Using cyclic voltammetry to better characterize sulfur cycling as a pathway for enhanced carbon preservation in mangrove habitats

Coastal vegetated habitats (CVHs), such as mangrove forests, are significant carbon sinks able to store carbon on timescales of decades to millennia via uptake and burial of atmospheric carbon dioxide (CO2) as organic carbon. Unfortunately, CVHs are shrinking due to coastal development, urbanization, and sea level rise, in many cases turning them into net sources of CO2. Therefore, proper restoration and management of CVHs are seen as important climate change mitigation strategies. Currently, however, we still do not have a good understanding of the processes that lead to carbon preservation in these habitats. One potential mechanism is organic matter sulfurization. Organic matter sulfurization is the process whereby sulfides react and bind with organic matter compounds making them less available for carbon remineralization. Therefore, elevated concentrations of sulfide in mangrove environments are likely indicative of locations where OM sulfurization occurs, ultimately enabling us to identify probable 'hotspots' of OM sulfurization. Sulfide concentrations can be highly variable in CVHs over tidal and diurnal cycles, limiting the traditional geochemical methods to extract and quantify sulfide. Here, we combine direct measurements of sulfide concentration with in situ cyclic voltammetry to derive a high resolution time series of sulfide, oxygen, and aqueous elemental sulfur concentrations over tidal cycles in several mangrove habitats in the Rookery Bay National Estuarine Research Reserve (Florida, USA). Preliminary sulfide screening tests using silver films reveal sulfide concentrations are maximal in rehabilitated mangrove areas as well as the top 3-4 cm of sediment in pristine mangrove areas. These results indicate sulfurization may be strongly impacted by mangrove restoration efforts.This project seeks to identify the conditions under which active OM sulfurization may occur in various mangrove habitats, improving our understanding of the importance of sulfur cycling in CVHs as a pathway to enhanced carbon preservation.