Sedge Fen Research Articles

Mire vegetation gradient established as a result of interaction with a water reservoir

In 1958, 85% of the peat-bog complex Kyselovský les, in the Czech Republic, was flooded with water from the Lipno reservoir. A new vegetation pattern has spontaneously developed in the newly established shoreline and replaced the original peat-bog vegetation dominated by bog pine ( Pinus rotundata Link) forest. This vegetation pattern consists of zonal strips with relatively sharp borders. This zonation is a mosaic of sedge fens, reed canary grass ( Phalaris arundinacea L.) beds, tussock cottongrass ( Eriophorum vaginatum L.) stands, and a community dominated by ericaceous shrubs. The study focused on the vegetation development of this zonal vegetation. Measurements of the water table level, groundwater pH, and conductivity, together with terrain microtopography, were done to estimate the ways in which the water reservoir influences the mire vegetation. The most important factor is lake water fluctuation, which explained most of the vegetation gradient variability. Lake water fluctuations were represented by lake water levels, which directly flooded a certain part of the gradient from 1990 to 2006 for a known number of days.

Palaeoenvironmental Reconstruction from Sediments at West Quay Road, Southampton

This detailed study of a 13m deep borehole from West Quay Road, Southampton documents estuary evolution over the Holocene in a locality which has received little attention in the literature. The work was undertaken by the Museum of London Archaeology Service Geoarchaeology department. The sediment sequence along with evidence from pollen, plant macrofossils, diatoms, ostracods, snails and radiocarbon dating shows the gradual drowning of the valley from the Lateglacial to the historic period. The evidence shows shifts in floral and faunal communities as coastal and estuarine habitats encroach inland with sea-level rise. Thick fen carr peat developed from the early Mesolithic over river terrace gravels and freshwater channels, while Boreal forest thrived in the surroundings. As tidal environments became more influential, a mosaic of reed beds and salt marsh pools developed by the late Mesolithic. A period of estuary contraction is indicated by the growth of freshwater sedge fen around the early to mid Neolithic, followed by clear marine transgression and persistence of estuarine mudflat environments into the historic period. The work supports the three phase model of Holocene estuary development of Long et al. (2000) which concluded that regional processes control estuary evolution. Although small-scale, this project contributes to the wider palaeogeographic and palaeoenvironmental picture within the Solent, and initiatives such as this form the backdrop for archaeological studies in the region. The length of the sedimentary archive and the amount of information gained show the value of geoarchaeological boreholes undertaken as part of developer-funded projects.

Wetland characterization using polarimetric RADARSAT-2 capability

The use of single-polarization (HH) RADARSAT-1 synthetic aperture radar (SAR) data has been shown to be important for wetland water extent characterization. However, the limited capability of the RADARSAT-1 single-polarization C-band SAR in vegetation type discrimination makes the use of clear-sky-dependent visible near-infrared (VNIR) satellite data necessary for wetland mapping. In this paper, the potential of polarimetric RADARSAT-2 data for wetland characterization is investigated. The Touzi incoherent decomposition is applied for the roll-invariant decomposition of wetland scattering. In contrast with the Cloude-Pottier decomposition that characterizes target scattering type with a real entity, α, the Touzi decomposition uses a complex entity, the symmetric scattering type, for unambiguous characterization of wetland target scattering. It is shown that, like the Cloude α scattering type, the magnitude αs of the symmetric scattering is not effective for vegetation type discrimination. The phase ϕαs of the symmetric scattering type has to be used for better characterization of wetland vegetation species. The unique information provided by ϕαs for an improved wetland class discrimination is demonstrated using Convair-580 polarimetric C-band SAR data collected over the Mer Bleue wetland in the east of Ottawa, Canada. The use of ϕαs makes possible the discrimination of shrub bog from sedge fen and even permits the discrimination between conifer-dominated treed bog and upland deciduous forest under leafy conditions.

