| 1. |
- Elberling, Bo, et al.
(författare)
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High Arctic soil CO2 and CH4 production controlled by temperature, water, freezing and snow
- 2008
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Ingår i: High-arctic ecosystem dynamics in a changing climate - Ten years of monitoring and research at Zackenberg Research Station, Northeast Greenland (Advances in Ecological Research). - 0065-2504. - 9780123736659 ; 40, s. 441-472
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Soil gas production processes, mainly anaerobic or aerobic soil respiration, drive major gas fluxes across the soil-atmosphere interface. Carbon dioxide (CO2) effluxes, an efflux which in most ecosystems is a result of both autotrophic and heterotrophic respiration, in particular have received international attention. The importance of both CO2 and methane (CH4) fluxes are emphasised in the Arctic because of the large amount of soil organic carbon stored in terrestrial ecosystems and changes in uptake and release due to climate changes. This chapter focuses on controls on spatial and temporal trends in subsurface CO2 and CH4 production as well as on transport and release of gases from the soil observed in the valley Zackenbergdalen. A dominance of near-surface temperatures controlling both spatial and seasonal trends is shown based on data obtained using closed chamber and eddy-correlation techniques as well as in manipulated field plots and in controlled incubation experiments. Despite variable temperature sensitivities reported, most data can be fairly well fitted to exponential temperature-dependent equations. The water content (at wet sites linked to the depth to the water table) is a second major factor regulating soil respiration processes, but the effect is quite different in contrasting vegetation types. Dry heath sites are shown to be periodically water limited during the growing season and respond therefore with high respiration rates when watered. In contrast, water saturated conditions during most of the growing season in the fen areas hinder the availability of oxygen, resulting in both CO2 and CH4 production. Thus, water table drawdown results in decreasing CH4 effluxes but increasing CO2 effluxes. Additional controls on gas production are shown to be related to the availability of substrate and plant productivity. Subsurface gas production will produce partial and total pressure gradient causing gas transport, which in well-drained soils is mainly controlled by diffusion, whereas gas advection, bubbles and transport through roots and stems may be important in more saturated soils. Bursts of CO2 gas have been observed during spring thaw and confirmed in controlled soil thawing experiments. Field observations as well as experimental work suggest that such bursts represent partly on-going soil respiration and a physical release of gas produced during the winter. The importance of winter soil respiration is emphasised because of the fact that microbial respiration in Zackenberg samples is noted down to a least -18 degrees C. Hence, the importance of winter respiration and burst events in relation to seasonal and future climate trends requires more than just summer measurements. For example, the autumn period seems important as snowfall prior to low air temperature may insulate the soil, keeping soil temperatures high. This will extend the period of high soil respiration rates and thereby increase the importance of the winter period for the annual carbon balance. Because of the complexity of factors controlling subsurface gas production, we conclude that different parts of the landscape will respond quite differently to the same climate changes as well as that short-term effects are likely to be different from long-term effects.
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| 2. |
- Elberling, Bo, et al.
(författare)
-
Soil and Plant Community Characteristics and Dynamics at Zackenberg
- 2008
-
Ingår i: High-arctic ecosystem dynamics in a changing climate - Ten years of monitoring and research at Zackenberg Research Station, Northeast Greenland (Advances in Ecological Research). - 0065-2504. - 9780123736659 ; 40, s. 223-248
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Arctic soils hold large amounts of nutrients in the weatherable minerals and the soil organic matter, which slowly decompose. The decomposition processes release nutrients to the plant-available nutrient pool as well as greenhouse gases to the atmosphere. Changes in climatic conditions, for example, changes in the distribution of snow, water balance and the length of the growing season, are likely to affect the complex interactions between plants, abiotic and biotic soil processes as well as the composition of soil micro- and macro-fauna and thereby the overall decomposition rates. These interactions, in turn, will influence soil-plant functioning and vegetation composition in the short as well as in the long term. In this chapter, we report on soils and. plant communities and their distribution patterns in the valley Zackenbergdalen and focus on the detailed investigations within five dominating plant communities. These five communities are located along an ecological gradient in the landscape and are closely related to differences in water availability. They are therefore indirectly formed as a result of the distribution of landforms, redistribution of snow and drainage conditions. Each of the plant communities is closely related to specific nutrient levels and degree of soil development including soil element accumulation and translocation, for example, organic carbon. Results presented here show that different parts of the landscape have responded quite differently to the same overall climate changes the last 10 years and thus, most likely in the future too. Fens represent the wettest sites holding large reactive buried carbon stocks. A warmer climate will cause a permafrost degradation, which most likely will result in anoxic decomposition and increasing methane emissions. However, the net gas emissions at fen sites are sensitive to long-term changes in the water table level. Indeed, increasing maximum active layer depth at fen sites has been recorded together with a decreasing water level at Zackenberg. This is in line with the first signs of increasing extension of grasslands at the expense of fens. In contrast, the most exposed and dry areas have less soil carbon, and decomposition processes are periodically water limited. Here, an increase in air temperatures may increase active layer depth more than at fen sites, but water availability will be critical in determining nutrient cycling and plant production. Field manipulation experiments of increasing temperature, water supply and nutrient addition show that soil-plant interactions are sensitive to these variables. However, additional plant-specific investigations are needed before net effects of climate changes on different landscape and plant communities can be integrated in a landscape context and used to assess the net ecosystem effect of future climate scenarios.
