Methane Dynamics in St. Louis Bay, Mississippi

• Main Author: Roberts, Hannah Marie
• Format: Text
• Language: unknown
• Published: The Aquila Digital Community 2014
• Subjects: methane; estuary; mass balance; radon; cavity ring-down spectroscopy; Oceanography; Oceanography and Atmospheric Sciences and Meteorology; St. Louis; Orca
• Online Access: https://aquila.usm.edu/masters_theses/39; https://aquila.usm.edu/context/masters_theses/article/1050/viewcontent/Roberts_H_thesis.pdf

A method of dissolved methane analysis was developed utilizing cavity ring-down spectroscopy and headspace equilibration. Samples of 70 mL were collected in 140 mL plastic syringes and equilibrated with a methane free headspace. Reproducibility was high (i.e. 4% typical RSD), and samples were successfully measured in the low nanomolar to high micromolar range. During method development, multiple research cruises were undertaken in the northern Gulf of Mexico. Stations included the Orca Basin, the Deepwater Horizon site, and the surrounding area. The Deepwater Horizon site showed no continuing leakage from October 2010 to June 2013. Samples collected from the northern Gulf of Mexico and the Orca Basin were in agreement with previous published work. Using the new methodology, the methane dynamics of St. Louis Bay, MS was researched through a mass balance approach. The mass balance equations allowed simpler fluxes of the estuary to be measured, while complex fluxes were calculated. The total methane inventory of St. Louis Bay was found to vary between 900-7000 moles. The dominant sink was found to be air-sea flux, which varied between 4000-100,000 mol/day. River flux was found to be insignificant, ranging between 70-400 mol/day. The rate of air-sea flux prevented the river flux from affecting the interior of the estuary. Sediment flux remained as the only source of methane to the interior. Radon measurements were collected to estimate the magnitude of the sediment flux; however, concentrations were too low to be precisely measured.