Intermediate Fen Research Articles

Electron Accepting Capacities of a Wide Variety of Peat Materials From Around the Globe Similarly Explain CO2 and CH4 Formation

AbstractIn organic soils, the availability of terminal electron acceptors (TEAs) determines the ratio of CO2 to CH4 formation under anoxic conditions. While the importance of electron accepting capacities (EACs) of organic matter is increasingly acknowledged, redox properties of organic matter have only been investigated in a limited set of peat and reference materials. Therefore, we incubated 60 peat samples from 15 sites covering a variety of both bog and poor to intermediate fen samples and characterized their capacities to serve as TEA for anaerobic CO2 formation. We quantified CO2 and CH4 formation and changes in available EAC in anoxic incubations of 56 days. In our experiment, on average 36.5% of CO2 could be attributed to CH4 formation, assuming an CO2:CH4 ratio for methanogenesis of 1:1. Regarding the remaining CO2 formed, for which a corresponding TEA would be needed, we could on average explain 70.8% by corresponding consumption of EAC from both organic and inorganic TEAs, the latter contributing less than 0.1%. When the initial EAC was high, CO2 formation from the apparent consumption of EAC was high and outweighed CO2 formation from methanogenesis. Rapid depletion of available EAC, especially in reactive peat, resulted in a higher share of CO2 from CH4 formation. Our study demonstrates that EAC provides the most important redox buffer for competitive suppression of methanogenesis in peat soils, particularly under fluctuating water table levels, when EAC is repeatedly regenerated. Moreover, electron budgets including EAC of organic matter could largely explain anaerobic CO2 production.

Variation in carbon and nitrogen concentrations among peatland categories at the global scale.

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.

Rich-fen bryophytes in past and recent mire vegetation in a successional land uplift area

Most rich-fen bryophyte species are currently declining and red listed in many European countries. Little is known about their past and current occurrence. We investigated past and recent bryophyte assemblages in mires in the land uplift coast of Finland. The study areas included primary succession areas where mire development started c. 6000 BP. In total, seven mires were studied in two successional transects along the land uplift coast. The past occurrences of rich-fen and other bryophytes were studied in 45 mire stratigraphic peat profiles, and recent occurrences were collected from 158 vegetation plots of 10 m × 10 m. Bryophyte subfossils indicated that the central parts of the basins developed first to wet rich fens with groundwater influence, which developed towards intermediate fens or poorer mire types. Most mire bryophytes occurred in about the same proportion in peat profiles as in recent vegetation. Five rich-fen species ( Hamatocaulis lapponicus, H. vernicosus, Meesia longiseta, M. triquetra and Pseudocalliergon trifarium) were clearly more common in peat profiles than in the present mire vegetation, where these species were very rare and appeared only in small patches without sporophytes. These rich-fen species have had markedly wider distributions in the past, probably linked to climate fluctuations, whereas current occurrences are becoming scarce because of multiple anthropogenic factors such mire drainage and climate change.

Dissimilar bacterial and fungal decomposer communities across rich to poor fen peatlands exhibit functional redundancy

to the chemical quality of carbon substrates for soil microbial decomposers, with leaves and roots deposited in the peat surface and subsurface that potentially decompose faster. This study characterized the bacterial and fungal communities present along a nutrient gradient ranging from rich to poor fen peatlands and assessed the metabolic potential of these communities to mineralize a variety of organic matter substrates of varying chemical complexity using substrate-induced respiration (SIR) assays. Distinct microbial communities existed between rich, intermediate and poor fens, but SIR in each of the three sites exhibited the same pattern of carbon mineralization, providing support for the concept of functional redundancy, at least under standardized in vitro conditions. Preferential mineralization of simple organic substrates in the rich fen and complex compounds in the poor fen was not observed. Similarly, no preference was given to ‘‘native’’ organic matter extracts derived from each fen, with microbial communities opting for the most bioavailable substrate. This study suggests that soil bacteria and fungi might be able to respond relatively rapidly to shifts in vegetation communities and subsequent changes in the quality of carbon substrate additions to peatlands associated with environmental and climatic change.