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| 3. |
- Forchhammer, Mads C., et al.
(författare)
-
Zackenberg in a circumpolar context
- 2008
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Ingår i: Advances in Ecological Research. - 0065-2504. ; 40, s. 499-544
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Throughout the Northern Hemisphere, changes in local and regional climate conditions are coupled to the recurring and persistent large-scale patterns of pressure and circulation anomalies spanning vast geographical areas, the so-called teleconnection patterns. Indeed, the atmospheric fluctuations described by the North Atlantic Oscillation (NAO) are closely associated with the last four decades of inter-annual variability in local snow and ice conditions observed in the Arctic. Since the NAO has also been connected with changes in the global climate, the behaviour of species, communities and other ecosystem elements at Zackenberg in relation to the NAO enables us to view these in circumpolar and global contexts. Large-scale systems like the NAO constitute the link between the global change and local climate variability to which ecosystem components respond. Here, we place selected ecosystem elements from the monitoring programme Zackenberg Basic presented in previous chapters in a circumpolar context related to NAO-mediated climatic changes. We begin by linking the local variability in winter weather conditions at Zackenberg to fluctuations in the NAO. We then proceed by linking the observed intra- and inter-annual behaviour of selected ecosystem elements to changes in the NAO. The functional ecosystem characteristics in focus are landscape gas exchange dynamics phenological patterns at different trophic levels, consumer-resource dynamics and community stability. The influence of the NAO is presented and discussed in a broader perspective based on information obtained from other arctic localities. The relation between the NAO and the Zackenberg winter weather, is nonlinear, reflecting differential effects of the NAO as the index moves between high and low phases. The inverse hyperbolic relationship found between the NAO and the amount of winter snow was also evident as non-linear response in organisms and systems to inter-annual changes in the NAO. Responses investigated included growth and reproduction in plants and animals, population dynamics and synchrony, inter-trophic interactions and community stability together with system feedback dynamics.
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| 4. |
- Grøndahl, Louise, et al.
(författare)
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Spatial and interannual variability of trace gas fluxes in a heterogeneous High Arctic landscape
- 2008
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Ingår i: High-arctic ecosystem dynamics in a changing climate - Ten years of monitoring and research at Zackenberg Research Station, Northeast Greenland (Advances in Ecological Research). - 0065-2504. - 9780123736659 ; 40, s. 473-498
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Summertime measurements of CO2 and CH4 fluxes were carried out over a range of high-arctic ecosystem types in the valley Zackenbergdalen since 1996 using both chamber and eddy covariance methodology. The net ecosystem CO2 exchange and CH4 flux data presented reveal a high degree of inter-annual variability within the dominant vegetation types in the valley, but also show distinct differences between them. In particular, the wet and dry parts of the valley show distinct differences. In general, the wet parts of the valley, the fens dominated by white cotton grass Eriophorum scheuchzeri, show high productivity, also in comparison with other sites, whereas CO2 uptake rates in the white arctic bell heather Cassiope tetragona and mountain avens Dryas spp.-dominated heaths are much smaller. Also within the different ecosystem types, a high degree of spatial variability can be documented. The spatial variability both within and between ecosystem types is especially pronounced for the CH4 flux and can, at least partly, be related to differences in vegetation composition and water table level. The importance of the CH4 emission from the various ecosystem types is evaluated both in relation to carbon and greenhouse gas budgets. In both wet and drier ecosystem components, inter-annual variability seems best explained through differences in the amount and distribution of snow in spring and the length of the growing season. A large number of replicate chamber measurements carried out over various vegetation types in the valley are used to produce a synthesis of 10 years of flux data available on growing season carbon dynamics and CH4 emission patterns in the individual parts of this high-arctic ecosystem and relates the differences between the ecosystems found in Zackenbergdalen to comparable sites in the circumpolar North.
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| 5. |
- Meltofte, Hans, et al.
(författare)
-
Introduction
- 2008
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Ingår i: High-arctic ecosystem dynamics in a changing climate - Ten years of monitoring and research at Zackenberg Research Station, Northeast Greenland (Advances in Ecological Research). - 0065-2504. - 9780123736659 ; 40, s. 1-12
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- Our continuously changing global environment requires continuous and detailed monitoring for us to understand how ecosystems are structured and function in response to climatic changes. Understanding the arctic ecosystems is of particular importance (Oechel et al., 1997). Indeed, rather than in boreal and temperate regions, the forecasted climatic changes will be first and most pronounced in the Arctic. Hence, performing long-term monitoring of an arctic ecosystem provides us with the unique ability to not only give "early warnings" of climate change impacts but also, and perhaps even more important, predict how and where in the ecosystem these will be most pronounced and with what consequences for stability, structure and function. Since 1995, Zackenberg Ecological Research Operations (ZERO) has monitored annually over 1500 variables concurrently across the physical and biological compartments of a single high-arctic terrestrial ecosystem in central Northeast Greenland. This makes ZERO the most integrated and comprehensive long-term monitoring and research programme presently operating in the Arctic. This book explores the complex physical and ecological long-term dynamics of a high-arctic terrestrial ecosystem. Since the book is based on data from ZERO, this introductory chapter presents the structural and organisational foundation for ZERO. Following our introduction are four chapters providing the climatic and ecological background together with a presentation of the study area. The rest of the book is devoted entirely to the physical, ecological and ecosystem processes.
