Date of Award
2026
Degree Type
Thesis
Degree Name
Master of Science in Biological and Environmental Sciences (MSBES)
Department
Geosciences
First Advisor
Dawn Cardace
Second Advisor
Serena Moseman-Valtierra
Abstract
Methane (CH4) emissions from continental serpentinizing systems represent a significant component of Earth’s carbon cycling. Despite increasing recognition of serpentinite-hosted water-rock interactions as a source of trace gases, standardized field methodologies for quantifying trace gas flux from groundwater wells and similar subsurface conduits remain limited. This study addresses that gap by evaluating the reliability and replicability of three chamber-based sampling methods for measuring gas flux in serpentinite-hosted groundwater systems accessed by groundwater monitoring wells. Field measurements were conducted at the Coast Range Ophiolite Microbial Observatory (CROMO) within the McLaughlin Natural Reserve in Lower Lake, California, a site characterized by active serpentinization. Methane flux was quantified from six groundwater wells using three collection approaches: (1) a custom-designed PVC well cap (5.1 cm × 5.1 cm in diameter), (2) a modified LI-COR Smart Chamber (34 cm height × 32 cm in diameter), and (3) a Tall external Chamber (205 cm in height × 30 cm in diameter). Real-time gas concentrations (CH4, CO2, and H2O) were measured using a LI-COR 7810 Trace Gas Analyzer during three repeated chamber deployments under both pre-purge and post-purge conditions at each well of interest in June of 2025.
This study tests the null hypothesis that mean methane flux does not differ among methods, against alternative hypotheses predicting that mean fluxes differ for each design and influences reported measurements. Statistical comparisons among methods were performed using analysis of variance (ANOVA) and non-parametric tests such as Kruskal Wallis and Dunn's Post-hoc. Additionally, coefficients of variation (CV%) were calculated to evaluate precision and repeatability of methane flux measurements within each chamber method.
Across all monitoring wells, the Tall External Chamber demonstrated the highest precision, with a mean coefficient of variation (CV%) of approximately 65% and most values clustering between 30-65% (Table 13). In contrast, the Smart Chamber exhibited moderate to poor precision (mean CV = 234%), while the Well Cap method showed the greatest instability, with highly skewed variability driven by extreme outliers (CV% up to 4360%).
Comparing these methodologies in an active serpentinizing location, this research aims to identify a standardized approach for groundwater well gas flux measurements. Reliable and reproducible measurement methods are essential for improving estimates of methane flux from serpentinizing environments and other subsurface systems. These methods can be applied to trace gas monitoring at legacy oil and gas infrastructure. Where abandoned, orphaned, and undocumented wells can serve as long-term sources for degassing. Emissions from these aging and forgotten wells remain poorly constrained, and standardized field methodologies are critical for improving regional and global methane inventories.
Recommended Citation
Stetson, Madison J., "COMPARATIVE ASSESSMENTS OF METHANE FLUX MEASUREMENT TECHNIQUES IN SERPENTINITE-INFLUENCED GROUNDWATER WELLS" (2026). Open Access Master's Theses. Paper 2744.
https://digitalcommons.uri.edu/theses/2744