Carbon sequestration in different wetland plant communities in the Big Cypress Swamp region of southwest Florida

Abstract

Wetlands offer many ecosystem services, including the long-term sequestering of carbon (C) in soil. Here we present a study of C sequestration rates in a relatively undisturbed wetland landscape of southwest Florida. Accordingly, carbon sequestration was determined in four wetland plant communities and an adjacent hydric pine flatwood community that represent a gradient of inundation extent. Going from the wettest to the driest, communities were designated as: deep slough, bald cypress (Taxodium distichum), wet prairie and pond cypress (Taxodium distichum var. imbricarium). An adjacent hydric pine flatwood community was also included in the study as a reference upland site. Three soil cores were collected from each of these communities and were analyzed for total C content. Core samples were also analyzed for 137Cs and 210Pb activity to estimate accretion rates. C sequestration rates (g-C m−2 yr−1) were the highest in the deep slough (98 ± 9) and bald cypress (98 ± 5) followed by the pond cypress (64 ± 7), wet prairie (39 ± 1) and pine flatwood (22 ± 5). These results suggest that impediment of decomposition by anaerobic conditions caused by prolonged wet cycles, may not account for all the variability in C sequestration rates observed in this subtropical setting. Instead, this variability could also be attributed to other factors like the quantity and chemical composition of the organic material reaching the soil. When methane emissions are taken into account, cypress-dominated (bald and pond cypress) and the deep slough communities act as net carbon sinks.