Relationships among testate amoebae (Protozoa), vegetation and water chemistry in five Sphagnum-dominated peatlands in Europe

To study the relationships between groups of organisms and the degree to which these relationships are consistent across major climatic gradients, we analysed the testate amoeba ( Protozoa ) communities, vegetation and water chemistry of one peatland in five countries: Switzerland, The Netherlands, Great Britain, Sweden and Finland, as part of the BERI (Bog Ecosystem Research Initiative) project. The relationships between the different data sets and subsets were investigated by means of detrended correspondence analysis, canonical correspondence analysis and Mantel permutation tests. The comparison of data on vegetation and testate amoebae showed that inter-site differences are more pronounced for the vegetation than for the testate amoebae species assemblage. Testate amoebae are a useful tool in multi-site studies and in environmental monitoring of peatlands because: (1) the number of species in Sphagnum -dominated peatlands is much higher than for mosses or vascular plants; (2) most peatland species are cosmopolitan in their distributions and therefore less affected than plants by biogeographical distribution patterns, thus differences in testate amoeba assemblages can be interpreted primarily in terms of ecology; (3) they are closely related to the ecological characteristics of the exact spot where they live, therefore they can be used to analyse small-scale gradients that play a major role in the functioning of peatland ecosystems. This study revealed the existence of small-scale vertical gradients within the vegetation and life-form niche separation in response to water chemistry. The deep-rooted plants such as Carex spp. and Eriophorum spp. are related to the chemistry of water sampled at or near the ground water table, whereas the mosses are not. Testate amoebae were shown to be ecologically more closely related to the chemistry of water sampled at or near the water table level and to the mosses than to the deep-rooted plants.     

Modeling Northern Peatland Decomposition and Peat Accumulation

To test the hypothesis that long-term peat accumulation is related to contemporary carbon flux dynamics, we present the Peat Decomposition Model (PDM), a new model of long-term peat accumulation. Decomposition rates of the deeper peat are directly related to observable decomposition rates of fresh vegetation litter. Plant root effects (subsurface oxygenation and fresh litter inputs) are included. PDM considers two vegetation types, vascular and nonvascular, with different decomposition rates and aboveground and belowground litter input rates. We used PDM to investigate the sensitivities of peat accumulation in bogs and fens to productivity, root:shoot ratio, tissue decomposability, root and water table depths, and climate. Warmer and wetter conditions are more conducive to peat accumulation. Bogs are more sensitive than fens to climate conditions. Cooler and drier conditions lead to the lowest peat accumulation when productivity is more temperature sensitive than decomposition rates. We also compare peat age–depth profiles to field data. With a very general parameterization, PDM fen and bog age–depth profiles were similar to data from the the most recent 5000 years at three bog cores and a fen core in eastern Canada, but they overestimated accumulation at three other bog cores in that region. The model cannot reliably predict the amount of fen peat remaining from the first few millennia of a peatland's development. This discrepancy may relate to nonanalogue, early postglacial climatic and nutrient conditions for rich-fen peat accumulation and to the fate of this fen peat material, which is overlain by a bog as the peatland evolves, a common hydroseral succession in northern peatlands. Because PDM sensitivity tests point to these possible factors, we conclude that the static model represents a framework that shows a consistent relationship between contemporary productivity and fresh-tissue decomposition rates and observed long-term peat accumulation. Received 19 June 2000; accepted 24 January 2001.     

Carbon sequestration in peatland: patterns and mechanisms of response to climate change

The response of peatlands to changes in the climatic water budget is crucial to predicting potential feedbacks on the global carbon (C) cycle. To gain insight on the patterns and mechanisms of response, we linked a model of peat accumulation to a model of peatland hydrology, then applied these models to empirical data spanning the past 5000 years for the large mire Store Mosse in southern Sweden. We estimated parameters for C sequestration and height growth by fitting the peat accumulation model to two age profiles. Then, we used independent reconstruction of climate wetness and model reconstruction of bog height to examine changes in peatland hydrology. Reconstructions of C sequestration showed two distinct patterns of behaviour: abrupt increases associated with major transitions in vegetation and dominant Sphagnum species (fuscum, rubellum–fuscum and magellanicum stages), and gradual decreases associated with increasing humification of newly formed peat. Carbon sequestration rate ranged from a minimum of 14 to a maximum of 72 g m^?2 yr^?1, with the most rapid changes occurring in the past 1000 years. Vegetation transitions were associated with periods of increasing climate wetness during which the hydrological requirement for increased seepage loss was met by rise of the water table closer to the peatland surface, with the indirect result of enhancing peat formation. Gradual decline in C sequestration within each vegetation stage resulted from enhanced litter decay losses from the near‐surface layer. In the first two vegetation stages, peatland development (i.e., increasing surface gradient) and decreasing climate wetness drove a gradual increase in thickness of the unsaturated, near‐surface layer, reducing seepage water loss and peat formation. In the most recent vegetation stage, the surface diverged into a mosaic of wet and dry microsites. Despite a steady increase in climate wetness, C sequestration declined rapidly. The complexity of response to climate change cautions against use of past rates to estimate current or to predict future rates of peatland C sequestration. Understanding interactions among hydrology, surface structure and peat formation are essential to predicting potential feedback on the global C cycle.     