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| 6. |
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| 7. |
- Andersen, Emil Alexander Sherman, et al.
(författare)
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Nitrogen isotopes reveal high N retention in plants and soil of old Norse and Inuit deposits along a wet-dry arctic fjord transect in Greenland
- 2020
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Ingår i: Plant and Soil. - : Springer. - 0032-079X .- 1573-5036. ; 455:1-2, s. 241-255
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Tidskriftsartikel (refereegranskat)abstract
- Aims: Plant growth in the Arctic is often nutrient limited due to temperature constraints on decomposition and low atmospheric input of nitrogen (N). Local hotspots of nutrient enrichment found in up to 4000-year-old archaeological deposits can be used to explore the recycling and long-term retention of nutrients in arctic ecosystems.Methods: We investigated old Inuit and Norse deposits (known as middens) and adjacent tundra ecosystems along a wet-dry fjord gradient in western Greenland to explore the isotopic fingerprinting of plant and soil carbon and nitrogen (C-13/C-12 and(15)N/N-14) derived from human presence.Results: At all locations we observed a significant isotopic fingerprint in soil and plant N related to human deposits. This demonstrates a century-long legacy of past human habitation on plant and soil characteristics and indicates a surprisingly high N retention in these ecosystems. This is consistent with the significantly higher plant biomass in areas with archaeological deposits.Conclusion: Vegetation composition and N in plants and soils displayed marked differences along the wet-dry fjord gradient. Furthermore, the profound nutrient enrichment and organic matter accumulation in archaeological deposits compared to surrounding tundra demonstrates a century-long legacy of past habitation on plant and soil characteristics as well as efficient N cycling with surprisingly limited N loss.
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| 8. |
- Björkman, Anne, 1981, et al.
(författare)
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Plant functional trait change across a warming tundra biome
- 2018
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Ingår i: Nature. - : Springer Science and Business Media LLC. - 0028-0836 .- 1476-4687. ; 562:7725, s. 57-62
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Tidskriftsartikel (refereegranskat)abstract
- The tundra is warming more rapidly than any other biome on Earth, and the potential ramifications are far-reaching because of global feedback effects between vegetation and climate. A better understanding of how environmental factors shape plant structure and function is crucial for predicting the consequences of environmental change for ecosystem functioning. Here we explore the biome-wide relationships between temperature, moisture and seven key plant functional traits both across space and over three decades of warming at 117 tundra locations. Spatial temperature–trait relationships were generally strong but soil moisture had a marked influence on the strength and direction of these relationships, highlighting the potentially important influence of changes in water availability on future trait shifts in tundra plant communities. Community height increased with warming across all sites over the past three decades, but other traits lagged far behind predicted rates of change. Our findings highlight the challenge of using space-for-time substitution to predict the functional consequences of future warming and suggest that functions that are tied closely to plant height will experience the most rapid change. They also reveal the strength with which environmental factors shape biotic communities at the coldest extremes of the planet and will help to improve projections of functional changes in tundra ecosystems with climate warming.
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| 9. |
- Björkman, Anne, 1981, et al.
(författare)
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Tundra Trait Team: A database of plant traits spanning the tundra biome
- 2018
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Ingår i: Global Ecology and Biogeography. - : Wiley. - 1466-822X .- 1466-8238. ; 27:12, s. 1402-1411
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Tidskriftsartikel (refereegranskat)abstract
- © 2018 The Authors Global Ecology and Biogeography Published by John Wiley & Sons Ltd Motivation: The Tundra Trait Team (TTT) database includes field-based measurements of key traits related to plant form and function at multiple sites across the tundra biome. This dataset can be used to address theoretical questions about plant strategy and trade-offs, trait–environment relationships and environmental filtering, and trait variation across spatial scales, to validate satellite data, and to inform Earth system model parameters. Main types of variable contained: The database contains 91,970 measurements of 18 plant traits. The most frequently measured traits (>1,000 observations each) include plant height, leaf area, specific leaf area, leaf fresh and dry mass, leaf dry matter content, leaf nitrogen, carbon and phosphorus content, leaf C:N and N:P, seed mass, and stem specific density. Spatial location and grain: Measurements were collected in tundra habitats in both the Northern and Southern Hemispheres, including Arctic sites in Alaska, Canada, Greenland, Fennoscandia and Siberia, alpine sites in the European Alps, Colorado Rockies, Caucasus, Ural Mountains, Pyrenees, Australian Alps, and Central Otago Mountains (New Zealand), and sub-Antarctic Marion Island. More than 99% of observations are georeferenced. Time period and grain: All data were collected between 1964 and 2018. A small number of sites have repeated trait measurements at two or more time periods. Major taxa and level of measurement: Trait measurements were made on 978 terrestrial vascular plant species growing in tundra habitats. Most observations are on individuals (86%), while the remainder represent plot or site means or maximums per species. Software format: csv file and GitHub repository with data cleaning scripts in R; contribution to TRY plant trait database (www.try-db.org) to be included in the next version release.
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| 10. |
- Björkman, Mats P., 1978, et al.