CO2exchange of a sedge fen in southern Finland–the impact of a drought period

CO₂exchange of a sedge fen in southern Finland–the impact of a drought period

CO2 exchange of a sedge fen in southern Finland-the impact of a drought period

Eddy covariance (EC) measurements of net ecosystem CO2 exchange (NEE) were conducted on a boreal sedge fen in southern Finland (61°50’N, 24.12’E) during a 1.5-yr period covering two summers in 2004.2005. The EC data were complemented by chamber measurements, which enabled the partition of the daytime NEE into respiration and photosynthesis. A special emphasis was put on the hydrometeorological responses of CO2 exchange during a drought period in July 2005. A mean CO2 efflux of 0.009 mg CO2 m-2 s-1 was observed during mid-winter (January.February), while the night-time respiration during the two Julys averaged 0.09 mgCO2 m-2 s-1. During both years the mean midday uptake in late July was about -0.16 mgCO2 m-2 s-1. An annual CO2 balance of -188 g CO2 m-2 was observed in 2005.Aslightly higher net sink of -219 gCO2 m-2 was estimated for 2004. The drought period experienced in July 2005 caused a clear depression in the daily NEE values. From the combined analysis of EC and chamber measurements it was concluded that this was mainly due to increased respiration, but evidence was also found of suppressed photosynthesis due to a high VPD.

Methanogenic Conditions in Northern Peat Soils

Anaerobic microbial activity in northern peat soils most often results in more carbon dioxide (CO 2 ) production than methane (CH4) production. This study examined why methanogenic conditions (i.e., equal molar amounts of CH4 production and CO2 production) prevail so infrequently. We used peat soils from two ombrotrophic bogs and from two rheotrophic fens. The former two represented a relatively dry bog hummock and a wet bog hollow, and the latter two represented a forested fen and a sedge-dominated fen. We quantified gas production rates in soil samples incubated in vitro with and without added metabolic substrates (glucose, ethanol, H2/CO2). None of the peat soils exhibited methanogenic conditions when incubated in vitro for a short time (< 5 days) and without added substrates. Incubating some samples > 50 days without added substrates led to methanogenic conditions in only one of four experiments. The anaerobic CO2:CH4 production ratio ranged from 5:1 to 40:1 in peat soil without additions and was larger in samples from the dry bog hummock and forested fen than the wet bog hollow and sedge fen. Adding ethanol or glucose separately to peat soils led to methanogenic conditions within 5 days after the addition by stimulating rates of CH4 production, suggesting CH4 production from both hydrogenotrophic and acetoclastic methanogenesis. Our results suggest that methanogenic conditions in peat soils rely on a constant supply of easily decomposable metabolic substrates. Sample handling and incubation procedures might obscure methanogenic conditions in peat soil incubated in vitro.

A multi-year perspective on methane cycling in a shallow peat fen in central New York State, USA

Minerotrophic sedge fens are common in sub-arctic regions and are a significant source of atmospheric methane (CH4), yet they have received less attention than other peatlands, such as boreal ombrotrophic bogs, which are smaller sources of CH4. At the process level, CH4 fluxes in sub-arctic systems are limited primarily by cold temperatures, and thus are sensitive to potential climate change. This study examined CH4 dynamics in a temperate sedge-fen to determine controls on the spatial and temporal variability in CH4 fluxes and, therefore, how the biogeochemistry of CH4 in sedge-fen peatlands may respond to predicted changes in climate. We used flux chambers and laboratory peat incubations over a six to seven-year period (1994–2000) to study fluxes, pools, and potential production of CH4 in a peat-forming wetland in central New York State, USA. Results showed that precipitation (i.e., dry years and depth to water table) exerted an important control on annual and seasonal patterns of CH4 fluxes. Mean summer flux rates ranged from 2258 nmol m−2 s−1 in the wettest year to −934 nmol m−2 s−1 (net consumption) in the driest year. CH4 concentrations in the surface peat were as low as 0.01 μatm and as high as 10 matm in the summer months depending on precipitation patterns. In contrast, CH4 concentrations were consistently two to three times greater in sub-surface than in surface peat, and pools persisted during dry years and were temporally less variable. Fluxes were only weakly associated with potential CH4 production rates, which showed little seasonal variation. In-vitro measurements of potential CH4 production did not sufficiently explain fluxes, suggesting a need for improved in-situ methods for measuring CH4 production. Site differences associated with different dominant vegetation had a significant effect on CH4 cycling in all years except the driest, suggesting sensitivity to vegetation changes. These results indicate that predicting responses of fen peatlands to environmental requires an improved understanding of the underlying microbial processes and mechanisms that control CH4 cycling.

