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Irrigation ditches as novel intermittent stream networks that provide energetic subsidies to terrestrial ecosystems via aquatic insect emergence
(Montana State University - Bozeman, College of Letters & Science, 2024) Heili, Nathaniel Maxwell; Chairperson, Graduate Committee: Wyatt F. Cross
Non-perennial streams dominate fluvial networks, comprising over half of lotic ecosystems globally. Although little attention has been paid to these systems relative to those that are perennial, perhaps even less is known about the ecology of artificial intermittent streams. In irrigated river valleys, ditches comprise a substantial proportion of surface water networks, but little is known about their relative contributions to lotic habitat, freshwater biodiversity, and ecosystem processes. Because ditches are abundant and permeate arid floodplains, they create new opportunities for cross-ecosystem subsidies through emergence of adult aquatic insects. Here, we mapped the extent of an irrigation ditch network relative to natural surface waters in the Gallatin River Valley, Montana, USA. We also quantified the magnitude, composition, and phenology of aquatic insect emergence in ditches throughout a full irrigation season and compare emergence to nearby natural streams in the valley. We found that non-perennial streams, both natural and artificial, dominated the surface-water network, representing over 70% of total length. Irrigation ditches also constituted 37% and 23% of total length and surface area of all waterbodies in the valley, respectively. Insect emergence production from ditches averaged 32.0 mg m -2 d -1 and exceeded fluxes from nearby natural streams, which contained more classically sensitive taxa (i.e., Ephemeroptera, Trichoptera, and Plecoptera). Ditches varied in water temperature, substrate size, and flow permanence, leading to distinct emergence timing, species composition, and magnitudes of biomass flux. One of the study ditches dried early because of more 'junior' water rights, but this ditch provided the largest emergence subsidy, including a pulse of dipteran emergence at the onset of flow cessation. Annual production from intermittent ditches was ~6 g m -2 y -1 and was comparable to estimates from natural perennial streams. Although our study focused on one river valley of the western US, results suggest that these ecosystems contribute broadly to lotic habitat, heterogeneity, and cross-ecosystem subsidies via aquatic insect emergence. Given increasing demand for water and changes to flow regimes and water management driven by climate change, additional study is needed on these novel and underappreciated artificial ecosystems.
Fertility and reproductive health decisions connected to climate change and adaptation in Greenland
(Montana State University - Bozeman, The Graduate School, 2024) Peterson, Malory Kaye; Chairperson, Graduate Committee: Elizabeth Rink; This is a manuscript style paper that includes co-authored chapters.
The capacity for Kalaallit, the Inuit people of Greenland, to adapt to the effects of climate change will depend on sociodemographic change, population distribution, and existing health inequities in the country. Reproduction in Greenland is influenced by connection to place and access to natural resources, factors that will vary with climate adaptation. Given existing fertility and reproductive health disparities among Kalaallit women, there is a compelling reason to explore how climate change effects and adaptation might influence fertility decisions and population dynamics in Greenland. Rooted in the principles of community based participatory research, this exploratory and comparative study investigated the social, environmental, and economic resources that affect fertility decisions for Kalaallit in Greenland. The research presented contextualizes drivers of fertility decisions within Greenland's climate adaptation policy options and presents strategies to guide health studies in Greenland with principles of community based participatory research. Interviews were conducted with 35 reproductive-aged (18-49 years) men and women and 26 interviews with policymakers and key stakeholders in two communities about climate adaptation, natural resources, economic development, and fertility and reproductive health. Interviews were analyzed using constructivist grounded theory in collaboration with a Kalaallit community research partner. Results indicate that improving community capacity to address existing housing, education, and economic inequities is critical to supporting fertility and reproductive health, irrespective of climate change impacts. Participants observed climate change effects and expressed positive attitudes about Kalaallit ability to adapt and capitalize on benefits of climate change. Evidence from this study indicates that addressing development disparities in Greenland may immediately support fertility and reproductive health for Kalaallit people and facilitate equitable climate adaptation.
The effects of guiding climate change education through a social justice lens
(Montana State University - Bozeman, College of Letters & Science, 2023) Arnold, John Francis; Chairperson, Graduate Committee: C. John Graves
Climate change is one of the largest environmental and justice issues facing our world. Many young people are listening to the science and taking action, but many more are not. This project addressed climate change through exploring consequences on society, addressing public health, and impacts on societal infrastructure and stability. The social inequality of climate impacts was highlighted throughout to better engage students. Baseline, survey data was collected before we addressed climate change. After learning about public health concerns, students took the survey again and completed a short reflection. Students finished the study, after learning about impacts on societal infrastructure by taking a third survey, completing a second reflection, and with an interview. Results varied due to inconsistent participation throughout the study. Many students demonstrated an increase in understanding of climate change, but evidence to demonstrate their depth of understanding examples of people most disproportionately affected by climate change was inconsistent. Finally, students underreported eco-anxiety in survey results compared to interview results.
