Boreal Wetlands Research Articles

Estimates of methane emission during the last 125,000 years in Northern Eurasia

The concentration of methane in the atmosphere has varied considerably during the last 125,000 years. Boreal wetlands represent one of the main sources of methane emissions into the atmosphere, the rate of which is largely controlled by climate. Changes in climate (mainly in the duration of the frost-free period) and in the extent of wetlands presumably caused variations in the methane production from boreal ecosystems. We chose Northern Eurasia to estimate both climatic changes and the area of methane-producing ecosystems, as it plays a leading role in methane emission. Palaeobotanic and palaeocryological data were used for the reconstruction. The two most recent warm stages: the Holocene Optimum (5500–6000 years BP) and the Last Interglacial Optimum (ca. 125,000 years BP) were studied. During these warm periods, both an area of tundra and the proportion of the wetlands within the boreal forest zone were considerably reduced. On the other hand, a longer frost-free period and higher precipitation would have caused higher methane production. The precipitation rise was apparently in part compensated by an increase in potential evaporation due to higher summer temperatures. Compared to methane emissions of about 9×10 6 t per year from modern forests of Northern Eurasia, emissions amounted to 86 and 44% of modern values for the region during the Holocene Optimum and Last Interglacial Optimum respectively. Under the greenhouse warming expected early in the 21st century, the climatic conditions may lead to a considerable increase of methane emission.

Effects of raised CO2 on potential CH4 production and oxidation in, and CH4 emission from, a boreal mire

1 In a glasshouse experiment we studied the effect of raised CO2 concentration (720 p.p.m.) on CH4 emission at natural boreal peat temperatures using intact cores of boreal peat with living vascular plants and Sphagnum mosses. After the end of the growing season half of the cores were kept unnaturally warm (17–20 °C). The potential for CH4 production and oxidation was measured at the end of the emission experiment. 2 The vascular cores (‘Sedge’) consisted of a moss layer with sedges, and the moss cores (‘Sphagnum’) of Sphagnum mosses (some sedge seedlings were removed by cutting). Methane efflux was 6–12 times higher from the Sedge cores than from the Sphagnum cores. The release of CH4 from Sedge cores increased with increasing temperature of the peat and decreased with decreasing temperature. Methane efflux from Sphagnum cores was quite stable independent of the peat temperatures. 3 In both Sedge and Sphagnum samples, CO2 treatment doubled the potential CH4 production but had no effect on the potential CH4 oxidation. A raised concentration of CO2 increased CH4 efflux weakly and only at the highest peat temperatures (17–20 °C). 4 The results suggest that in cool regions, such as boreal wetlands, temperature would restrict decomposition of the extra substrates probably derived from enhanced primary production of mire vegetation under raised CO2 concentrations, and would thus retard any consequent increase in CH4 emission.

Effect of temperature on production of CH4 and CO2 from Peat in a Natural and Flooded Boreal Forest Wetland

Flooding of a small boreal forest wetland (979) in northwestern Ontario, caused the formation of peat islands, which resulted in an approximate 10 °C increase in peat temperatures at a depth of 50 cm. Peat collected from the flooded wetland and a natural unflooded wetland was incubated anaerobically at temperatures of 4 °C, 15 °C, and 20 to 25 °C. Flooding of the wetland greatly increased CH4 production rates by increasing the ratio of CH4:CO2 produced from 979 peat (40% : 60%) compared to 632 peat (20% : 80%), at both preflood and postflood temperatures, likely due to the altered hydrological and geochemical conditions within the peat mats due to flooding. CH4 and CO2 production rates approximately tripled for every 10 °C temperature increase and may have been linked to to the metabolic rate of the methanogens or the fermentors independent of the substrate quality. Methane production rates from deep peat deposits within the islands were also significant and responded well to temperature increases despite peat 14C ages of 1000 years. Due to the large quantity of carbon stored within natural wetlands, artificial reservoirs may act as a significant and long term source of CH4 to the atmosphere.

