288 research outputs found
Permafrost collapse is accelerating carbon release
No full textThe sudden collapse of thawing soils in the Arctic might double the warming from greenhouse gases released from tundra, warn Merritt R. Turetsky and colleagues
From Causes to Consequences: Understand the impacts of permafrost thaw as an integrated system
No full textUnderstanding the causes and consequences of permafrost thaw is one of the key challenges facing northern communities and researchers today. With northern environments warming at twice the global average, climate change is driving widespread changes in permafrost environments that provide the foundation for ecological-, social-, economic-, and human-wellbeing. In this thesis I aim to enhance the understanding of permafrost environments as an integrated system that considers humans and communities as part of the permafrost system. In chapter 1, I conduct a scoping review of permafrost peer-reviewed literature related to the consequences of permafrost thaw. I show that over 95% of the literature focuses on permafrost thaw impacts to ecosystem processes and that over 75% of northern communities lack permafrost thaw related measurements within 75km of them. In Chapter 2, I quantify the consequences of permafrost thaw on land-users. I show that permafrost thaw accounts for a third, and potentially as much as a half of all hazards that land-users faces when on the land. In chapter 3, I respond to an emergent challenge from chapter 2 about the need for permafrost vulnerability data at a scale that is more relevant to community-level planning. I map the spatial distribution of terrain vulnerable permafrost thaw at a scale that is relevant to community adaptation planning. Data generated in chapter 3 are then used in chapter 4 where I assess how the degree of thermokarst formation within permafrost peatlands varies across a latitudinal (climatic) gradient (i.e., space-for-time substitutions) to make inferences about how thaw will progress in a warming climate. I show that at northern latitudes, peatland permafrost remains climate-protected with relatively little thaw. Conversely, I show that at the southern latitudes, widespread thaw has occurred with areas of lower elevation being most vulnerable. Overall, the findings of this thesis show the importance of considering communities and their needs at the forefront of any permafrost related study. When done, not only does an enhanced and enriched understanding of the permafrost system emerge, but the knowledge and information generated is more easily accessed and applied by communities and decision makers
Effects of Disturbance and Landscape Position on Vegetation Structure and Productivity in Ontario Boreal Forests: Implications for Woodland Caribou (Rangifer tarandus caribou) Forage
No full textHypotheses explaining recent declines in the abundance of woodland caribou in boreal Ontario include increased disturbances and predation. Caribou may select peatlands to avoid predation. Peatlands are regarded as low productivity, nutrient-limited systems, caribou may face a trade-off between predation risk and nutrient intake through foraging. I quantified differences in plant community and plant foliar quality in boreal stands across drainage class, disturbance type and time-following-disturbance. I found that understory productivity was influenced more by drainage and time-following-disturbance than by disturbance type. I also quantified variation among stand characteristics and plant functional types using measures of plant foliar quality. Foliar quality varied mostly by plant functional type. Overall, this thesis does not support the hypothesis that caribou face a trade-off between forage quality and predation risk by selecting peatlands, as peatlands had greater levels of understory productivity and foliar quality relative to uplands
Effects of soil rewetting and thawing on soil gas fluxes: a review of current literature and suggestions for future research
No full text"The rewetting of dry soils and the thawing of frozen soils are short-term, transitional phenomena in terms of hydrology and the thermodynamics of soil systems. The impact of these short-term phenomena on larger scale ecosystem fluxes is increasingly recognized, and a growing number of studies show that these events affect fluxes of soil gases such as carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), ammonia (NH3) and nitric oxide (NO). Global climate models predict that future climatic change is likely to alter the frequency and intensity of drying-rewetting events and thawing of frozen soils. These future scenarios highlight the importance of understanding how rewetting and thawing will influence dynamics of these soil gases. This study summarizes findings using a new database containing 338 studies conducted from 1956 to 2011, and highlights open research questions. The database revealed conflicting results following rewetting and thawing in various terrestrial ecosystems and among soil gases, ranging from large increases in fluxes to non-significant changes. Studies reporting lower gas fluxes before rewetting tended to find higher post-rewetting fluxes for CO2, N2O and NO; in addition, increases in N2O flux following thawing were greater in warmer climate regions. We discuss possible mechanisms and controls that regulate flux responses, and recommend that a high temporal resolution of flux measurements is critical to capture rapid changes in gas fluxes after these soil perturbations. Finally, we propose that future studies should investigate the interactions between biological (i.e., microbial community and gas production) and physical (i.e., porosity, diffusivity, dissolution) changes in soil gas fluxes, apply techniques to capture rapid changes (i.e., automated measurements), and explore synergistic experimental and modelling approaches.
