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  • 1
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Synthesis of results from several Arctic and boreal research programmes provides evidence for the strong role of high-latitude ecosystems in the climate system. Average surface air temperature has increased 0.3 °C per decade during the twentieth century in the western North American Arctic and boreal forest zones. Precipitation has also increased, but changes in soil moisture are uncertain. Disturbance rates have increased in the boreal forest; for example, there has been a doubling of the area burned in North America in the past 20 years. The disturbance regime in tundra may not have changed. Tundra has a 3–6-fold higher winter albedo than boreal forest, but summer albedo and energy partitioning differ more strongly among ecosystems within either tundra or boreal forest than between these two biomes. This indicates a need to improve our understanding of vegetation dynamics within, as well as between, biomes. If regional surface warming were to continue, changes in albedo and energy absorption would likely act as a positive feedback to regional warming due to earlier melting of snow and, over the long term, the northward movement of treeline. Surface drying and a change in dominance from mosses to vascular plants would also enhance sensible heat flux and regional warming in tundra. In the boreal forest of western North America, deciduous forests have twice the albedo of conifer forests in both winter and summer, 50–80% higher evapotranspiration, and therefore only 30–50% of the sensible heat flux of conifers in summer. Therefore, a warming-induced increase in fire frequency that increased the proportion of deciduous forests in the landscape, would act as a negative feedback to regional warming.Changes in thermokarst and the aerial extent of wetlands, lakes, and ponds would alter high-latitude methane flux. There is currently a wide discrepancy among estimates of the size and direction of CO2 flux between high-latitude ecosystems and the atmosphere. These discrepancies relate more strongly to the approach and assumptions for extrapolation than to inconsistencies in the underlying data. Inverse modelling from atmospheric CO2 concentrations suggests that high latitudes are neutral or net sinks for atmospheric CO2, whereas field measurements suggest that high latitudes are neutral or a net CO2 source. Both approaches rely on assumptions that are difficult to verify. The most parsimonious explanation of the available data is that drying in tundra and disturbance in boreal forest enhance CO2 efflux. Nevertheless, many areas of both tundra and boreal forests remain net sinks due to regional variation in climate and local variation in topographically determined soil moisture. Improved understanding of the role of high-latitude ecosystems in the climate system requires a concerted research effort that focuses on geographical variation in the processes controlling land–atmosphere exchange, species composition, and ecosystem structure. Future studies must be conducted over a long enough time-period to detect and quantify ecosystem feedbacks.
    Type of Medium: Electronic Resource
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  • 2
    Electronic Resource
    Electronic Resource
    Oxford, UK : Blackwell Science Ltd
    Global change biology 6 (2000), S. 0 
    ISSN: 1365-2486
    Source: Blackwell Publishing Journal Backfiles 1879-2005
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Geography
    Notes: Measurements of the spatial variability of methane (CH4) emissions, net CO2 ecosystem exchange (NEE), and dissolved carbon (CH4, CO2, and DOC) were made in a boreal patterned peatland in northern Sweden in the summers (May to September) of 1992 and 1993. Carbon balance terms were measured and the carbon balance inferred at different peatland surface topography features (e.g. ridges, lawns, and pools) and at different positions within the peatland (e.g. plateau, margin). Combining these data permits a comparison of the carbon balance at the peatland scale for the two field seasons.Trends in the spatial variability of the net carbon storage, as determined by the difference between inputs and outputs, suggest that carbon storage decreased in lawns from the margin of the peatland to the central plateau, while the reverse trend occurred in ridges. This indicates a difference in carbon exchange processes between sites with different surface topography due to differences in soil moisture and temperature.Total carbon storage for the peatland, weighted for topographic variability, indicates that the peatland gained carbon in 1992 (2.0 g C m− 2), but lost carbon in 1993 ( −  7.6 g C m− 2). There was little variation in mean seasonal air temperature and total precipitation between the two years suggesting that the timing and magnitude of temperature and precipitation variation within the growing season are important for the season carbon balance. Because the carbon storage differences were small relative to the potential errors we conclude that the peatland was neither a net sink nor source of atmospheric carbon. This research demonstrates the importance of position in a peatland for the inference of long-term carbon accumulation and the assessment of contemporary exchange rates.
