Bo Elberling - Academia.edu (original) (raw)
Papers by Bo Elberling
Global Change Biology, 2009
Water and nutrient fluxes for single stands of different tree species have been reported in numer... more Water and nutrient fluxes for single stands of different tree species have been reported in numerous studies, but comparative studies of nutrient and hydrological budgets of common European deciduous tree species are rare. Annual fluxes of water and inorganic nitrogen (N) were established in a 30-year-old common garden design with stands of common ash (Fraxinus excelsior), European beech (Fagus sylvatica L.), pedunculate oak (Quercus robur), small-leaved lime (Tilia cordata Mill.), sycamore maple (Acer pseudoplatanus) and Norway spruce (Picea abies [L.] Karst.) replicated at two sites in Denmark, Mattrup and Vall during 2 years. Mean annual percolation below the root zone (mm yr À1 AE SE, n 5 4) ranked in the following order: maple (351 AE 38)4lime (284 AE 32), oak (271 AE 25), beech (257 AE 30), ash (307 AE 69) ) spruce (75 AE 24). There were few significant tree species effects on N fluxes. However, the annual mean N throughfall flux (kg N ha À1 yr À1 AE SE, n 5 4) for spruce (28 AE 2) was significantly larger than for maple (12 AE 1), beech (11 AE 1) and oak (9 AE 1) stands but not different from that of lime (15 AE 3). Ash had a low mean annual inorganic N throughfall deposition of 9.1 kg ha À1 , but was only present at Mattrup. Annual mean of inorganic N leaching (kg ha À1 yr À1 AE SE, n 5 4) did not differ significantly between species despite of contrasting tree species mean values; beech (25 AE 9)4oak (16 AE 10), spruce (15 AE 8), lime (14 AE 8) ) maple (1.9 AE 1), ash (2.0 AE 1). The two sites had similar throughfall N fluxes, whereas the annual leaching of N was significantly higher at Mattrup than at Vall. Accordingly, the sites differed in soil properties in relation to rates and dynamics of N cycling. We conclude that tree species affect the N cycle differently but the legacy of land use exerted a dominant control on the N cycle within the short-term perspective (30 years) of these stands.
Plant and Soil, 2011
Northern peatland methane (CH 4 ) budgets are important for global CH 4 emissions. This study aim... more Northern peatland methane (CH 4 ) budgets are important for global CH 4 emissions. This study aims to determine the ecosystem CH 4 budget and specifically to quantify the importance of Phalaris arundinacea by using different chamber techniques in a temperate wetland. Annually, roughly 70±35% of ecosystem CH 4 emissions were plant-mediated, but data show no evidence of significant diurnal variations related to convective gas flow regardless of season or plant growth stages. Therefore, despite a high percentage of arenchyma, P. arundinacea-mediated CH 4 transport is interpreted to be predominantly passive. Thus, diurnal variations are less important in contrast to wetland vascular plants facilitating convective gas flow. Despite of plant-dominant CH 4 transport, net CH 4 fluxes were low (-0.005-0.016 μmol m −2 s −1 ) and annually less than 1% of the annual C-CO 2 assimilation. This is considered a result of an effective root zone oxygenation resulting in increased CH 4 oxidation in the rhizosphere at high water levels. This study shows that although CH 4 , having a global warming potential 25 times greater than CO 2 ,i s emitted from this P. arundinacea wetland, less than 9% of the C sequestered counterbalances the CH 4 emissions to the atmosphere. It is concluded that P. arundinacea-dominant wetlands are an attractive C-sequestration ecosystem.
