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.<br>

近年来部分滨海湿地的有机碳（organic carbon, OC）埋藏速率较历史时期显著升高。对此可能的解释包括：老旧有机碳的持续矿化作用，或是未被纳入考量的埋藏速率测量方法所引入的人为假象；亦或是该趋势真实反映了有机碳埋藏过程的加速。本研究通过对比铅-210（210Pb）、铯-137（137Cs）及表层标记层（surface marker horizons, MH）所得到的埋藏速率，量化了佛罗里达西南部红树林与咸淡水沼泽样地的有机碳埋藏速率。通过木质素/有机碳比值的年龄-深度剖面，我们评估了岩芯向下再矿化是否会相对于木质素消耗有机碳库；同时利用木质素酚类量化了木质素降解的变异程度。过去120年间，全部7个岩芯的有机碳埋藏速率均提升至原水平的1.4至6.2倍。我们认为这些提升代表了净埋藏速率的加速。相对海平面上升的变化是该加速过程最可能的大尺度驱动因子，而大型风暴带来的沉积物沉积则可导致埋藏速率的周期性升高。红树林样地的有机碳与木质素埋藏速率均高于内陆沼泽样地，表明两类生境的有机碳埋藏影响因子存在固有差异。红树林土壤更高的有机碳埋藏速率意味着其向内陆淡水沼泽的扩张，可能会使这些区域的埋藏速率较仅由加速趋势带来的提升更为显著。从区域尺度来看，本研究结果表明，埋藏过程在滨海湿地碳收支中所占的比例正大幅增长。