    Type of Medium: Electronic Resource
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  • 3
    ISSN: 1573-515X
    Keywords: Soil aluminum ; Precambrian shield ; organically bound aluminum ; saturation indices ; lichen-bedrock surfaces
    Source: Springer Online Journal Archives 1860-2000
    Topics: Chemistry and Pharmacology , Geosciences
    Notes: Abstract Solid phase controls of dissolved aluminum chemistry of soil and surface waters were investigated in several pristine, low order Precambrian shield catchments. Soil extraction and leaching experiments were conducted to quantify the various pools of solid phase soil aluminum and their relative mobility. Reactive soil aluminum (exchangeable + organic + amorphous forms), comprised 〈 20% of the total soil aluminum. Leaching soils with pH 3.0 HCl solutions indicated that Na4P2O7 extractable aluminum (largely organic complexes) was the most mobile form of reactive soil aluminum. Aluminum hydroxide from vermiculate interlayers was also mobilized from all soil horizons and its contribution to dissolved aluminum increased with soil depth. Runoff and soil waters from organic LFH and Ah soil horizons were highly undersaturated with respect to Al(OH)3 solid-phases. Several natural bedrock surfaces (metagranites) covered with moss or lichen were leached with HCl solutions. Significantly more aluminum was removed from bedrock surfaces colonized with the mossRacomitrium microcarpon compared to that of the lichen-covered surfaces. Aluminum removal increased dramatically as the acidity of the leaching solution increased to pH 3.0. Leachates solutions collected from bedrock surfaces became increasingly undersaturated with respect to Al(OH)3 minerals at lower pH values. Aluminum solubility appears to be controlled by equilibrium with organic complexation, modified by kinetically constrained dissolution of interlayer aluminum.
    Type of Medium: Electronic Resource
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  • 4
    ISSN: 1572-9729
    Keywords: Elemental transport ; hydrologic pathways ; spatial heterogeneity ; Precambrian shield
    Source: Springer Online Journal Archives 1860-2000
    Topics: Biology , Energy, Environment Protection, Nuclear Power Engineering , Agriculture, Forestry, Horticulture, Fishery, Domestic Science, Nutrition
    Notes: Abstract The hydrology and elemental transport within five low order Precambrian shield catchments was investigated during 1988–90. Catchments were subdivided and instrumented to examine the vertical and horizontal fluxes of elements within and between two distinct landscape types: open, lichen-covered bedrock outcrops and patches of conifer forest. The dominant hydrologic pathways were Horton overland flow in the lichen-bedrock areas and shallow subsurface flow through organic rich LFH (forest floor) and Ah soil horizons in the forested areas. Annual runoff coefficients ranged from 0.3 to 0.7. Runoff chemistry was acidic (pH 4.01–4.72), with organic anion equivalents (RCOO-), comprising 60 and 69% of the anion charge total for bedrock and forest runoff, respectively. Forested plots exported more H+ (2.6x), DOC (1.4x), Al (1.6x) and Fe (1.8x) and less N (0.40x), P (0.13x), particulate C (0.08x), Ca2+ (0.38x), Mg2+ (0.83x), Na+ (0.85x) and K+ (0.32x) per unit area than the bedrock-lichen plots. The catchments exhibited a net export of H+ (34), Mg2+ (24), Na+ (20), K+ (4) (units in eq ha-1 yr-1) and C (16), Si (5.6), Al (1.6) and Fe (0.47) (units kg ha-1 yr-1). The catchments retained N (5.66), P (0.08), Mn (0.03) (units kg ha-1 yr-1), and Ca2+ (37), and Cl- (3) (units eq ha-1 yr-1). The strong retention of Ca2+ within the treed soil islands resulted in extremely low export rates of base cations (-15 to 38 eq ha-1 yr-1). The spatial distribution and hydrologic and biogeochemical linkages associated with each landscape unit interact to control element transport within the study catchments.