Though a number of studies have reported CO2 fluxes from the Arctic, few of these include measure... more Though a number of studies have reported CO2 fluxes from the Arctic, few of these include measurements from winter time and it is often assumed that emission rates during winter time are either constant or negligible. These assumptions are often made because no data are available or consist of relatively few measurements which appear to give small and constant emission
Ecosystems, 2015
The Arctic climate is projected to change during the coming century, with expected higher air tem... more The Arctic climate is projected to change during the coming century, with expected higher air temperatures and increased winter snowfall. These climatic changes might alter litter decomposition rates, which in turn could affect carbon (C) and nitrogen (N) cycling rates in tundra ecosystems. However, little is known of seasonal climate change effects on plant litter decomposition rates and N dynamics, hampering predictions of future arctic vegetation composition and the tundra C balance. We tested the effects of snow addition (snow fences), warming (open top chambers), and shrub removal (clipping), using a full-factorial experiment, on mass loss and N dynamics of two shrub tissue types with contrasting quality: deciduous shrub leaf litter (Salix glauca) and
Frontiers in microbiology, 2012
Nitrous oxide (N(2)O) is an important greenhouse gas and ozone depleter, but the global budget of... more Nitrous oxide (N(2)O) is an important greenhouse gas and ozone depleter, but the global budget of N(2)O remains unbalanced. Currently, ∼25% of the global N(2)O emission is ascribed to uncultivated tropical soils, but the exact locations and controlling mechanisms are not clear. Here we present the first study of soil N(2)O emission from the Pantanal indicating that this South American wetland may be a significant natural source of N(2)O. At three sites, we repeatedly measured in situ fluxes of N(2)O and sampled porewater nitrate [Formula: see text] during the low water season in 2008 and 2009. In 2010, 10 sites were screened for in situ fluxes of N(2)O and soil [Formula: see text] content. The in situ fluxes of N(2)O were comparable to fluxes from heavily fertilized forests or agricultural soils. An important parameter affecting N(2)O emission rate was precipitation, inducing peak emissions of >3 mmol N(2)O m(-2) day(-1), while the mean daily flux was 0.43 ± 0.03 mmol N(2)O m(-2)...
Advances in Ecological Research, Vol 40, 2008
... The most abundant species is S. arctica. Other common species are A. alpinus, tundra starwort... more ... The most abundant species is S. arctica. Other common species are A. alpinus, tundra starwort Stellaria crassipes, northern woodrush Luzula confusa, arctic woodrush Luzula Arctica and arctic tundra grass Poa arctica. The ...
Nature Climate Change, 2013
ABSTRACT Thawing permafrost represents a poorly understood feedback mechanism of climate change i... more ABSTRACT Thawing permafrost represents a poorly understood feedback mechanism of climate change in the Arctic, but with a potential impact owing to stored carbon being mobilized1–5. We have quantified the long-term loss of carbon (C) from thawing permafrost in Northeast Greenland from 1996 to 2008 by combining repeated sediment sampling to assess changes in C stock and >12 years of CO2 production in incubated permafrost samples. Field observations show that the activelayer thickness has increased by >1 cm yr1 but thawing has not resulted in a detectable decline in C stocks. Laboratory mineralization rates at 5 �C resulted in a C loss between 9 and 75%, depending on drainage, highlighting the potential of fast mobilization of permafrost C under aerobic conditions, but also that C at near-saturated conditions may remain largely immobilized over decades. This is confirmed by a three-pool C dynamics model that projects a potential C loss between 13 and 77% for 50 years of incubation at 5 �C.
Advances in Ecological Research, Vol 40, 2008
Advances in Ecological Research, 2008
ABSTRACT This chapter focuses on hydrology together with sediment and solute transport in the Zac... more ABSTRACT This chapter focuses on hydrology together with sediment and solute transport in the Zackenberg area in relation to climate variability during 1995-2005. The. results indicate decreasing precipitation and increasing evapotranspiration during the study years. Theoretically, this should result in decreasing run-off, but no such trend is found in the run-off from the period. Model calculations justify that the loss of water available for run-off is compensated by an increased contribution of meltwater from glaciers within the catchment. It is found that extreme events can dominate the output of sediment and solutes for the catchment.