(författare)
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A comparison of annual and seasonal carbon dioxide effluxes between sub-Arctic Sweden and High-Arctic Svalbard
- 2010
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Ingår i: Polar Research. - : Norwegian Polar Institute. - 1751-8369. ; 29:1, s. 75-84
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Tidskriftsartikel (refereegranskat)abstract
- Recent climate change predictions suggest altered patterns of winter precipitation across the Arctic. It has been suggested that the presence, timing and amount of snow all affect microbial activity, thus influencing CO2 production in soil. In this study annual and seasonal emissions of CO2 were estimated in High-Arctic Adventdalen, Svalbard, and sub-Arctic Latnjajaure, Sweden, using a new trace gas-based method to track real time diffusion rates through the snow. Summer measurements from snow-free soils were made using a chamber-based method. Measurements were obtained at different snow regimes in order to evaluate the effect of snow depth on winter CO2 effluxes. Total annual emissions of CO2 from the sub-Arctic site (0.662–1.487 kg CO2 m-2 yr-1) were found to be more than double the emissions from the High-Arctic site (0.369–0.591 kg CO2 m-2 yr-1). There were no significant differences in winter effluxes between snow regimes or vegetation types, indicating that spatial variability in winter soil CO2 effluxes are not directly linked to snow cover thickness or soil temperatures. Total winter emissions (0.004–0.248 kg CO2 m-2) were found to be in the lower range of those previously described in the literature. Winter emissions varied in their contribution to total annual production between 1 and 18%. Artificial snow drifts shortened the snow-free period by two weeks and decreased annual CO2 emission by up to 20%. This study suggests that future shifts in vegetation zones may increase soil respiration from Arctic tundra regions.
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| 11. |
- Björkman, Mats P., 1978, et al.
(författare)
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Winter carbon dioxide effluxes from Arctic ecosystems - A presentation of a novel trace gas method and comparison with previously used methodologies
- 2009
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Ingår i: Eos Trans. AGU, 90(52), Fall Meet. Suppl., Abstract A54D-03..
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Konferensbidrag (refereegranskat)abstract
- Winter CO2 efflux from subnivean environments is an important component of annual C budgets in arctic ecosystems and consequently makes prediction and estimations of winter processes as well as incorporations of these processes into existing models important. Several methods have been used for estimating winter CO2 production, by using different snow pack assumptions. Here, measurements from three commonly used methods and one novel trace gas method used during the winter 2007-2008 are compared and discussed: (1) measurements with chamber on snow surface, Fsnow, (2) chamber measurements directly on the soil, Fsoil, after snow removal, (3) diffusion measurements, F2-point, within the snow pack, and (4) a novel trace gas technique, FSF6, with multiple gas sampling within the snow pack. According to measurements in shallow and deep snow cover in High-arctic Svalbard and Sub-arctic Sweden total winter emissions from the trace gas technique, 0.004-0.248 kg CO2 m-2, were found to be in the lower range of those previously described in the literature, however, results from all four methods differ by up to two orders of magnitude. Highest mean winter CO2 effluxes were observed using Fsoil, 7.7-216.8 mg CO2 m-2 h-1, and lowest values using FSF6, 0.8-12.6 mg CO2 m-2 h-1. Fsnow and F2-point were both within the lower range, 2.1-15.1 mg CO2 m-2 h-1 and 6.8-11.2 mg CO2 m-2 h-1, respectively. Differences are considered a result of contrasting methods but also that the assumptions within the methods are not equivalent when quantifying CO2 production and effluxes to the atmosphere. As snow can act as a barrier for CO2, Fsoil is assumed to measure soil production whereas FSF6, Fsnow and F2-point are considered better approaches for quantifying exchange processes between the soil, snow, and the atmosphere. This study indicates that estimation of winter CO2 emissions might vary more due to the method used than due to the actual variation in soil CO2 production or release. This is of major concern, especially when CO2 efflux data is used in climate models or in carbon budget calculations and highlights the need for further development and validation of techniques.
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| 12. |
- Björkman, Mats P., 1978, et al.
(författare)
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Winter carbon dioxide effluxes from Arctic ecosystems: An overview and comparison of methodologies
- 2010
-
Ingår i: Global Biogeochemical Cycles. ; 24, s. GB3010-
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Tidskriftsartikel (refereegranskat)abstract
- The winter CO2 efflux from subnivean environments is an important component of annual C budgets in arctic ecosystems and consequently makes prediction and estimations of winter processes as well as incorporations of these processes into existing models important. Several methods have been used for estimating winter CO2 effluxes, involving different assumptions about the snow pack, all aiming to quantify CO2 production. Here, four different methods are compared and discussed: (1) measurements with a chamber on the snow surface, Fsnow; (2) chamber measurements directly on the soil, Fsoil, after snow removal; (3) diffusion measurements, F2-point, within the snow pack; and (4) a trace gas technique, FSF6, with multiple gas sampling within the snow pack. According to measurements collected from shallow and deep snow cover in High-Arctic Svalbard and Sub-Arctic Sweden during the winter of 2007-2008, the four methods differ by up to two orders of magnitude in their estimates of total winter emissions. The highest mean winter CO2 effluxes, 7.7-216.8 mg CO2 m-2 h-1, were observed using Fsoil and lowest values, 0.8-12.6 mg CO2 m-2 h-1, using FSF6. The Fsnow and F2-point methods were both within the lower range, 2.1-15.1 mg CO2 m-2 h-1 and 6.8-11.2 mg CO2 m-2 h-1, respectively. These differences are considered to be a result of contrasting methods, but also because the assumptions within the methods are not the same when quantifying CO2 production and effluxes to the atmosphere. Since snow can act as a barrier to CO2, Fsoil is assumed to measure soil production, whereas FSF6, Fsnow and F2-point are considered better approaches for quantifying exchange processes between the soil, snow, and the atmosphere. This study indicates that estimates of winter CO2 emissions may vary more as a result of the method used than due to the actual variation in soil CO2 production or release. This is a major concern, especially when CO2 efflux data are used in climate models or in carbon budget calculations, thus highlighting the need for further development and validation of accurate and appropriate techniques.
