial divides between headwardly eroding streams or shifting river channels, and further bog growth was ultimately constrained by the width of the interfluve and the depth of river incision. The Belec Lake bog was the first to approach its limiting height because its narrow interfluve could only support a low water-table mound.7 Although peatland succession largely followed the same conservative pathway at each site, both the pace and direction of these pathways were set by geological processes, which are probably the decisive drivers for the evolution of this large peat basin.Journal of Ecology(2004)92, 1036 –1053 [ABSTRACT FROM AUTHOR]

Presents a study that investigated the rates of peat accumulation during the postglacial period in several sites from Alaska to Newfoundland, with special emphasis on northern Minnesota. Relationship between mass and age; Locations of sites from which peat cores were collected; Influence of age on accumulated dry mass in North American peat deposits.

Hydraulic head was overpressured at middepth in a 4.2-m thick raised bog in the Glacial Lake Agassiz peatlands of northern Minnesota, and fluctuated in response to atmospheric pressure. Barometric efficiency (BE), determined by calculating ratios of change in hydraulic head to change in atmospheric pressure, ranged from 0.05 to 0.15 during July through November of both 1997 and 1998. The overpressuring and a BE response were caused by free-phase gas contained primarily in the center of the peat column between two or more semielastic, semiconfining layers of more competent peat. Two methods were used to determine the volume of gas bubbles contained in the peat, one using the degree of overpressuring in the middepth of the peat, and the other relating BE to specific yield of the shallow peat. The volume of gas calculated from the overpressuring method averaged 9%, assuming that the gas was distributed over a 2-m thick overpressured interval. The volume of gas using the BE method averaged 13%. Temporal changes in overpressuring and in BE indicate that the volume of gaseous-phase gas also changed with time, most likely because of rapid degassing (ebullition) that allowed sudden loss of gas to the atmosphere. Estimates of gas released during the largest ebullition events ranged from 0.3 to 0.7 mol m−2 d−1. These ebullition events may contribute a significant source of methane and carbon dioxide to the atmosphere that has so far largely gone unmeasured by gas-flux chambers or tower-mounted sensors. [ABSTRACT FROM AUTHOR]

(1) A topographic survey was conducted with both laser and electronic levels across a spring fen, a raised bog and the water track (fen) between them, in the Lost River Peatland of northern Minnesota. (2) The survey demonstrated that the spring fen consisted of a peat mound whose slopes were steeper than that of the bog. (3) Three successive surveys in 1982 and 1983 showed altitudinal changes in benchmarks fixed in trees relative to a base level on a power-line pylon located in the water track. Nearly all benchmarks rose, with the greatest rises occurring near the centres of the raised bog (11 cm) and spring fen (6 cm) in contrast to very slight rises across the water track. (4) The most likely explanation for this altitudinal change is a swelling of the sub surface peat in response to artesian fluid pressure generated by regional hydraulic gradients. (5) Very precise determinations of altitude are thus possible with a laser or electronic level on an unstable peat substrate, providing great care is taken in surveying techniques. [ABSTRACT FROM AUTHOR]

(1) Red Lake Peatland m northern Minnesota covers an area of about 80 × 15 km which is uninterrupted by streams or uplands and consists of a vast patterned complex of rinsed bogs and water tracks. Infra-red photography and LANDSAT imagery have been used to examine their interrelationships (2) To the west a large water track up to 5 km broad carries minerotrophic water from uplands adjacent to the peatland. This western water track is differentiated into a series of transverse ridges (strings) and linear pools (flarks), among which are much larger teardrop-shaped islands consisting of a forested head and a long tail of dwarf birch (Betula pumila var glandulifera) leading downslope. (3) Rinsed bogs with radiating lines of spruce trees and 'bog drains' form the watershed divides to the east. The bogs are fringed downslope by non patterned Sphagnum lawns on which incipient water tracks arise. These recipient tracks lead downslope into well-defined water tracks that flow between other rinsed bogs apparently shaping these bogs into ovoid islands several kilometres long. (4) The major types of vegetation of the Red Lake Peatland were determined subjectively by the Braun-Blanquet method and are characterized by different water chemistry (5) Two types of bog vegetation occur on the rinsed bogs and ovoid islands. They have waters of low pH (range 3.8-4.1), low Ca[sup 2+] concentration (range 0.5-2.1 mg l[sup -1]) and low conductivity. K[sub corr] (range 12-50 ·S cm[sup -1]). (6) Three types of fen vegetation occur on stnngs, flarks and teardrop islands in the water tracks these fens are characterized by high pH (range 5.2-7.0), high Ca[sup 2+] concentration (range 3.0-19.6 mg l[sup -1]) and high K[sub corr] (range 23-128 µS cm[sup -1]). (7) Poor fens closely resemble bog or fen vegetation, but they may be distinguished by their location water chemistry and the presence or absence of certain indicator species. Poor fens occur on the broad Sphagnum lawns... [ABSTRACT FROM AUTHOR]

Examines the regional associations between raised bogs and the climate, groundwater and landscape of northwestern Minnesota. Absence of relation to the westward climatic gradient; Groundwater movement during droughts; Relation of bogs to physiographic features.