Resource use by old and modern dairy cattle breeds on semi-natural mountain pastures, Central Norway

The objective of this pilot study was to compare resource use in a mountainous summer farming landscape between old and modern dairy cow breeds during a five-day period. The modern breed used a larger part of the landscape than the old breed, most likely due to differences in habitat patterns. The old breed group preferred semi-natural pastures, while the modern breed preferred overgrown semi-natural meadows, intermediate fen, intermediate wooded fen, and grass-rich sub-alpine birch woodland. Both breeds spent most time grazing grasses, but the modern breed showed a higher frequency of grasses and Vaccinium myrtillus in its diet, while the old breed showed a higher frequency of bushes and trees. The pilot study shows some trends supplementing and strengthening earlier results on how modern and traditional cattle breeds are differing in their impact on vegetation based on their use of space and their different diets.

Homoacetogenesis: A potentially underappreciated carbon pathway in peatlands

Due to anaerobic conditions, peatland soils store globally significant amounts of carbon and are an important source of methane, a potent greenhouse gas. One component of anaerobic carbon cycling, homoacetogenesis (i.e., acetate formation from carbon dioxide and dihydrogen via the acetyl-CoA pathway), has rarely been quantified in natural environments because it is commonly viewed as being thermodynamically unfavorable. Here we show that in a laboratory incubation using a tracer method, homoacetogenesis occurred at significant rates in soils from three peatlands (bog, intermediate fen, and cedar swamp) despite thermodynamic conditions that appeared to be unfavorable for this process. Homoacetogens consumed dihydrogen at rates up to 3- to 10-times faster than methanogens, and homoacetogenesis accounted for 16–63% of total acetate production, with the balance likely coming from fermentation processes. Our results show that homoacetogenesis can play an important role in regulating acetate dynamics, methane production, and carbon cycling in peatlands.

Examining the role of allogenous and autogenous factors in the long-term dynamics of a temperate headwater peatland (southern Québec, Canada)

Plant macrofossil and testate amoebae analyses were conducted on a sedimentary core taken from a headwater peatland located near the summit of a hill at the northern extension of the Adirondack Mountains (Québec, Canada). The aims were to reconstruct the developmental stages of the peatland and to examine the allogenous and autogenous factors associated with its long-term dynamics. Results were compared with a quantitative paleoclimatic reconstruction based on the modern analog technique using pollen data from the same core. The long-term development of the peatland (pond—rich fen—intermediate fen—poor fen—bog) mainly reflects an autogenous hydroseral succession. Active peat accumulation under the relatively dry climate of the Early Holocene suggests that summer temperature was a critical factor in peat accumulation through enhanced biomass production. A major long-term decrease in net peat accumulation rates and a progressive decline of mean water-table depth occurred during the Mid- to Late-Holocene (7900–500calyr BP), even though annual precipitation was abundant at the time. The high summer temperature associated to the highest evapotranspiration rates maintained a low water table which in turn led to strong humification of the peat. A similar, synchronous pattern in vertical peat accumulation dynamics characterized another nearby peatland. Based on these results, we suggest that small peatlands situated atop a watershed and/or within a small watershed are ecosystems sensitive to changes in precipitation and/or evapotranspiration, due to their limited water supply.

Small-scale variability in peatland pore-water biogeochemistry, Hudson Bay Lowland, Canada

The Hudson Bay Lowland (HBL) of northern Ontario, Manitoba and Quebec, Canada is the second largest contiguous peatland complex in the world, currently containing more than half of Canada's soil carbon. Recent concerns about the ecohydrological impacts to these large northern peatlands resulting from climate change and resource extraction have catalyzed a resurgence in scientific research into this ecologically important region. However, the sheer size, heterogeneity and elaborate landscape arrangements of this ecosystem raise important questions concerning representative sampling of environmental media for chemical or physical characterization. To begin to quantify such variability, this study assessed the small-scale spatial (1m) and short temporal (21day) variability of surface pore-water biogeochemistry (pH, dissolved organic carbon, and major ions) in a Sphagnum spp.-dominated, ombrotrophic raised bog, and a Carex spp.-dominated intermediate fen in the HBL. In general, pore-water pH and concentrations of dissolved solutes were similar to previously reported literature values from this region. However, systematic sampling revealed consistent statistically significant differences in pore-water chemistries between the bog and fen peatland types, and large within-site spatiotemporal variability. We found that microtopography in the bog was associated with consistent differences in most biogeochemical variables. Temporal changes in dissolved solute chemistry, particularly base cations (Na+, Ca2+ and Mg2+), were statistically significant in the intermediate fen, likely a result of a dynamic connection between surficial waters and mineral-rich deep groundwater. In both the bog and fen, concentrations of SO42− showed considerable spatial variability, and a significant decrease in concentrations over the study period. The observed variability in peatland pore-water biogeochemistry over such small spatial and temporal scales suggests that under-sampling in northern peatland environments could lead to erroneous conclusions concerning the abundance and distribution of natural elements and pollutants alike.

