Scholarship & Research
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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 Hydrologic-carbon cycle linkages in a subalpine catchment(Montana State University - Bozeman, College of Agriculture, 2008) Riveros-Iregui, Diego Andres; Chairperson, Graduate Committee: Brian L. McGlynn.The feedbacks between the water and the carbon cycles are of critical importance to global carbon balances. Forests and forest soils in northern latitudes are important carbon pools because of their potential as sinks for atmospheric carbon. However there are significant unknowns related to the effects of hydrologic variability, mountainous terrain, and landscape heterogeneity in controlling soil carbon dioxide (CO 2) efflux. Mountainous terrain imposes large spatial heterogeneity in the biophysical controls of soil CO 2 production and efflux, including soil temperature, soil water content, vegetation, substrate, and soil physical properties. Strong spatial and temporal variability in biophysical controls can lead to large heterogeneity in the magnitude of soil CO 2 efflux. This dissertation research investigates the relationships between these biophysical controls and the resultant CO 2 efflux across the soil-atmosphere interface in a 393-ha subalpine catchment of the Northern Rocky Mountains. This study incorporates knowledge gained through field observations (2 growing seasons) at multiple locations distributed across the watershed, and a range of empirical analytical techniques including a modeling approach to estimate point to catchment scale soil CO 2 efflux. Variability in soil CO 2 efflux was strongly related to topography and landscape structure. Riparian meadows were found to have the highest rates of cumulative soil CO 2 efflux across the entire watershed, likely due to more accumulation of soil water than upland sites, leading to enhanced plant and microbial respiration in riparian meadows. Landscape context and appreciation of organized heterogeneity are critical to estimation and interpretation of watershed-scale rates of soil CO 2 efflux and for up-scaling plot or point measurements of soil CO 2 efflux to larger spatial scales. This dissertation provides examples and suggestions for corroboration and integration of soil and canopy level CO 2 fluxes and for process understanding of spatiotemporal variability of biogeochemical processes driven by the hydrologic cycle.