Dataset: Increasing rates of carbon burial in southwest Florida coastal wetlands

Rates of organic carbon (OC) burial in some coastal wetlands appear to be greater in recent years than they were in the past. Possible explanations include ongoing mineralization of older OC or the influence of an unaccounted-for artifact of the methods used to measure burial rates. Alternatively, the trend may represent real acceleration in OC burial. We quantified OC burial rates of mangrove and brackish marsh sites in southwest Florida through a comparison of rates derived from 210Pb, 137Cs, and surface marker horizons (MH). Age/depth profiles of lignin:OC were used to assess whether down-core remineralization had depleted the OC pool relative to lignin, and lignin phenols were used to quantify the variability of lignin degradation. OC burial rates increased in all seven cores by factors ranging from 1.4 to 6.2 over the past 120 years. We propose that these increases represent net acceleration. Change in relative sea-level rise is the most likely large-scale driver of acceleration, and sediment deposition from large storms can contribute to periodic increases. Mangrove sites had higher OC and lignin burial rates than interior marsh sites, indicating inherent differences in OC burial factors between the two habitat types. The higher OC burial rates in mangrove soils mean that their encroachment into interior, freshwater marshes has the potential to increase burial rates in those locations even more than might be expected from the acceleration trends. Regionally, these findings suggest that burial represents a substantially growing proportion of the coastal wetland carbon budget.