A water-budget approach to restoring a sedge fen affected by diking and ditching

A vast, ground-water-supported sedge fen in the Upper Peninsula of Michigan, USA was ditched in the early 1900 s in a failed attempt to promote agriculture. Dikes were later constructed to impound seasonal sheet surface flows for waterfowl management. The US Fish and Wildlife Service, which now manages the wetland as part of Seney National Wildlife Refuge, sought to redirect water flows from impounded C-3 Pool to reduce erosion in downstream Walsh Ditch, reduce ground-water losses into the ditch, and restore sheet flows of surface water to the peatland. A water budget was developed for C-3 Pool, which serves as the central receiving and distribution body for water in the affected wetland. Surface-water inflows and outflows were measured in associated ditches and natural creeks, ground-water flows were estimated using a network of wells and piezometers, and precipitation and evaporation/evapotranspiration components were estimated using local meteorological data. Water budgets for the 1999 springtime peak flow period and the 1999 water year were used to estimate required releases of water from C-3 Pool via outlets other than Walsh Ditch and to guide other restoration activities. Refuge managers subsequently used these results to guide restoration efforts, including construction of earthen dams in Walsh Ditch upslope from the pool to stop surface flow, installation of new water-control structures to redirect surface water to sheet flow and natural creek channels, planning seasonal releases from C-3 Pool to avoid erosion in natural channels, stopping flow in downslope Walsh Ditch to reduce erosion, and using constructed earthen dams and natural beaver dams to flood the ditch channel below C-3 Pool. Interactions between ground water and surface water are critical for maintaining ecosystem processes in many wetlands, and management actions directed at restoring either ground- or surface-water flow patterns often affect both of these components of the water budget. This approach could thus prove useful in guiding restoration efforts in many hydrologically altered and managed wetlands worldwide.

Differences in Sedge Fen Vegetation Upstream and Downstream from a Managed Impoundment

The U.S. Fish and Wildlife Service proposed the restoration of wetlands impacted by a series of drainage ditches and pools located in an extensive undeveloped peatland in the Seney National Wildlife Refuge, Michigan. This study examined the nature and extent of degradation to the Marsh Creek wetlands caused by alteration of natural hydrology by a water-storage pool (C-3 Pool) that intersects the Marsh Creek channel. We tested the hypothesis that a reduction in moderate-intensity disturbance associated with natural water-level fluctuations below the C-3 dike contributed to lower species richness, reduced floristic quality and a larger tree and shrub component than vegetation upstream from the pool. Wetland plant communities were sampled quantitatively and analyzed for species richness, floristic quality and physiognomy. Aerial photographs, GIS databases and GPS data contributed to the characterization and analysis of the Marsh Creek wetlands. Results showed that there was lower species richness in vegetated areas downstream from the pool, but not the anticipated growth in shrubs. Wetland vegetation upstream and downstream from the pool had similar floristic quality, except for a greater number of weedy taxa above the pool. Seepage through the pool dike and localized ground-water discharge created conditions very similar to those observed around beaver dams in Marsh Creek. In essence, the dike containing the C-3 Pool affected hydrology and wetland plant communities in a manner similar to an enormous beaver dam, except that it did not allow seasonal flooding episodes to occur. Management actions to release water from the pool into the original Marsh Creek channel at certain times and in certain amounts that mimic the natural flow regime would be expected to promote greater plant species richness and minimize the negative impacts of the dike.