Advances in Ecological Research, 2008
Ecology and evolution, 2013
The High Arctic winter is expected to be altered through ongoing and future climate change. Winte... more The High Arctic winter is expected to be altered through ongoing and future climate change. Winter precipitation and snow depth are projected to increase and melt out dates change accordingly. Also, snow cover and depth will play an important role in protecting plant canopy from increasingly more frequent extreme winter warming events. Flower production of many Arctic plants is dependent on melt out timing, since season length determines resource availability for flower preformation. We erected snow fences to increase snow depth and shorten growing season, and counted flowers of six species over 5 years, during which we experienced two extreme winter warming events. Most species were resistant to snow cover increase, but two species reduced flower abundance due to shortened growing seasons. Cassiope tetragona responded strongly with fewer flowers in deep snow regimes during years without extreme events, while Stellaria crassipes responded partly. Snow pack thickness determined wheth...
Water Resources Research, 1998
Gas transport induced by temporal pressure fluctuations in the atmosphere can be an important mec... more Gas transport induced by temporal pressure fluctuations in the atmosphere can be an important mechanism for transport of atmospheric oxygen within the unsaturated zone. Moreover, the presence of oxygen in the unsaturated zone may be a factor controlling oxidation of sulphide minerals and other redox processes. A field study was carried out in a glacial aquifer with a 10-12 m thick sandy unsaturated zone to explore gas exchange between the atmosphere and the unsaturated zone. The exchange occurs through a ``geological window'' in a till layer which covers the sandy unsaturated zone. Observed pressure distribution and oxygen concentrations within the unsaturated zone were compared to numerical simulations with SUTRA, a finite element and fluid density dependent groundwater flow model. The simulations were carried out by modeling the gas pressure distribution within the unsaturated zone based on atmospheric pressure time series. The spatial variation in permeability observed from borehole logging was implemented in the model. The analysis demonstrated a good match between the field observations and the numerical simulations. During an atmospheric pressure cycle, atmospheric oxygen migrated more than 10 md-1 horizontally in the capped unsaturated zone. The analysis shows that both the amplitude and the length of the period of pressure variations are important for the transport of oxygen, and it shows that the combined effects determine the extent of a subsurface zone where atmospheric oxygen can reach.
Soil Biology and Biochemistry, 2014
ABSTRACT
Polar Research, 2010
The influence of goose grazing intensity and open-topped chambers (OTCs) on near-surface quantiti... more The influence of goose grazing intensity and open-topped chambers (OTCs) on near-surface quantities and qualities of soil organic carbon (SOC) was evaluated in wet and mesic ecosystems in Svalbard. This study followed up a field experiment carried out in 2003-05 (part of the project Fragility of Arctic Goose Habitat: Impacts of Land Use, Conservation and Elevated Temperatures). New measurements of soil CO 2 effluxes, temperatures and water contents were regularly made from July to November 2007. SOC stocks were quantified, and the reactivity and composition measured by basal soil respiration (BSR) and solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy. Results reveal variations in soil carbon cycling, with significant seasonal trends controlled by temperature, water content and snow. Experimental warming (OTCs) increased near-surface temperatures in the growing season, resulting in significantly higher CO 2 effluxes. Different grazing intensities had no significant effects on observed soil respiration, but BSR rates at the mesic site (13-23 mgCO 2 g soil-C -1 h -1 ) were highest with moderate grazing and lowest in the absence of grazing. A limited effect of grazing on microbial respiration is consistent with a lack of significant differences in SOC quantity and quality. NMR data show that the composition of A-horizon SOC is dominated by O-N-alkyl C and alkyl C groups, and less by carboxyl C and aromatic C groups: but again no marked variation in response to grazing was evident. It can be concluded that two years after a goose grazing experiment, SOC cycling was less than the natural variation within contrasting vegetation types.