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| 13. |
- Björkman, Mats P., 1978, et al.
(författare)
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Winter fluxes of carbon dioxide – a comparison of current methodology
- 2008
-
Ingår i: The 15th ITEX workshop, Reykjavik, Iceland, 9–12 October 2008..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- During winter as much as 47 % of the land mass of the northern hemisphere may experience the insulating effect of a snow-cover, during which vast areas have a longer snow-covered period than growing season. The snow cover allows soil microbial activities to continue during winter with a production of CO2 as a result. Estimations of winter fluxes are difficult since snow is a highly complex media, with large uncertainties as a result. Using a newly developed trace gas diffusion technique this project aims to improve winter flux estimations and to minimise the uncertainties given by the snow-cover itself. Current methodology for winter CO2 emissions will be presented and evaluated together with a discussion on measurement standardization.
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| 14. |
- Blok, Daan, et al.
(författare)
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Contrasting above- and belowground organic matter decomposition and carbon and nitrogen dynamics in response to warming in High Arctic tundra
- 2018
-
Ingår i: Global Change Biology. - : Wiley. - 1354-1013. ; 24:6, s. 2660-2672
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Tidskriftsartikel (refereegranskat)abstract
- Tundra regions are projected to warm rapidly during the coming decades. The tundra biome holds the largest terrestrial carbon pool, largely contained in frozen permafrost soils. With warming, these permafrost soils may thaw and become available for microbial decomposition, potentially providing a positive feedback to global warming. Warming may directly stimulate microbial metabolism but may also indirectly stimulate organic matter turnover through increased plant productivity by soil priming from root exudates and accelerated litter turnover rates. Here, we assess the impacts of experimental warming on turnover rates of leaf litter, active layer soil and thawed permafrost sediment in two high-arctic tundra heath sites in NE-Greenland, either dominated by evergreen or deciduous shrubs. We incubated shrub leaf litter on the surface of control and warmed plots for 1 and 2 years. Active layer soil was collected from the plots to assess the effects of 8 years of field warming on soil carbon stocks. Finally, we incubated open cores filled with newly thawed permafrost soil for 2 years in the active layer of the same plots. After field incubation, we measured basal respiration rates of recovered thawed permafrost cores in the lab. Warming significantly reduced litter mass loss by 26% after 1 year incubation, but differences in litter mass loss among treatments disappeared after 2 years incubation. Warming also reduced litter nitrogen mineralization and decreased the litter carbon to nitrogen ratio. Active layer soil carbon stocks were reduced 15% by warming, while soil dissolved nitrogen was reduced by half in warmed plots. Warming had a positive legacy effect on carbon turnover rates in thawed permafrost cores, with 10% higher respiration rates measured in cores from warmed plots. These results demonstrate that warming may have contrasting effects on above- and belowground tundra carbon turnover, possibly governed by microbial resource availability.
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| 15. |
- Buchwal, Agata, et al.
(författare)
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Temperature sensitivity of willow dwarf shrub growth from two distinct High Arctic sites
- 2018
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Ingår i: International Journal of Biometeorology. - : Springer Science and Business Media LLC. - 0020-7128 .- 1432-1254.
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Tidskriftsartikel (refereegranskat)abstract
- The High Arctic region has experienced marked climate fluctuations within the past decades strongly affecting tundra shrub growth. However, the spatial variability in dwarf shrub growth responses in this remote region remains largely unknown. This study characterizes temperature sensitivity of radial growth of two willow dwarf shrub species from two distinct High Arctic sites. The dwarf shrub Salix arctica from Northern Greenland (82°N), which has a dry continental High Arctic climate, is linked with Salix polaris from central Svalbard (78° N), which experiences a more oceanic High Arctic climate with relatively mild winters. We found similar positive and significant relationships between annual growth of both Salix dwarf shrub species and July–August air temperatures (1960–2010), despite different temperature regimes and shrub growth rates at the two sites. Also, Salix dwarf shrub growth was significantly negatively correlated with Arctic and North Atlantic Oscillation (AO/NAO) indices; S. arctica from Northern Greenland was negatively correlated with previous autumn (AO index) and current summer AO and NAO indices, and S. polaris with the summer NAO index. The results highlight the importance of both local and regional climatic drivers for dwarf willow shrub growth in harsh polar desert habitats and are a step in the direction of identifying and scaling changes in plant growth across the High Arctic.
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| 16. |
- Chadburn, Sarah E., et al.