Land cover mapping, fire regeneration, and scaling studies in the Canadian boreal forest with 1 km AVHRR and Landsat TM data

A multitemporal 1 km advanced very high resolution radiometer (AVHRR) land cover analysis approach was used as the basis for regional land cover mapping, fire disturbance‐regeneration, and multiresolution land cover scaling studies in the boreal forest ecosystem of central Canada. The land cover classification was developed by using regional field observations from ground and low‐level aircraft transits to analyze spectral‐temporal clusters that were derived from an unsupervised cluster analysis of monthly normalized difference vegetation index (NDVI) image composites (April‐September 1992). Quantitative areal proportions of the major boreal forest components were determined for a 821 km × 619 km region, ranging from the southern grasslands‐boreal forest ecotone to the northern boreal transitional forest. The boreal wetlands (mostly lowland black spruce, tamarack, mosses, fens, and bogs) occupied approximately 33% of the region, while lakes accounted for another 13%. Upland mixed coniferous‐deciduous forests represented 23% of the ecosystem. A SW‐NE productivity gradient across the region is manifested by three levels of tree stand density for both the boreal wetland conifer and the mixed forest classes, which are generally aligned with isopleths of regional growing degree days. Approximately 30% of the region was directly affected by fire disturbance within the preceding 30–35 years, especially in the Canadian Shield Zone where large fire‐regeneration patterns contribute to the heterogeneous boreal landscape. Intercomparisons with land cover classifications derived from 30‐m Landsat Thematic Mapper (TM) data provided important insights into the relative accuracy of the 1 km AVHRR land cover classification. Primarily due to the multitemporal NDVI image compositing process, the 1 km AVHRR land cover classes have an effective spatial resolution in the 3–4 km range; therefore fens, bogs, small water bodies, and small patches of dry jack pine cannot be resolved within the wet conifer mosaic. Major differences in the 1‐km AVHRR and 30‐m Landsat TM‐derived land cover classes are most likely due to differences in the spatial resolution of the data sets. In general, the 1 km AVHRR land cover classes are vegetation mosaics consisting of mixed combinations of the Landsat classes. Detailed mapping of the global boreal forest with this approach will benefit from algorithms for cloud screening and to atmospherically correct reflectance data for both aerosol and water vapor effects. We believe that this 1 km AVHRR land cover analysis provides new and useful information for regional water, energy, carbon, and trace gases studies in BOREAS, especially given the significant spatial variability in land cover type and associated biophysical land cover parameters (e.g., albedo, leaf area index, FPAR, and surface roughness). Multiresolution land cover comparisons (30 m, l km, and 100 km grid cells) also illustrated how heterogeneous landscape patterns are represented in land cover maps with differing spatial scales and provided insights on the requirements and challenges for parameterizing landscape heterogeneity as part of land surface process research.