Methane and methanogen community dynamics across a boreal peatland nutrient gradient

Field and lab-based methane (CH4) fluxes and methanogen community structure were characterized across three peatlands in central Ontario (Canada) representing a successional and nutrient gradient from rich to poor fens. Air temperature was a strong and significant predictor of both CH4 and carbon dioxide (CO2) fluxes among the three sites. Net CH4 efflux and in vitro CH4 production potential were significantly greater in the rich and intermediate than the poor fen site. Although the poor fen site had the lowest water table position, this was not a significant predictor of CH4 emissions and in general the 3 sites were relatively wet compared to many northern peatlands. Consistently, during spring and fall, ethanol stimulated in vitro CH4 production potential from the poor fen, but not the rich and intermediate sites, indicating substrate limitation for CH4 production in the poor fen. Lower rates of CH4 production and emissions in the poor fen site were consistent with our hypotheses based on poorer substrate quality and a lack of sedges in that peatland type. However phylogeny of dominant methanogens inferred from terminal restriction fragment length polymorphism (T-RFLP) analyses of 16S rDNA illustrated inconsistencies with previous reports of methanogens in northern peatlands. For example members likely of the family Methanosaetaceae (obligate high-affinity acetate fermenters) comprised a substantial portion of total methanogen population in the poor fen. In contrast, members of the order Methanomicrobiales (obligate CO2 reducers) were important methanogens in the rich and intermediate fens and not detected in the poor fen. Methanogen community structure based on T-RFLP across the 3 sites was distinct during spring, while during fall methanogen communities in the poor fen samples were still somewhat distinct from those in the rich and intermediate fens. Methanogen diversity (community richness and evenness) was not correlated with rates of CH4 production in the spring when soil respiration, and presumably rhizosphere activity, was slow. However, diversity was a significant predictor of CH4 production in the early fall (when both production and emissions rates were higher), indicating that methanogen diversity can potentially play a role in biogeochemical cycling and greenhouse gas emissions in northern peatlands.

Peatland Stream Lipid Biogeochemistry Features in an Intermediate Fen Peatland, Ontario Canada

Changes in climate and land use pressures in the boreal region may influence peatland stream sediment organic carbon (C) dynamics. Fifteen to 50% of stream sediment organic C resides in recalcitrant pools, with the lipids accounting for up to 25% of the peatland C pool. Nevertheless, lipid mineralization within peatlands and their draining stream sediments is poorly understood. Potential esterase activity, which is known to be an important enzyme group in recalcitrant C decomposition, is presented as an indicator of lipid hydrolysis in three streams surrounding an intermediate fen peatland. Organic C concentration ranged from 5 to 250 g C kg−1 sediment during the sampling period, with the recalcitrant C pool accounting for 15 to 20%. Fourier Transform Infrared (FT-IR) spectra were typical of humic-like substances, such as aliphatic compounds (including lipids), phenolic and other aromatic structures, carboxyl groups, and polysaccharide structures. Esterase activity was positively correlated with organic C and total nitrogen (N) concentrations, and sediment pH. Esterase was most active in the presence of high organic C fractions and recalcitrant C, supporting the hypothesis that lipid hydrolysis in the peatland stream sediments may be an important and underestimated component of peatland C sequestration dynamics.

Importance of the Water Table in Controlling Dissolved Carbon along a Fen Nutrient Gradient

Boreal fens are minerotrophic peatlands that act as important control points for dissolved C between upland and aquatic ecosystems. Fens occupy a minerotrophic continuum from “rich,” having high water tables and large nutrient contributions from upland sources, to “poor,” having low water tables and small nutrient contributions. Dissolved C within these fens will be influenced by the degree of minerotrophy, which in turn impacts peat pore water acidity and alkalinity and downstream productivity. To examine how dissolved C concentrations change along the minerotrophic gradient and to explore possible mechanisms controlling their concentration, pore water chemistry was analyzed from piezometers at 25‐, 50‐, and 100‐cm depths in rich, intermediate, and poor fens during the snow‐free periods of 2005, 2006 (dissolved organic C [DOC] only), 2007, and 2008. We found that dissolved inorganic C (DIC) concentrations increased with higher water tables (poor < intermediate < rich) and wetter years (2005 < 2007 ∼ 2008). In contrast, DOC concentrations decreased with higher water tables (rich < intermediate < poor), but the effect differed among years. Wetter conditions resulted in high DOC concentrations in the intermediate fen, low concentration in the poor fen, and no change in the rich fen. Correlation analyses suggest that DIC concentrations may be linked to groundwater contribution of carbonate materials and DOC to ionic strength and mechanisms of productivity and decomposition. Although further experimentation is required to verify these mechanisms, the evidence points to the importance of minerotrophic status when considering the role of peatlands in watershed C balances and their response to changing climate.

