Semester of Graduation

August 2019

Degree

Master of Science (MS)

Department

Oceanography and Coastal Science

Document Type

Thesis

Abstract

Tidal marshes have been recognized for providing a number of important ecological services including soil carbon sequestration. However, the loss of tidal marsh habitat due to climate change and anthropogenic stressors exposes previously stored soil organic carbon (SOC) to oxidation. The vulnerability of SOC to oxidation depends on its chemical stability and environmental conditions limiting decomposition. Labile organic carbon (LC), decomposes quickly unless abiotic conditions limit decomposition. Recalcitrant organic carbon (RC) decomposes slower and is stored for longer time periods. Predicting long-term storage of SOC is complicated by the potential for multiple SOC sources, differences in chemical stability, and variation in environmental conditions that may preserve chemically LC. To increase understanding of soil carbon dynamics in tidal marshes, SOC sources and chemical stabilities were assessed along an estuarine salinity gradient, and along a time series of marsh creation. Additionally, relationships between labile and recalcitrant carbon, vegetation characteristics, and environmental factors (i.e. elevation, mineral sediment) were examined. Soil cores were collected in tidal freshwater (n = 4), brackish (n = 3), and salt (n = 4) marshes in Barataria Bay, Louisiana, and in six created dredge sediment marshes across a 32-year chronosequence, and a natural reference marsh (n = 6) in Sabine National Wildlife Refuge in southwestern Louisiana. To examine the source (algal, C4, or C3 plant) of total organic and refractory SOC, δ13C analyses were used. Acid hydrolysis digestion was used to fractionate the SOC into ‘labile’ and ‘refractory’ components. Across all marshes an average of 73% of SOC was recalcitrant indicating it is chemically stable. Across the salinity gradient, LC, RC and SOC densities were highest in the freshwater marshes. LC and RC stocks increased with marsh age in the created marshes, but the RC stock increased two times faster. LC and RC accumulation rates were not significantly different between created marshes of different ages and the natural reference marsh. Overall this study illustrates that a majority of SOC in coastal marshes of Louisiana is derived from local vegetation and is chemically stable therefore more likely to contribute to long term carbon storage.

Committee Chair

Quirk, Tracy

Available for download on Friday, June 19, 2020

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