Spectral reflectance measurements of boreal wetland and forest mosses

High‐spectral resolution reflectance data were acquired in the laboratory for several species of boreal forest and peatland mosses. Feather mosses and lichens (forests), brown mosses (rich fens), and Sphagnum species (bogs and poor fens) were collected from sites in the northern study area (NSA) of the Boreal Ecosystem‐Atmosphere Study (BOREAS) near Thompson, Manitoba, and from three peatlands in southeastern New Hampshire. Because mosses are indirect indicators of soil moisture, trace gas flux, and carbon accumulation, these data may enable hyperspectral remote sensing systems, such as the airborne visible and infrared imaging spectrometer and the compact airborne spectrographic imager (AVIRIS) (CASI), as well as future systems such as Lewis and the first New Millennium Project, to infer differences in hydrology and carbon cycling in boreal ecosystems at small spatial scales (< 1–900 m2). Mosses exhibit distinctly different spectral characteristics from vascular plants in the visible, near‐infrared (NIR) and short‐wave infrared (SWIR) regions. In the visible portion of the spectrum, mosses exhibit typical absorption in the blue and red regions but differ from vascular plants in having a “green” peak reflective of the color (red, brown, or green) of the individual species. The moss reflectance in the NIR spectral region is typically less reflective than the same region in vascular plants and is characterized by strong water absorption features located at approximately 1.00 and 1.20 μm, resulting in pronounced reflectance peaks at approximately 0.85, 1.10, and 1.30 μm (identified as NIR 1, 2, and 3, respectively). The variations in the relative brightness of the three NIR peaks in each of the three groups of mosses (Sphagnum, feather, and brown mosses) are diagnostic and may be indicative of different cellular characteristics. The slope of the NIR plateau as determined by the NIR 3/1 ratio, as well as the shape of the NIR 1 peak and relative dominance of NIR 2, separate the three groups. In addition, the NIR 1 peak in Sphagnum species is marked by a minor absorption feature at 0.85 μm, which is absent in all brown mosses and feather mosses, as well as in vascular plants. Because this absorption feature results in a narrow NIR 1 peak, and the red absorption is also narrow in Sphagnum, the standard normalized difference vegetation index/simple vegetation index ratio (NDVI/VI) methods do not work well in characterizing biomass or greenness. The overall reflectance of mosses in the SWIR region (1.50–2.50 μm) is lower than that of vascular plants because of the higher water content of the moss tissue. In lichens, reflectance in this region is higher than either mosses or vascular plants, due likely to tissue dryness. The lichens included in this study are most dissimilar from mosses and vascular plants in the visible portion of the spectrum.

Seasonal trends in energy, water, and carbon dioxide fluxes at a northern boreal wetland

Micrometeorological measurements were made over a northern boreal fen near Thompson, Manitoba, Canada, as part of the Boreal Ecosystem‐Atmosphere Study. The measurement period extended from the start of snowmelt until the early fall, at which time senescence was widespread throughout the fen. Data analysis concentrated on identifying seasonal trends in energy, water, and carbon dioxide fluxes and linking them to observed surface cover changes. Albedos (solar and photosynthetically active radiation (PAR)) showed large decreases over the melt period, reaching seasonal lows at the end of melt. Solar albedo increased in the summer in response to vegetation growth on the fen, while PAR albedo remained constant. Incoming and outgoing longwave flux seasonal trends were similar, so seasonal changes in net radiation were driven by the net solar flux. During the spring thaw, the melting of snow and ground ice was equal to about 28% of the daily total net radiation, while the soil heat flux accounted for about 5%. Bowen ratios at this time were above unity. Mean Bowen ratio decreased to 0.70 during the period between spring thaw and leaf‐out. As the vascular vegetation cover developed, Bowen ratios decreased to seasonal lows of 0.10–0.20 near midsummer and then increased to above unity during senescence. The daily evaporative fraction (EF) was highest (≥0.80) during midsummer when the vascular vegetation was in full leaf and actively photosynthesizing, and EF decreased to a mean of 0.55 during senescence. Eddy correlation measurements of carbon dioxide flux showed the fen acting as a net sink for CO2 only while the vascular vegetation was actively photosynthesizing with a daily mean flux of −0.81 g CO2‐C m−2 d−1 (standard error = 0.16). Before leafing and during senescence the fen was a net source of CO2. Integrated over the study period of 124 days, the fen experienced a net loss of 30.4 g CO2 m−2 to the atmosphere.

Boreal diatom ponds: A rare wetland associated with nesting whooping cranes

This paper documents and characterizes a rare form of boreal wetland associated with the nests of whooping cranes, an endangered species. Diatom ponds are found in wetlands in association with bulrush marshes. They are shallow ( 1000 m in diameter, may evaporate down to diatom muck by late summer, are strongly influenced by dissolution of gypsum, and are circumneutral to alkaline and high in sulphates. Aquatic macrophytes are few. Pond waters are clear, and the predominant primary producers are a benthic diatom community that gives the ponds a characteristic yellow color (viewed from the air). As the diatom ponds dry, they change color from yellow to pink (when water table is at the surface) to cream (due to a dried diatom and sulphate crust). Diatomaceous earth or sedimentary peat underlies the ponds, which exist in a dynamic relationship with bulrush marshes, wet meadows, fens, and bogs. In the U.S. wetland classification system, diatom ponds fit most nearly within the palustrine, unconsolidated bottom, aquatic bed type. In the Canadian wetland classification system, the diatom ponds might fit in the marsh/shallow open water complex, with a new distinction at the type level. The association between nesting cranes and diatom ponds may be due to a combination of factors such as long sight lines for detection of predators, the proximity of bulrush (their favored nesting material), and use of the ponds for feeding.

