Carbon stocks in Mid-Atlantic tidal marshes

Sound estimations of blue carbon (C) stocks have important implications for global carbon accounting. This is especially true in tidal marshes because of their capacity to accumulate and store large quantities of C. Reliable field data, however, have historically been limited. More recent research has focused on general estimates of C stocks in the conterminous United States but without regard to the differences in soil characteristics, which vary based on the particular geomorphic setting where a marsh has formed. This may lead to inaccuracies in C stock estimates at a regional scale. In this study, we set out to measure tidal marsh C stocks in the Mid-Atlantic region and to understand the impact of geomorphology on the variability of C storage. We collected and analyzed 455 samples from 72 pedons distributed across five pedogeomorphic units (PGUs) representative of the Mid-Atlantic region: (1) submerged upland, (2) estuarine fresh, (3) estuarine non-fresh, (4) coastal barrier, and (5) coastal mainland. Carbon stocks were measured for each pedon, and significant differences in mean C stocks were found among the five PGUs. Differences became more pronounced with increased sampling depth (up to 200 cm). Additionally, we found that C stocks change spatially and systematically within certain types of marshes. These results suggest that geomorphic setting, which influences the pedogenesis of tidal marsh soils, has a meaningful impact on C storage and must be considered for accurate C accounting.