Document Type



Doctor of Philosophy (PhD)


Biomedical Sciences

First Advisor's Name

James W. Fourqurean

First Advisor's Committee Title

Committee chair

Second Advisor's Name

William T. Anderson

Second Advisor's Committee Title

Committee member

Third Advisor's Name

Ronald Benner

Third Advisor's Committee Title

Committee member

Fourth Advisor's Name

John S. Kominoski

Fourth Advisor's Committee Title

Committee member

Fifth Advisor's Name

Steven F. Oberbauer

Fifth Advisor's Committee Title

Committee member


Blue Carbon, decomposition, CO2

Date of Defense



Coastal marine sediments have recently been identified as globally important stocks of organic carbon (Corg) that, if compromised, could significantly exacerbate global greenhouse gas emissions. While resource managers and policy makers are eager to incorporate this ecosystem service into seagrass ecosystem valuation frameworks, similar to those already in existence for terrestrial forests, there has been insufficient information regarding how environmental conditions and seagrass ecology control carbon storage. These include the influence of the seagrass to the production and preservation of soil organic matter, the fate of stored carbon following conversion of coastal wetlands, and the interactions between organic and inorganic carbon cycling. This dissertation intends to to understand the drivers of Corg storage and preservation to better prioritize and evaluate the worth of seagrasses to large scale carbon cycles and greenhouse gas mitigation planning.

Long-term experiments and thorough field surveys reveal that seagrasses are not categorically necessary nor sufficient for long-term Corg storage. Soil Corg stocks as well as their recalcitrance and breakdown rates are all correlated with sediment grain size, where muddy, fine sediments have higher Corg stocks that are less likely to breakdown. Sediment grain size can be influenced by the presence of seagrasses at some sites, likely where the leaf canopy can modify local hydrology enough to create a depositional environmental that wouldn’t otherwise exist. However, similar depositional environments that collect and store Corg can be obtained through local geomorphological features and natural hydrology, independent of benthic flora. This distinction has important implications on how soil C is managed to continue its preservation.

The relation between seagrass Corg and CO2 can be blurred by calcification and carbonate dissolution processes that occur concurrently, and have direct but antagonistic effects on CO2. Carbonate processes are dependent on local environmental factors, though augmented by biological processes, thus the ability of carbonate processes to interfere with seagrass Corg storage and loss is limited to geographic areas where processes can occur. Warm, shallow waters, like those in Florida Bay, encourage calcification, though the magnitude of soil inorganic and organic carbon interaction can vary locally as well.

Seagrasses are declining globally thus additional ecosystem value via greenhouse gas mitigation could greatly benefit conservation efforts. To make conservation efforts worthwhile to greenhouse gas mitigation, these findings help to consider and prioritize sites where risk and impact of Corg lost is more severe.





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