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Item The effect of permafrost thaw and geologic substrate on dissolved organic carbon mobilization and transformation in northern streams(Montana State University - Bozeman, College of Agriculture, 2019) Wologo, Ethan Andrew; Chairperson, Graduate Committee: Stephanie A. Ewing; Sarah Shakil, Scott Zolkos, Sadie Textor, Stephanie Ewing, Jane Klassen, Robert G.M. Spencer, David C. Podgorski, Suzanne E. Tank, Michelle A. Baker, Jonathan A. O'Donnell, Kimberly P. Wickland, Sydney S.W. Foks, Jay P. Zarnetske, Joseph Lee-Cullin, Futing Liu, Yuanhe Yang, Pirkko Kortelainen, Jaana Kolehmainen, Joshua F. Dean, Jorien E. Vonk, Robert M. Holmes, Gilles Pinay, Michaela M. Powell, Jansen Howe, Rebecca Frei and Benjamin W. Abbott were co-authors of the article, 'No evience of dissolved organic matter priming in permafrost stream networks: a circumpolar assessment' submitted to the journal 'Global biogeochemical cycles' which is contained within this thesis.; Stephanie Ewing, Jonathan A. O'Donnell, Jim Paces, Rob Striegl, Duane Froese and Joshua Koch were co-authors of the article, 'Groundwater connection and doc transport in the Yukon River Basin: uranium and strontium isotopes in permafrost catchments' submitted to the journal 'Global biogeochemical cycles' which is contained within this thesis.Permafrost landscapes exhibit unique hydrology that is linked both chemically and physically to nutrient cycling and geochemical processes. Permafrost thaw is expected to result in a positive feedback to Earth's climate system through carbon release to the atmosphere; this potential demands better understanding of hydrologic pathways in permafrost landscapes in the face of global change. The work that follows is divided into two main bodies of research that explore both carbon dynamics and isotope geochemistry of river waters draining permafrost catchments in the Yukon River Basin (YRB). The first study uses in-vitro incubations of stream water from seven permafrost regions to investigate how biolabile carbon additions (acetate) and inorganic nutrients (nitrogen and phosphorus) 'prime' water-column dissolved organic carbon (DOC) decomposition. No priming effect from biolabile carbon addition was evident through changes in DOC concentrations or compositional transformations, but consumption of added acetate was correlated with ambient nutrient concentrations. Sites with fine-textured, ice-rich substrate and proximal thermokarst features had higher ambient DOC and nutrient concentrations, and consequently the fastest rates of acetate consumption. We conclude that the fate of biolabile DOC released from degrading permafrost will depend largely on inorganic nutrient availability in receiving waterbodies. The second part of this thesis focuses on hydrology of intermediate-sized catchments in the YRB. We evaluate uranium isotope activity ratios ([234U/238U]) as tracers of groundwater-surface water connection in thawing permafrost landscapes. Streams draining loess-mantled areas had [234U/238U] values moderately increased relative to meteoric values. Streams draining low-order catchments with rocky substrate and surface disturbance exhibit dramatically increased [234U/238U] values, consistent with groundwater connection. In addition, we observed higher DOC concentrations both in areas influenced by recent thaw and where flow is restricted by ice-rich silt. The transformation of northern stream chemistry will likely continue as northern permafrost environents warm, with greatest resilience of ground ice in loess-blanketed areas not subject to thermal erosion by groundwater. As subsurface storage expands and groundwater exchange intensifies, ecosystems within and connected to northern streams will also be transformed, with implications for resource managers concerned with fish and wildlife management in these systems.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 Surface-atmosphere exchange of carbon dioxide, water, and heat across a dryland wheat-fallow rotation(Montana State University - Bozeman, College of Agriculture, 2015) Vick, Elizabeth Segourney K.; Chairperson, Graduate Committee: Paul C. Stoy; Paul C. Stoy was co-author of the article, 'The influence of dryland agriculture wheat-fallow rotation on the exchange of carbon, water, and heat with the atmosphere' submitted to the journal 'Journal of agriculture, ecosystems and environment' which is contained within this thesis.Summerfallow - the practice of keeping a field out of production during the growing season - is a common practice in dryland wheat (Triticum aestivum L.) cropping systems, including those of Montana. It is currently unknown how seasonal patterns of carbon dioxide, water, and heat flux between ecosystems and the atmosphere differ between fallow and wheat. This study quantifies the impact of dryland wheat vs. chemical fallow agricultural management practices on these important surface-atmosphere exchanges using the eddy covariance method across a winter wheat - spring wheat - fallow rotation in the Judith Basin, MT. I used a suite of meteorological sensors to measure relative humidity, air temperature, soil moisture, wind speed and direction, incident and reflected shortwave radiation, upwelling and downwelling longwave radiation, crop height, and soil heat flux to further quantify the impacts of this cropping sequence on biophysical attributes of the land surface and to model turbulent fluxes. Both wheat fields were carbon sinks on the order of 110 to 205 g C m -2 during the April to September study periods of 2013 and 2014, while the fallow field was a carbon source to the atmosphere on the order of 135 g C m -2 during the April to September study period of 2014. Evapotranspiration (ET) was over 100 mm greater in a spring wheat field than in a simultaneously measured fallow field during the 2014 study period, and modeled maximum daily atmospheric boundary layer height was up to 800 m higher in fallow compared to spring wheat. Results demonstrate that fallow has a detrimental impact to soil carbon resources yet is less water intensive, with consequences for regional climate via its impacts on atmospheric boundary layer development and global climate via its carbon metabolism.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.