Растительность болот в бассейне реки Муроягун (Сургутское Полесье, Западная Сибирь)

The author’s field research, performed in July 2000, was aimed at the descriptive survey of the diversity of mire vegetation in the poorly known West Siberian area, the so called Surgut Polesje. The palsa ridge-and-lake and palsa ridge-and-pool bog complexes dominate the area landscape. Such bogs make for the core of vast and heterogeneous mire systems, the other elements of the latter being transitional bogs and treeless or wooded fens. The mire systems are separated from each other only by rivers; the fens are located on river valley slopes. The following mire vegetation complexes (mire sites) were described: 1) oligotrophic palsa ridge-and-lake or palsa ridge-and-pool; 2) palsa ridge-and-hollow; 3) meso­trophic or heterotrophic aapa-mire; 4) mesotrophic-eutrophic sedge or sedge-peatmoss poor fen; 5) wooded sedge fen with low Betulatortuosa; 6) wooded sedge fen with one or two layers of Pinussibirica and Betulapubescens. The investigated mire vegetation displays a high degree of syntaxonomical diversity, belonging to the 4 classes, Oxycocco-Sphagnetea, Scheuchzerio-Cariceteanigrae, Phragmito-Magnocaricetea,and Alneteaglutinosae, with 4 orders, 6 alliances, and 8 associations, listed in the tables. There are no rare communities in the area, to the possible exception of some types of wooded sedge fens. The mire system margins along rivers and flowing lakes seem to be potentially most interesting for a vege­tation scientist.

Controls on evapotranspiration at a subarctic sedge fen

AbstractIn this study, 10 years (1990–99) of summertime data collected at a representative sedge fen in the Hudson Bay Lowland (HBL) are used to investigate the energy and water balance dynamics of subarctic wetlands. The summertime climatic characteristics at the study site during the 10 year study period are also examined. It is shown that mean cumulative summertime precipitation Pavg for the study decade closely approximates the 30 year mean Pavg. However, the mean summertime air temperature Tavg for the study decade is 1 °C higher than the 30 year mean Tavg.To examine the energy and water balance dynamics at the study site, the variation in each of their respective components throughout the study decade is considered. Little variation is observed in cumulative summertime net radiation $Q^{*}_{\rm cum}$ and cumulative summertime ground heat flux QGcum; however, substantial year‐to‐year variation is evident in cumulative summertime water deficit WDcum, cumulative summertime precipitation Pcum, cumulative summertime sensible heat flux QHcum, and cumulative summertime latent heat flux QEcum. It is noted that the variability in QEcum is particularly significant because it consumes the largest proportion of the available summertime energy, and is the largest component of the summertime water balance at this subarctic wetland.Past research has suggested that Q*, P, and T have the most influence on summertime QE at high‐latitude wetlands. To test this hypothesis at our study site, QEcum, Pcum, Tavg and $Q^{*}_{\rm cum}$ from each year in the study decade were examined. It is observed that high QEcum is associated with high Pcum, Tavg and $Q^{*}_{\rm cum}$, and that low QEcum is associated with low Pcum and Tavg. To identify the hydroclimatological variables that are most responsible for controlling QEcum dynamics at the sedge fen, a stepwise linear regression was performed. This analysis indicates that Pcum and $Q^{*}_{\rm cum}$ are the most important hydroclimatological controls over QEcum. However, it is demonstrated that the variability in Pcum is more responsible than the variability in $Q^{*}_{\rm cum}$ for the variability in QEcum during the study decade because of its higher coefficient of variation. The results of this study have broader applicability to wetlands in other parts of the subarctic ecoregion, including the Mackenzie River Basin (MRB). For example, past studies have shown similarities in the energy balance regimes at wetland sites from the HBL and MRB. Copyright © 2001 John Wiley &amp; Sons, Ltd.

