| 1. |
- Björk, Robert G., 1974, et al.
(författare)
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Temporal pattern of CO2, CH4 and N2O fluxes and soil microbial structure from snow-covered Alpine plant communities
- 2006
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Ingår i: Abstracts and Proceedings of the Geological Society of Norway. ; :4
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Global warming is expected to have large effects on carbon exchange between the biosphere and the atmosphere in the Arctic. Arctic ecosystems, which can be a net sink in the summer, are often a net source of CO2 to the atmosphere on an annual basis. Few studies on winter CO2 and CH4 efflux have been conducted in the subarctic part of Sweden. So far, no integrated estimates of winter fluxes of CO2, CH4 or N2O has been reported from the alpine areas in the Scandinavian mountains. As much as 44 to 53% of the northern hemispheres landmass may be snow covered for parts of the year. The depth and spatial spread of snow cover is a result of moisture availability, duration of temperatures bellow 0ºC, storm frequency and the more local factors such as wind redistribution and compaction. In future climate scenarios, predictions of warmer climate and increased precipitations are often mentioned, but to which extent is more uncertain. However, the major changes in precipitation will occur over the North Pacific, North Atlantic and Scandinavia. The controlling factor for microbial activity in the organic layer during winter in alpine areas is the development of a consistent snow cover, which effectively decouples the soil from the atmospheric temperature. The air and soil temperature the days before snow cover development is important, as it sets the temperature conditions for the whole winter period. Soil microbial activity is markedly reduced below temperatures of 0 to -5°C, when the soil starts to freeze and free water becomes limited. Nitrogen mineralisation, nitrification and denitrification can, however, be maintained down to -4°C, and N2O production (from denitrification) in frozen soils has potential to affect annual dynamics and budgets of N (although the soil pore water content prior to freezing is an important regulating factor for winter N2O production). Snowbed communities are rarely, if ever, subjected to temperatures as low as -5°C, which implies that they may be favourable for microbial activity during the winter. Furthermore, tundra soil microbial biomass reaches its annual peak under snow, and fungi account for most of the biomass. However, how the microbial community changes during winter and snowmelt are poorly know and, in particular, in relation to trace gas fluxes. Flux of CO2, CH4 and N2O through a seasonal snowpack, using Fick’s law, from four plant communities with different snow regime and how it changes during snowmelt in the subarctic-alpine part of Sweden will be presented. We will also try to relate the trace gas fluxes to the soil microbial community composition using phospholipid fatty acid analysis.
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| 2. |
- Björk, Robert G., 1974, et al.
(författare)
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Temporal variation in soil microbial communities and the influence of snow cover
- 2007
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Ingår i: The 14th ITEX workshop, Falls Creek, Victoria, Australia, 2–6 February 2007..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- Global climate change is projected to have a large impact in arctic and alpine areas. Future projections with increased temperature also include increased precipitation, but to which extent is uncertain. However, the major changes in precipitation will occur over the North Pacific, North Atlantic and Scandinavia. As much as 44 to 53% of the northern hemispheres landmass may be snow covered for parts of the year and in higher alpine terrain the increased precipitation will lead to a greater snow accumulation. The controlling factor for microbial activity in the organic layer during winter in alpine areas is the development of a consistent snow cover, which effectively decouples the soil from the atmospheric temperature. The air and soil temperature the days before snow cover development is important, as it sets the temperature conditions for the whole winter period. Soil microbial activity is markedly reduced below temperatures of 0 to -5°C, when the soil starts to freeze and free water becomes limited. Nitrogen mineralisation, nitrification and denitrification can, however, be maintained down to -4°C, and N2O production (from denitrification) in frozen soils could potentially affect the annual dynamics and budgets of N. Snowbed communities are rarely, if ever, subjected to temperatures as low as -5°C, which implies that they may be favourable for microbial activity during the winter. Furthermore, tundra soil microbial biomass reaches its annual peak under snow, and fungi account for most of the biomass. However, how the microbial community changes during winter and snowmelt is poorly known and, in particular, in relation to trace gas fluxes. The objective of our study was, therefore, to investigate the temporal pattern of soil microbial structure in four plant communities with contrasting snow cover and nitrogen turnover. This study was conducted at Latnjajaure Field Station (LFS) located in the midalpine region in northern Sweden. The study includes four different plant communities, heath snowbed, heath meadow, meadow snowbed, and mesic meadow. To characterize the soil microbial community we used phospholipid fatty acid analysis (PLFA), which is a method targeting the fatty acid profiles of membrane phospholipids microorganisms. The results show that at each individual sampling occasion the four plant communities’ exhibits different soil microbial structure. However, the temporal variation is larger than the difference across plant communities. This temporal shift in microbial structure seems to be partially related to the fatty acid 18:2ω6, indicative of fungi, which show a high proportion in soils protected by snow and decreases after snow melt. Furthermore, the shift in microbial structure during the season is more modest in snowbeds than the mesic heath and meadow.
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| 3. |
- Björk, Robert G., 1974, et al.