Polar Research, 2010
Winter respiration in snow-covered ecosystems strongly influences annual carbon cycling, underlin... more Winter respiration in snow-covered ecosystems strongly influences annual carbon cycling, underlining the importance of processes related to the timing and quantity of snow. Fences were used to increase snow depth from 30 to 150 cm, and impacts on respiration were investigated in heath and mesic meadow, two common vegetation types in Svalbard. We manually measured ecosystem respiration from July 2007 to July 2008 at a temporal resolution greater than previously achieved in the High Arctic (campaigns: summer, eight; autumn, six; winter, 17; spring, nine). Moisture contents of unfrozen soil and soil temperatures throughout the year were also recorded. The increased snow depth resulted in significantly higher winter soil temperatures and increased ecosystem respiration. A temperature-efflux model explained most of the variation of observed effluxes: meadows, 94 (controls) and 93% (fences); heaths, 84 and 77%, respectively. Snow fences increased the total non-growing season efflux from 70 to 92 (heaths) and from 68 to 125 g CO 2-C m -2 (meadows). The non-growing season contributed to 56 (heaths) and 42% (meadows) of the total annual carbon respired. This proportion increased with deeper snow to 64% in both vegetation types. Summer respiration rates were unaffected by snow fences, but the total growing season respiration was lower behind fences because of the considerably delayed snowmelt. Meadows had higher summer respiration rates than heaths. In addition, non-steady state CO 2 effluxes were measured as bursts lasting several days during spring soil thawing, and when ice layers were broken to carry out winter efflux measurements.
Journal of Sedimentary Research, 2011
Ikaite is considered a metastable mineral forming and stable only at low temperatures and therefo... more Ikaite is considered a metastable mineral forming and stable only at low temperatures and therefore an indicator of low-temperature carbonate precipitation often associated with cold marine seeps. It is found world-wide but most spectacularly in Ikka Fjord in southwest Greenland as submarine carbonate tufa columns. Here, ikaite is formed as a result of submarine spring water mixing with cold seawater. As ikaite disintegrates at temperatures above 6-7uC, it has been speculated that global warming could endanger this unique habitat as well as other sites. In Ikka Fjord in situ water chemistry in and around an ikaite column measured continuously over two years showed that the column water is alkaline (pH . 9-10) throughout the year with temperatures of 21.3-6.0 uC and conductivities of 5.7-7.9 mS cm 21 , favoring year-round growth of columns at 4-5 cm per month. Short-term in situ measurements with needle micro sensors from both older dehydrated and calcified parts and more recently formed solid parts of an ikaite tufa column showed similar pH and temperature values, including a temperature variation over the tidal cycle. In the uppermost, recently deposited ikaite matrix, spring water escaping at the top causes passive drag of seawater into the porous ikaite matrix, leading to a mixing layer several centimeters thick that has pH values intermediate to the spring water in the column and the surrounding seawater. We conclude that the main part of the columns, consisting of fossilized ikaite (inverted to calcite) partly sealed by calcifying coralline algae and with year-round flow of alkaline freshwater through distinct channels, are resistant to warming. In the more diffuse top part of the columns, the formation of ikaite, and thus column growth, will be limited in the future due to increased fjord water temperature during the , 3 summer months a year.
Journal of Quaternary Science, 2002
Terraces of different age in the Zackenberg delta, located at 74°N in northeast Greenland, have p... more Terraces of different age in the Zackenberg delta, located at 74°N in northeast Greenland, have provided the opportunity for an interdisciplinary approach to the investigation of Holocene glacial, periglacial, pedological, biological and archaeological conditions that existed during and after delta deposition.The raised Zackenberg delta accumulated mainly during the Holocene Climatic Optimum, starting slightly prior to 9500 cal. yr BP (30
Journal of Archaeological Science, 2011
Remains from Paleo-Eskimo cultures are well-documented, but complete preservation is rare. Two ki... more Remains from Paleo-Eskimo cultures are well-documented, but complete preservation is rare. Two kitchen middens in Greenland are known to hold extremely well-preserved organic artefacts. Here, we assess the fate of the Qajaa site in Western Greenland under future climate conditions based on site characteristics measured in situ and from permafrost cores. Measurements of thermal properties, heat generation, oxygen consumption and CO 2 production show that the kitchen midden can be characterized as peat but produces 4e7 times more heat than natural sediment. An analytical model from permafrost research has been applied to assess future thawing of the midden. Results show that the preservation conditions are controlled by freezing temperatures and a high water/ice content limiting the subsurface oxygen availability. Threats to the future preservation are related to thawing followed by drainage and increasing subsurface oxygen availability and heat generation. The model predicts that the unique 4000-year-old Saqqaq layer below more than 1 m of peat is adequately protected against thawing for the next 70 years.
