Date of Award
2026
Degree Type
Thesis
Degree Name
Master of Science in Biological and Environmental Sciences (MSBES)
Department
Geosciences
First Advisor
Soni Pradhanag
Abstract
Coastal wetlands are typically considered greenhouse sinks, specifically playing an important role in the global carbon cycle (Chmura et al., 2003), but new studies have pointed to anthropogenic interference leading to the understanding that altered tidal salt marshes may also be producers of methane to the atmosphere, contributing to the greenhouse effect. Hydrologic alteration including due to sea level rise (SLR), peat subsidence, impounded water, and decreased accretion rate disruption can have negative effects on marsh biochemistry leading to potential changes in electron acceptor availability, redox gradient shifts, and microbial community structure within the environment. This research is intended to be a window into the microscale hydrological dynamics of salt marsh environments. We integrated a geophysical method utilizing electrical resistivity tomography (ERT) which, measures resistivity, with static chamber based greenhouse gas measurements to examine greenhouse gas fluxes at high tide in the semi-diurnal system of two Rhode Island salt marshes: one that has been hydrologically remediated, Canonchet Salt Marsh, and one state-protected site, Fox Hill Salt Marsh. Resistivity surveys offer salinity and water table positions, and can be used as a proxy for subsurface porewater relevant to methanogenesis conditions. Methane (CH4) and Carbon Dioxide (CO2) concentration data points were collected as short span time series along proximity transects from open water to inland during the initial hour of high tide a using a static chamber, alongside soil characterization including organic matter, soil moisture, porewater salinity, pH, and oxidation reduction potential of porewater. Results show spatial and site specific variability in fluxes and marsh platform characteristics. Methane flux was the highest near open water at both sites while 6 carbon dioxide measured concentration and flux was more pronounced at Inland Chambers, particularly at remediated Canonchet. Canonchet’s CH4 fluxes ranged from -0.43 to 17.92 µmol m-2 h-1 while Fox Hill’s ranged from 0.76 to 60.93 µmol m-2 h-1 Carbon dioxide fluxes at Canonchet ranged from 0.38 to 5.09 µmol m-2 s-1, and at Fox Hill from 1.17 to 6.24 µmol m-2 s-1. Back to back ERT surveys captured minor shifts in the top 2 meters of subsurface resistivity, providing context for observed gas dynamics. Our findings reveal that proximity to the open water, and platform characteristics are associated with variation in measured gas fluxes, specifically, Water Chambers having the most variability in gas flux where subsurface imagery shows the most complex and flow path emphasized structure.
Recommended Citation
Motta, Sophia, "EXPLORATORY INVESTIGATION OF GREENHOUSE GAS EMISSIONS IN A NATURAL AND RESTORED SALT MARSH" (2026). Open Access Master's Theses. Paper 2720.
https://digitalcommons.uri.edu/theses/2720