Date of Award

5-10-2026

Date Published

June 2026

Degree Type

Thesis

Degree Name

Master of Science (MS)

Department

Earth & Environmental Sciences

Advisor(s)

Aaron Mohammed

Keywords

Acid rock drainage;Hydrogeology;Numerical modeling;Permafrost;Rusting rivers

Abstract

Over 200+ remote streams across Alaska’s Brooks Range have been documented turning orange in recent years, with the onset of discoloration occurring in 2018 or 2019 for most streams. Initial analyses point to subsurface acid rock drainage (ARD) driven by permafrost thaw as a likely cause. Here, we develop a 2-dimensional coupled heat, water, and solute transport model of an ARD impacted site to assess thaw and solute transport dynamics in the system. Particular focus was on the impact that varying snowpack depths had on permafrost stability. Pyrite oxidation and solute transport dynamics were simulated using a simplified approach via a zero-order temperature and saturation dependent rate for sulfate production. Transport dynamics were examined for sensitivity to two factors: depth to the pyrite source and rate of production. Results show that under both high and low snow conditions, a deeper annual snowpack promotes greater permafrost thaw. The strongest thaw signals appear in 2018 and 2019, coinciding with the highest snow years and the onset of stream discoloration in the Brooks Range. Thaw is greater in the high snow model relative to the low snow model, with a talik forming in the high snow model in May of 2018 that is not present in the low snow model. Greater thaw drives an increase in upslope sulfate production, by allowing unsaturated, unfrozen conditions to persist at greater depths and for a longer duration. Transport simulations show good agreement between the documented onset of discoloration and measured sulfate concentrations when the pyrite source is available at shallow depths (≤ 2.3 m) and under relatively high sulfate production conditions. A relatively high production rate implies that ARD in the Brooks Range is likely microbially mediated. Future work is necessary to better constrain the complex biogeochemistry at play, the influence of preferential flow, and the distribution of pyrite within the system.

Access

Open Access

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Available for download on Thursday, June 17, 2027

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