Distribution of tropospheric methane over Siberia in July 1993

Airborne observations of atmospheric methane (CH4) mixing ratio were carried out over Siberia during July 15–30, 1993, using a continuous measurement system. The distribution of CH4 in the upper troposphere at an altitude of about 7 km was highly variable (1.72–1.91 parts per million, or ppm), being affected by intrusion of stratospheric air, long‐range transport of CH4 from the source region, and a synoptic‐scale mixing process. During flights along nearly constant latitude between Yakutsk (62.10°N, 129.50°E) and Nizhnevartovsk (60.57°N, 76.40°E) on July 19 and 28 we observed large‐scale enhancements of CH4 from near 90° to 100°E with a horizontal scale of more than 500km. Accompanied by high humidity and low mixing ratios of CO2 and O3, the air masses with enhanced CH4 mixing ratio were considered to be affected by lower tropospheric air. The probable source region of the CH4 was inferred to be the West Siberian Lowland, which contains vast wetlands and huge oil/gas fields. The distribution of CH4 in the lower troposphere (0.1–3 km) over the boreal wetlands in the West Siberian Lowland, ranging from 1.85 ppm to 2.75 ppm, showed large accumulations near the ground in the morning. The shortterm temporal variations in the vertical profile of CH4 mixing ratio revealed that the accumulated CH4 was transported to the free troposphere with the growth of the mixed layer. On the other hand, the distribution of CH4 (0.1–1 km) over the tundra areas in the Siberian Arctic was less variable (1.81–1.84 ppm), and little accumulation was observed.

The influence of temperature on CO2 and methane fluxes at a flooded boreal wetland in Hokkaido, Japan

The influence of temperature on CO2 and methane fluxes at a flooded boreal wetland in Hokkaido, Japan

Controls on CH4 flux from an Alaskan boreal wetland

Factors controlling the flux of the radiatively important trace gas methane (CH4) from boreal wetlands were examined at three sites along a moisture gradient from a treed low‐shrub bog to an open floating graminoid bog in Fairbanks, Alaska. In the summer of 1992 average static chamber flux measurements were −0.02, 71.5, and 289 mg CH4/m2/d in dry, wet, and floating mat communities, respectively. In contrast, the warmer, drier 1993 field season flux measurements were −0.02, 42.9 and 407 mg CH4/m2/d. The data indicate that despite net oxidation of CH4 in the dry regions of the bog, the wetland is a net source of CH4, with fluxes ranging across three orders of magnitude between different plant communities. Comparison with water levels suggests that CH4 flux is turned on and off by changes in site hydrology. In sites where sufficient moisture is present for methanogenesis to occur, CH4 flux appears to be temperature limited, responding exponentially to soil temperature changes. The combined effects of hydrology and temperature create hot spots of CH4 flux within boreal wetlands. The plant communities within Lemeta Bog respond differently to changes in temperature and moisture availability, creating both positive and negative feedbacks to potential global climate change.

Ecological controls on methane emissions from a Northern Peatland Complex in the zone of discontinuous permafrost, Manitoba, Canada

