COMMUNITY-ENGAGED AND EMPIRICALLY GROUNDED APPROACHES TO ISOTOPIC VARIABILITY AND AGRICULTURAL TRANSFORMATION

Philip L. Moffatt

doi:10.7273/000007429

Climate warming and variability are reshaping precipitation patterns, with topography influencing regional climate responses and affecting water resources, agriculture, and ecosystems. Stable isotopes of hydrogen (δ2H) and oxygen (δ18O) in precipitation offer insights into water cycle dynamics, but linking isotopic variability to meteorological processes remains challenging. At the same time, climate-driven agricultural challenges—such as aridification, drought vulnerability, and yield instability—reinforce reliance on industrial practices that degrade ecosystems. Regenerative agriculture (RA) is emerging as a regional alternative to address environmental degradation and improve grower economic stability. However, the transition to RA requires understanding the systemic barriers and drivers of change. This dissertation combines citizen science and community engagement to investigate (1) the meteorological processes driving daily precipitation isotope variability and (2) the transformation toward RA, including its challenges, opportunities, and support needs. We collaborated with a citizen-science precipitation network to collect daily samples at 18 locations in the Pacific Northwest, USA (n=2371). Using air mass trajectory data combined with meteorological and topographic variables, we applied Random Forest and Multiple Linear Regression to identify key drivers of isotopic variability, build a predictive model for daily precipitation isotopes, and generate spatiotemporal isoscapes to analyze patterns related to seasonal moisture transport pathways. The model explains 63% of daily isotopic variability, with key drivers differing between the windward and leeward sides of the Cascades: the windward side is influenced by the Pacific Ocean, while the leeward side experiences a rainshadow effect and a continental climate. Upwind rainout, parameterized through our novel methodology using air mass trajectories and temperature (surface and cloud top), play a dominant role in windward isotopic variability. Surface temperature and precipitation amount have stronger effects on δ²H in the leeward region, supporting sub-cloud evaporation as the primary driver. The model also provides a regionally dispersed δ2H lapse rate estimate of -33.5 0/00/km (-3.4 0/00/km δ18O), and trajectory cluster analysis reveals seasonal isotope patterns driven by northwesterly storm trajectories (30-50% of storms), which enhance Pacific moisture transport and draw colder air from the Canadian Rockies in winter. Additionally, isotopic indicators suggest that terrestrial moisture recycling plays a significant role in the leeward region. These findings create a novel isotopic dataset for the Pacific Northwest, providing high-resolution (4 km) daily precipitation isoscapes. Tools that enhance hydrologic modeling, improve tracer-aided model calibration, and refine assumptions about isotopic variability in a rainshadow setting. Community engagement shaped the development of research questions and a conceptual systems model to understand the agricultural-food system. We used a systems approach, starting with a model of the Intermountain West, USA, and refining it through regional models in three workshops held in Spokane, WA, Farmington, NM, and Alamosa, CO. Agricultural-food system leaders in these workshops assessed the current and future states of RA. Using a guided transformation framework, we examined stressors driving growers toward RA, as well as barriers and opportunities for transformation. In the Intermountain West, RA transformation is driven by small, transdisciplinary teams. Grower peer-to-peer networks are central to RA transformation and require investment and collaboration with USDA researchers and land-grant universities. Structured participatory processes are key to fostering learning and building community capacity. County and University Extension staff, with their long-standing relationships in local communities, can become trained facilitators, supporting sustained transformations. Key barriers to scalability include a lack of medium-scale infrastructure for processing and distribution, while increasing consumer interest in soil health and food quality highlights the need for peer-reviewed research to identify practices that optimize product quality. Our findings demonstrate how a community-engaged, systems approach can identify gaps and practical steps for RA transformation, emphasizing the importance of training facilitators and formalizing their roles within regional peer-learning networks to catalyze RA transformation and overcome barriers.

COMMUNITY-ENGAGED AND EMPIRICALLY GROUNDED APPROACHES TO ISOTOPIC VARIABILITY AND AGRICULTURAL TRANSFORMATION

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