Global Change Biology, 2009
Water and nutrient fluxes for single stands of different tree species have been reported in numer... more Water and nutrient fluxes for single stands of different tree species have been reported in numerous studies, but comparative studies of nutrient and hydrological budgets of common European deciduous tree species are rare. Annual fluxes of water and inorganic nitrogen (N) were established in a 30-year-old common garden design with stands of common ash (Fraxinus excelsior), European beech (Fagus sylvatica L.), pedunculate oak (Quercus robur), small-leaved lime (Tilia cordata Mill.), sycamore maple (Acer pseudoplatanus) and Norway spruce (Picea abies [L.] Karst.) replicated at two sites in Denmark, Mattrup and Vall during 2 years. Mean annual percolation below the root zone (mm yr À1 AE SE, n 5 4) ranked in the following order: maple (351 AE 38)4lime (284 AE 32), oak (271 AE 25), beech (257 AE 30), ash (307 AE 69) ) spruce (75 AE 24). There were few significant tree species effects on N fluxes. However, the annual mean N throughfall flux (kg N ha À1 yr À1 AE SE, n 5 4) for spruce (28 AE 2) was significantly larger than for maple (12 AE 1), beech (11 AE 1) and oak (9 AE 1) stands but not different from that of lime (15 AE 3). Ash had a low mean annual inorganic N throughfall deposition of 9.1 kg ha À1 , but was only present at Mattrup. Annual mean of inorganic N leaching (kg ha À1 yr À1 AE SE, n 5 4) did not differ significantly between species despite of contrasting tree species mean values; beech (25 AE 9)4oak (16 AE 10), spruce (15 AE 8), lime (14 AE 8) ) maple (1.9 AE 1), ash (2.0 AE 1). The two sites had similar throughfall N fluxes, whereas the annual leaching of N was significantly higher at Mattrup than at Vall. Accordingly, the sites differed in soil properties in relation to rates and dynamics of N cycling. We conclude that tree species affect the N cycle differently but the legacy of land use exerted a dominant control on the N cycle within the short-term perspective (30 years) of these stands.
Plant and Soil, 2011
Northern peatland methane (CH 4 ) budgets are important for global CH 4 emissions. This study aim... more Northern peatland methane (CH 4 ) budgets are important for global CH 4 emissions. This study aims to determine the ecosystem CH 4 budget and specifically to quantify the importance of Phalaris arundinacea by using different chamber techniques in a temperate wetland. Annually, roughly 70±35% of ecosystem CH 4 emissions were plant-mediated, but data show no evidence of significant diurnal variations related to convective gas flow regardless of season or plant growth stages. Therefore, despite a high percentage of arenchyma, P. arundinacea-mediated CH 4 transport is interpreted to be predominantly passive. Thus, diurnal variations are less important in contrast to wetland vascular plants facilitating convective gas flow. Despite of plant-dominant CH 4 transport, net CH 4 fluxes were low (-0.005-0.016 μmol m −2 s −1 ) and annually less than 1% of the annual C-CO 2 assimilation. This is considered a result of an effective root zone oxygenation resulting in increased CH 4 oxidation in the rhizosphere at high water levels. This study shows that although CH 4 , having a global warming potential 25 times greater than CO 2 ,i s emitted from this P. arundinacea wetland, less than 9% of the C sequestered counterbalances the CH 4 emissions to the atmosphere. It is concluded that P. arundinacea-dominant wetlands are an attractive C-sequestration ecosystem.