1. The vascular flora of 65 raised bogs was determined across climatic gradients in eastern North America. The major geographic patterns in species richness and floristic composition were analysed using linear regression, detrended correspondence analysis (DCA), and canonical correspondence analysis (CCA). 2. The vascular bog flora consists of 81 species in this region. Four major floristic regions distinguished by DCA correspond to the geographic zonation of bog land- forms. Each of these floristic regions is characterized by a different mean value for species richness. 3. Raised bogs in the southern-continental floristic region (I) contain fewer than 20 species and have the most impoverished vascular floras in eastern North America. In the transitional-continental (II) and northern-continental (III) regions. the bog flora is slightly larger. although the mean number of species remains below 26. 4. The richest bog floras are found in the maritime region (IV), where species richness declines along a latitudinal gradient from 50 species in the south (subregion IV.1) to 32 in the north (subregion IV.2). 5. The relationship of species richness to various environmental factors was analysed using linear regression. The most important factors are mean annual precipitation (MAP) and annual freezing degree-days (FDD) with a base temperature of 0°C. Factors that are also significantly related to species richness are mean annual temperature (MAT), the number of wet-to-dry habitats. and the concentration of magnesium and sodium in the surface water. No significant relationship was found for growing degree-days (base temperature = 5°C.), mean annual snow depth. or spatial dimensions of bogs. 6. The regressions indicate that a climatic threshold of 1000mm of annual precipitation and 1000 freezing degree-days separates the floristically rich maritime bogs from the floristically impoverished bogs of northern and continental regions. [ABSTRACT FROM AUTHOR]

Two peat mounds have developed in the Lost River peatland of northern Minnesota. One has the chemical and physical properties of an extremely rich fen and the other has the properties, of a raised bog. The two mounds are separated by a water truck with poor-fen vegetation and chemistry. The vegetation at Lost River can be divided into live noda that correspond to landform units: spring-fen channel, springs fen forest, marginal swamp forest, water track, and raised bog. These vegetation types have well-defined ranges for pit and calcium concentration. Ordinations of the vascular plant and bryophyte data indicate a close relationship between the vegetation and both moisture and chemical gradients. The link between vegetation and chemistry is also supported by plots of species richness vs. pH and calcium concentration in which the peak in species numbers occurs within the rich-fen range. The chemistry of the surface waters at Lost River is largely determined by the mixing of alkaline groundwater with precipitation, because the entire peatland is located at least seasonally within a discharge zone for groundwater. Mixing models indicate that the amount of groundwater within the surface waters ranges from 50% in the spring-fen channels to 1% on the raised bog. The development of the two Feat mounds was reconstructed from peat cores collected near the crests of the spring-fen mound and raised bog. The raised bog developed over a depression, which was first filled in with ten peat before minerotrophic sphagna invaded the site around 2625 B.P. By 2200 B.P. all fen indicator species had disappeared and the site was dominated by assemblages similar to those in the present raised bog. The spring-fen mound, however, developed over m rise in the mineral substrate, which was not covered by peat until 3000 B.P. The mound was quickly colonized by Sphagnum and no fen indicators appeared until 1160 B.P. At this time the bog vegetation was replaced by a sedge fen containing assemblages similar to the present spring-fen channel. This sharp reversal from bog to fen under the spring-fen mound can best be explained by the discharge of alkaline groundwater at the peat surface in sufficient quantities to convert the bog vegetation to a spring-fen channel. [ABSTRACT FROM AUTHOR]

Raised bogs represent end-products of peatland development that are generally assumed to be decoupled from the regional groundwater system. However, the development of two peat mounds in northern Minnesota was driven by three major reversals in its groundwater-flow regime. A 4000-year record of groundwater flow was reconstructed by stratigraphic studies that utilized both botanical indicators of the surface-water chemistry, and mineral indicators of the pore-water chemistry and chemical weathering regime. The mineral stratigraphy indicated that the peat mounds were initially formed under a discharge (upward flow) regime. During the succeeding moist period, these peat mounds developed into raised bogs as their water-table mounds drove local recharge (downward) flow into the mineral substratum. A major reversal to a prevailing discharge regime at 1200 BP, however, converted the smaller peat mound into a spring fen and weathered the silicate minerals within the peat profile of the larger mound. This reversal was apparently caused by the onset of extended droughts, which dissipate the water table mound within these peat landforms. [ABSTRACT FROM PUBLISHER]

Peatlands represent large terrestrial carbon banks. Given that most peat accumulates in boreal regions, where low temperatures and water saturation preserve organic matter, the existence of peat in (sub)tropical regions remains enigmatic. Here we examined peat and plant chemistry across a latitudinal transect from the Arctic to the tropics. Near-surface low-latitude peat has lower carbohydrate and greater aromatic content than near-surface high-latitude peat, creating a reduced oxidation state and resulting recalcitrance. This recalcitrance allows peat to persist in the (sub)tropics despite warm temperatures. Because we observed similar declines in carbohydrate content with depth in high-latitude peat, our data explain recent field-scale deep peat warming experiments in which catotelm (deeper) peat remained stable despite temperature increases up to 9 °C. We suggest that high-latitude deep peat reservoirs may be stabilized in the face of climate change by their ultimately lower carbohydrate and higher aromatic composition, similar to tropical peats. Large peatlands exist at high latitudes because flooded conditions and cold temperatures slow decomposition, so the presence of (sub)tropical peat is enigmatic. Here the authors show that low-latitude peat is preserved due to lower carbohydrate and greater aromatic content resulting in chemical recalcitrance. [ABSTRACT FROM AUTHOR]