Lacelle D, Radtke K, Clark ID, Fisher D, Lauriol B, Utting N, Whyte LG. 2011. Geomicrobiology and occluded O2-CO2-Ar gas analyses provide evidence of microbial respiration in ancient terrestrial ground ice. Earth and Planetary Science Letters 306: 46-54.
These authors compared the gas composition of ice from massive ground ice bodies (e.g. 30 000-year-old buried snowbanks) to atmospheric gas concentrations and gas contents from glacial ice. They also cultivated some microorganisms collected from within the ice, and used some non-culture-dependent methods to examine the diversity of those organisms.
Loss of O2, as determined by comparison of the ratio of O2 to Ar in samples, as well as changes to the 13C-CO2 contents indicate heterotrophic microbial activity in the ice, most likely by organisms living in high-salt brine channels in cracks in the ice, using dissolved organic carbon as both energy and C source.
This paper provides an overview of methods for extracting and measuring the gases trapped in microscopic bubbles in permafrost and ground ice, as well as interesting findings about microbial activities.
Showing posts with label Canadian Arctic Archipelago. Show all posts
Showing posts with label Canadian Arctic Archipelago. Show all posts
Thursday, August 25, 2011
Lacelle et al. 2008
Lacelle D, Juneau V, Pellerin A, Lauriol B, Clark ID. 2008. Weathering regime and geochemical conditions in a polar desert environment, Haughton impact structure region, Devon Island, Canada. Canadian Journal of Earth Science 45: 1139-1157.
These authors examined the soils and waters near the Haughton crater on Devon Island, to determine the importance of chemical and mechanical weathering in this polar desert environment. They examined dissolved material in streams, lakes, snow, and groundwaters, and the size distribution, shape, and chemical composition of particles from soils in several different local landforms and parent materials.
Despite low temperatures, low precipitation, and very low vegetation presence, significant chemical weathering was found. Signs of chemical weathering, rather than mechanical, include rounded surfaces and pits in sand particles and the concentrations of Ca2+, Mg2+, and HCO3- in waters. Signs of mechanical weathering were also found, including sharp fracture lines in particles.
A gradient of increasing chemical weathering and decreasing mechanical weathering was found from the surface to the permafrost table. Thermal buffering reduces the frequency of frost-driven forces and thermal expansion from daily at the surface to annually at the permafrost table. The permafrost acts as a barrier to water movement, creating relatively wet condtions at depth that allow aqueous chemistry including the dissolution of dolomite to proceed.
These authors examined the soils and waters near the Haughton crater on Devon Island, to determine the importance of chemical and mechanical weathering in this polar desert environment. They examined dissolved material in streams, lakes, snow, and groundwaters, and the size distribution, shape, and chemical composition of particles from soils in several different local landforms and parent materials.
Despite low temperatures, low precipitation, and very low vegetation presence, significant chemical weathering was found. Signs of chemical weathering, rather than mechanical, include rounded surfaces and pits in sand particles and the concentrations of Ca2+, Mg2+, and HCO3- in waters. Signs of mechanical weathering were also found, including sharp fracture lines in particles.
A gradient of increasing chemical weathering and decreasing mechanical weathering was found from the surface to the permafrost table. Thermal buffering reduces the frequency of frost-driven forces and thermal expansion from daily at the surface to annually at the permafrost table. The permafrost acts as a barrier to water movement, creating relatively wet condtions at depth that allow aqueous chemistry including the dissolution of dolomite to proceed.
Friday, February 19, 2010
Liptzin 2006
Liptzin D. 2006. A banded vegetation pattern in a High Arctic community on Axel Heiberg Island, Nunavut, Canada. Arctic, Antarctic, and Alpine Research 38: 216-223.
This author attempted to explain the observation of banded vegetation on a slope that lacked the usual factors that generate such patterns. In temperate and tropical locations, banded vegetation, also known as “tiger stripes”, forms on shallow slopes in dry areas with a consistent direction of water flow. Plants at a position on the slope increase water retention and facilitate further colonization by plants. Similarly, some locations experience consistent wind direction carrying sea spray that kills trees at some positions. In cold environments, patterned ground from cryoturbation on shallow slopes can also lead to banded vegetation. However, the study site in this paper lacks all of these features, including cryoturbation despite the presence of permafrost within 50cm at most locations.
Some aspect of soil properties is the obvious explanatory hypothesis, which this author explores after describing the transects measuring plant diversity and the soil pits used to examine soil properties. In general, features that would normally be expected to influence plant diversity and abundance such as soil moisture or exchangeable cation levels, had no significant impact in the various statistical tests employed in this study. However, soil type did have some effect, as a few species of plants were found only on sandy soil, and nitrogen levels were negatively correlated with species richness.