Alkalinity and acidity cycling and fluxes in an intermediate fen peatland in northern Ontario

Peatlands are important to global carbon (C) sequestration and surface water acid–base status, both of which are affected by peatland alkalinity and acidity cycling. Relationships among sulfate (SO4 2−), nitrate (NO3 −), organic acids (OA−), base cations (i.e., Ca2+, Mg2+, K+, and Na+), proton (H+) acidity, and bicarbonate (HCO3 −) alkalinity were investigated in an intermediate fen peatland in northern Ontario during 2004 (an average precipitation year) and 2005 (a dry summer). Potential evapotranspiration was higher and the water table, groundwater input from the uplands, and runoff were lower during 2005. Net inputs of base cations, HCO3 −, SO4 2−, and OA−, and to a lesser degree NO3 −, were lower during the drier year, mainly due to lower groundwater transfer to the fen. Fen porewater HCO3 − concentration and net output were also lower in the drier year, whereas Ca2+, Mg2+, and SO4 2− concentrations and net output were higher. During the climatically average year, N immobilization, carbonic acid (H2CO3) dissociation, and OA dissociation were equally important H+-producing reactions. Peat cation exchange accounted for 50% of the H+ sink, while SO4 2− reduction and denitrification accounted for an additional 20 and 25% of the H+ sink, respectively. During the dry year, S oxidation accounted for 55% of the H+ net production, while that for H2CO3 dissociation was 70% lower than that during the climatically average year. Peat cation exchange consumed three times the acidity, and accounted for 92% of the H+ consumption during the dry year compared to the climatically average year. This was consistent with a three-fold higher net base cation export from the fen during the dry year. Based on the study results, a conceptual model was developed that describes the role of acidity formation and its implications to intermediate fen acidification.

Occurrence and habitat choice of waders in a high mountain sedimentation flat on Hardangervidda, South Norway

Studies of the occurrence and nesting habitat choice of waders were conducted at Finsefetene (1200 m a.s.l.), a high mountain sedimentation flat on the Hardangervidda plateau, South Norway during 1967-1984. Eight species occurred in the study area during the period, either regularly such as Calidris temminckii, Actitis hypoleucos, Charadrius hiaticula, Calidris alpina, or occasionally, such as Tringa totanus, Calidris maritima, Pluvialis apricaria and Phalaropus lobatus. The densities of the whole wader community on the sedimentation flat were related to the proportion of snow-free areas at Finse around 10 July, and on the date when Finsefetene becomes totally snow-free (DFSF). Of the eight species, only C. temminckii and P. lobatus were found to be positively correlated with the extent of snow-free area, while C. alpina and C. lobatus were positively correlated with DFSF. In low density years the nests were usually placed in the same locations, these obviously being optimal sites. The majority of C. temminckii nests were located in the two intermediate fen vegetation associations, and according to its availability the Caricion canescentis-nigrae was clearly selected for. Two other preferred plant associations on drier ground, Lactucion alpinae and Arctostaphyleto-Cetrarion nivalis, were also selected for. Nest location preferences for vegetation associations are also indicated for the other wader species, but the data on these are limited. Changes in river flow causing varying water levels in the surroundings are a pronounced ecological trait on Finsefetene. In years with a heavy spring flood many nests would be submerged. The location of the nests in relation to a so-called «Zero point», varied from 34 cm below to 210 cm above. In high density years the nests of the most common species, C. temminckii, were spread over most of the flat. In years with a late spring flood, after the nesting had started, some low situated nests were flooded. To visualize the wader community pattern, the distribution of the variable number and scattered nest locations were plotted on maps. Details in nest locations of C. temminckii are given for each year; for the other recorded species the map covers all years. The Finsefetene sedimentation flat proved to be a valuable high mountain habitat for wader populations on Hardangervidda.

