Thesis (Ph.D.)--Aberdeen University, 2009. / Title from web page (viewed on Aug. 26,2009). Includes bibliographical references.

The intent of this study is to describe and analyze the interrelations of vegetation and environment in the east-central sector of the Mackenzie River Delta, Northwest Territories. It traces the sequence and function of the allogenic events which create varying habitat systems and determines whether environmental modification, once initiated on terra nova is directional - in either a physical or floristic expression. In determining the sequence and influence of physical environmental factors, the following parameters were measured, employing standard instruments and field investigation techniques: micro-relief; depth, areal extent, and duration of flooding; thickness, areal extent, and particle-size distribution of annual deposits of alluvium; magnitude and significance of erosion; patterns of microclimatic variation (including air temperature and humidity, evaporativity, precipitation, wind speed, solar radiation, and net radiation); lake and channel temperatures; soil pH, moisture (hygrotope class), and temperature; development of varying active layer depths; and freezeback of the active layer. To analyze the vegetation of the study area, the phytosociologic methods of the Braun- Blanquet (Zurich-Montpellier) school were applied. Nine seral associations and the climax ecosystem were studied; each was fitted into a successional category. Plant succession was analyzed by reconstructing the course of vegetative development from pioneer to climax community with the aid of successional transects. Results of this study indicate that environmental and floristic changes in the Mackenzie Delta are directional - that given the formation of new ground, such as on the slipoff slope of a shifting channel, ecologic variation will follow a predictable direction. As the seral sequence advances, autogenic influences become dominant over the allogenic initiators until in the climax association, relatively steady-state conditions of environment and vegetation are attained. / Arts, Faculty of / Geography, Department of / Graduate

This study shows how the feeding behaviour of the increasing number of geese impacts their fragile breeding grounds in the Arctic region of Svalbard and, ultimately, may affect the geese themselves.  On arrival in their breeding grounds in spring, pink-footed geese, in common with other goose species, forage for below-ground plant parts.  This grubbing behaviour disturbs tundra ecosystems.  This thesis investigates the extent and distribution of grubbing on Svalbard, its impact on tundra ecosystems and feedbacks to the goose population in the long term. Grubbing geese reduce the abundance of plants, including moss, in tundra vegetation and cause the loss of substantial quantities of soil carbon.  A multi-habitat field manipulation experiment demonstrated that the impact of grubbing varies between communities; wetter communities with high moss cover are less negatively affected, but these are more likely to be grubbed by geese, particularly in valley bases and low lying coastal areas.  Using data collected in this project, the long-term effect of geese on tundra was simulated.  This resulted in predictions that geese will cause substantial degradation of their habitat if the population increases by another 50% to 75,000. Due to the negative effect of grubbing on vegetation, the long-term sustainable size of the population of pink-footed geese breeding on Svalband is estimated to be 95,000, less than 30% of the number expected based on the tundra’s productivity.  Pink-footed geese are therefore “ecosystem engineers” of the tundra, as they affect resource availability and “carrying capacity engineers”, as by degrading their own habitat they reduce the size of the goose population that it can support.

One central goal in ecology is to understand how biodiversity, and key organismal traits, interact with ecosystem properties and processes, and ultimately to understand and predict how these interactions will be affected by rapid environmental change. Thus, global change experiments and observational gradients in diversity provide the opportunity to examine and test hypotheses about how organismal traits, multiple dimensions of biodiversity, and ecosystem function will respond to environmental change. In Arctic tundra, increased nitrogen (N) and phosphorus (P) availability accompanying rapid warming is thought to significantly alter plant community composition and ecosystem function. The following four chapters examine hypotheses about the responses of species’ traits, multiple dimensions of biodiversity, and ecosystem function to the effects Arctic warming. Chapter 1 examines plant community composition and the capacity for ecosystem function (net ecosystem exchange, ecosystem respiration, and gross primary production) across a gradient of experimental N and P addition expected to more closely approximate warming-induced fertilization, demonstrating declines in plant diversity and an increase in the capacity for ecosystem carbon uptake at the highest level of fertilization. Chapter 2 examines a set of physiological and functional leaf traits across the same N and P gradient in order to evaluate the possible physiological mechanisms underlying community and ecosystem responses, highlighting the effects of increasing nutrient availability for deciduous shrub species. Chapter 3 found that single-dose, long-term nutrient addition (i.e., > 20 years) led to significant declines in multiple dimensions of diversity (taxonomic, functional and phylogenetic), and that these effects persist through time, increasing for dimensions that capture organismal traits (functional and phylogenetic). Finally, Chapter 4 examined the relationship between multidimensional diversity and ecosystem function across a natural gradient of diversity, and found that taxonomic diversity and functional diversity were significantly and positively related to whole ecosystem productivity, and, conversely, functional evenness and dispersion were significantly and negatively related to ecosystem productivity. Cumulatively, these four chapters advance our understanding of the connections between communities and ecosystems in a rapidly changing ecosystem.

