Mangroves are among the most significant organic carbon sinks on Earth. However, the drivers of mangrove carbon remain poorly understood due to the lack of data on organic carbon across different types of estuaries. In this study, boosted regression tree (BRT) was used to relate Total Organic Carbon (TOC) concentrations to explanatory variables describing water quality, nutrients, and meteorological characteristics of four estuaries in southwest Florida, USA. TOC concentrations were primarily enhanced by low salinity, with elevated NO₂