Global ETD Search

1	Effects of shoreline retrogressive thermokarst slumping on the productivity and food web structure of upland Arctic lakes: an experimental approach. Moquin, Paul 19 December 2011 (has links) To assess the affects of permafrost degradation on key components of the aquatic food web, an in situ manipulative mesocosm experiment was performed in an upland, unslumped Arctic lake located near Inuvik, Northwest Territories. In total, twelve replicate mesocosms were established, 3 control and 3 replicates of 3 treatment levels each dosed with differing amounts of sediments sourced from a nearby thermokarst slumped lake. Findings from the experiment showed that pelagic autotrophic processes had the greatest potential to contribute to higher trophic levels regardless of treatment. Even in the high sediment treatment level, which showed the least pelagic autotrophic production, pelagic autotrophic production was two orders of magnitude greater than pelagic heterotrophic production and 5 times greater than benthic autotrophic or heterotrophic production. Sediment treatment had no significant effect on benthic primary productivity; however, a 500% increase in benthic heterotrophic production was observed. This raises the possibility that increased activity in benthic heterotrophic production is the first step in thermokarst-affected lake ecosystem succession leading to the proliferation of benthic primary production observed in many slumped lakes in the western Canadian Arctic. Water column phosphorus concentrations increased with increasing sediment treatment while pelagic primary production decreased and zooplankton biomass increased. These results suggest that the initial effect of thermokarst disturbance is an enrichment of the system and that top-down predation from zooplankton regulate the abundance of phytoplankton in these systems. If incidences of thermokarst disturbance continue to increase as predicted by current climate models/scenarios, results from this study suggest that the structure and function of Arctic aquatic ecosystems will be significantly impacted. This study highlights the need for further research to obtain a better mechanistic and predictive understanding of the potential effects of thermokarst disturbance on the geochemistry and ecology of Arctic lakes at relevant spatial and temporal scales. / Graduate Aquatic Ecology Arctic ecosystems Climate change Permafrost degradation
2	Terrestrial respiration across tundra vegetation types Borgelt, Jan January 2017 (has links) Large amounts of carbon (C) are stored in tundra soils. Global warming may turn tundra ecosystems from C sinks into sources or vice versa, depending on the balance between gross primary production (GPP), ecosystem respiration (ER) and the resulting net ecosystem exchange (NEE). We aimed to quantify the summer season C balance of a 27 km2 tundra landscape in subarctic Sweden. We measured CO2 fluxes in 37 widely distributed plots across five tundra vegetation types and in 7 additional bare soil plots, to assess effects of abiotic and biotic components on C exchange. C fluxes in bare soils were low and differed to all vegetation types. Thus, accounting for differences between bare soils and vegetated parts is crucial for upscaling a C balance using a landcover classification map. In addition, we found that both NEE and ER, varied within and across different tundra vegetation types. The C balance model for the growing season 2016 revealed a net C loss to the atmosphere. Most vegetation types acted as CO2 sources, with highest source strength in dense shrub vegetation at low elevations. The only considerable C sinks were graminoid-dominated upland meadows. In addition, we found a shift in C balance between different heath vegetation types, ranging from C source in dense deciduous shrub vegetation (Mesic Heath and Dry Heath) to C sink in low growing shrub vegetation (Extremely Dry Heath). These results highlight the importance to account for differences between vegetation types when modelling C fluxes from plot to landscape level. Arctic ecosystems tundra carbon respiration climate change Natural Sciences Naturvetenskap
3	Phosphorus speciation across elevation and vegetation in soils of the subarctic tundra : A solution 31P NMR approach Krohn, Johannes January 2017 (has links) In tundra, phosphorus (P) is an important macronutrient for plants and microorganisms. A major fraction of P exists as organic compounds in the topsoil which can be mineralized to bioavailable inorganic P. Since mineralization is positively related to temperature, climate warming is likely to increase P bioavailability but the extend of these changes may also depend on vegetation cover and soil properties. I assessed organic and inorganic P concentrations across an elevation and vegetation gradient in northern Sweden using one dimensional (1D) solution 31P nuclear magnetic resonance spectroscopy. I hypothesized that concentration of labile soil P will decrease with increasing elevation (decreasing temperature) and that soils with meadow vegetation will contain higher concentrations of labile P than heath soils. Concentration of labile P in the form of Resin-P and polyphosphates decreased with elevation whereas less labile orthophosphate monoesters increased. Across vegetation types, polyphosphates were more abundant in heath and meadow contained higher concentrations of monoesters. The inverse response of Resin-P and monoesters to elevation may be best explained by lowered organic P mineralization in colder climate. High concentrations of polyphosphates at the lowest elevation may indicate an increased presence of fungal communities associated with mountain birch forest. Heath seemed to be more dominated by fungal communities than meadow and higher concentration of monoesters in meadow indicated a higher soil sorption capacity. In a broader view, the results may suggest that a warmer climate increases mineralization of organic P in form of orthophosphate monoesters to more labile P forms. This effect might be enhanced by an upward movement of the tree line and might be more pronounced in heath than meadow soils due to a higher fungal activity. Climate warming arctic ecosystems tundra phosphorus Solution 31P NMR Earth and Related Environmental Sciences Geovetenskap och miljövetenskap