Methane emissions were measured by a static chamber technique in a diverse peatland complex in the Northern Study Area (NSA) of the Boreal Ecosystem Atmosphere Study (BOREAS). Sampling areas represented a wide range of plant community and hydrochemical gradients (pH 3.9–7.0). Emissions were generally larger than those reported from other boreal wetland environments at similar latitude. Seasonal average fluxes from treed peatlands (including palsas) ranged from 0 to 20 mg CH4 m−2 d−1 compared with 92 to 380 mg CH4 m−2 d−1 in open graminoid bogs and fens (with maximum single fluxes up to 1355 mg CH4 m−2 d−1). Permafrost‐related collapse scars had similarly high CH4 emissions, particularly in the lag areas where continuous measurements of water table, peat surface elevation, and peat temperature showed that the peat surface adjusted to a falling water table in the abnormally dry 1994 season, maintaining warm, saturated conditions and high CH4 flux later into the season than nonfloating sites. A predictive model for CH4 flux and environmental variables was developed using multiple stepwise regression. A combined variable of mean seasonal peat temperature at the average position of the water table explained most of the spatial variability in log CH4 flux (r2 = 0.64), with height above mean water table (HMWT), water chemistry (Kcorr, pH, Ca), tree cover, and herbaceous plant cover explaining additional variance (r2 = 0.81). Canonical correspondence analysis (CCA) of combined vascular and bryophyte data with environmental variables showed that CH4 flux was negatively correlated with HMWT, the second axis of vegetation variability, and was only weakly correlated with chemistry, the first axis. Sedge and tree cover were correlated with high and low CH4 fluxes, respectively, while shrub cover was of less predictive value. Microtopographic groupings of hummocks and hollows were separated in terms of CH4 flux at the intermediate ranges of the moisture gradient. These data show that multivariate vegetation analyses may provide a useful framework for integrating the complex environmental controls on CH4 flux and extrapolating single point chamber measurements to the landscape scale using remote sensing. (Key words: CH4 flux, peatland, vegetation, and remote sensing.)

Holocene climate and vegetation in the Milford drainage basin, Maine, U.S.A., and their implications for human history

A 9200 14C year fossil pollen record from a small kettle lake in central Maine, northeast U.S.A., records the development of nearby upland vegetation throughout the Archaic, Ceramic, and Historic periods of human history. The Early Archaic period (9000 to 8000 B.P.) began as open woodland dominated by Picea, Populus, and Larix, which was replaced by Pinus forest. During the Middle Archaic (8000-6000 B.P.) Tsuga-dominated forest, which developed ca. 7400 B.P., was followed by Pinus forest (ca. 6400 B.P.). The Late Archaic (6000-3000 B.P.) was a period of great transition; Tsuga forest developed again ca. 5700 B.P., but was abruptly replaced by northern hardwood forest ca. 4700 B.P. That Late Archaic expansion of hardwoods would have provided better forage for beaver. Coincidentally, boreal wetland mammals such as beaver (Castor canadensis) and muskrat (Ondatra zibethicus) increase in faunal assemblages of local archaeological sites, while remains of anadromous fish decrease. We postulate that the apparent increase in human populations throughout the region during the Late Archaic may be attributed to an increase in the resource base within both upland and wetland areas resulting from the development of hardwood forest in response to climatic cooling.

Methyl and Total Mercury in Boreal Wetland Plants, Experimental Lakes Area, Northwestern Ontario

AbstractA review of Hg concentrations cited in the literature reveals values in the general sequence: grassland herbs < trees and shrubs < aquatic macrophytes < Sphagnum < mosses < lichens < fungi, excluding those samples collected near point sources of environmental Hg. Samples of vegetation collected from wetland and upland catchments in the Experimental Lakes Area contained from 4 to 160 μg total Hg (THg) kg−1 and 0.1 to 139 μg methyl Hg (MeHg) kg−1. The lowest concentrations of both THg and MeHg were found in the leaves and needles of trees and shrubs, and the highest concentrations occurred in bryophytes, both feather mosses and Sphagnum. Analysis of sections of the mosses revealed larger concentrations of MeHg in the upper live section, whereas THg concentrations increased slightly down the stem into the dead portions. In terms of broad ecological grouping, THg and MeHg concentrations increased the closer the plant's habitat to the water table, though certain upland mosses also contained very large THg and MeHg concentrations. When combined with biomass data, the vegetation of an ombrotrophic wetland contained an average of 30 μg THg m−2 and 0.4 μg MeHg m−2, dominantly (45 and 73%, respectively) in the mosses. These values are similar to that contained in the peat porewater, but small compared to the estimate of the stock of THg and MeHg contained in the 1.7 m thick peat (12 000 and 200 μg m−2, respectively).