The discussion section of this paper is an excellent example of a chain of logical reasoning working through a series of potential explanations. While this paper is interesting, it’s only relevant to my own studies in a narrow area around potential starting points in looking for explanations for whatever patterns I may find in my biogeography studies in 2010. However, this paper seems remarkably suitable as an introduction to the basics of modern soil science research, and may be relevant to my not-quite-mothballed interest in an undergraduate course about the current state of the scientific literature.
This author attempted to explain the observation of banded vegetation on a slope that lacked the usual factors that generate such patterns. In temperate and tropical locations, banded vegetation, also known as “tiger stripes”, forms on shallow slopes in dry areas with a consistent direction of water flow. Plants at a position on the slope increase water retention and facilitate further colonization by plants. Similarly, some locations experience consistent wind direction carrying sea spray that kills trees at some positions. In cold environments, patterned ground from cryoturbation on shallow slopes can also lead to banded vegetation. However, the study site in this paper lacks all of these features, including cryoturbation despite the presence of permafrost within 50cm at most locations.
Some aspect of soil properties is the obvious explanatory hypothesis, which this author explores after describing the transects measuring plant diversity and the soil pits used to examine soil properties. In general, features that would normally be expected to influence plant diversity and abundance such as soil moisture or exchangeable cation levels, had no significant impact in the various statistical tests employed in this study. However, soil type did have some effect, as a few species of plants were found only on sandy soil, and nitrogen levels were negatively correlated with species richness.
The discussion section of this paper is an excellent example of a chain of logical reasoning working through a series of potential explanations. While this paper is interesting, it’s only relevant to my own studies in a narrow area around potential starting points in looking for explanations for whatever patterns I may find in my biogeography studies in 2010. However, this paper seems remarkably suitable as an introduction to the basics of modern soil science research, and may be relevant to my not-quite-mothballed interest in an undergraduate course about the current state of the scientific literature.
Wednesday, January 6, 2010
Siciliano et al. 2009
Siciliano SD, Ma WK, Ferguson S, Farrell RE. 2009. Nitrifier dominance of Arctic soil nitrous oxide emissions arises to due fungal competition with denitrifiers for nitrate. Soil Biology and Biochemistry 41: 1104-1110.
These authors examined the nitrous oxide emissions, microbial communities, and some components of nitrogen cycling in soils from three landforms at Truelove Lowland, on Devon Island. Previous results (Ma et al. 2007) had indicated that Arctic nitrous oxide emissions are not sensitive to soil moisture, at least in the range of 50% to saturated water filled pore space. This study includes a series of incubations of soil samples at a range of temperatures similar to ambient conditions, and treatments to disrupt fungi or particular types of prokaryotes.
Large differences in community composition were found between the three landforms, with the highest biomass and fungi:bacteria ratio in the wet sedge meadow and lowest in the raised beach crest (the lower foreslope was intermediate by these measures). Competition between fungi and denitrifiers for soil nitrate pools was inferred as the mechanism allowing dominance of emitted N2O by nitrifiers; fungi and denitrifiers are busy scavenging every available electron acceptor starting with nitrate and running all the way down to N2 gas, so almost any N2O that escapes was generated by nitrifiers in conditions not favoured by either of the other major groups.
This paper serves to demonstrate the very complex nature of soil biology, especially regarding the multiple and interacting pathways that may produce or consume materials of interest such as N2O. The references in this paper should be useful for digging into this complexity.
These authors examined the nitrous oxide emissions, microbial communities, and some components of nitrogen cycling in soils from three landforms at Truelove Lowland, on Devon Island. Previous results (Ma et al. 2007) had indicated that Arctic nitrous oxide emissions are not sensitive to soil moisture, at least in the range of 50% to saturated water filled pore space. This study includes a series of incubations of soil samples at a range of temperatures similar to ambient conditions, and treatments to disrupt fungi or particular types of prokaryotes.
Large differences in community composition were found between the three landforms, with the highest biomass and fungi:bacteria ratio in the wet sedge meadow and lowest in the raised beach crest (the lower foreslope was intermediate by these measures). Competition between fungi and denitrifiers for soil nitrate pools was inferred as the mechanism allowing dominance of emitted N2O by nitrifiers; fungi and denitrifiers are busy scavenging every available electron acceptor starting with nitrate and running all the way down to N2 gas, so almost any N2O that escapes was generated by nitrifiers in conditions not favoured by either of the other major groups.
This paper serves to demonstrate the very complex nature of soil biology, especially regarding the multiple and interacting pathways that may produce or consume materials of interest such as N2O. The references in this paper should be useful for digging into this complexity.
Monday, November 2, 2009
Jones and Henry 2003
Jones GA, Henry GHR. 2003. Primary plant succession on recently deglaciated terrain in the Canadian High Arctic. Journal of Biogeography 30: 277-296.