Though a number of studies have reported CO2 fluxes from the Arctic, few of these include measure... more Though a number of studies have reported CO2 fluxes from the Arctic, few of these include measurements from winter time and it is often assumed that emission rates during winter time are either constant or negligible. These assumptions are often made because no data are available or consist of relatively few measurements which appear to give small and constant emission
Ecosystems, 2015
The Arctic climate is projected to change during the coming century, with expected higher air tem... more The Arctic climate is projected to change during the coming century, with expected higher air temperatures and increased winter snowfall. These climatic changes might alter litter decomposition rates, which in turn could affect carbon (C) and nitrogen (N) cycling rates in tundra ecosystems. However, little is known of seasonal climate change effects on plant litter decomposition rates and N dynamics, hampering predictions of future arctic vegetation composition and the tundra C balance. We tested the effects of snow addition (snow fences), warming (open top chambers), and shrub removal (clipping), using a full-factorial experiment, on mass loss and N dynamics of two shrub tissue types with contrasting quality: deciduous shrub leaf litter (Salix glauca) and
Frontiers in microbiology, 2012
Nitrous oxide (N(2)O) is an important greenhouse gas and ozone depleter, but the global budget of... more Nitrous oxide (N(2)O) is an important greenhouse gas and ozone depleter, but the global budget of N(2)O remains unbalanced. Currently, ∼25% of the global N(2)O emission is ascribed to uncultivated tropical soils, but the exact locations and controlling mechanisms are not clear. Here we present the first study of soil N(2)O emission from the Pantanal indicating that this South American wetland may be a significant natural source of N(2)O. At three sites, we repeatedly measured in situ fluxes of N(2)O and sampled porewater nitrate [Formula: see text] during the low water season in 2008 and 2009. In 2010, 10 sites were screened for in situ fluxes of N(2)O and soil [Formula: see text] content. The in situ fluxes of N(2)O were comparable to fluxes from heavily fertilized forests or agricultural soils. An important parameter affecting N(2)O emission rate was precipitation, inducing peak emissions of >3 mmol N(2)O m(-2) day(-1), while the mean daily flux was 0.43 ± 0.03 mmol N(2)O m(-2)...
Advances in Ecological Research, Vol 40, 2008
... The most abundant species is S. arctica. Other common species are A. alpinus, tundra starwort... more ... The most abundant species is S. arctica. Other common species are A. alpinus, tundra starwort Stellaria crassipes, northern woodrush Luzula confusa, arctic woodrush Luzula Arctica and arctic tundra grass Poa arctica. The ...
Nature Climate Change, 2013
ABSTRACT Thawing permafrost represents a poorly understood feedback mechanism of climate change i... more ABSTRACT Thawing permafrost represents a poorly understood feedback mechanism of climate change in the Arctic, but with a potential impact owing to stored carbon being mobilized1–5. We have quantified the long-term loss of carbon (C) from thawing permafrost in Northeast Greenland from 1996 to 2008 by combining repeated sediment sampling to assess changes in C stock and >12 years of CO2 production in incubated permafrost samples. Field observations show that the activelayer thickness has increased by >1 cm yr1 but thawing has not resulted in a detectable decline in C stocks. Laboratory mineralization rates at 5 �C resulted in a C loss between 9 and 75%, depending on drainage, highlighting the potential of fast mobilization of permafrost C under aerobic conditions, but also that C at near-saturated conditions may remain largely immobilized over decades. This is confirmed by a three-pool C dynamics model that projects a potential C loss between 13 and 77% for 50 years of incubation at 5 �C.
Advances in Ecological Research, Vol 40, 2008
Advances in Ecological Research, 2008
ABSTRACT This chapter focuses on hydrology together with sediment and solute transport in the Zac... more ABSTRACT This chapter focuses on hydrology together with sediment and solute transport in the Zackenberg area in relation to climate variability during 1995-2005. The. results indicate decreasing precipitation and increasing evapotranspiration during the study years. Theoretically, this should result in decreasing run-off, but no such trend is found in the run-off from the period. Model calculations justify that the loss of water available for run-off is compensated by an increased contribution of meltwater from glaciers within the catchment. It is found that extreme events can dominate the output of sediment and solutes for the catchment.
Advances in Ecological Research, 2008
Ecology and evolution, 2013
The High Arctic winter is expected to be altered through ongoing and future climate change. Winte... more The High Arctic winter is expected to be altered through ongoing and future climate change. Winter precipitation and snow depth are projected to increase and melt out dates change accordingly. Also, snow cover and depth will play an important role in protecting plant canopy from increasingly more frequent extreme winter warming events. Flower production of many Arctic plants is dependent on melt out timing, since season length determines resource availability for flower preformation. We erected snow fences to increase snow depth and shorten growing season, and counted flowers of six species over 5 years, during which we experienced two extreme winter warming events. Most species were resistant to snow cover increase, but two species reduced flower abundance due to shortened growing seasons. Cassiope tetragona responded strongly with fewer flowers in deep snow regimes during years without extreme events, while Stellaria crassipes responded partly. Snow pack thickness determined wheth...