Global and regional importance of the tropical peatland carbon pool

Accurate inventory of tropical peatland is important in order to (a) determine the magnitude of the carbon pool; (b) estimate the scale of transfers of peat‐derived greenhouse gases to the atmosphere resulting from land use change; and (c) support carbon emissions reduction policies. We review available information on tropical peatland area and thickness and calculate peat volume and carbon content in order to determine their best estimates and ranges of variation. Our best estimate of tropical peatland area is 441 025 km² (～11% of global peatland area) of which 247 778 km² (56%) is in Southeast Asia. We estimate the volume of tropical peat to be 1758 Gm³ (～18–25% of global peat volume) with 1359 Gm³ in Southeast Asia (77% of all tropical peat). This new assessment reveals a larger tropical peatland carbon pool than previous estimates, with a best estimate of 88.6 Gt (range 81.7–91.9 Gt) equal to 15–19% of the global peat carbon pool. Of this, 68.5 Gt (77%) is in Southeast Asia, equal to 11–14% of global peat carbon. A single country, Indonesia, has the largest share of tropical peat carbon (57.4 Gt, 65%), followed by Malaysia (9.1 Gt, 10%). These data are used to provide revised estimates for Indonesian and Malaysian forest soil carbon pools of 77 and 15 Gt, respectively, and total forest carbon pools (biomass plus soil) of 97 and 19 Gt. Peat carbon contributes 60% to the total forest soil carbon pool in Malaysia and 74% in Indonesia. These results emphasize the prominent global and regional roles played by the tropical peat carbon pool and the importance of including this pool in national and regional assessments of terrestrial carbon stocks and the prediction of peat‐derived greenhouse gas emissions.     

Decomposition and Peat Accumulation in Rich Fens of Boreal Alberta, Canada

Fens are important components of Canada’s western boreal forests, occupying about 63% of the total peatland area and storing about 65% of the peatland carbon. Rich fens, dominated by true moss-dominated ground layers, make up more than half of the fens in the region. We studied organic matter accumulation in three rich fens that represent the diversity in structural types. We used in situ decomposition socks, a new method that examines actual decomposition throughout the upper peat profile over an extended period of time. We coupled our carbon loss data with macrofossil analyses and dated peat profiles using ²¹⁰Pb. Across the three rich fens and in the top 39 cm of the peat column, dry mass increases on average 3.1 times. From our dry mass loss measurements, we calculate that annual mass loss from the top 39 cm varies from 0.52 to 1.08 kg m². Vertical accumulation during the past 50 years has varied from 16 to 32 cm and during these 50 years, organic matter accumulation has averaged 174 g m⁻² y⁻¹ compared to 527 g m² y⁻¹ dry mass loss, with additional mass losses of 306 g m² y⁻¹ from peat between 50 and 150 years of age. Organic matter accumulation from our rich fens compares well with literature values from boreal bogs, whereas peat bulk densities increase about three times within the uppermost 40 cm, much more than in bogs. Hence, rich fens accumulate peat not because the plant material is especially hard to decompose, is acidic, or has the catotelm especially close to the surface, but because dense, rapidly produced inputs outweigh the relatively rapid decomposition process of the upper peat column. Author Contributions: DHV conceived study; KS, KW, SF, & DHV performed research; DHV, KW analyzed data; DHV, KW contributed new methods; DHV, KW wrote the paper.     

Soil surface CO2 flux in a Minnesota peatland

Soil surface CO₂ flux was measured in hollow and hummock microhabitats in a peatland in north central Minnesota from June to October in 1991. We used a closed infrared gas exchange system to measure soil CO₂ flux. The rates of CO₂ evolution from hummocks (9.8 ± 3.5 g m⁻² d⁻¹, [mean ± SE]) were consistently higher than those from hollows (5.4 ± 2.9 g m⁻² d⁻¹) (the hummock values included the contribution of moss dark respiration, which may account for 10–20% of the total measured flux). The soil CO₂ flux was strongly temperature-dependent (Q₁₀ ≈ 3.7) and appeared to be linearly related to changes in water table depth. An empirical multiplicative model, using peat temperature and water table depth as independent variables, explained about 81% of the variance in the CO₂ flux data. Using the empirical model with measurements of peat temperature and estimates of hollow/hummock microtopographic distribution (relative to water table elevation), daily rates of “site-averaged” CO₂ evolution were calculated. For the six-month period (May–October), the total soil CO₂ released from this ecosystem was estimated to be about 1340 g CO₂ m⁻². Published as Paper No. 9950, Journal Series, Nebraska Agricultural Research Division, University of Nebraska, Lincoln, NE, USA.     

Effects on water chemistry after drainage of a bog for forestry

Drainage for forestry has received increasing interest during recent decades. Generally, drainage concerns wet mineral soils while the utilization of peatlands is a matter of controversy. The peatlands mainly involved are fens, while forestry on bogs is an insignificant activity. Consequently, hydrology of bogs and effects of drainage on their hydrochemistry are little known.The investigation performed aimed at elucidating the parent conditions and the drainage impact on the hydrology and hydrochemistry of an ombrotrophic bog. Two bogs were first compared during a calibration period of two years and then, after drainage of one of them, during a period of three years. The second bog was kept virgin as a control.Considerable influences on runoff and stream water quality were found from the surrounding mineral soil uplands of the bog. Significant differences occurred between the chemical composition of the groundwater in the mineral soil and in the bog peat.Effects on runoff water from drainage of the bog deviate from drainage of minerotrophic peatlands with respect to decreased concentrations and losses of organic carbon and nitrogen. From two small bog catchments within the drained bog, there generally were greater losses of nutrients than from the catchment as a whole. Furthermore, the runoff from the drained bog decreased in comparison with the undrained condition. However, there were also similarities to drainage of other peatlands as regards increased pH, alkalinity and concentrations of sulphate. Also, concentrations of total-phosphorus increased in spite of a decreased phosphate (MRP) concentration.