These authors examined five glacial foregrounds on Ellesmere Island, one intensively and the other 4 “extensively”, to determine patterns of succession among plant communities on sterile ground. The ecological literature recognizes several different modes of succession, including a categorization by Henry and Svoboda (1987) based on the relative strengths of biotic and abiotic factors. This model of succession recognizes 3 modes; directional succession with species replacement, directional succession without species replacement, and non-directional succession without replacement. They are arranged in increasing importance of abiotic factors, referred to here as “environmental resistance”, which operates in opposition to “biological driving forces”.
In temperate regions, where much of the relevant ecological theory has been developed, biotic factors are mainly competition. In the High Arctic, a successional pattern consistent with directional-with-replacement was found, demonstrating that this can occur even in environments with obviously severe abiotic factors. However, these authors argue that the biotic factor driving this succession was probably not competition, because total plant cover remains below 10% by area even at the fourth stage recognized here, and species richness is always very low. The polar oasis landscape with 80-100% plant cover was never reached within the approximately 50-year old glacial forelands examined by these authors, though it is likely that competition is important in that “stage 5” level of High Arctic succession.
Other biotic variables suggested playing a role in successional dynamics in the High Arctic included facilitation and life-history characteristics. These factors are not independent; later successional species such as Salix arctica appear not to be able to establish until soil fertility has been improved by mats of very-early-colonizing mosses, and are long-lived, slow-growing species that contribute little to the early seed bank and seed rain. Thus, multiple plant and environmental characteristics appear to interact when structuring early communities.
I read this paper to try to gain some understanding of ecological succession and the role of time-since-deglaciation among the ecosystems of Alexandra Fjord. Rather than being distinct successional stages in sequence as I had previously supposed, it appears the various lowland ecosystems are all of a similar age, and have different vegetation communities as a result of other factors besides simply relative proximity to the Twin Glacier. Dryas integrefolia and Cassiope tetragona were important parts of this study, and both appear in stage 4, after primary-colonizing mosses, and early-colonizing forbs such as Papaver radicatum and early-colonizing deciduous shrubs like Saxifraga spp. Both Dryas and Cassiope form associations with mycorrhyzal fungi, a requirement that may slow their colonization of novel habitats; earlier-spreading plants do not form these associations, and instead may be limited by seed dispersal.
This was helpful in organizing the structure of the manuscript I am currently working on, which will describe some of the soil biotic communities both in the Alexandra Fjord lowlands and in the adjacent polar desert. It is not a simple story of succession from one ecosystem to the next, but succession does play a role.
These authors examined five glacial foregrounds on Ellesmere Island, one intensively and the other 4 “extensively”, to determine patterns of succession among plant communities on sterile ground. The ecological literature recognizes several different modes of succession, including a categorization by Henry and Svoboda (1987) based on the relative strengths of biotic and abiotic factors. This model of succession recognizes 3 modes; directional succession with species replacement, directional succession without species replacement, and non-directional succession without replacement. They are arranged in increasing importance of abiotic factors, referred to here as “environmental resistance”, which operates in opposition to “biological driving forces”.
In temperate regions, where much of the relevant ecological theory has been developed, biotic factors are mainly competition. In the High Arctic, a successional pattern consistent with directional-with-replacement was found, demonstrating that this can occur even in environments with obviously severe abiotic factors. However, these authors argue that the biotic factor driving this succession was probably not competition, because total plant cover remains below 10% by area even at the fourth stage recognized here, and species richness is always very low. The polar oasis landscape with 80-100% plant cover was never reached within the approximately 50-year old glacial forelands examined by these authors, though it is likely that competition is important in that “stage 5” level of High Arctic succession.
Other biotic variables suggested playing a role in successional dynamics in the High Arctic included facilitation and life-history characteristics. These factors are not independent; later successional species such as Salix arctica appear not to be able to establish until soil fertility has been improved by mats of very-early-colonizing mosses, and are long-lived, slow-growing species that contribute little to the early seed bank and seed rain. Thus, multiple plant and environmental characteristics appear to interact when structuring early communities.
I read this paper to try to gain some understanding of ecological succession and the role of time-since-deglaciation among the ecosystems of Alexandra Fjord. Rather than being distinct successional stages in sequence as I had previously supposed, it appears the various lowland ecosystems are all of a similar age, and have different vegetation communities as a result of other factors besides simply relative proximity to the Twin Glacier. Dryas integrefolia and Cassiope tetragona were important parts of this study, and both appear in stage 4, after primary-colonizing mosses, and early-colonizing forbs such as Papaver radicatum and early-colonizing deciduous shrubs like Saxifraga spp. Both Dryas and Cassiope form associations with mycorrhyzal fungi, a requirement that may slow their colonization of novel habitats; earlier-spreading plants do not form these associations, and instead may be limited by seed dispersal.