Postglacial history of a marl fen: vegetational stability at Byron-Bergen Swamp, New York

Byron-Bergen Swamp, an 800-ha mire complex in western New York, is a mosaic of hardwood–conifer forest, white cedar swamp, and open nonforested fens dominated by sedges, other herbs, and shrubs. The mire is a sloping, spring-fed rich fen in which marl deposition occurs in the open fens but not under forest. Two cores, 120 m apart, one in a marl fen and the other in a hardwood–conifer swamp, were taken to investigate the history of the mire. Sediment, pollen stratigraphy, and 14C chronology show that the Holocene record of local vegetation at each coring site was very different. One site was first a shallow marl pool (10 700 – 5600 years BP), then an open shrub–conifer vegetation, and finally a closed hardwood–conifer swamp. The other site progressed from a pine–spruce–tamarack swamp (10 700 – 8000 years BP) to a white cedar swamp (7500–3500 years BP) and then to a marl sedge fen (3500 years BP – present). The spatial arrangement of swamp forest and marl fen changed through time, responding to marl accumulation and lateral shifts in drainage pathways. Marl deposition occurred continuously at each site, although at different times, for several thousand years. The pattern of vegetation change that we found is not congruent with that predicted from classical hydrarch succession.Key words: marl, mire development, pollen stratigraphy, rich fen.

Methane emission from Swedish mires: National and regional budgets and dependence on mire vegetation

A national land use inventory program was used to estimate the flux of methane from Swedish mires. During the snow‐free season in 1994, methane fluxes were monitored at 60% (n = 619) of the total number of permanent inventory plots for the four mire vegetation classes included. The methane flux was measured only once at each inventory plot using transparent static chambers, yielding 3157 (89%) accepted flux rates. The temperature during the measurement period was close to the long‐term (30 year) average in the north and much warmer in the south. The precipitation was lower than the long‐term average. Average flux rates, specific for each mire vegetation class and geographical region, varied between 8 and 238 mg CH4 m−2 d−1. The national averages ± SE (mg CH4 m−2 d−1) were hummock communities, 24±6; transitional fens, 15±2; short sedge fens, 49±4; and tall sedge fens, 97±22. To derive the annual flux, the number of days with a daily average air temperature over 5°C was used. The annual methane fluxes for each mire vegetation class and region varied between 1.5 and 40 g CH4 m−2 yr−1. The annual methane fluxes (average ± SE in g m−2 yr−1) for each mire vegetation class for the whole of Sweden were hummock sites, 4.9±1.3; transitional fens, 2.5±0.5; low sedge fens, 8.2±0.8; and tall sedge fens, 16.5±3.6. The methane flux (±95% confidence limits) in 1994 from the monitored mire types in Sweden was 0.29±0.05 Tg CH4. The low and tall sedge mires accounted for 96% of the methane emitted.

Effects of spring flood and water level draw‐down on methane dynamics in the littoral zone of boreal lakes

1. The annual dynamics of methane (CH4) in a temporarily flooded meadow, mire bank, lacustrine sedge fen, temporarily and continuously inundated sedge (Carex sp.) and reed (Phragmites australis) marshes were studied from June to November in the humic mesoeutrophic Lake Mekrijärvi and in eutrophicated parts of the mesotrophic Lake Heposelkä in the southern part of East Finland. The effects of water level and temperature on littoral CH4 fluxes were determined. Vegetation zonation along the moisture gradient, and associated CH4 fluxes, were evaluated.2. The CH4 flux increased along the moisture gradient from –0.2 to 14.2 mg CH4 m–2 h–1, and was highest in the permanently inundated marshes. The duration of anoxia in the sediment caused differences in the CH4 flux. Estimated emissions for the period 1 June – 30 September in continuously inundated sparse reed and sedge marshes, drying sedge marsh, and lacustrine sedge fen were 13, 11 and 6 g CH4 m–2, respectively.3. In continuously inundated vegetation, the fluxes were highest in late July/early August. The seasonal CH4 flux pattern suggested that the fluxes were regulated by the supply of organic matter during the course of the summer and the water level. In the temporarily flooded zone, the seasonal CH4 flux dynamics was greatly affected by changes in the lake water level, the fluxes being highest during the spring flood in early June.

