First Advisor

Jennifer L. Morse

Term of Graduation

Summer 2026

Date of Publication

8-12-2026

Document Type

Thesis

Degree Name

Master of Science (M.S.) in Environmental Science and Management

Department

Environmental Science and Management

Language

English

Subjects

Greenhouse gas flux, Methane, Restoration, Wetland

Physical Description

1 online resource (xii, 57 pages)

Abstract

Coastal wetlands are biogeochemical hotspots that capture and transform carbon and nutrients. Wetland restoration is increasingly used as a climate mitigation strategy because of wetlands' capacity to sequester large amounts of carbon. However, low-salinity tidal marshes exhibit high variability in methane (CH4) emissions, which could partially offset carbon sequestration under certain conditions. Understanding the drivers of CH4 variability is crucial for restoration and conservation work. This project uses an observational research approach to assess the relationships between environmental factors and carbon dioxide (CO2) and CH4 soil gas fluxes in a restored low-salinity tidal marsh characterized by mixed emergent plant communities. The static chamber method was used to collect gas samples from fifteen gas collars installed in three areas of Wallooskee-Youngs Marsh, located in the Columbia River estuary in Oregon, USA. Samples were collected bi-weekly to monthly between June 2024 and September 2025. Relationships between each gas flux and environmental variables were modeled with boosted regression trees. CH4 fluxes varied seasonally and spatially, but there was also within-chamber variability. The CH4 boosted regression tree model explained 23% of variance in CH4 flux. Temperature and the height of standing water had the highest relative influence on the model. The predictors in the CO2 boosted regression tree model explained 27% of variability in CO2 flux, and temperature had the highest relative influence. High CH4 flux variability at the site underscores the importance of monitoring restored sites to accurately construct site carbon budgets. Capturing the full range of current CH4 variability in tidal wetlands is especially important because the data can serve as a baseline to compare to changes in greenhouse gas dynamics that result from sea level rise and increased temperature and atmospheric CO2 concentrations.

Rights

© 2026 Zoie Brauser

In Copyright. URI: http://rightsstatements.org/vocab/InC/1.0/ This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s).

Persistent Identifier

https://archives.pdx.edu/ds/psu/45119

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