The relationship between soil temperature and CO₂ flux from undisturbed soil cores was examined during freeze-up of arctic tundra. Three habitats which dominate tundra topography, polygon trough, ridge and basin, produced significantly different amounts of CO₂ when soil temperatures were above 0 C. A significant positive correlation between soil temperatures between 10 to -7 C and CO₂ flux from each habitat was established. Substantial quantities of CO₂ were produced during freeze-up period when soil temperatures remained near 0 C for an extended period, and the CO₂ production continued at reduced levels as the soil temperature dropped below 0 C. When soil temperatures reached -7 C and the study was terminated, the CO₂ flux was reduced to a low level, but did not reach extinction. A maximum CO₂ flux of 2925 mg CO₂/m²/day from the trough habitat was observed when the soil temperature was 10 C, and the minimum CO₂ flux of 131 mg/m²/day was observed when the soil temperature was -7 C. These data are consistant with the hypothesis that soil microorganisms in arctic tundra are capable of physiological activity in the range of 0 to -7 C. / Master of Science

The acid phosphomonoesterase activity associated with two major rooting strategies in arctic tundra plants was examined: that of Eriophorum vagina tum, a dominant plant in tussock tundra ecosystems, with its predominantly non-mycorrhizal root system; and that of ectomycorrhizal roots. Eriophorum has phosphatase activity which is evenly distributed along its root surface, has a pH optimum at soil pH (3.5-4.0), and continues at substantial rates at 1 °C. Inorganic phosphorus inhibits activity only 7 to 19%. In addition, Eriophorum has phosphatase activity associated with all the "below-ground" components of its tussock growth form: dead roots, leaf sheaths, and soil. Plants with higher tissue phosphorus growing in soils with higher available phosphate in general had higher live and dead root, leaf sheath, and soil phosphatase activity in both natural and manipulated sites of higher plant productivity. Yearly and seasonal variation sometimes exceeded differences among treatments, suggesting that enzyme activity would not provide a reliable measure of plant or soil phosphorus levels. Experiments with radiolabeled inositol hexaphosphate showed that Eriophorum is able to hydrolyze and absorb inorganic phosphate from an organic phosphate source. A comparison of enzyme hydrolysis rates with inorganic phosphate assimilation rates indicates that organic phosphate hydrolysis may occur as rapidly as inorganic phosphate absorption. Inorganic phosphate released by root surface phosphatase activity could satisfy approximately 65% of the annual phosphate demand of Eriophorum. Phosphatases of two ectomycorrhizal fungi (Cenococcum geophilum and Entoloma sericeum) responded similarly to growth in axenic culture at 2 or 50 micromolar KH₂PO₄ or sodium inositol hexaphosphate: surface Vmax estimates were significantly greater for 2 micromolar- than for 50 micromolar-grown isolates. The presence of constitutive extracellular soluble phosphatase activity resulted in the appearance of inorganic phosphate in media initially supplied only with organic phosphate. The surface acid phosphatase activity of field-collected ectomycorrhizal roots of arctic Salix and Betula, however, did not respond in a consistent way to differences in soil characteristics. Activity differed more among "color types" or fungal types than among sites of different soil characteristics. / Ph. D.

Thesis (M.SC.) - Carleton University, 2007. / Includes bibliographical references (p. 154-161). Also available in electronic format on the Internet.

The arctic tundra has been warming disproportionately faster than the global mean. Although the tundra has historically been a carbon sink, the current state of its carbon balance is highly uncertain. Large warming induced changes to tundra ecosystems complicate our ability to model tundra carbon cycling. In this dissertation I explore the impact of herbivores on dry heath vegetation and carbon flux, herbivore impact on dry heath tundra canopy, and lastly, the impact higher vegetation has on the conditions under which the tundra transitions from a carbon sink to a carbon source. Chapter 1 presents a study on the impact long term herbivore absence has on dry heath tundra. I measured vegetation cover, abundances of plant growth forms and carbon flux. I demonstrate the herbivore exclusion in this tundra ecosystem results in higher vegetation abundance and greater carbon uptake. Moreover, under average environmental conditions during the measurement period, I show that excluding herbivores resulted in net carbon uptake under average temperature and light conditions during the measurement period. In chapter 2 I build upon my result from chapter 1. I quantify differences in canopy structure due to herbivore exclusion and integrate this into carbon flux estimates. I show that that different herbivore assemblages have significantly different effect on carbon fluxes. Specifically, exclusion of large herbivores results in higher carbon uptake compared to exclusion of large and small herbivores. I also demonstrate that incorporating canopy structure results in significantly lower carbon uptake during morning and evening hours than carbon flux estimates based on my results from chapter 1 would suggest. In chapter 3 I quantify the conditions under which tussock tundra transitions from a carbon sink to source and how that is impacted by increasing vegetation abundance. I show that under low light, tundra with higher vegetation abundance must surpass higher temperatures to become carbon sources compared to tundra with lower vegetation abundance. However, under high light, the conditions are reversed, and tundra with higher vegetation abundance become carbon sources at lower temperatures than tundra with lower vegetation.

No description available.

This study examines the impact of snowmelt runoff on nutrient transfer from the terrestrial to the aquatic (lake) portion of a subarctic catchment 6 km WSW from Schefferville, Quebec. / Statistically significant differences in snow chemistry were recorded among the tundra, woodland and forest snowpacks. Significant overland substantial scouring of nutrients from the organic horizons were recorded in the tundra, woodland and forest. A calculation designed to generate, on a daily basis, 70% of the meltwater from the terrestrial catchment to the lake indicates overland flow is a predominant route of meltwater during the spring. This calculation made possible the determination of daily nutrient mass transfer from land to lake. The daily nutrient mass balance of input and output to Elizabeth Lake during springmelt indicates significant retention of land source nutrients. Deuterium/hydrogen measurements aided in determining mixing of snowmelt and lake water. The data indicate snowmelt water is undistinguishable from lake water at depths greater than 1.0 m. / It is concluded that snowmelt runoff is an important event for nutrient transfer from terrestrial to aquatic systems in this environment.