Modelling the interannual variability of net ecosystem CO2 exchange at a subarctic sedge fen

AbstractThis paper presents an empirical model of net ecosystem CO2 exchange (NEE) developed for a subarctic fen near Churchill, Manitoba. The model with observed data helps explain the interannual variability in growing season NEE. Five years of tower‐flux data are used to test and examine the seasonal behaviour of the model simulations. Processes controlling the observed interannual variability of CO2 exchange at the fen are examined by exploring the sensitivity of the model to changes in air temperature, precipitation and leaf area index. Results indicate that the sensitivity of NEE to changing environmental controls is complex and varies interannually depending on the initial conditions of the wetland. Changes in air temperature and the timing of precipitation events have a strong influence on NEE, which is largely manifest in gross ecosystem photosynthesis (GEP). Climate change scenarios indicate that warmer air temperatures will increase carbon acquisition during wet years but may act to reduce wetland carbon storage in years that experience a large water deficit early in the growing season. Model simulations for this subarctic sedge fen indicate that carbon acquisition is greatest during wet and warm conditions. This suggests therefore that carbon accumulation was greatest at this subarctic fen during its early developmental stages when hydroclimatic conditions were relatively wet and warm at approximately 2500 years before present.

RESPONSE OF CO2AND CH4EMISSIONS FROM PEATLANDS TO WARMING AND WATER TABLE MANIPULATION

Projected changes in climate could shift northern peatlands from their current status as net C sinks toward that of being net C sources by changing soil temperatures and hydrology. We assessed the importance of water table and soil temperature as controls over ecosystem respiration in a bog and sedge fen in northern Minnesota, USA, by means of a manipulative mesocosm experiment. Fifty-four intact monoliths were removed from a bog and a fen and installed in insulated tanks that permitted control of the water table and were heated by overhead infrared heaters. The experimental design was a fully crossed factorial combination of two communities, three water tables, and three heat levels. Ecosystem respiration as indicated by emission of CO2 and CH4, dissolved nutrient fluxes, and productivity were measured and summarized for each growing season from 1995 to 1997. Seasonal ecosystem respiration (ER) as indicated by CO2 emissions responded almost exclusively to soil temperature and did not differ between community types (∼630 g C/m2) or with water table level. These results suggest that community type, within certain limits, will not be an important factor in predicting temperature-driven increases in ER. The response of CH4 flux to soil temperature and water table setting became progressively stronger in each succeeding growing season. Seasonal CH4 emissions were on average three times higher in the bog than in the fen mesocosms (21 vs. 7 g C/m2). Aboveground net primary productivity and dissolved N retention were also higher in the bog mesocosms. There were strong correlations between CH4 flux and N retention, but generally weak correlations between CH4 and plant primary production. The relatively lower CH4 emissions from the fen mesocosms appear to result mainly from higher rates of methanotrophy in the aerated zone, possibly reinforced by the effects of higher porewater N concentrations and lower primary productivity compared to the bogs. The results confirm the existence of strong environmental controls over ER and methanogenesis, which are modulated by complex interactions between plant community and soil nutrient dynamics. The differential responses of these ecosystem functions to climate change may complicate efforts to predict future changes in C dynamics in these important repositories of soil C.

Postglacial history of a marl fen: vegetational stability at Byron-Bergen Swamp, New York

Byron-Bergen Swamp, an 800-ha mire complex in western New York, is a mosaic of hardwood-conifer forest, white cedar swamp, and open nonforested fens dominated by sedges, other herbs, and shrubs. The mire is a sloping, spring-fed rich fen in which marl deposition occurs in the open fens but not under forest. Two cores, 120 m apart, one in a marl fen and the other in a hardwood-conifer swamp, were taken to investigate the history of the mire. Sediment, pollen stratigraphy, and 14 C chronology show that the Holocene record of local vegetation at each coring site was very different. One site was first a shallow marl pool (10 700 - 5600 years BP), then an open shrub-conifer vegetation, and finally a closed hardwood-conifer swamp. The other site progressed from a pine- spruce-tamarack swamp (10 700 - 8000 years BP) to a white cedar swamp (7500-3500 years BP) and then to a marl sedge fen (3500 years BP - present). The spatial arrangement of swamp forest and marl fen changed through time, responding to marl accumulation and lateral shifts in drainage pathways. Marl deposition occurred continu- ously at each site, although at different times, for several thousand years. The pattern of vegetation change that we found is not congruent with that predicted from classical hydrarch succession.