(författare)
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Carbon stocks and fluxes in the high latitudes : using site-level data to evaluate Earth system models
- 2017
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 14:22, s. 5143-5169
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Tidskriftsartikel (refereegranskat)abstract
- It is important that climate models can accurately simulate the terrestrial carbon cycle in the Arctic due to the large and potentially labile carbon stocks found in permafrost-affected environments, which can lead to a positive climate feedback, along with the possibility of future carbon sinks from northward expansion of vegetation under climate warming. Here we evaluate the simulation of tundra carbon stocks and fluxes in three land surface schemes that each form part of major Earth system models (JSBACH, Germany; JULES, UK; ORCHIDEE, France). We use a site-level approach in which comprehensive, high-frequency datasets allow us to disentangle the importance of different processes. The models have improved physical permafrost processes and there is a reasonable correspondence between the simulated and measured physical variables, including soil temperature, soil moisture and snow. We show that if the models simulate the correct leaf area index (LAI), the standard C3 photosynthesis schemes produce the correct order of magnitude of carbon fluxes. Therefore, simulating the correct LAI is one of the first priorities. LAI depends quite strongly on climatic variables alone, as we see by the fact that the dynamic vegetation model can simulate most of the differences in LAI between sites, based almost entirely on climate inputs. However, we also identify an influence from nutrient limitation as the LAI becomes too large at some of the more nutrient-limited sites. We conclude that including moss as well as vascular plants is of primary importance to the carbon budget, as moss contributes a large fraction to the seasonal CO2 flux in nutrient-limited conditions. Moss photosynthetic activity can be strongly influenced by the moisture content of moss, and the carbon uptake can be significantly different from vascular plants with a similar LAI. The soil carbon stocks depend strongly on the rate of input of carbon from the vegetation to the soil, and our analysis suggests that an improved simulation of photosynthesis would also lead to an improved simulation of soil carbon stocks. However, the stocks are also influenced by soil carbon burial (e.g. through cryoturbation) and the rate of heterotrophic respiration, which depends on the soil physical state. More detailed below-ground measurements are needed to fully evaluate biological and physical soil processes. Furthermore, even if these processes are well modelled, the soil carbon profiles cannot resemble peat layers as peat accumulation processes are not represented in the models. Thus, we identify three priority areas for model development: (1) dynamic vegetation including (a) climate and (b) nutrient limitation effects; (2) adding moss as a plant functional type; and an (3) improved vertical profile of soil carbon including peat processes.
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| 17. |
- Elberling, Bo, et al.
(författare)
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Arctic vegetation damage by winter-generated coal mining pollution released upon thawing
- 2007
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Ingår i: Environmental Science and Technology. - : American Chemical Society (ACS). - 0013-936X .- 1520-5851. ; 41:7, s. 2407-2413
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Tidskriftsartikel (refereegranskat)abstract
- Acid mine drainage (known as AMD) is a well-known environmental problem resulting from the oxidation of sulfidic mine waste. In cold regions, AMD is often considered limited by low temperatures most of the year and observed environmental impact is related to pollution generated during the warm summer period. Here we show that heat generation within an oxidizing, sulfidic, coal-mining waste-rock pile in Svalbard (78 degrees N) is high enough to keep the pile warm (roughly 5 degrees C throughout the year) despite mean annual air temperatures below -5 degrees C. Consequently, weathering processes continue year-round within the waste-rock pile. During the winter, weathering products accumulate within the pile because of a frozen outer layer on the pile and are released as a flush within 2 weeks of soil thawing in the spring. Consequently, spring runoff water contains elevated concentrations of metals. Several of these metals are taken up and accumulated in plants where they reach phytotoxic levels, including aluminum and manganese. Laboratory experiments document that uptake of Al and Mn in native plant species is highly correlated with dissolved concentrations. Therefore, future remedial actions to control the adverse environmental impacts of cold region coal-mining need to pay more attention to winter processes including AMD generation and accumulation of weathering products.
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| 18. |
- Faucherre, Samuel, et al.
(författare)
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Short and Long-Term Controls on Active Layer and Permafrost Carbon Turnover Across the Arctic
- 2018
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Ingår i: Journal of Geophysical Research - Biogeosciences. - : American Geophysical Union (AGU). - 2169-8953 .- 2169-8961. ; 123:2, s. 372-390
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Tidskriftsartikel (refereegranskat)abstract
- Decomposition of soil organic matter (SOM) in permafrost terrain and the production of greenhouse gases is a key factor for understanding climate change-carbon feedbacks. Previous studies have shown that SOM decomposition is mostly controlled by soil temperature, soil moisture, and carbon-nitrogen ratio (C:N). However, focus has generally been on site-specific processes and little is known about variations in the controls on SOM decomposition across Arctic sites. For assessing SOM decomposition, we retrieved 241 samples from 101 soil profiles across three contrasting Arctic regions and incubated them in the laboratory under aerobic conditions. We assessed soil carbon losses (Closs) five times during a 1 year incubation. The incubated material consisted of near-surface active layer (ALNS), subsurface active layer (ALSS), peat, and permafrost samples. Samples were analyzed for carbon, nitrogen, water content, δ13C, δ15N, and dry bulk density (DBD). While no significant differences were observed between total ALSS and permafrost Closs over 1 year incubation (2.3 ± 2.4% and 2.5 ± 1.5% Closs, respectively), ALNS samples showed higher Closs (7.9 ± 4.2%). DBD was the best explanatory parameter for active layer Closs across sites. Additionally, results of permafrost samples show that C:N ratio can be used to characterize initial Closs between sites. This data set on the influence of abiotic parameter on microbial SOM decomposition can improve model simulations of Arctic soil CO2 production by providing representative mean values of CO2 production rates and identifying standard parameters or proxies for upscaling potential CO2 production from site to regional scales.
