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 $\pm 119,439\pm$ 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 $\le$ 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.

沿海蓝碳系统（红树林，海草草甸和潮汐盐沼）以其在沉积池中隔离大量碳（C）的功效而著称，而保护这些碳库的有效管理措施需要了解河口内的空间变异性。这项研究分析了澳大利亚东部三个亚热带河口的33个沿海蓝色碳沉积物核。我们测量了土壤剖面下的深度，碳含量和干密度。估计深达三米的红树林，海草和盐沼的平均碳储量为738$\pm 119，439\pm$分别为72和823±138 Mg C ha ^-1。线性回归模型显示，在红树林和盐沼中，距海洋和碳储量之间的关系很显着（p $\le$分别为0.001和p <0.01），但城市化河口中的红树林显示倒数。我们在红树林和盐沼而非海草的碳库中观察到的与河口位置有关的差异可能对管理行动和生态过程具有重要意义。