This was helpful in organizing the structure of the manuscript I am currently working on, which will describe some of the soil biotic communities both in the Alexandra Fjord lowlands and in the adjacent polar desert. It is not a simple story of succession from one ecosystem to the next, but succession does play a role.
Tuesday, October 6, 2009
Cockell and Stokes 2004
Cockell CS, Stokes MD. 2004. Widespread colonization by polar hypoliths. Nature 431: 414.
These authors present a short report about the colonization of the undersides of rocks in the polar deserts by cyanobacteria and unicellular green algae. Where rocks have a protected but accessible underside, these organisms colonize, forming a pale green band a few centimetres across, between the part of the rock too exposed and dry, and too dark for photosynthesis. In polygon terrain, where the ground is sorted by frost heave (“periglacial processes”) and even large rocks are periodically jostled, areas of finer texture form in the centers of polygons, with larger rocks around the edges. The edge rocks were 100% colonized, while central areas were 5% colonized.
These authors present a short report about the colonization of the undersides of rocks in the polar deserts by cyanobacteria and unicellular green algae. Where rocks have a protected but accessible underside, these organisms colonize, forming a pale green band a few centimetres across, between the part of the rock too exposed and dry, and too dark for photosynthesis. In polygon terrain, where the ground is sorted by frost heave (“periglacial processes”) and even large rocks are periodically jostled, areas of finer texture form in the centers of polygons, with larger rocks around the edges. The edge rocks were 100% colonized, while central areas were 5% colonized.
Friday, September 4, 2009
Broll et al. 1999
Broll G, Tarnocai C, Mueller G. 1999. Interactions between vegetation, nutrients and moisture in soils in the Pangnirtung Pass area, Baffin island, Canada. Permafrost and Periglacial Processes 10: 265-277.
These authors examined soils from 6 pedons in Pangnirtung Pass, a north-south pass between mountains on Cumberland Peninsula. Three pedons were from moist soils, and three from dry soils. The moisture content drove a major difference in soil structure: dry soils are not cryoturbated, resulting in strong differences in nutrient content and mineralization rates.
The goal of the study was to compare in detail these differences between dry and moist soils. This seems very similar to my PhD goals surrounding examinations of Polar Desert soils. This study thus represents a possible template for some of my own investigations.
These authors examined soils from 6 pedons in Pangnirtung Pass, a north-south pass between mountains on Cumberland Peninsula. Three pedons were from moist soils, and three from dry soils. The moisture content drove a major difference in soil structure: dry soils are not cryoturbated, resulting in strong differences in nutrient content and mineralization rates.
The goal of the study was to compare in detail these differences between dry and moist soils. This seems very similar to my PhD goals surrounding examinations of Polar Desert soils. This study thus represents a possible template for some of my own investigations.
Wednesday, September 2, 2009
Bockheim 1979
Bockheim JG. 1979. Properties and relative age of soils of southwestern Cumberland peninsula, Baffin island, N.W.T., Canada. Arctic and Alpine Research 11: 289-306.
This author sampled soils from more than 60 sites on the Cumberland peninsula of Baffin Island, mostly near the hamlet of Pangnirtung. This covered soils from two tundra vegetations (Dwarf shrub-sedge-moss-lichen on lowlands and coastal, stony sedge-moss-lichen in highlands and northern fjords) and the Polar Desert of Baffin island. The tundra soils ranged from mesic to subxeric, while the desert near Penny icecap was xeric. A similar gradient driven by latitude rather than altitude is referenced in Tedrow (1973).
Descriptions are made of the pH and various exchangeable and free minerals in the soils, along with how those components change with depth in each area. pH increases with depth, for example, especially in the Polar Desert. Phosphorus was found in surprisingly high levels in all soils. The active layer, or at least the layer above the permafrost, is much deeper than found on Ellesmere island, and appears to be deeper than 1m everywhere studied in this paper.
This author sampled soils from more than 60 sites on the Cumberland peninsula of Baffin Island, mostly near the hamlet of Pangnirtung. This covered soils from two tundra vegetations (Dwarf shrub-sedge-moss-lichen on lowlands and coastal, stony sedge-moss-lichen in highlands and northern fjords) and the Polar Desert of Baffin island. The tundra soils ranged from mesic to subxeric, while the desert near Penny icecap was xeric. A similar gradient driven by latitude rather than altitude is referenced in Tedrow (1973).
Descriptions are made of the pH and various exchangeable and free minerals in the soils, along with how those components change with depth in each area. pH increases with depth, for example, especially in the Polar Desert. Phosphorus was found in surprisingly high levels in all soils. The active layer, or at least the layer above the permafrost, is much deeper than found on Ellesmere island, and appears to be deeper than 1m everywhere studied in this paper.
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