Author Type

Graduate Student

Date of Award

Spring 5-8-2026

Document Type

Dissertation

Publication Status

Version of Record

Submission Date

May 2026

Department

Geosciences

College Granting Degree

Charles E. Schmidt College of Science

Department Granting Degree

Geosciences

Degree Name

Doctor of Philosophy (PhD)

Thesis/Dissertation Advisor [Chair]

Xavier Comas

Abstract

Peatlands store about a third of the global soil carbon pool and are among the most important natural sources of biogenic greenhouse gases, including methane (CH4) and carbon dioxide (CO2). While biogenic gas production in peatlands has been studied extensively over the last few decades, the physical controls that regulate how these gases accumulate within the soil matrix and their influence on gas dynamics as they get released to the atmosphere still remain uncertain. Most studies investigating biogenic gas dynamics in peatlands have inferred in-situ gas distribution either exclusively from measurements of gas flux releases, or have focused on individual peatland systems without considering variability in peat physical properties. For example, the role of peat matrix structure in controlling gas accumulation, migration, and release dynamics remains poorly constrained, especially across peatlands that differ in climate, vegetation, and internal physical properties.

This dissertation combines a series of laboratory and field-based investigations across boreal, subtropical, and tropical peatlands to examine how peat physical structure influences in-situ gas accumulation and gas release. To better understand these controls, this research used a combination of minimally invasive hydrogeophysical methods. These methods primarily focused on ground-penetrating radar (GPR), constrained with gas traps, time-lapse cameras, gas chromatography, moisture probes, porosity measurements, hydraulic conductivity analysis, and peat geochemical characterization. These methods were applied both across controlled peat monolith experiments and natural peatland systems in the field in order to evaluate gas behavior at multiple spatial and temporal scales.

In the first study, controlled laboratory conditions within peat monoliths showed that biogenic gas does not accumulate uniformly through peat profiles, but by developing discrete gas-rich zones (hot spots) associated with differences in the internal peat structure. Time-lapse GPR measurements were able to monitor these gas-rich zones through time and showed that structurally favorable portions of the peat matrix act as preferential gas storage locations. In the second study, field investigations in boreal peatlands of Maine showed that gas accumulation and release vary strongly near pool-margin environments and are influenced by peat stratigraphy, hydrologic interconnectivity, and connected permeable sediment pathways that alter gas migration and retention. In the third study, comparative laboratory experiments using a series of peat monoliths collected from Maine, Florida, Colombia, and Brunei demonstrated that peat matrix properties exert a major control on gas storage, CH4 flux, CO2 flux and inferred in-situ gas production. These results further showed that some peat types exhibit a strong relation between in-situ gas storage and gas release, whereas others retain gas longer to release it more intermittently.

The results presented throughout these three studies show that peat matrix structure is a primary control on biogenic gas dynamics across peatland environments and that gas flux measurements alone cannot fully explain in-situ gas storage within peat profile. By integrating hydrogeophysical observations with direct gas measurements across multiple peat types and observational scales, this dissertation provides insight into how peat physical structure influences the transfer of stored gas into atmospheric release across contrasting peat-forming systems.

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