The Effect of Long-Term Drainage on Plant Community Composition, Biomass, and Productivity in Boreal Continental Peatlands
No full textThis thesis is an investigation of the effects of long-term drainage on plant community composition, biomass and productivity in boreal continental peatlands. Because bogs are ombrotrophic, I hypothesized that bog plant community composition, biomass and productivity would be affected by drainage less than fens. I identified six Alberta peatlands (2 bogs, 4 fens) that were affected by long-term drainage through road construction or drainage ditches. I found that understory species composition in fens changed more in response to drainage than in bogs, and was related to the degree of canopy closure. Woody biomass increased in all poor fens sites with drainage, while understory biomass was not affected. I investigated the influence of drainage on primary productivity in two sites, and found that tree and moss productivity responded differently. These results have implications for peatland carbon cycling, as an increase in woody biomass will affect litter quality and future fire risk
Wildfire in peatlands and the effect of smouldering combustion on carbon and mercury emissions
No full textWarming in the boreal forest region will increase fire size, severity, and frequency. This may result in peatlands making up a larger proportion of future burned area, shifting them from a net sink of atmospheric carbon (C) to a net source. In addition, mercury (Hg) that accumulates in peat is susceptible to re-release to the atmosphere during peat fires. Here I investigated the physical properties driving depth of burn and emissions of C and Hg. I found the interaction between bulk density and water content to be the most important factor in predicting depth of burn, CO2, and CO emissions. This was not the case for CH4 and Hg emissions. These results also indicate that previously reported CO:CO2 and CH4:CO2 emission ratios are underestimating C emissions from smouldering peat. The quantity of C released from burning peat underscores the importance of considering fire in peatland C budgets
Effects of Peat Development and Wildfire on Permafrost Peatland Carbon Stocks in the Northwest Territories, Canada
No full textPermafrost responses to wildfire range from rapid recovery to irreversible thaw with large consequences for ecosystem function and carbon cycling. This study used a chronosequence of permafrost peat plateau sites in Northwest Territories, Canada that vary in time-following-fire to ask questions about active layer and organic carbon stock recovery during post-fire succession. Radiocarbon dating of basal peat layers showed the sites varied in the timing of peat initiation from 2416 - 8619 cal yr BP. Cumulative organic carbon stocks increased with peatland initiation age and peat thickness, with older peatlands experiencing more recent fire activity. Overall results show that permafrost plateau organic carbon stocks were driven more by variation in peat initiation than time-following-last fire and that, at least for top-down active layer thickening, carbon stocks can be resistant to fire. We suggest direct or indirect measurement of peat initiation age may be useful information for fire managers
Are Plants Able to Utilize Nitrogen Released from Thawing Permafrost? Implications for Carbon Cycling and Feedback with the Climate System
No full textClimate warming in high-latitude regions triggers widespread permafrost thaw, releasing massive amounts of carbon and nitrogen that were previously frozen in soil organic matter, through increased microbial activity. Climate warming has motivated extensive research on permafrost carbon release; however, fewer studies have addressed whether plants can access new nitrogen sources, potentially increasing primary productivity. Two research questions were explored using Carex aquatilis in sites experiencing thaw and thermokarst in interior Alaska: 1) does C. aquatilis ammonium uptake vary with depth and time-since-thaw; 2) does variation in C. aquatilis growth characteristics and ammonium uptake correlate with aboveground primary production? An ammonium uptake experiment was conducted on C. aquatilis roots, determining that deep roots took up equal if not greater amounts of ammonium than shallow roots. I also found that rooting depth was positively correlated with aboveground biomass, providing a plausible mechanism for increased N uptake post-thaw to impact aboveground plant productivity.Natural Sciences and Engineering Research Council of CanadaNorthern Scientific Training Progra
Evaluating trait-based ecology in Sphagnum moss
No full textInvestigations into the distribution and abundance of non-vascular plants have largely focused on their diversity and productivity in given environments. A trait-based approach, which considers intraspecific variation and evolution of functional traits and how plant–environment interactions influence ecosystem processes has not been explored in this plant group. A way forward is to evaluate moss traits within the context of theories such as resource economics theory (RET) and optimal partitioning theory (OPT), which provide clear mechanistic predictions for pattern of trait responses that reflects the life-history strategies of species. RET posits that plant traits are coordinated for fast or slow resource acquisition and growth strategies. OPT predicts that plants would invest in the organ receiving the most limiting resource. Collectively, these theories can provide insights into how traits influence ecophysiological adaptation of different species and the importance of intraspecific variability in this plant group. In this thesis, I used combinations of factorial and field experiments to evaluate the trait-based ecology in Sphagnum moss traits in the context of the RET and OPT. In the first chapter, I used a factorial experiment involving light, moisture and plant density to test whether two ecologically disparate Sphagnum species conformed to the fast-slow strategies predicted by RET and often observed in vascular plants. Consistent with OPT, Sphagnum diverted biomass from branch to capitulum under moisture stress to optimize atmospheric sources of moisture. In the second chapter, I used factorial experiments involving plant origin (hummock versus hollow), light, and moisture to show that intraspecific trait variability influences the range of environment that Sphagnum occupies within peatland, and therefore matters to the ecophysiology of this plant group. In the third chapter, I explore trait variability in Sphagnum moss at different spatial scales. I found that the traits varied the most within patches, which is the smallest sampling unit but also that the mechanisms controlling different traits may be operating at different spatial scales. Collectively, the studies showed that Sphagnum traits are integrated for performance but that the relationships among traits operates differently from that of vascular plants. Nonetheless, the traits are adaptable to the trait-based framework and could be tested against additional ecological theories
The long-term effects of drainage on carbon cycling in a boreal fen
No full textI investigated the effects of multi-decadal water table drawdown on carbon (C) exchange, as well as functional relationships between C fluxes and environmental controls, in a boreal rich fen. Drainage increased ecosystem respiration of CO2 and decreased CH4 fluxes, but did not affect understory primary productivity. Drainage altered plant responses to light availability, as well as the responses of ecosystem respiration and CH4 flux to water table position. In a laboratory experiment, I found that drainage reduced potential CO2 and CH4 fluxes suggestive of decreased peat substrate quality. Together, these results indicate that long-term drying increases C losses and that both environmental conditions and substrate quality influenced C fluxes post-drainage. My findings suggest that C losses from increased ecosystem respiration may not be mitigated by increases in plant productivity or decreases in substrate quality, and that long-term drainage reduced C storage capacity in this boreal fen.Natural Sciences and Engineering Research Council of Canad
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