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| 19. |
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| 20. |
- Keuschnig, Christoph, et al.
(författare)
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Reduced methane emissions in former permafrost soils driven by vegetation and microbial changes following drainage
- 2022
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Ingår i: Global Change Biology. - : Wiley. - 1354-1013 .- 1365-2486. ; 28:10, s. 3411-3425
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Tidskriftsartikel (refereegranskat)abstract
- In Arctic regions, thawing permafrost soils are projected to release 50 to 250 Gt of carbon by 2100. This data is mostly derived from carbon-rich wetlands, although 71% of this carbon pool is stored in faster-thawing mineral soils, where ecosystems close to the outer boundaries of permafrost regions are especially vulnerable. Although extensive data exists from currently thawing sites and short-term thawing experiments, investigations of the long-term changes following final thaw and co-occurring drainage are scarce. Here we show ecosystem changes at two comparable tussock tundra sites with distinct permafrost thaw histories, representing 15 and 25years of natural drainage, that resulted in a 10-fold decrease in CH4 emissions (3.2±2.2 vs. 0.3±0.4mg C-CH4m−2day−1), while CO2 emissions were comparable. These data extend the time perspective from earlier studies based on short-term experimental drainage. The overall microbial community structures did not differ significantly between sites, although the drier top soils at the most advanced site led to a loss of methanogens and their syntrophic partners in surface layers while the abundance of methanotrophs remained unchanged. The resulting deeper aeration zones likely increased CH4 oxidation due to the longer residence time of CH4 in the oxidation zone, while the observed loss of aerenchyma plants reduced CH4 diffusion from deeper soil layers directly to the atmosphere. Our findings highlight the importance of including hydrological, vegetation and microbial specific responses when studying long-term effects of climate change on CH4 emissions and underscores the need for data from different soil types and thaw histories.
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| 21. |
- Kramshöj, Magnus, et al.
(författare)
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Biogenic volatile release from permafrost thaw is determined by the soil microbial sink
- 2018
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Ingår i: Nature Communications. - : Springer Science and Business Media LLC. - 2041-1723. ; 9
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Tidskriftsartikel (refereegranskat)abstract
- Warming in the Arctic accelerates thawing of permafrost-affected soils, which leads to a release of greenhouse gases to the atmosphere. We do not know whether permafrost thaw also releases non-methane volatile organic compounds that can contribute to both negative and positive radiative forcing on climate. Here we show using proton transfer reaction–time of flight–mass spectrometry that substantial amounts of ethanol and methanol and in total 316 organic ions were released from Greenlandic permafrost soils upon thaw in laboratory incubations. We demonstrate that the majority of this release is taken up in the active layer above. In an experiment using 14C-labeled ethanol and methanol, we demonstrate that these compounds are consumed by microorganisms. Our findings highlight that the thawing permafrost soils are not only a considerable source of volatile organic compounds but also that the active layer regulates their release into the atmosphere.
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| 22. |
- Kropp, Heather, et al.
(författare)
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Shallow soils are warmer under trees and tall shrubs across Arctic and Boreal ecosystems
- 2021
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Ingår i: Environmental Research Letters. - : IOP Publishing. - 1748-9326. ; 16:1
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Tidskriftsartikel (refereegranskat)abstract
- Soils are warming as air temperatures rise across the Arctic and Boreal region concurrent with the expansion of tall-statured shrubs and trees in the tundra. Changes in vegetation structure and function are expected to alter soil thermal regimes, thereby modifying climate feedbacks related to permafrost thaw and carbon cycling. However, current understanding of vegetation impacts on soil temperature is limited to local or regional scales and lacks the generality necessary to predict soil warming and permafrost stability on a pan-Arctic scale. Here we synthesize shallow soil and air temperature observations with broad spatial and temporal coverage collected across 106 sites representing nine different vegetation types in the permafrost region. We showed ecosystems with tall-statured shrubs and trees (>40 cm) have warmer shallow soils than those with short-statured tundra vegetation when normalized to a constant air temperature. In tree and tall shrub vegetation types, cooler temperatures in the warm season do not lead to cooler mean annual soil temperature indicating that ground thermal regimes in the cold-season rather than the warm-season are most critical for predicting soil warming in ecosystems underlain by permafrost. Our results suggest that the expansion of tall shrubs and trees into tundra regions can amplify shallow soil warming, and could increase the potential for increased seasonal thaw depth and increase soil carbon cycling rates and lead to increased carbon dioxide loss and further permafrost thaw.
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| 23. |
- Kuhry, Peter, et al.