Water Resources Research, 1998
Gas transport induced by temporal pressure fluctuations in the atmosphere can be an important mec... more Gas transport induced by temporal pressure fluctuations in the atmosphere can be an important mechanism for transport of atmospheric oxygen within the unsaturated zone. Moreover, the presence of oxygen in the unsaturated zone may be a factor controlling oxidation of sulphide minerals and other redox processes. A field study was carried out in a glacial aquifer with a 10-12 m thick sandy unsaturated zone to explore gas exchange between the atmosphere and the unsaturated zone. The exchange occurs through a ``geological window'' in a till layer which covers the sandy unsaturated zone. Observed pressure distribution and oxygen concentrations within the unsaturated zone were compared to numerical simulations with SUTRA, a finite element and fluid density dependent groundwater flow model. The simulations were carried out by modeling the gas pressure distribution within the unsaturated zone based on atmospheric pressure time series. The spatial variation in permeability observed from borehole logging was implemented in the model. The analysis demonstrated a good match between the field observations and the numerical simulations. During an atmospheric pressure cycle, atmospheric oxygen migrated more than 10 md-1 horizontally in the capped unsaturated zone. The analysis shows that both the amplitude and the length of the period of pressure variations are important for the transport of oxygen, and it shows that the combined effects determine the extent of a subsurface zone where atmospheric oxygen can reach.
Soil Biology and Biochemistry, 2014
ABSTRACT
Polar Research, 2010
The influence of goose grazing intensity and open-topped chambers (OTCs) on near-surface quantiti... more The influence of goose grazing intensity and open-topped chambers (OTCs) on near-surface quantities and qualities of soil organic carbon (SOC) was evaluated in wet and mesic ecosystems in Svalbard. This study followed up a field experiment carried out in 2003-05 (part of the project Fragility of Arctic Goose Habitat: Impacts of Land Use, Conservation and Elevated Temperatures). New measurements of soil CO 2 effluxes, temperatures and water contents were regularly made from July to November 2007. SOC stocks were quantified, and the reactivity and composition measured by basal soil respiration (BSR) and solid-state 13 C nuclear magnetic resonance (NMR) spectroscopy. Results reveal variations in soil carbon cycling, with significant seasonal trends controlled by temperature, water content and snow. Experimental warming (OTCs) increased near-surface temperatures in the growing season, resulting in significantly higher CO 2 effluxes. Different grazing intensities had no significant effects on observed soil respiration, but BSR rates at the mesic site (13-23 mgCO 2 g soil-C -1 h -1 ) were highest with moderate grazing and lowest in the absence of grazing. A limited effect of grazing on microbial respiration is consistent with a lack of significant differences in SOC quantity and quality. NMR data show that the composition of A-horizon SOC is dominated by O-N-alkyl C and alkyl C groups, and less by carboxyl C and aromatic C groups: but again no marked variation in response to grazing was evident. It can be concluded that two years after a goose grazing experiment, SOC cycling was less than the natural variation within contrasting vegetation types.