Presence or absence of fish as a cue to macroinvertebrate abundance in boreal wetlands

Presence or absence of fish as a cue to macroinvertebrate abundance in boreal wetlands

Use of boreal forested wetlands by Pacific loons (Gavia pacifica Lawrence) and horned grebes (Podiceps auritus L.): relations with limnological characteristics

Use of boreal forested wetlands by Pacific loons (Gavia pacifica Lawrence) and horned grebes (Podiceps auritus L.): relations with limnological characteristics

The Arctic Boundary Layer Expedition (ABLE‐3B): July–August 1990

The Arctic Boundary Layer Expedition (ABLE) 3B used data from ground‐based, aircraft, and satellite platforms to characterize the chemistry and dynamics of the troposphere in subarctic and Arctic regions of midcontinent and eastern Canada during July–August 1990. This paper reports the experimental design for ABLE 3B and a brief overview of results. The detailed results are presented in a series of papers in this issue. The chemical composition of the atmospheric mixed layer over remote tundra, boreal wetland, and forested environments was influenced by emissions of CH4 and nonmethane hydrocarbons from biogenic sources, emissions of gases and aerosols from local biomass burning, and transport of pollutants into the study areas from urban/industrial sources. Minimum concentrations of both trace gas and aerosol species in boundary layer air were associated with Arctic source areas. In the free troposphere the biospheric influence was undetectable, and major sources of chemical variability were related to long‐range transport of pollutants into the study areas from biomass burning and industrial sources in Alaska and the Great Lakes regions, respectively. Minimum concentrations of both trace gas and aerosol species in the free troposphere were associated with a persistent, widespread air mass which both chemistry and air mass trajectory analyses suggested had originated in the tropical Pacific. Subsidence of air from the upper troposphere and lower stratosphere frequently enhanced ozone and influenced other trace gas and aerosol species at midtropospheric altitudes. The North American Arctic is a complex dynamical and chemical environment with considerable spatial and temporal variability in aerosol and trace gas concentrations. The use of atmospheric chemical indicators for climate change detection will require a much more comprehensive Arctic monitoring program than currently exists.

GROUND-LIVING SPIDERS, OPILIONIDS, AND PSEUDOSCORPIONS OF PEATLANDS IN QUEBEC

AbstractPeatlands were studied in temperate, boreal, subarctic, and arctic wetland regions of Quebec, mainly using pitfall traps. Altogether, 169 species of spiders, belonging to 14 families, were collected; 73 species were found only in the temperate-boreal region, 58 only in the subarctic-arctic region, and 38 in both regions. The most species-rich spider families were Linyphiidae (58.3% of all species), Lycosidae (12.4%), and Gnaphosidae (7.1%). Families occurring only, or mainly, in the temperate (and boreal) region were Hahniidae, Dictynidae, Salticidae, Liocranidae, and Theridiidae. Linyphiidae, especially Erigoninae, were typical of the subarctic region. Alopecosa aculeata (Clerck) and Pardosa hyperborea (Thorell) (Lycosidae), Theonoe stridula Crosby (Theridiidae), and Ceratinella brunnea Emerton (Linyphiidae) were found in six of the seven study areas. Seven of the eight opilionid species were found in the temperate region, but Mitopus morio (Fabricius) occurred only in the subarctic bogs. The only pseudoscorpion, Microbisium brunneum (Hagen), was caught in the temperate, boreal, and subarctic regions. The percentage of spiders collected in bogs of both Quebec and southern Ontario was 64% in the temperate region and only 27% in the subarctic region. Almost 50% of species from bogs in the Manitoba taiga were found also in Quebec. About a third of the Quebec bog spiders are Holarctic.