An interpreter's guide to filmmaking
(Montana State University - Bozeman, College of Arts & Architecture, 2022) Andrus, Olivia Fay; Chairperson, Graduate Committee: Dennis Aig
Politically divisive topics like climate change are notoriously difficult to effectively communicate to the public. Using a different communication approach called interpretation within the filmmaking process, we can bridge the gap current climate change films have today with their audience. Interpretation means "a mission-based communication process that forges emotional and intellectual connections between the interests of the audience and the meanings inherent in the resource," according to the National Association of Interpretation (What is interpretation?). In this paper I will analyze the history behind interpretation and the methodology in implementing this communication style within films. Through the works of various filmmakers such as, My Octopus Teacher (2020), Ice on Fire (2019), and Ocean Souls (2020), my own experience creating an interpretive short film, The Dolphin Dilemma, this paper will discuss how specific interpretive communication methods can take politically divisive subjects, like climate change and more effectively communicate science within documentaries.
Reconstructing large herbivore abundance and environmental interactions in postglacial North America
(Montana State University - Bozeman, College of Letters & Science, 2023) Wendt IV, John Arthur Frederic; Chairperson, Graduate Committee: David B. McWethy; This is a manuscript style paper that includes co-authored chapters.
Large herbivores drive critical ecological processes, yet their long-term dynamics and effects are poorly understood due to the limitations of existing paleoherbivore proxies. To address these shortcomings, long-term records of paleoherbivores were constructed by (i) applying new analytical techniques to existing bison fossil datasets; and (ii) examining fecal steroid data that characterize temporal changes in ungulate abundance and community composition. These paleoherbivore reconstructions were analyzed in relation to their environmental contexts to better understand herbivore-ecosystem interactions through time in three separate studies: First, spatiotemporal changes in postglacial bison distribution and abundance in North America were examined by summarizing fossil bison observations. Bison observations were compared with simulated climate variables in a distribution modeling framework to project probable bison distributions in 1000-year intervals from the Last Glacial Maximum to present in light of changing climatic drivers over time. Since the Bolling-Allerod Interstadial (14.7-12.9 ka) the geographic distribution of bison is primarily explained by seasonal temperature patterns. Second, Holocene records of bison abundance were compared to paleofire reconstructions spanning the midcontinental moisture gradient to determine the relative dominance of herbivores and fire as biomass consumers. Bison dominated biomass consumption in dry settings whereas fire dominated consumption in wetter environments. Historical distributions of herbivory and burning resemble those of Sub-Saharan Africa, suggesting a degree of generality in the feedbacks and interactions that regulate long-term consumer dynamics. Third, the utility of fecal steroids in lake sediments for reconstructing past herbivore abundance and identity was tested by (i) characterizing the fecal steroid signatures of key North American ungulates, (ii) comparing these signatures with multiproxy data preserved in lake sediments from the Yellowstone Northern Range, and (iii) comparing influxes of fecal steroids over time to historical records of ungulate biomass and use. Bison and/or elk were abundant at Buffalo Ford Lake over the past c. 2300 years. Ungulate densities in the watershed were highest in the early 20 th century and likely contributed to decreases in forage taxa and possibly increased lake production. These results demonstrate long-term ecological impacts of herbivores and highlight opportunities for continued development of paleoherbivore proxies.
Climate change at the air-water interface affects giant salmonfly (Pteronarcys californica) emergence timing and adult lifespan
(Montana State University - Bozeman, College of Letters & Science, 2023) Roche, Alzada Lois; Chairperson, Graduate Committee: Lindsey K. Albertson
Aquatic invertebrates experience complex temperature regimes throughout their life history, especially during the vulnerable life stage transition from aquatic to terrestrial habitats. When climate warming interacts with snowmelt in high elevation systems, it creates a novel set of conditions in which spring water temperatures remain within a narrow range from year-to-year while summer water and air temperatures rise. Giant salmonflies (Pteronarcys californica) depend on spring water temperature cues to time their large, synchronous emergence in early summer, but it is unknown how variable temperatures after this springtime cue affect life-history traits. We experimentally tested how changes in temperature in the 6 weeks before and after emergence affect emergence timing, emergence success, and adult lifespans. We found that the timing of emergence was 2.8 days earlier with each degree of warming during the weeks preceding emergence. However, there was no evidence that emergence success was affected by higher water temperature within our test temperature range (13-23°C). In the terrestrial adult stage, adult lifespans were shortened by increased air temperatures, especially when water temperatures during the aquatic juvenile stage had also been increased. The predicted lifespan was almost five times longer at the coldest air and water temperature combination than at the warmest (28 vs. 6 days). The shortest lifespans observed (3 days) are not likely to prevent successful reproduction, given that salmonflies can mate and oviposit within days of emergence. Still, because salmonflies can oviposit repeatedly for up to 80% of their lifespan, shortened lifespans may reduce total egg production and thus fitness. Our results indicate that rising water and air temperatures will impact not only the life history of the insects, but also the organisms in the riparian zone that rely on salmonfly emergence by altering the timing, magnitude, and duration of the nutrients provided by these large-bodied aquatic insects.