Polar Research, 2010
Winter respiration in snow-covered ecosystems strongly influences annual carbon cycling, underlin... more Winter respiration in snow-covered ecosystems strongly influences annual carbon cycling, underlining the importance of processes related to the timing and quantity of snow. Fences were used to increase snow depth from 30 to 150 cm, and impacts on respiration were investigated in heath and mesic meadow, two common vegetation types in Svalbard. We manually measured ecosystem respiration from July 2007 to July 2008 at a temporal resolution greater than previously achieved in the High Arctic (campaigns: summer, eight; autumn, six; winter, 17; spring, nine). Moisture contents of unfrozen soil and soil temperatures throughout the year were also recorded. The increased snow depth resulted in significantly higher winter soil temperatures and increased ecosystem respiration. A temperature-efflux model explained most of the variation of observed effluxes: meadows, 94 (controls) and 93% (fences); heaths, 84 and 77%, respectively. Snow fences increased the total non-growing season efflux from 70 to 92 (heaths) and from 68 to 125 g CO 2-C m -2 (meadows). The non-growing season contributed to 56 (heaths) and 42% (meadows) of the total annual carbon respired. This proportion increased with deeper snow to 64% in both vegetation types. Summer respiration rates were unaffected by snow fences, but the total growing season respiration was lower behind fences because of the considerably delayed snowmelt. Meadows had higher summer respiration rates than heaths. In addition, non-steady state CO 2 effluxes were measured as bursts lasting several days during spring soil thawing, and when ice layers were broken to carry out winter efflux measurements.
Journal of Sedimentary Research, 2011
Ikaite is considered a metastable mineral forming and stable only at low temperatures and therefo... more Ikaite is considered a metastable mineral forming and stable only at low temperatures and therefore an indicator of low-temperature carbonate precipitation often associated with cold marine seeps. It is found world-wide but most spectacularly in Ikka Fjord in southwest Greenland as submarine carbonate tufa columns. Here, ikaite is formed as a result of submarine spring water mixing with cold seawater. As ikaite disintegrates at temperatures above 6-7uC, it has been speculated that global warming could endanger this unique habitat as well as other sites. In Ikka Fjord in situ water chemistry in and around an ikaite column measured continuously over two years showed that the column water is alkaline (pH . 9-10) throughout the year with temperatures of 21.3-6.0 uC and conductivities of 5.7-7.9 mS cm 21 , favoring year-round growth of columns at 4-5 cm per month. Short-term in situ measurements with needle micro sensors from both older dehydrated and calcified parts and more recently formed solid parts of an ikaite tufa column showed similar pH and temperature values, including a temperature variation over the tidal cycle. In the uppermost, recently deposited ikaite matrix, spring water escaping at the top causes passive drag of seawater into the porous ikaite matrix, leading to a mixing layer several centimeters thick that has pH values intermediate to the spring water in the column and the surrounding seawater. We conclude that the main part of the columns, consisting of fossilized ikaite (inverted to calcite) partly sealed by calcifying coralline algae and with year-round flow of alkaline freshwater through distinct channels, are resistant to warming. In the more diffuse top part of the columns, the formation of ikaite, and thus column growth, will be limited in the future due to increased fjord water temperature during the , 3 summer months a year.
Journal of Quaternary Science, 2002
Terraces of different age in the Zackenberg delta, located at 74°N in northeast Greenland, have p... more Terraces of different age in the Zackenberg delta, located at 74°N in northeast Greenland, have provided the opportunity for an interdisciplinary approach to the investigation of Holocene glacial, periglacial, pedological, biological and archaeological conditions that existed during and after delta deposition.The raised Zackenberg delta accumulated mainly during the Holocene Climatic Optimum, starting slightly prior to 9500 cal. yr BP (30
Journal of Archaeological Science, 2011
Remains from Paleo-Eskimo cultures are well-documented, but complete preservation is rare. Two ki... more Remains from Paleo-Eskimo cultures are well-documented, but complete preservation is rare. Two kitchen middens in Greenland are known to hold extremely well-preserved organic artefacts. Here, we assess the fate of the Qajaa site in Western Greenland under future climate conditions based on site characteristics measured in situ and from permafrost cores. Measurements of thermal properties, heat generation, oxygen consumption and CO 2 production show that the kitchen midden can be characterized as peat but produces 4e7 times more heat than natural sediment. An analytical model from permafrost research has been applied to assess future thawing of the midden. Results show that the preservation conditions are controlled by freezing temperatures and a high water/ice content limiting the subsurface oxygen availability. Threats to the future preservation are related to thawing followed by drainage and increasing subsurface oxygen availability and heat generation. The model predicts that the unique 4000-year-old Saqqaq layer below more than 1 m of peat is adequately protected against thawing for the next 70 years.