Methane Emissions from Wetlands in the Midboreal Region of Northern Ontario, Canada

Methane (CH4) fluxes were measured by a static chamber technique from May to October 1991 at 19 wetland sites near Cochrane, northern Ontario, representative of the Clay Belt Midboreal region of central Canada. Seasonal average fluxes of CH4 from the peatlands ranged from 0.4 to 67.5 mg°m—2°d—1 (0.06—10.1 g°m—2°yr—1). Beaver ponds showed the highest fluxes of CH4, from both the open water section (seasonal average 290 mg°m—2°d—1, 44g°m—2°yr—1) and the adjacent marsh areas where the water table rose close to or above the soil surface (91—350 mg°m—2°d—1, 13—35 g°m—2°yr—1). Seasonal mean water table position, particularly at the microtopographic scale of hummock and hollow, explained most of the variability in CH4 emission among wetlands (r2 = 0.74). Trophic status, such as pore—water Ca, Mg, and pH had little correlation with CH4 emissions. Broad—scale peatland classifications that do not account for hydrological differences at the microtopographic level are inadequate for predicting CH4 flux in boreal wetlands, particularly in forested ecosystems where conifer swamps are diverse and comprise the major peatland class. Based on areal estimates of the different wetland types in the Clay Belt, we estimate an annual CH4 flux of 3.4 g°m—2°yr—1, generally lower than that used in extrapolations to continental— or global—scale methane budgets.

Land and water interface zones

This paper reports analyses of C pools and fluxes in land-water interface zones completed at the International Workshop: Terrestrial Biospheric Carbon Fluxes; Quantification of Sinks and Sources of CO2 (Bad Harzburg, Germany, March 1-5, 1993). The objective was to determine the role of these zones as global sinks of atmospheric CO2 as part of a larger effort to quantify global C sinks and sources in the past (ca. 1850), the present, and the foreseeable future (ca. 2050). Assuming the world population doubles by the year 2050, storage of atmospheric C in reservoirs will also double, as will river loads of atmospheric C and nutrients. It is estimated that C sinks in temperate and boreal wetlands have decreased by about 50%, from 0.2 to 0.1 Gt C yr-1. since 1850. The total decrease for wetlands may be considerably larger when tropical wetlands are taken into account, however, the area and C density of tropical wetlands are not well known at this time. Changes in cultivation practices and improved sampling of methaneogenesis have caused estimates of CH4 emissions from ricelands to drop substantially from 150 to 60 Tg yr-1. Even with doubled N and P loads, rivers are unlikely to fertilize more than about 20% of the new primary production in the coastal ocean. The source of C for this new production may not be the atmosphere, however, because the coastal ocean exchanges large quantities of DIC with the open ocean. Until the C fluxes from air-sea exchange of CO2 and DIC are better quantified, the C-sink potential of the coastal ocean will remain a major uncertainty in the global C cycle. Analysis of model simulations of oceanic C uptake reconfirmed that the open ocean appears to take up about 2.0 Gt C yr-1 from the atmosphere and that model estimates are in better accord now, ±0.5 Gt C yr-1, than ever before. Land use management must consider the unique C sinks in coastal and alluvial wetlands in order to minimize the future negative impacts of agriculture and urban development. Long-term monitoring will be essential to prove the success, or failure, of management practices to sustain wetlands in the future. Relative to the other systems examined at the workshop, the C-sink capacity of the ocean (excluding estuaries) is not likely to be measurably affected in the foreseeable future by the management scenarios considered at the workshop.

Runoff Generation in a High Boreal Wetland in Northern Canada

The stable isotope composition of water and major-ion concentrations were measured in a small catchment tributary to Manners Creek, situated in the zone of discontinuous permafrost near Fort Simpson, Northwest Territories. Hydrograph separation calculations based on δ18O and δ2 H values of snow, active-layer water, and streamflow reveal that snowmelt contributions were secondary to active-layer storage contributions throughout the spring freshet period of 1990. At the time of peak spring runoff an estimated 40 to 50 % of streamflow was contributed by snowmelt, while over the entire spring period only 25 to 30 % of streamflow was contributed by snowmelt. Overland and pipe flow are shown to be important mechanisms of rapid snowmelt runoff from permafrost slopes.