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Item Measuring methane emissions from American bison (Bison bison L.) using eddy covariance(Montana State University - Bozeman, College of Agriculture, 2019) Cook, Adam Anderson; Chairperson, Graduate Committee: Paul C. StoyAmerican bison (Bison bison L.) have recovered from the brink of extinction over the past century. Bison offer potential environmental benefits as they re-occupy their native range, but many specific impacts of bison reintroduction are not well understood. Methane emissions are known to be a major climate impact of ruminants, but few measurements for bison exist due to challenges caused by their mobile grazing habits and safety issues associated with direct measurements. Here, we measure the methane and carbon dioxide fluxes from a bison herd on winter range using the eddy covariance technique. Methane emissions were negligible (mean = 0.0024 micromole m -2 s -1, SD = 0.0102 micromole m -2 s -1) before and after bison grazed in the area sampled by the eddy covariance flux footprint with the exception of a single spike possibly attributable to thawing soil or the presence of white-tailed deer (Odocoileus virginianus Z.). Methane fluxes when bison were present in the study area averaged 0.041 micromole m -2 s -1 (SD = 0.046 micromole m -2 s -1), similar to previous measurements over sheep and cattle pastures, but with little diurnal pattern due to a lack of consistent bison movement habits over the course of each day. An eddy covariance flux footprint analysis coupled to bison location estimates from automated camera images calculated methane flux with a median of 56.5 micromole s -1 per animal and a mean of 91.6 micromole s-1 per animal, approximately 50 and 75% of established emission rates for range cattle, respectively. Eddy covariance measurements are a promising way to measure methane and carbon dioxide flux from large ruminants on native range and we recommend comparisons amongst alternate grazing systems to help identify management strategies that are cognizant of climate.Item Land-atmosphere exchange of carbon and energy at a tropical peat swamp forest in Sarawak, Malaysia(Montana State University - Bozeman, College of Agriculture, 2017) Tang Che Ing, Angela; Chairperson, Graduate Committee: Paul C. Stoy; Paul C. Stoy, Kevin K. Musin, Edward B. Aeries, Joseph Wenceslaus, Mariko Shimizu, Ryuichi Hirata and Lulie Melling were co-authors of the article, 'The role of biophysical drivers in controlling the variability of net ecosystem CO 2 exchange in a tropical peat forest in Sarawak, Malaysian Borneo' submitted to the journal 'Global change biology' which is contained within this thesis.; Paul C. Stoy, Kevin K. Musin, Edward B. Aeries, Joseph Wenceslaus, Mariko Shimizu, Ryuichi Hirata and Lulie Melling were co-authors of the article, 'The exchange of water and energy between a tropical peat forest and the atmosphere: seasonal trends and comparison against global tropical rainforests' submitted to the journal 'Geophysical research letters' which is contained within this thesis.; Paul C. Stoy, Kevin K. Musin, Edward B. Aeries, Joseph Wenceslaus, Mariko Shimizu, Ryuichi Hirata and Lulie Melling were co-authors of the article, 'Eddy covariance measurements of methane flux at a tropical peat forest in Sarawak, Malaysian Borneo' submitted to the journal 'Agricultural and forest meteorology' which is contained within this thesis.Tropical peatlands comprise 11% of the global peat area of ca. 400 Mha and are estimated to store about 89 Gt of carbon (C). However, considerable uncertainties remain about their present role in global C cycle as interannual ecosystem-scale measurements of undisturbed tropical peat forests have not been measured to date. Hence, an eddy covariance tower was instrumented in a tropical peat forest in Sarawak, Malaysia over four years from 2011 to 2014. We found that the forest was a net source of CO 2 to the atmosphere during every year of measurement. The inter-annual variation in net ecosystem CO 2 exchange (NEE) was largely modulated by the variation in gross primary production (GPP), which was jointly controlled by vapor pressure deficit (VPD) and leaf area index (LAI) in addition to photosynthetically active photon flux density (PPFD). Greater reduction of GPP in 2011 and 2012, are likely attributed to the relative low atmospheric transmission due to massive peat fires in Indonesia. Similarly, no analysis to our knowledge has measured whole-ecosystem methane (CH 4) flux from a tropical peat forested wetland to date despite their importance to global CH 4 budget. The two-month average of C-CH 4 flux measurements, on the order of 0.024 g C-CH 4 m -2 d -1, suggests that tropical peat forests are not likely to be disproportionally important to global CH 4 flux. Results demonstrate a limited ability for simple models to capture the variability in the diurnal pattern of CH 4 efflux, but also consistent responses to soil moisture, water table height, and precipitation over daily to weekly time scales. The sensible heat flux (H) and latent heat flux (LE) and their ratio (the Bowen ratio, Bo) at the study ecosystem were relatively invariant compared to other tropical rainforests. The average daily LE across the calendar year tended to be higher at MY-MLM (11 MJ m -2 day -1) than most other tropical rainforest ecosystems in the FLUXNET2015 database. Results demonstrate important differences in the seasonal patterns in water and energy exchange in tropical rainforest ecosystems that need to be captured by models to understand how ongoing changes in tropical rainforest extent impact the global climate system.Item Microbially mediated biogeochemical cycles in polar ice covered lakes(Montana State University - Bozeman, College of Agriculture, 2016) Michaud, Alexander Bryce Olson; Chairperson, Graduate Committee: John C. Priscu; Trista J. Vick-Majors, Mark L. Skidmore and John C. Priscu were co-authors of the article, 'Field testing of a clean, hot water drill used for access to