CONTROLS ON ENERGY AND CARBON FLUXES FROM SELECT HIGH-LATITUDE TERRESTRIAL SURFACES

While the physical processes driving energy fluxes in the high latitudes are universal, some of the controlling factors such as permafrost, temperature, and vegetation play a special role. Annual net radiation at Arctic treeline is larger over subarctic forest than over tundra as a result of smaller albedo during the snow-cover period. The absorbed solar radiation is notably larger in late winter. During the snow-free period, in well-watered areas, there is a hierarchy in potential evaporation from very high rates for shallow tundra lakes and ponds to low rates for well-drained upland heath terrain. With abundant moisture and warm conditions, open coniferous forests, dwarf deciduous forests, and sedge fens have similar energy and water balances. During the growing season when moisture is limiting, a sedge fen, more so than a coniferous forest, curtails its evaporation rate. Under cold conditions, however, coniferous forest has the smaller evaporation. Soil heat fluxes in summer comprise from 10% to 15% of the net radiation and are fairly uniform both temporally and spatially. The carbon budget of peatlands, which are major global repositories of carbon, responds strongly to air and soil temperatures and to the water balance. Warm and wet conditions support strong photosynthesis and a substantial methane flux. Warm and dry conditions favor strong respiration carbon losses from plants and soil. In a 2 × CO2 world, substantial changes in temperature, precipitation, and energy and water balances are anticipated and these will drive substantial changes in the high-latitude carbon budget. [Key words: energy and carbon fluxes, high latitudes.]

Scaling net ecosystem CO2 exchange from the community to landscape‐level at a subarctic fen

SummaryLandscape‐ and community‐level CO2 measurements were made at a subarctic sedge fen near Churchill Manitoba during the 1997 growing season. Climatic conditions were warmer and drier than the 30‐y normal. Landscape‐scale micrometeorological measurements indicated that the wetland gained 49 g CO2 m−2 during the growing season. Chamber‐scale measurements from the main vegetation community types showed that small hummocks (Carex spp. sites) dominated the CO2 exchange, yielding an effective scaling factor of 70%. Scaled parameters of two algorithms describing photosynthesis and respiration for each community type show strong similarity to those derived at the landscape level. Scaling photosynthesis, respiration, and net ecosystem CO2 exchange from the community to landscape‐level over the season is within the maximum probable error of each methodological approach and helps substantiate the 1997 CO2 budget. We explore the equilibrium response of net ecosystem CO2 exchange of this fen to climatic change by examining the feedback of water table position on vegetation distribution and nitrogen availability. Based on the effective scaling factors computed for each community type, we hypothesize that a small decrease in mean water table position could nearly triple the net uptake of CO2 at this wetland.

Comparing the performance of the Canadian land surface scheme @class) for two subarctic terrain types

The Canadian Land Surface Scheme (CLASS) is tested for two major terrain types found in the northern Hudson Bay Lowland. Soil temperature and energy balance measurements for sedge fen wetland and dwarf willow‐birch forest near Churchill, Manitoba, are compared with simulations both with and without the new organic soil parametrization that has been developed for CLASS (Letts et al., 2000), for eight datasets spanning six years (1990 through 1995). With the exception of the sensible heat flux at the sedge site, the new version of CLASS with the organic soil parametrization improves the energy budget simulation at each of the research sites. Both the latent (QE) and ground (QG) heat flux were modelled well; however, some modifications were required to simulate the continued evaporation from these sites once the water table receded below the first soil layer. The sensible heat flux (QH) was the least well simulated component of the energy balance in both versions. Temperatures for the top two soil layers were consistently overestimated by the mineral soil parametrization for both terrain types, whereas the organic soil parametrization showed significant improvement. The new water table diagnostic algorithm in the organic soil version satisfactorily estimates the position of the water table, even under a large range of climatic conditions. The inclusion of organic soil parameters in CLASS, and the subsequent improved handling of soil moisture, is a significant contribution to model development, and provides a physically‐based capability for simulating northern peatlands within land surface models.