A forest entombed in ice: a unique record of mid-Holocene climate and ecosystem change in the northern Rocky Mountains, USA
(Montana State University - Bozeman, College of Letters & Science, 2022) Stahle, Daniel Kent; Chairperson, Graduate Committee: David McWethy; This is a manuscript style paper that includes co-authored chapters.
Across the high alpine of the northern Rocky Mountains small vestiges of perennial ice have endured for thousands of years. These ice patches reside hundreds of meters above modern treeline, with some persisting through mid-Holocene warmth and others establishing at the onset of a cooler period that began around 5,000-5,500 years BP. Recent warming-driven melting at the margins of one ice patch high on the Beartooth Plateau of northern Wyoming exposed over 30 intact mature whitebark pine (Pinus albicaulis) tree boles, all > 25 cm in diameter. We extracted cross-sectional samples from the stems of 27 preserved logs, and radiocarbon dated annual growth rings from 11 of these trees, anchoring the chronology to a date range spanning 5,947 to 5,436 years BP + or - 51.3 years. From this fossil wood chronology, we developed estimates of warm-season, annual, and biennial average temperatures for upper-elevation treeline during the mid-Holocene. To identify the predominant climate-growth relationships of the subfossil trees, we sampled live whitebark pine trees growing at an adjacent treeline site approximately 120 m lower in elevation. Temperature was found to be the major driver of variability in tree growth at the modern treeline location, with trees producing narrower (wider) rings during periods of cooler (warmer) growing season temperatures. Using linear and non-linear transfer functions based upon the stable statistical relationship between modern tree growth and temperature, we reconstructed past temperature estimates from the ice patch subfossil ring-width chronology. Our results provide estimates of mid-Holocene warm-season (and biennial) average temperatures ranging from 5.7-6.5 °C (-0.44-0.26 °C) respectively. A multi-century regional cooling trend beginning around 5,650 years BP resulted in average temperatures declining below a warm-season (biennial) critical threshold of ~5.8 °C (-0.34 °C), likely leading to the eventual death of the whitebark pine stand and subsequent formation of the ice-patch. This high-quality paleo-ecological dataset reveals a major shift in the alpine and forest ecotone on the Beartooth Plateau following the mid-Holocene warm period and offers further insight on the thermal limits of whitebark pine trees in the Greater Yellowstone Ecosystem.
Reconstructing the age, provenance, and thermal history of the basal Great Valley forearc basin, northern California
(Montana State University - Bozeman, College of Letters & Science, 2022) Romero, Mariah Christina; Chairperson, Graduate Committee: Devon A. Orme; This is a manuscript style paper that includes co-authored chapters.
Forearc basins are important sediment archives of Earth's geologic history, preserving a record of the erosional history of magmatic arcs, subduction zone dynamics, and climatic changes over millions of years. However, questions remain about the early developmental stages of a forearc basin, including the relationship between a forearc basin and its underlying basement, and thermal histories of exhumed, ancient forearc basins that preserve extensive sedimentary successions. This dissertation examines the basement underlying the Great Valley Forearc basin, the upper Coast Range Ophiolite and ophiolitic breccia, and Great Valley Group strata using sedimentology, sandstone modal petrography, geochronology, thermochronology, and cathodoluminescence, photoluminescence, and Raman spectroscopy. Chapter 1 evaluates Upper Jurassic-Lower Cretaceous strata and underlying Coast Range Ophiolite in the northwestern Sacramento basin to constrain the timing of initial deposition within the Great Valley Forearc, identify potential provenances, and provide a tectonic model for the early development of the forearc. Detrital zircon and petrographic data from a localized breccia interval directly underlying basal forearc strata indicate provenance from the Coast Range Ophiolite and North American margin, with formation ongoing by ~151 Ma. Detrital zircon data from Upper Jurassic-Lower Cretaceous strata yield maximum depositional ages between ~165-141 Ma and are interpreted to reflect diachronous deposition in segmented depocenters during the early development of the forearc that was proximal to the Sierra Nevada-Klamath magmatic. Chapter 2 utilizes apatite and zircon (U-Th)/He thermochronology to constrain the thermal history of the Sacramento basin, which includes documenting minimum burial temperatures for the western outcrop belt to have exceeded 85°C with cooling in the Cenozoic, whereas the subsurface strata of the central-eastern parts of the basin reached ~180-200°C with cooling in the middle-Late Cretaceous and Cenozoic. Chapter 3 examines gabbro and granitic basement rock underlying the Great Valley Forearc, along with several zircon U-Pb age standards, to demonstrate that radiation damage in zircon can non-destructively be estimated using cathodoluminescence spectroscopy, a complementary technique to photoluminescence and Raman spectroscopy. This dissertation highlights the significance of studying forearc basins along with their accompanying basement component, as the linked relationship is crucial for understanding how forearc basins evolve.