Pathways of anaerobic carbon cycling across an ombrotrophic‐minerotrophic peatland gradient

Peatland soils represent globally significant stores of carbon, and understanding carbon cycling pathways in these ecosystems has important implications for global climate change. We measured aceticlastic and autotrophic methanogenesis, sulfate reduction, denitrification, and iron reduction in a bog, an intermediate fen, and a rich fen in the Upper Peninsula of Michigan for one growing season. In 3‐d anaerobic incubations of slurried peat, denitrification and iron reduction were minor components of anaerobic carbon mineralization. Experiments using 14C‐labeled methanogenic substrates showed that methanogenesis in these peatlands was primarily through the aceticlastic pathway, except early in the growing season in more ombrotrophic peatlands, where the autotrophic pathway was dominant or codominant. Overall, methane production was responsible for 3‐70% of anaerobic carbon mineralization. Sulfate reduction accounted for 0‐26% of anaerobic carbon mineralization, suggesting a rapid turnover of a very small sulfate pool. A large percentage of anaerobic carbon mineralization (from 29% to 85%) was unexplained by any measured process, which could have resulted from fermentation or possibly from the use of organic molecules (e.g., humic acids) as alternative electron acceptors.

Nutrient control of microbial carbon cycling along an ombrotrophic‐minerotrophic peatland gradient

Future climate change and other anthropogenic activities are likely to increase nutrient availability in many peatlands, and it is important to understand how these additional nutrients will influence peatland carbon cycling. We investigated the effects of nitrogen and phosphorus on aerobic CH4 oxidation, anaerobic carbon mineralization (as CO2 and CH4 production), and anaerobic nutrient mineralization in a bog, an intermediate fen, and a rich fen in the Upper Peninsula of Michigan. We utilized a 5‐week laboratory nutrient amendment experiment in conjunction with a 6‐year field nutrient fertilization experiment to consider how the relative response to nitrogen and phosphorus differed among these wetlands over the short and long term. Field fertilizations generally increased nutrient availability in the upper 15 cm of peat and resulted in shifts in the vegetation community in each peatland. High nitrogen concentrations inhibited CH4 oxidation in bog peat during short‐term incubations; however, long‐term fertilization with lower concentrations of nitrogen stimulated rates of CH4 oxidation in bog peat. In contrast, no nitrogen effects on CH4 oxidation were observed in the intermediate or rich fen peat. Anaerobic carbon mineralization in bog peat was consistently inhibited by increased phosphorus availability, but similar phosphorus additions had few effects in the intermediate fen and stimulated CH4 production and nutrient mineralization in the rich fen. Our results demonstrate that nitrogen and phosphorus are important controls of peatland microbial carbon cycling; however, the role of these nutrients can differ over the short and long term and is strongly mediated by peatland type.

Progress Towards a Species Inventory for Conservation of Bryophytes in Ireland

Ireland has one of the richest bryofloras in Europe, with a wealth of Atlantic species that is shared only with western Scotland. Until recently knowledge of Irish bryophyte distribution has nevertheless been insufficient to inform conservation priorities. Intensive field surveys of rare and threatened bryophytes in Ireland were therefore carried out during 1999-2005 and are continuing. The draft Red List of Irish bryophytes from 1998 has already been greatly altered by this work, with deletion of 53 taxa that were under-recorded, whereas 24 taxa have been newly discovered in Ireland and several others that had been lost for more than a century have been rediscovered. The result should eventually be a more reliable Red List that provides an effective tool for conservation of threatened bryophytes, by recognising which taxa are really threatened and which populations are of greatest importance in a European context. Action to protect bryophytes in Ireland can then be developed more effectively. It has been realised that certain habitats are especially threatened, most notably the montane 'Northern Hepatic Mat', but also some coastal sites and intermediate fens.

Palaeoecology of a palsa and a filled thermokarst pond in a permafrost peatland, subarctic Québec, Canada

Radiocarbon dating and macrofossil data from a palsa and a filled thermokarst pond within a subarctic permafrost peatland were used to reconstruct their evolution and to distinguish between allogenic and autogenic processes that had been involved in their development. Peat began to accumulate in the peatland basin shortly after 6000 cal. BR The initial stage was a shallow bay or a salty marsh, followed by a wet marsh triggered by a relatively rapid drop in sea level related to a rapid isostatic uplift of land. By 5640 cal. BP, the site had transformed into a rich fen. A high rate of peat accumulation led to the establishment of a short-lived intermediate fen by 4610 cal. BP and to a poor fen from 4200 cal. BP until 1760 cal. BP. Low water-tables associated with decreased precipitation occurred between 5170 and 4610 cal. BP, and 3100 and 1760 cal. BP Between 1760 and the Little Ice Age, there was ombrotrophication of the site largely as a result of a thick peat accumulation. During this period, autogenic processes had controlled the general hydrosere, while allogenic processes, mainly precipitation, had influenced species composition. Permafrost established during the Little Ice Age leading to palsa formation and it has been melting in response to recent climate warming and precipitation increases. Macrofossil results from the filled thermokarst pond show that plant succession used the followed hydrosere: Calliergon giganteum and Sphagnum riparium when the pond's depth was at a maximum, S. riparium and C. giganteum when the pond was partly filled in, and S. lindbergii and S. riparium since the pond has been completely filled in.

