Comparing Carbon Percentage and Isotopic Composition in Mangrove Soils Using Bulk Analysis and Fine Fraction Methods

Session: 37th Annual Undergraduate Research Exhibition Sponsored by Sigma Gamma Epsilon (Posters)

Presenting Author:

Estefania Rodriguez Morillo

Authors:

Rodriguez Morillo, Estefania¹, Aguilar Enriquez, Beatriz Alejandra², Smoak, Joseph M³, Breithaupt, Josh L⁴, Rosenheim, Brad E⁵

(1) College of Arts and Sciences, University of South Florida, Saint Petersburg, Florida, USA, (2) College of Marine Science, University of South Florida, St Petersburg, Florida, USA, (3) School of Geosciences, University of South Florida, St Petersburg, Florida, USA, (4) Coastal & Marine Laboratory, Florida State University, St Teresa, Florida, USA, (5) College of Marine Science, University of South Florida, St Petersburg, Florida, USA,

Abstract:

Mangrove ecosystems are known for their ability to sequester and store atmospheric carbon in their peat soils. As a result, mangrove restoration or creation has become a natural solution to climate change.  Restored and created mangroves especially contain a variety of lithological units, including sand, peat, and organic-rich mud, each with distinct physical and biogeochemical properties. Depending on the research objective, different analytical methods are used to quantify and characterize organic carbon in mangrove soils, ranging from bulk sample analysis for general organic carbon stock estimation to fine-fraction (<63 µm) analysis for radiocarbon dating. As such, the workload and complexity of comparative research between restored/created and natural mangroves can be considerable. This study aims to answer the question of whether there is a difference in organic carbon percentage and stable isotopic signature between the fine and bulk methods. To do this assessment, samples were collected from Tampa Bay and Naples (U.S.A.) and separated into three lithological units described in the field: peat, organic-rich mud, and sand. Samples were acidified with 1N HCl to remove the inorganic carbon fraction and analyzed using an Elemental Analyzer to determine organic carbon percentage and stable carbon isotopic signature. The results demonstrated that the <63 µm method yielded higher carbon percentage values compared to the bulk method across all three lithological units. In the <63 µm method, most of the sample is being filtered out, and only a finer organic carbon-rich fraction of the sediment is assessed for carbon content and isotopic composition. In contrast, the bulk method analyzes the entire sample after acid treatment, resulting in a more heterogeneous sample and, often to lower carbon percentage quantities. This study contributes to a better understanding of effective methods and techniques for optimizing the work done in the laboratory estimating blue carbon in mangrove ecosystems. Further research can help refine these methods to more efficiently enhance our understanding of this aquatic ecosystem and its role in the carbon cycle.