Investigating the ability of arbuscular mycorrhizal fungi to mitigate the negative effects of warming and drought on native perennial forbs
(Montana State University - Bozeman, College of Letters & Science, 2022) Eggers, Jessica Avery; Chairperson, Graduate Committee: Laura Burkle; This is a manuscript style paper that includes co-authored chapters.
The ability of arbuscular mycorrhizal fungi (AMF) to mitigate the negative effects of warming and drought on plant hosts is known for crop species but is poorly understood for native, perennial forbs. Examining the indirect influence of AMF on forbs' responses to these stressors will provide a more complete understanding of how native forbs will be affected by climate change. In an experimental greenhouse study, we inoculated two native forb species (Achillea millefolium and Linum lewisii) with three separate AMF species (Rhizophagus clarus, Claroideoglomus etunicatum, and Gigaspora rosea), then exposed plants, including an uninoculated control treatment, to varying degrees of drought and heat stress in a factorial design. We tested the effects of warming or drought treatments on plants' physical, floral, phenological, and physiological traits, including biomass, height, floral abundance, flower size, first date of flowering, floral scent, and photosynthetic performance. For both forbs, AMF ameliorated the negative effects of drought and warming on plant survival and vegetative growth, but the magnitude of effect was specific to the forb species, climate treatment, and AMF inoculant. AMF also produced changes in forb phenology, floral scent (volatile organic compounds), and flowering success and duration, which have broad implications for plant-pollinator interactions and the links between belowground and aboveground symbioses. Together, these results indicate that AMF can assist native forbs in surviving, growing, and reproducing in a warmer and drier climate.
Physiological traits and stress tolerances of three high-elevation pine species
(Montana State University - Bozeman, College of Letters & Science, 2023) Wasteneys, Chloe Elizabeth; Chairperson, Graduate Committee: Danielle Ulrich
The increasing frequency and intensity of drought and heat events are increasing forest mortality rates worldwide. To improve restoration and management effort effectiveness for at- risk tree species and to accurately predict how these species will respond to future climates, the physiological mechanisms of seedling establishment and survival need to be fully understood. Using a greenhouse common garden approach, we compared the physiological traits and stress tolerances of three high-elevation five-needle pine species, Pinus albicaulis (PIAL), P. flexilis (PIFL), and P. longaeva (PILO). We measured a suite of physiological response curves to determine photosynthetic capacity, high-light tolerance, drought tolerance, and heat tolerance traits. We compared these traits among the three species (Q1), among three different ages of PIAL seedlings (2-, 3-, and 5-years-old; Q2), and among seven families of 2-year-old PIAL originating from different locations (Q3). Among species (Q1), only one heat tolerance trait (Tcrit, the temperature at which minimal fluorescence begins to increase) significantly differed and increased from PILO to PIFL to PIAL, suggesting that PIAL had greater heat tolerance than PIFL and PILO. Among PIAL ages (Q2), two drought tolerance traits, saturated water content (SWC) and leaf mass per area (LMA), and two heat tolerance traits, Tcrit and T50_EL (temperature that results in a 50% increase in electrolyte leakage), significantly differed among ages. SWC decreased, LMA and Tcrit increased, and T50_EL partially increased with increasing age, suggesting that older PIAL seedlings may be more drought and heat tolerant than younger PIAL seedlings. Among PIAL families (Q3), no traits significantly differed. However, we observed four significant correlations between our measured traits and growing season mean temperature and vapor pressure deficit of the seven PIAL families. Families from relatively cooler, wetter locations tended to have greater high-light tolerance and greater heat tolerance (based on T50_EL) while families from relatively warmer, drier locations tended to have greater heat tolerances (based on Tcrit and T50 measured with chlorophyll fluorescence). Together, these findings improve our understanding of physiological mechanisms underlying seedling establishment and our ability to predict how these species may be affected by future climates.

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