Blue Carbon Sequestration Within Northern Florida Intertidal Wetlands - Response to Climate Change and Holocene Climate Variability

Blue carbon habitats such as salt marshes and mangroves are being recognized as aquatic critical zones with their highly efficient ability to store carbon and their susceptibility to recent climatic and anthropogenic changes. Increased temperatures and a decreased frequency of freeze events in northern Florida over the last few decades, for example, are facilitating the poleward encroachment of mangroves into salt marshes, which may lead to regional increases in carbon sequestration as mangroves store more carbon than salt marshes. To determine changes in carbon storage with respect to this recent mangrove expansion and to the development of these wetlands over the Holocene and Anthropocene, soil cores spanning 2-3 m in length were collected from wetlands at similar latitudes on the Atlantic and Gulf of Mexico coasts of northern Florida. Visually, the two coastlines are drastically different, with the Gulf coastline having taller trees and higher abundances of Rhizophora mangle (in addition to the most prevalent mangrove species on both coasts, Avicennia germanins) compared to the Atlantic coastline. The cores collected from both coasts are also substantially different, with the Atlantic coast cores being longer than the Gulf cores while also having a shorter extent of peats compared to the Gulf.

Initial results from the top 20 cm of the Atlantic coast cores suggest there is currently more carbon being stored within the transitional zone between marsh and mangroves compared to the individual marsh and mangrove zones. This larger storage in the transition is postulated to result from this zone being further from the waterway on which the mangrove zone fringes upon and from the short stature of the mangrove trees being able to capture more organic matter with the outgoing tides. Additionally, there appears to be a spike in both carbon content and lignin at approximately 1 m below the surface of the Atlantic coast transition core, suggesting there may have been a prior expansion of mangroves and that the increase in carbon associated with the expansion does get stored. Analyses on the Gulf cores, as well as the development of age models for both costs, will allow us to further determine how each coast differs with their carbon storage with both recent climate change and throughout their development over the mid- to late-Holocene.