Methane and carbon dioxide exchange in two Gulf of Mexico coastal wetland environments—Apalachicola and Barataria bays
Nicholas D Ward1, Thomas S Bianchi2, Chris L Osburn3, Eurico J. D'Sa4, Dong S Ko5, Ishan Joshi6, Ana Arellano2, Joanna D Kinsey7 and Diana Oviedo-Vargas8, (1)University of Florida, Geological Sciences, Ft Walton Beach, WA, United States, (2)University of Florida, Department of Geological Sciences, Ft Walton Beach, FL, United States, (3)North Carolina State University, (4)Louisiana State University, Baton Rouge, LA, United States, (5)Naval Research Laboratory, Stennis Space Center, MS, United States, (6)Louisiana State University, Department of Oceanography and Coastal Sciences, Baton Rouge, LA, United States, (7)North Carolina State University, Marine, Earth, and Atmospheric Sciences, Raleigh, NC, United States, (8)North Carolina State University Raleigh, Raleigh, NC, United States
Abstract:
The abundance of dissolved greenhouse gasses (e.g. CO
2 and CH
4) in coastal regions is closely linked to organic matter and gas fluxes from rivers and wetlands along with biological/photochemical processes. Here we present a spatial analysis of the abundance and isotopic composition of CO
2 and CH
4 in two unique bays in the Gulf of Mexico. Barataria Bay, LA, is a particle-dominated coastal marsh environment to the west of the Mississippi River Delta. Apalachicola Bay, FL, receives inputs both from marshes and DOM-rich black water rivers such as the Apalachicola and Carabelle Rivers. Measurements made along the intersection of these two rivers with the sea showed a positive correlation between salinity and CO
2 concentrations (R
2 = 0.99). For example, CO
2 values along the Carabelle River plume ranged from 320 to 3750 ppm across a salinity gradient of 0 to 30 psu. A lack of significant fluvial inputs in Barataria Bay resulted in less variability of CO
2 levels, which ranged from 420 to 940 ppm across a much smaller salinity gradient (roughly 23-30 psu). δ
13CO
2 values ranged from -12.0 to -20.0‰ in Apalachicola Bay and -13.7 to -22.2‰ in Barataria Bay.
CH4 concentrations in Apalachicola Bay ranged from 3-80 ppm. Maximal CH4 concentrations were observed along shallow floodplains near the drainage of the Apalachicola River (salinity = 0.5 psu). The isotopic composition of CH4 ranged from -81.7 to -45.5‰ in Apalachicola Bay with maximal values coinciding with the highest CH4 concentrations. δ13CH4 was positively correlated with CH4 concentrations in primarily marine waters (e.g. salinity = 29-31 psu; R2 = 0.98), but this trend was significant within the entire study boundaries (R2 = 0.20). CH4 concentrations were generally higher in the shallow marsh environment of Barataria Bay, ranging from 7 to 114 ppm. δ13CH4 ranged from -79.0 to -54.5‰ in Barataria Bay, and in some regions δ13CH4 was negatively correlated to CH4 concentration as is expected in a closed system where oxidation plays an important role is reducing CH4 levels. Results from this study illustrate the dynamic interface between coastal wetlands, rivers, and marine environments.
