CARBON SEQUESTRATION IN FLORIDA KARST SPRING RUN SEDIMENTS

Organic sediments deposited in anaerobic settings such as wetlands and lakes represent a significant global carbon sink. Organic carbon sequestration rates in sediment deposits along spring runs downstream of karst spring vents have remained largely unstudied. Many of Florida’s rivers are fed by karst spring systems and thus carbon sequestration in spring run sediments may be an important component of the regional carbon cycle. Carbon sequestration rates were measured in 13 Florida spring runs including near Hart, Otter, Fanning, Manatee, Ichetucknee, Gilchrist Blue, Salt, Silver Glen, DeLeon, Alexander, Volusia Blue, Gemini, and Wekiwa springs, just downstream of headspring vents. Bulk density and organic carbon content of sediments were used to calculate organic carbon density. Age control was provided using AMS radiocarbon dating of bulk organic sediments and, separately, plant macrofossils where available. Radiocarbon data indicated that most of the spring runs accumulated organic-rich sediment for hundreds to thousands of years. Average measured carbon sequestration rates ranged from 1.23 to 36.13 g C m^-2 yr^-1, values similar to those obtained for local freshwater and saltwater wetland systems and lower than those reported for some Florida freshwater lakes. Several of the spring runs had down-core radiocarbon dates that were out of stratigraphic order, which demonstrated the potential for sediment resuspension and mixing in this setting and represented a potential source of error in estimating carbon sequestration rates that should be considered in the interpretation of results.