(författare)
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Lability classification of soil organic matter in the northern permafrost region
- 2020
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Ingår i: Biogeosciences. - : Copernicus GmbH. - 1726-4170 .- 1726-4189. ; 17:2, s. 361-379
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Tidskriftsartikel (refereegranskat)abstract
- The large stocks of soil organic carbon (SOC) in soils and deposits of the northern permafrost region are sensitive to global warming and permafrost thawing. The potential release of this carbon (C) as greenhouse gases to the atmosphere does not only depend on the total quantity of soil organic matter (SOM) affected by warming and thawing, but it also depends on its lability (i.e., the rate at which it will decay). In this study we develop a simple and robust classification scheme of SOM lability for the main types of soils and deposits in the northern permafrost region. The classification is based on widely available soil geochemical parameters and landscape unit classes, which makes it useful for upscaling to the entire northern permafrost region. We have analyzed the relationship between C content and C-CO2 production rates of soil samples in two different types of laboratory incubation experiments. In one experiment, ca. 240 soil samples from four study areas were incubated using the same protocol (at 5 degrees C, aerobically) over a period of 1 year. Here we present C release rates measured on day 343 of incubation. These long-term results are compared to those obtained from short-term incubations of ca. 1000 samples (at 12 degrees C, aerobically) from an additional three study areas. In these experiments, C-CO2 production rates were measured over the first 4 d of incubation. We have focused our analyses on the relationship between C-CO2 production per gram dry weight per day (mu gC-CO2 gdw(-1) d(-1)) and C content (%C of dry weight) in the samples, but we show that relationships are consistent when using C = N ratios or different production units such as mu gC per gram soil C per day (mu gC-CO2 gC(-1) d(-1)) or per cm(3) of soil per day (mu gC-CO2 cm(-3) d(-1)). C content of the samples is positively correlated to C-CO2 production rates but explains less than 50% of the observed variability when the full datasets are considered. A partitioning of the data into landscape units greatly reduces variance and provides consistent results between incubation experiments. These results indicate that relative SOM lability decreases in the order of Late Holocene eolian deposits to alluvial deposits and mineral soils (including peaty wetlands) to Pleistocene yedoma deposits to C-enriched pockets in cryoturbated soils to peat deposits. Thus, three of the most important SOC storage classes in the northern permafrost region (yedoma, cryoturbated soils and peatlands) show low relative SOM lability. Previous research has suggested that SOM in these pools is relatively undecomposed, and the reasons for the observed low rates of decomposition in our experiments need urgent attention if we want to better constrain the magnitude of the thawing permafrost carbon feedback on global warming.
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| 24. |
- Liu, Yijing, et al.
(författare)
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Snow redistribution decreases winter soil carbon loss in the Arctic dry heath tundra
- 2024
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Ingår i: Agricultural and Forest Meteorology. - 0168-1923. ; 356
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Tidskriftsartikel (refereegranskat)abstract
- Rapid warming increases winter soil carbon dioxide (CO2) efflux in Arctic tundra ecosystems, which can significantly offset carbon (C) uptake during growing seasons and affect the overall annual C balance. In winter, the Arctic landscape is predominantly covered with snow, which is vital for regulating ecological processes. Nevertheless, the impact of snow redistribution on the spatial distribution of winter soil CO2 efflux remains uncertain. In this study, we fitted an empirical model to quantify changes in total winter soil CO2 efflux based on accumulated snow depths, using in situ measurements from a snow manipulation experiment in a dry heath tundra ecosystem of Western Greenland. By employing a distributed snow model, we upscaled the spatial-temporal variations in winter soil CO2 efflux for a dry heath region of approx. 6 km2 during 2010–2020. We found that the total winter soil CO2 efflux increases linearly with the increasing total snow depth. In our study plots, the annual mean winter CO2 efflux ranged from 55 to 58 g C m−2 year−1 in ambient plots and 62 to 71 g C m−2 year−1 in snow addition plots (due to the snow fence) during 2013–2020. Spatially, wind-induced snow redistribution caused the annual mean winter CO2 efflux to vary from 51 to 76 g C m−2 year−1. Winter soil CO2 loss increased by 6 % if snow redistribution was not taken into account, primarily due to snow mass losses from the process of snow redistribution (such as blowing snow sublimation). Our results highlight the importance of snow redistribution on winter soil CO2 emissions, particularly when using regional land models in predictions of annual C balance in the Arctic ecosystems under a changing climate.
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| 25. |
- Mishra, Umakant, et al.
(författare)
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Spatial heterogeneity and environmental predictors of permafrost region soil organic carbon stocks
- 2021
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Ingår i: Science Advances. - : American Association for the Advancement of Science (AAAS). - 2375-2548. ; 7:9
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Tidskriftsartikel (refereegranskat)abstract
- Large stocks of soil organic carbon (SOC) have accumulated in the Northern Hemisphere permafrost region, but their current amounts and future fate remain uncertain. By analyzing dataset combining >2700 soil profiles with environmental variables in a geospatial framework, we generated spatially explicit estimates of permafrost-region SOC stocks, quantified spatial heterogeneity, and identified key environmental predictors. We estimated that Pg C are stored in the top 3 m of permafrost region soils. The greatest uncertainties occurred in circumpolar toe-slope positions and in flat areas of the Tibetan region. We found that soil wetness index and elevation are the dominant topographic controllers and surface air temperature (circumpolar region) and precipitation (Tibetan region) are significant climatic controllers of SOC stocks. Our results provide first high-resolution geospatial assessment of permafrost region SOC stocks and their relationships with environmental factors, which are crucial for modeling the response of permafrost affected soils to changing climate.
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