Preservation is defined as the capacity for coastal blue carbon decomposition to be inhibited due to saline anaerobic conditions, and for long-term sequestration within soils. Fine-grained sediments typical of alluvial floodplains, fluvial deltas and to some extent estuarine floodplains will inhibit decomposition more than sandy coastal barrier sediments (Saintilan et al., 2013) and carbon will be more concentrated in these regions. Due to significant decline in hydrodynamic energy as tributaries enter estuaries, fluvial deltas are composed predominantly of finer grain sizes (although pro-delta and delta fronts may have highly variable grain sizes) yet are influenced by tidal inundation resulting in saline conditions ideal for ongoing preservation of stored carbon. Coastal barrier sediments that are typically dominated by sands store less carbon due to greater oxidation of sediments (Kelleway et al., 2016) and in some locations, frequent reworking.

Saintilan, N., Rogers, K., Mazumder, D., and Woodroffe, C. (2013). Allochthonous and autochthonous contributions to carbon accumulation and carbon store in southeastern Australian coastal wetlands. Estuarine, Coastal and Shelf Science 128, 84-92.