Quantifying 'Blue Carbon' Exports from Salt Marshes Using Radium Isotopes

Description/Abstract/Artist Statement

In this study, we seek to determine if there is significant groundwater flushing within a salt marsh environment and to what degree this groundwater contributes to carbon exports from the salt marsh to the ocean. We also seek to categorize whether inorganic carbon in the water is exported as alkalinity or dissolved carbon dioxide and, as a result, how long we can expect it to remain sequestered in the ocean. Data collection occurred at The Nature Conservancy’s Brownsville Preserve on the Eastern Shore of Virginia. We collected samples of surface water from the onsite stream and of groundwater from four sites near the stream for radium and carbon analysis. We also gathered segments of a sediment core from six depths at one of the sites for radium and thorium analysis. Using the Radium Delayed Coincedence Counter (RaDeCC) method, we measured the concentration of radioactive radium-223 and radium-224 isotopes in the samples in order to quantify the water flux through the groundwater system and estimate the rate of flushing of radium compared to the background rate of radium generation from its parent material, thorium. In the scope of this study, radium and thorium were in secular equilibrium in every sample collected, indicating no significant groundwater flushing. However, this does not preclude the occurrence of flushing at other depths or locations not sampled. Also discussed are the abundance of inorganic carbon in the system and its speciation, whether it contributes alkalinity to the waters or exists primarily as dissolved carbon dioxide, and any spatial variations in this pattern.

Presenting Author Name/s

Andrew Lindgren

Faculty Advisor/Mentor

Joseph Tamborski, David Burdige

Faculty Advisor/Mentor Department

Ocean and Earth Sciences Department

College Affiliation

College of Sciences

Presentation Type

Poster

Disciplines

Geochemistry | Geology | Hydrology

Session Title

Poster Session

Location

Learning Commons Lobby @ Perry Library

Start Date

3-25-2023 8:30 AM

End Date

3-25-2023 10:00 AM

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Mar 25th, 8:30 AM Mar 25th, 10:00 AM

Quantifying 'Blue Carbon' Exports from Salt Marshes Using Radium Isotopes

Learning Commons Lobby @ Perry Library

In this study, we seek to determine if there is significant groundwater flushing within a salt marsh environment and to what degree this groundwater contributes to carbon exports from the salt marsh to the ocean. We also seek to categorize whether inorganic carbon in the water is exported as alkalinity or dissolved carbon dioxide and, as a result, how long we can expect it to remain sequestered in the ocean. Data collection occurred at The Nature Conservancy’s Brownsville Preserve on the Eastern Shore of Virginia. We collected samples of surface water from the onsite stream and of groundwater from four sites near the stream for radium and carbon analysis. We also gathered segments of a sediment core from six depths at one of the sites for radium and thorium analysis. Using the Radium Delayed Coincedence Counter (RaDeCC) method, we measured the concentration of radioactive radium-223 and radium-224 isotopes in the samples in order to quantify the water flux through the groundwater system and estimate the rate of flushing of radium compared to the background rate of radium generation from its parent material, thorium. In the scope of this study, radium and thorium were in secular equilibrium in every sample collected, indicating no significant groundwater flushing. However, this does not preclude the occurrence of flushing at other depths or locations not sampled. Also discussed are the abundance of inorganic carbon in the system and its speciation, whether it contributes alkalinity to the waters or exists primarily as dissolved carbon dioxide, and any spatial variations in this pattern.