CHARACTERIZATION AND QUANTIFICATION OF BLACK CARBON IN WETLAND SOILS OF BIG CYPRESS NATIONAL PRESERVE LOCATED IN SOUTHWEST FLORIDA

Black carbon is partially combusted organic matter which is typically resilient to chemical, thermal, and biotic degradation. Black carbon is produced either naturally in wildfire events or anthropogenically during the inefficient combustion of fossil fuels. The unique properties of black carbon promotes its participation in several environmental processes such as chemical sorption and long term carbon storage. This study focuses on the quantification and characterization of black carbon in the soil of Big Cypress National Preserve (BCNP), location, FL; black carbon is readily incorporated into subtropical wetland soils. Several 12-inch-long/1.5-inch-thick cores were extracted at major ecologic boundaries along Turner River in BCNP. These ecologic boundaries include the Pineland zone, Freshwater slough, Sawgrass plain zone, Mangrove zone, and the beachfront. Ten grams of dried sediment from each core were processed with a chemo-thermal oxidation method, where black carbon was quantified by mass. In this chemo-thermal method, HNO₃ was used to digest carbonate minerals and salts. Thermally labile organic matter, such as leaf litter, was removed from the sample by combustion at 375ºC for 18 hours. The isolated black carbon was imaged via scanning electron microscopy and characterized into charcoal or soot based on morphological appearance/size. Charcoal particles are often large (400-900 µm) and retain cell wall structure. Soot particles tend to be small (5-10 µm) and are semispherical particles. Based on quantitative and microscopy data, soot was abundantly present in the sawgrass plain soils; sawgrass plain soil contained approximately 13 wt. % black carbon. In contrast, pineland soils, were mostly enriched with charcoal particles; pineland soils contained approximately 7 wt. % black carbon. By further understanding these depositional trends, it may be possible to use black carbon as a proxy to better understand the geologic history of wildfires and climate change.