Local Geomorphological Gradients Affect Sedimentary Organic Carbon Storage: A Blue Carbon Case Study From Sub-Tropical Australia

Coastal blue carbon systems (mangrove forests, seagrass meadows and tidal saltmarshes) are renowned for their efficacy at sequestering large amounts of carbon (C) in sedimentary sinks and effective management action to preserve these C stocks requires an understanding of spatial variability within an estuary. This study analysed 33 coastal blue carbon sediment cores across three subtropical estuaries of Eastern Australia. We measured depth, C content and dry bulk density down the soil profile. Mean C stocks for mangroves, seagrass and saltmarsh, up to a 3 metre depth, were estimated to be 738 +/- 119, 439 +/- 72, and 823 +/- 138 Mg C ha(-1), respectively. Linear regression models showed the relationship between distance from ocean and C stocks was significant in mangroves and saltmarsh (p <= 0.001 and p < 0.01, respectively), with the exception of mangroves in an urbanised estuary which displayed the inverse. The differences we observed in C stocks in mangroves and saltmarsh, not seagrass, in relation to location within the estuary may have important implications for management actions and ecological processes. (C) 2021 Elsevier B.V. All rights reserved.