4	Seasonality of resource limitation of stream biofilm : Nutrient limitation of an arctic stream in northern Sweden Hauptmann, Demian January 2019 (has links) Arctic ecosystems are sensitive to climate change and this biome is experiencing accelerated warming. Climate change in the arctic is projected to further alter precipitation and temperature patterns, which may influence land-water interactions in the future. Such changes have the potential to affect aquatic biofilm communities (i.e., algae, bacteria, and fungi) that form the base of riverine food webs, yet are sensitive to changes in thermal and light regimes, and are potentially limited by macronutrients like carbon (C), nitrogen (N) and phosphorus (P). This study investigated the patterns of resource limitation for autotrophic and heterotrophic biofilms in the Arctic using nutrient diffusing substrata (NDS) in a river network in northern Sweden (Miellajokka). Continuous NDS deployments (March until September) in a birch forest stream were combined with a spatial survey of nutrient limitation in late summer across 20 sites that encompassed a variety of nutrient, light, and temperature combinations. Results show that nutrient limitation of autotrophic processes was common during summer, but also that light inhibited algal growth in early season, and that temperature accelerated rates of activity throughout the growing season. By comparison, heterotrophic processes were less influenced by temperature, unless experimentally supplied with N and P. Alongside persistent N limitation, co-limitation by macronutrients (NP: autotrophic and heterotrophic biofilm, or CNP: heterotrophic biofilm) dominated the overall pattern of limitation over time and space. However, results from the spatial survey suggested that the identity of the primary limiting nutrient can change from N to P, based on differences in chemistry that arise from varying catchment features. As arctic studies are often conducted at individual sites during summer, they may miss shifts in the drivers of stream productivity that arise from variable nutrient, temperature, and light regimes. This study attempted to capture those changes and identify conditions where one might expect to see transitions in the relative importance of physical and chemical factors that limit biofilm development. These results also highlight the challenge of identifying the single most important limiting nutrient (e.g., N versus P) in streams and rivers across the Arctic, as I found that both nutrients could play this role within a single, relatively small drainage system. Climate change arctic ecosystems nutrient limitation biofilm resource limitation Natural Sciences Naturvetenskap Earth and Related Environmental Sciences Geovetenskap och miljövetenskap
5	Citizen Science i Abisko : Hur ser förutsättningarna ut inom forskning i nordliga ekosystem? / Citizen Science in Abisko : What are the possibilities within arctic ecosystem research? Viippola, Lotta January 2015 (has links) In this paper I examine the possibilities for researchers in the field of climate change in the arctic ecosystems to collaborate with people of the common public for monitoring or to answer scientific questions, sometimes called Citizen Science. I have done this by focusing on the research community of Abisko, northern Sweden. I present a number of examples of possible projects that I have collected through literature, interviews and field work with researchers. Furthermore, I argue that Citizen Science projects might be a tool for nature guides in reaching adventurous visitors searching for more understanding of climate change, ecosystems, and who also want to contribute to real science. However, Citizen Science can also be a part of the democratization of a community when local people get engaged. Thus different aspects of Citizen Science are suitable for different target groups. arctic ecosystems Citizen Science Citizen Science models Community Science nature guiding arktiska ekosystem medborgarforskning frivilligbaserad forskning naturguidning
6	A History of Place: Using Phytolith Analysis to Discern Holocene Vegetation Change on Sanak Island, Western Gulf of Alaska Wilbur, Cricket C. January 2013 (has links) No description available. Archaeology Botany Climate Change Conservation Earth Ecology Environmental Science Freshwater Ecology Geology Limnology Native Americans Natural Resource Management Paleobotany Paleoclimate Science Paleoecology Plant Biology Pollen Paleolimnology Phytoliths Phytolith Analysis Aleutian Islands Sanak Island Western Gulf of Alaska Stomata Maritime tundra Grasses Dicotyldons Arctic ecosystems Climate change Paleoenvironmental reconstruction Holocene Lake sediment

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