(författare)
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Temporal variation in soil microbial communities in Alpine tundra
- 2008
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Ingår i: Soil Biology & Biochemistry. - : Elsevier BV. - 0038-0717. ; 40:1, s. 266-268
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Tidskriftsartikel (refereegranskat)abstract
- Temporal variation in soil microbial communities was studied at a mid-alpine environment in Latnjajaure, northern Sweden, using phospholipid fatty acid (PLFA) analysis. The results show two seasonal shifts in microbial composition. The first shift was associated with snowmelt and mainly related to a decrease in fungal PLFAs, accompanied by an increase in branched 17:0 and methylated PLFAs (biomarkers for Gram-positive- and actinobacteria, respectively), resulting in a decrease in the ratio of fungi-to-bacteria. The second shift occurred across the growing, season, and was associated with a switch from shorter to longer PLFAs and an increase in 18:1 omega 7 (biomarker for Gram-negative bacteria). Vegetation, snow cover dynamics, and N turnover seem to be of minor importance to broadscale microbial community structure in this area. (c) 2007 Elsevier Ltd. All rights reserved.
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| 4. |
- Klingberg, Jenny, 1978, et al.
(författare)
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Observations of Ground-level Ozone and NO2 in Northernmost Sweden, Including the Scandian Mountain Range
- 2009
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Ingår i: Ambio. ; 38:8, s. 448-451
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Tidskriftsartikel (refereegranskat)abstract
- Ozone was measured using passive diffusion samplers at alpine Latnjajaure (980 m above sea level [asl]) in the northern Scandian Mountain Range during spring and summer 2006–2008, and year-round at three further sites in northernmost Sweden 2004–2008. These observations were compared with ozone concentrations from three permanent monitoring stations using ultraviolet absorption instruments. Ozone concentrations at Latnjajaure were higher than at the closest monitoring site, illustrating the importance of high elevation for ozone. At the northern sites the ozone spring peak was more pronounced, higher, and earlier (April maximum) compared to a site in south Sweden (May maximum). During summer, ozone concentrations were higher in south Sweden. Presently, the growing season largely starts after the ozone spring peak in north Sweden but is likely to start earlier in the future climate. This could lead to an increased risk for ozone effects on vegetation if the current yearly ozone cycle persists.
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| 5. |
- Björk, Robert G., 1974, et al.
(författare)
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Biocomplexity and biogeochemical cycling in terrestrial ecosystems
- 2008
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Ingår i: 1st Workshop and planning meeting ‘Winter processes in arctic tundra ecosystems’, Longyearbyen, Svalbard, 9-11 June 2008..
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Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The activities concerted within Tellus are aiming at adding essential knowledge to the system scale aspects of fluxes and transformation of carbon (C) in the terrestrial domain. The systems studied are the Arctic, the alpine area of the Scandes, and organic soils in southern Sweden (including both forest and agricultural systems). The main research sites are Skogaryd, in the boreal forest, and Latnjajaure Field Station in the western Abisko Mountains. The overall aim with the present work at Skogaryd is to increase our fundamental understanding of process involved in cycling of C and nitrogen (N) in forest ecosystems, and generate high quality data on C/N cycle from drained forested organic soils using micrometeorological methods, laser and automatic chambers techniques. Skogaryd is also included in NitroEurope, an EU project focusing on modelling and up-scaling of greenhouse gas fluxes, and is incorporated in two interdisciplinary research centres at University of Gothenburg, Tellus (http://www.tellus.science.gu.se/english/) and Gothenburg Atmospheric Science Centre (GAC; http://www.chalmers.se/gmv/gac-en/). Furthermore, our research group has been instrumental in the establishment of the International Tundra Experiment (ITEX) network by Professor Ulf Molau who chaired ITEX 1992-1996 and Latnjajaure Field Station have been a master site within the network since 1992. As an outcome, much of the research in Latnjajaure during the 90ies was focused plant responsiveness to global change. However, since 2002 the research has expanded and projects are now running that are dealing with snow-vegetation-soil interactions. Recently, a collaboration with Dr. Elisabeth J. Cooper, of the University Centre in Svalbard (UNIS), and Prof. Bo Elberling, University of Copenhagen, was initiated focusing on winter soil respiration and comparing sub-arctic and high-arctic trace gas fluxes. Currently, we have these projects running in tundra ecosystems: 1.Climate-related changes in tundra ecosystems – An IPY project (PIs Björk and Molau with others). 2.Temporal pattern of CO2, CH4 and N2O fluxes and soil microbial structure in snow-covered ecosystems (PIs Björk, Elberling, Klemedtsson, and Cooper). 3.The responsiveness of tundra ecosystems to warming: linking above- and below-ground components (PI Björk). There is also a project under evaluation by the Swedish Research Council, which are entitled ‘The fate of carbon in high-arctic tundra ecosystems under changing snow cover conditions’. The research questions that we want to address within this winter ecology network are 1) to increase our understand of the C dynamics (thus explicitly linking ecosystem C sequestration pattern and soil microbial dynamics) in tundra ecosystems, and, particularly, (2) to improve the winter resolution of carbon dioxide (and other greenhouse gases) effluxes to the atmosphere. Furthermore, (3) to understand the influence of changing snow cover, both in depth and duration, for the C dynamics in tundra ecosystems.
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| 6. |
- 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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| 7. |
- Björkman, Mats P., 1978, et al.
(författare)
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Winter fluxes of carbon dioxide – a comparison of current methodology
- 2008
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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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