    Type of Medium: Electronic Resource
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  • 5
    Publication Date: 2019-08-17
    Description: We analyzed the relationship between net ecosystem exchange of carbon dioxide (NEE) and irradiance (as photosynthetic photon flux density or PPFD), using published and unpublished data that have been collected during midgrowing season for carbon balance studies at seven peatlands in North America and Europe, NEE measurements included both eddy-correlation tower and clear, static chamber methods, which gave very similar results. Data were analyzed by site, as aggregated data sets by peatland type (bog, poor fen, rich fen, and all fens) and as a single aggregated data set for all peatlands. In all cases, a fit with a rectangular hyperbola (NEE = alpha PPFD P(sub max)/(alpha PPFD + P(sub max) + R) better described the NEE-PPFD relationship than did a linear fit (NEE = beta PPFD + R). Poor and rich fens generally had similar NEE-PPFD relationships, while bogs had lower respiration rates (R = -2.0 micro mol m(exp -2) s(exp -1) for bogs and -2.7 micro mol m(exp -2) s(exp -1)) for fens) and lower NEE at moderate and high light levels (P(sub max)= 5.2 micro mol m(exp -2) s(exp -1) for bogs and 10.8 micro mol m(exp -2) s(exp -1) for fens). As a single class, northern peatlands had much smaller ecosystem respiration (R = -2.4 micro mol m(exp -2) s(exp -1)) and NEE rates (alpha = 0.020 and P(sub max)= 9.2 micro mol m(exp -2) s(exp -1)) than the upland ecosystems (closed canopy forest, grassland, and cropland). Despite this low productivity, northern peatland soil carbon pools are generally 5-50 times larger than upland ecosystems because of slow rates of decomposition caused by litter quality and anaerobic, cold soils.
    Keywords: Earth Resources and Remote Sensing
    Type: Paper 97GB03367 , Global Biogeochemical Cycles (ISSN 0886-6236); 12; 1; 115-126
    Format: text
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  • 6
    Publication Date: 2015-04-15
    Description: Significant climate risks are associated with a positive carbon–temperature feedback in northern latitude carbon-rich ecosystems, making an accurate analysis of human impacts on the net greenhouse gas balance of wetlands a priority. Here, we provide a coherent assessment of the climate footprint of a network of wetland sites based on...
    Print ISSN: 0027-8424
    Electronic ISSN: 1091-6490
    Topics: Biology , Medicine , Natural Sciences in General
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  • 7
    Publication Date: 2000-01-01
    Print ISSN: 0885-6087
    Electronic ISSN: 1099-1085
    Topics: Architecture, Civil Engineering, Surveying , Geography
    Published by Wiley
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  • 8
    Publication Date: 2002-01-01
    Print ISSN: 1027-5606
    Electronic ISSN: 1607-7938
    Topics: Geography , Geosciences
    Published by Copernicus on behalf of European Geosciences Union (EGU).
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  • 9
    Publication Date: 2013-09-12
    Description: Long-term impacts of drier conditions on the hydrology of northern peatlands are poorly understood. We used long-term drainage near a historic drainage ditch, separating an area from the main peatland, as an analogue for long-term drying in a northern temperate bog. The objective was to identify the impact of drier conditions on ecohydrological processes and groundwater flow patterns in an area now forested and an area that maintained a bog-like character. Groundwater flow patterns alternated between mostly downward flow and occasionally upward flow in the bog area and were mostly upward-orientated in the forested area, which suggested that there the flow pattern had shifted from bog- to fen-like conditions. Flow patterns were in agreement with changes in post-drainage hydraulic conductivities, storage capacity of the peat and water table levels. Compared to the bog, hydraulic conductivities in the forested area were one to three orders of magnitude lower in the uppermost 0.75 m of peat (paired t test, p 〈 0.05). Bulk density had increased and the water table level was lower and more strongly fluctuating in the forested area. Our findings suggest hydraulic gradients and flow patterns have changed due to increased evapotranspiration and interception with the emergence of a tree cover. The smaller size of the now-forested area relative to the remaining bog area appeared to be important for the hydrological change. With the main Mer Bleue bog as hinterland, enhanced runoff to the drainage channel had little effect on hydrologic and vegetation patterns. In the cut-off, smaller, now forested area pervasive changes in vegetation and hydrologic processes occurred. The difference in response to local drainage raises questions about tipping points with respect to the impact of drying on peatland ecosystems that need to be addressed in future research.
    Print ISSN: 1027-5606
    Electronic ISSN: 1607-7938
    Topics: Geography , Geosciences
    Published by Copernicus on behalf of European Geosciences Union (EGU).
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  • 10
    Publication Date: 1993-12-01
    Print ISSN: 0012-9658
    Electronic ISSN: 1939-9170
    Topics: Biology
    Published by Wiley on behalf of Ecological Society of America (ESA).
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