subglacial aquatic environments' submitted to the journal 'Antarctic science' which is contained within this dissertation.; Mark L. Skidmore, Andrew C. Mitchell, Trista J. Vick-Majors, John C. Priscu, Carlo Barbante, Clara Turetta and Will vanGelder were co-authors of the article, 'Solute sources and geochemical processes in subglacial Lake Whillans, west Antarctica' in the journal 'Geology' which is contained within this dissertation.; John E. Dore, Trista J. Vick-Majors, Mark L. Skidmore and John C. Priscu were co-authors of the article, 'Microbial methane transformations beneath the west Antarctic ice sheet' submitted to the journal 'Science' which is contained within this dissertation.; This dissertation contains one article of which Alexander Bryce Olson Michaud is not the main author.Lakes are important sites for globally-relevant biogeochemical cycles mediated by microorganisms. In the Arctic, seasonally ice covered thermokarst lakes are a large component in Earth's carbon cycle due to their methane emissions from organic carbon degradation. In the Antarctic, over 400 unexplored lakes exist beneath the Antarctic ice sheet with unknown biogeochemical contributions to the Earth system. This dissertation seeks to investigate the biogeochemical role of microorganisms in the lake habitat and how they interact with the seasonal and permanent ice covers of lakes in polar environments. Microbiologically clean hot water drilling was used to access a subglacial lake beneath Antarctica's ice to collect, for the first time, intact sediment and water samples. Laboratory experiments on Arctic and Antarctic, seasonally and perennially, respectively, ice covered lakes were used to investigate the impact of lake ice freezing regimes on microorganisms. My results show that subglacial lake sediments beneath the West Antarctic Ice Sheet contain solute ratios that suggest relict marine sediments were deposited during previous interglacial periods. Microbial activity overprints the marine geochemical signature to produce fluxes of ions into the Subglacial Lake Whillans water column, which ultimately drains to the Southern Ocean. Microbial activity in Subglacial Lake Whillans is partially fueled by biologically-formed methane diffusing from below our deepest collected (~38 cm) subglacial sediment samples. The ice above Subglacial Lake Whillans appears to be an important source of molecular oxygen for microorganisms to drive oxidative physiologies. My experimental evidence shows microorganisms incorporate into lake ice cover to, potentially, avoid increasing stressors from progressive lake ice freezing. Taken together, the results from this dissertation reinforce the hypothesis that subglacial environments beneath the Antarctic ice sheet are habitats for life. Further, the microorganisms in subglacial lakes participate in globally-relevant biogeochemical cycles. Here, I extend the extent of the biosphere and show sediments at the base of ice sheets are an active component of the Earth system.Item Effect of permafrost thaw on methane and carbon dioxide exchange in two western Alaska peatlands(Montana State University - Bozeman, College of Agriculture, 2013) Johnston, Carmel Eliise; Chairperson, Graduate Committee: Stephanie A. Ewing; Stephanie A. Ewing, Jennifer W. Harden, Paul C. Stoy, Ruth K. Varner, Kimberly P. Wickland, Joshua Koch, Christopher Fuller and Mark T. Jorgenson were co-authors of the article, '2.0 effect of permafrost thaw on CO 2 and CH 4 exchange in a western Alaska peatland chronosequence' submitted to the journal 'Environmental research letters' which is contained within this thesis.; Stephanie A. Ewing, Merritt R. Turetsky, Jennifer W. Harden, A. David McGuire and Miriam Jones were co-authors of the article, '3.0 effect of recent permafrost thaw on the spatial distribution of CO 2 and CH 4 exchange in a western Alaska peatland' submitted to the journal 'Environmental research letters' which is contained within this thesis.Methane (CH 4) causes about 20% of greenhouse gas radiative forcing despite its relatively short lifetime (~10 y) and low concentration (1800 ppb) in the atmosphere. Wetlands are the largest natural source of CH 4, amounting to 22% of CH 4 production globally, with emission of CH 4-C by both diffusion and ebullition pathways. Permafrost peatlands store about 10% of permafrost C and 5% of global belowground C; hence CH 4- C emission with peatland permafrost thaw is of concern. We quantified temporal and spatial aspects of CH 4 and CO 2 emissions from northern peatlands using two approaches: (1) a ~1000 y thaw chronosequence in remote western Alaska (Innoko Flats Wildlife Refuge; May-September, 2011), and (2) lateral transects in intermediate age (~20-500 y) collapse-scar bog features at a well-instrumented site near Fairbanks, Alaska (Alaska Peatland Experiment (APEX)/Bonanza Creek Long Term Experimental Research site; June-September, 2012). At Innoko Flats, peak CH 4 production was observed in features aged 30-590 y since thaw, which had warmer soils than younger sites and shallower water tables than older sites. Average surface flux at these 30-590 y sites (+2.52 ± 0.98 mg CH 4-C m -2 hr -1) was greater than estimated ebullition flux (0.13 ± 0.05 mg CH 4-C m -2 hr -1) based on an observed rate of 0.78 ± 0.33 mL m -2 hr -1. Net ecosystem exchange of CO 2-C (NEE) did not differ among chronosequence features, and offset CH 4-C emissions by a factor of 2 to 400 when considered as 100-y global warming potential. At APEX, bogs reflecting <100 y since most recent thaw showed high variability in CH 4 exchange, but rates were generally consistent with levels at the Innoko 30-590 y sites (mean of 5.42 ± 1.16 mg CH 4-C m -2 hr -1). APEX bogs showed greater balance between CH 4-C efflux and CO 2-C influx, with CH 4-C fluxes offsetting 80-140% of NEE during the growing season when considered as 100-y global warming potential. We argue that CH 4 contributes most significantly to post-thaw C loss over timescales of decades to centuries in these northern peatlands.