Limited effects of six years of fertilization on carbon mineralization dynamics in a Minnesota fen

Peatlands, including fens, are important ecosystems in the context of the global carbon cycle. Future climate change and other anthropogenic activities are likely to increase nutrient loading in many peatland ecosystems and a better understanding of the effects of these nutrients on peatland carbon cycling is necessary. We investigated the effects of six years of nitrogen and phosphorus fertilization, along with liming, on carbon mineralization dynamics in an intermediate fen in northern Minnesota. Specifically, we measured CO 2 and CH 4 emission from intact peat cores, as well as CH 4 production and CH 4 consumption at multiple depths in short-term laboratory incubations. Despite increased nitrogen and phosphorus availability in the upper 5 cm of peat, increased pH, and clear shifts in the vegetation community, fertilization and liming had limited effects on microbial carbon cycling in this fen. Liming reduced the net flux of CO 2 approximately 3-fold compared to the control treatment, but liming had no effect on CH 4 emissions from intact cores. There were no nutrient effects on CO 2 or CH 4 emissions from intact cores. In all treatments, rates of CH 4 production increased with depth and rates of CH 4 consumption were highest near the in situ water-table level. However, nutrient and liming had no effect on rates of CH 4 production or CH 4 consumption at any depth. Our results suggest that over at least the intermediate term, the microbial communities responsible for soil carbon cycling in this peatland are tolerant to wide ranges of nutrient concentrations and pH levels and may be relatively insensitive to future anthropogenic nutrient stress.

Phosphorus retention and movement across an ombrotrophic-minerotrophic peatland gradient

An understanding of the mechanisms controlling nutrient availability and retention in and across ecosystems allows for a greater understanding of the role of nutrients in maintaining ecosystem structure and function. To examine the underlying mechanisms of phosphorus (P) cycling in northern peatlands, we compared the retention and movement of P across a natural hydrologic/pH gradient in nine peatlands by applying as a light rain an in situ tracer amount of 32PO4 −3 to track changes in P pools (vegetation, soil, microbial) over 30 days. The 31P concentrations of available P, microbial P, and the root P at 10–20 cm did not differ across the gradient, although total soil P and aboveground vegetation P content (μg m−2) increased from bog to rich fen. Total retention of 32P in the first 24 hours of application was greatest in the bogs and intermediate fens (90–100%) and was very low (20–50%) in the rich fens. Retention of P in the different pools was dependent on the type of peatland and changed with time. In the first 24 hours in the bogs and intermediate fens, the microbial pool contained the largest amount of 32P, but by the seventh day, the aboveground vegetation contained the largest amount. In the rich fen, the recovered 32P was almost equally divided between the aboveground vegetation and the litter layer with very little in other pools. Therefore, although bogs and intermediate fens have a small total P pool, they have similar P availability to rich fens because of rapid cycling and efficient retention of P.

Calcium and pH in north and central Swedish mire waters

Summary We present data on calcium concentrations and pH in mire waters collected from different mire types in central and northern Sweden, compiled from published literature or calculated from field determinations of electrical conductivity and pH. Measurements of electrical conductivity (after subtracting that of H+ ions) were used to calculate the most probable Ca concentrations, but only when pH was 4.7 or higher. At lower pH the possible errors become too large. The data support a continuous gradient in water chemistry, but with considerable overlap, from mineral‐poor ombrotrophic bogs and minerotrophic extremely poor fens, to moderately poor fens, intermediate fens, moderately rich fens and finally to extremely rich fens, rather than a discrete division. However, for hydrological reasons, we wish to retain the separation of ombrotrophy (bog) from minerotrophy (fen). The frequency histogram of pH values from central and northern Sweden shows a bimodal tendency, although a considerable number of mires still occur close to the minimum (pH 5.3). Over‐sampling in species‐rich areas could have contributed to the depth of this apparent minimum, but not to its position along the pH scale. Changes in calcium concentrations in mire waters during the last 50 years are discussed and related to changes in pH and conductivity.