Theses and Dissertations at Montana State University (MSU)
Permanent URI for this communityhttps://scholarworks.montana.edu/handle/1/732
Browse
3 results
Search Results
Item Microbial community composition and the transformation of dissolved organic matter in supraglacial environments(Montana State University - Bozeman, College of Agriculture, 2016) Smith, Heidi Jean; Chairperson, Graduate Committee: Christine Foreman; Markus Dieser and Christine Foreman were co-authors of the article, 'Organic matter shapes community compositon in glacial environments' submitted to the journal 'International Society for Microbial Ecology (ISME)' which is contained within this dissertation.; Rachel Foster, Diane McKnight, John Lisle, Daniela Tienken, Marcel Kuypers and Christine Foreman were co-authors of the article, 'Microbial formation of labile glacial organic carbon' submitted to the journal 'Nature geosciences' which is contained within this dissertation.; Michelle Tigges, Juliana D'Andrilli, Albert Parker, Brian Bothner and Christine Foreman were co-authors of the article, 'Supraglacial dissolved organic matter: a labile but unsustainable carbon source' submitted to the journal 'Limnology and oceanography' which is contained within this dissertation.; Amber Schmidt, Rachel Foster, Sten Littmann, Marcel Kuypers and Christine Foreman were co-authors of the article, 'Biofilms on glacial surfaces: hotspots for biological activity' submitted to the journal 'Nature biofilms and microbiomes' which is contained within this dissertation.Relating microbial community composition to ecosystem function is a fundamental goal in ecological analyses, with physico-chemical parameters largely controlling this relationship. This investigation aimed to elucidate the impact of physicochemical factors on biodiversity in glacial habitats, with an emphasis on dissolved organic matter (DOM). DOM is a complex mixture of organic compounds and the primary substrate for microbial activity. Considering the variety of DOM sources in aquatic systems, little is still known about the biological release and bio-transformation of microbially-derived, autochthonous DOM. Continental Antarctica, typically lacking terrestrial carbon inputs, is largely governed by autochthonous DOM, making it an ideal site to investigate microbial biodiversity and the microbial formation of DOM. Different glacial ecosystems were selected, with a strong focus on the supraglacial Cotton Glacier stream, to investigate: i) the microbial diversity and underlying environmental factors governing biogeographical trends, ii) the contribution of exuded carbon to the DOM pool and subsequent heterotrophic uptake/transformation, and iii) how biofilm influences nutrient cycling in supraglacial environments. Findings from this study highlight distinct microbial assemblages in meltwater streams/sediments, ice, snow, and cryoconite across local and regional geographic scales. Specifically, nutrient availability and DOM quality influenced trends in microbial diversity. In situ DOM exudation was sufficiently high to support bacterial carbon demands, while the spatial organization of microorganisms in biofilms was advantageous in transferring nutrients between community members. Furthermore, compared to other more recalcitrant and chemically heterogeneous DOM sources, the highly labile supraglacial DOM was unable to sustain the same magnitude of microbial metabolism. The present study revealed dynamic carbon cycling in supraglacial environments, mediated by the tight coupling between in situ carbon fixation, DOM exudation, and rapid consumption. Statistical analyses failed to show the impact of any physical parameters on community composition. However, data from the Greenland Ice Sheet imply that interactions between community composition and meltwater dynamics are susceptible to environmental changes, shifting ecosystem function and microbial communities, with unforeseen consequences to downstream environments. A multi-scale approach contributed to a better understanding of microbial biogeography, carbon cycling, and cellular spatial organization in glacial surface environments.Item Ecosystem dynamics and temporal variations in a microbially dominated, coastal antarctic lake(Montana State University - Bozeman, College of Agriculture, 2009) Dieser, Markus; Chairperson, Graduate Committee: John C. Priscu; Christine Foreman (co-chair)This study investigated the microbial ecology of Pony Lake, Antarctica. The main objectives of this research were to 1) characterize physicochemical parameters in Pony Lake during the transition from ice covered to ice free, 2) highlight seasonal and inter-seasonal alterations in lake parameters, 3) relate the physicochemical conditions in the ice and water column to microbial processes and community structure, 4) characterize the effects of phototransformation of dissolved organic matter (DOM) on its bioavailability to bacteria, and 5) demonstrate the role of carotenoid pigments in protecting cells against environmental stresses. Also included are results from three McMurdo Dry Valley lakes on the survivability of microbes encapsulated within the lake ice covers. The results of this study highlight the sensitivity of Antarctic environments and the close coupling of environmental conditions and biological processes. Inter-seasonal differences in weather conditions and snow accumulation strongly affected the physicochemistry of this lacustrine system. Biological processes were closely tied to the physicochemical lake conditions. As a consequence planktonic abundances, production rates, and community structure evolved distinctly in each year. Bacterial production was regulated by the quality of DOM. Whereas nutrient availability appeared to play a minor role in eutrophic Pony Lake water, it became more critical for microbial communities found within the ice column of Antarctic lakes. Especially in the ice cover of the McMurdo Dry Valley lakes, enhanced microbial diversity and survivability was associated with particles (nutrient enriched micro-zones) within an otherwise ultra-oligotrophic habitat. In Pony Lake ice, microbial activity and community structure differed with respect to different strata within the ice column, induced by freeze-concentration of solutes, bioavailability of DOM, and oxygen gradients. A comparison of carotenoid pigmented and non-pigmented heterotrophic bacteria indicated that pigmentation provides enhanced resistance to environmental stresses such as freeze-thaw cycles or solar radiation. Collectively, the Pony Lake data demonstrated that microorganisms that persist throughout the year were able to survive much more severe conditions while entrapped within the ice compared to those observed in the lake water during summer months. Further, this study contributes to a better understanding of the biogeochemical carbon cycle in a microbially dominated system.Item Diffuse reflectance spectroscopy for the characterization of calcareous glacial till soils from north central Montana(Montana State University - Bozeman, College of Agriculture, 2006) Steward, Genevieve Christine; Chairperson, Graduate Committee: David Brown.Diffuse reflective spectroscopy (DRS) is a method of soil carbon (C) quantification. In this study, the Vis-NIR (350 - 2500 nm) and MIR (2500-25000 nm) regions were evaluated to determine respective predictive accuracies of soil organic and inorganic carbon (SOC and SIC, respectively). The dataset included 315 soil samples of glacial till origin, obtained from six independent farm sites within the Golden Triangle region of Montana, with depths ranging from 0-100 cm. For Vis-NIR analysis, Local vs. Regional vs. Global calibration sets were compared by six-fold cross validation by site of C predictions developed by Partial Least Squares (PLS) regression and Boosted Regression Trees (BRT). First derivative spectral data was used along with four preparation methods: (i) field moist and (ii) dry cores, (iii) 2-mm sieved ("Sieved") and (iv) milled samples (<200-um, "Milled") were used to evaluate the potential application to in-situ analysis. The most accurate SOC predictions were from Milled samples using a Local calibration set. SOC predictions were a result of SOM electronic absorptions within the visible region.