Date of Award

2025-05-01

Degree Name

Doctor of Philosophy

Department

Environmental Science and Engineering

Advisor(s)

Craig Tweedie

Abstract

TThe Arctic is warming rapidly, driving widespread environmental change across coastal landscapes, including permafrost thaw, shoreline erosion, and shifts in sediment and carbon dynamics, pose growing challenges for predicting carbon cycling and climate feedbacks. This dissertation investigates the spatiotemporal variability of erosion, decomposition, and nearshore turbidity in Elson Lagoon, Alaska (1955–2023), to better understand how carbon, nitrogen, and sediment are mobilized, transformed, and potentially emitted as greenhouse gases in Arctic coastal systems. Chapter 2 presents a high-resolution analysis of shoreline change and erosion-driven material fluxes spanning nearly seven decades. Drawing on 795 soil data points, airborne LiDAR, and five shoreline time steps, sediment, carbon, and nitrogen export were quantified across diverse geomorphic surfaces and bluff heights. Fluxes varied by surface type, with older drained lake basins exhibiting the highest per-meter carbon fluxes, while widespread polygonised tundra contributed the greatest total flux due to spatial extent. Bluff height further influenced fluxes, with erosion rates more than doubling in tall bluffs (>3 m) over the study period, while shorter bluffs exhibited comparatively stable behavior. Climate trends, particularly shifting wind patterns and warming, may have contributed to the slight decline in erosion observed during the most recent decade (2014 to 2023). Mean annual fluxes across Elson Lagoon were approximately 1,200 kg sediment m⁻¹ yr⁻¹, 130 kg C m⁻¹ yr⁻¹, and 6.6 kg N m⁻¹ yr⁻¹. Sensitivity analyses revealed that simplified models ignore geomorphic variability can overestimate cumulative carbon loss by 9–11%, underscoring the need to incorporate fine-scale bluff morphology and surface-specific soil properties into Arctic coastal erosion models. Chapter 3 focuses on better understanding greenhouse gas emissions from eroding coastal permafrost. Using laboratory incubations, field data, and temperature-dependent modeling, CO₂ fluxes were estimated for eroding soils in Elson Lagoon. We tested the effects of temperature, soil depth, salinity, and seawater exposure on SOC loss, finding that seawater exposure increased carbon loss by up to threefold compared to permafrost alone. Similarly, temperature and soil depth significantly influenced decomposition, while salinity had no consistent effect. Sensitivity analyses revealed that simplified models which ignore temperature sensitivity and/or distinguish between treatments can overestimate CO2 by 7–11%. Models yielded annual CO₂ flux estimates of 11.33–12.61 kg CO₂-C m⁻¹ yr⁻¹, or 441–491 Mg CO₂-C yr⁻¹ across 39 km of the Elson Lagoon shoreline, from 1955 to 2023. These and other findings underscore the significant and underrepresented role of Arctic coastal permafrost in regional and global carbon budgets. Chapter 4 examines how changing weather dynamics are amplifying sediment delivery and reshaping nearshore dynamics. To understand how turbidity reflects environmental changes, the spatiotemporal variability of total suspended solids (TSS) was assessed using field sampling and machine learning. Water samples collected along a nearshore transect revealed strong spatial gradients in TSS, with elevated concentrations closest to shore. Random forest models trained on wind components, precipitation, and distance from shore outperformed other approaches (R² = 0.97), identifying sustained easterly and westerly winds as dominant drivers of turbidity, with precipitation acting as a proxy for episodic riverine sediment inputs. Long-term turbidity predictions (2000–2023) revealed increasing variability and frequency of high-turbidity events, likely driven by intensified storm activity and precipitation extremes. TSS was positively correlated with pCO₂ and correlated with chlorophyll-a, suggesting that sediment disturbance may enhance microbial and primary productivity, potentially fueling carbon remineralization. As projected shifting weather patterns may amplify sediment and organic carbon fluxes, it becomes increasingly important to understand the physical and biogeochemical coupling of Arctic nearshore systems. Together, these chapters provide a spatially and temporally resolved framework for understanding the mobilization, transformation, and fate of permafrost carbon in a rapidly changing Arctic coastal system.

Language

en

Provenance

Received from ProQuest

File Size

179 p.

File Format

application/pdf

Rights Holder

Sasha Victoria Peterson

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