Total organic carbon (TOC) sediment stocks as a CO₂ mitigation service require exclusion of allochthonous black (BC) and particulate inorganic carbon corrected for water–atmospheric equilibrium (PIC_eq). For the first time, we address this bias for a temperate salt marsh and a coastal tropical seagrass in BC hotspots that represent two different blue carbon ecosystems of Malaysia and Australia. Seagrass TOC stocks were similar to the salt marshes with soil depths < 1 m (59.3 ± 11.3 and 74.9 ± 18.9 MgC ha^− 1, CI 95 % respectively). Both ecosystems showed larger BC constraints than did their pristine counterparts. However, the seagrass meadows’ mitigation services were largely constrained by both higher BC/TOC and PIC_eq/TOC fractions (38.0 % ± 6.6 and 43.4 % ± 5.9 %, CI 95 %) and salt marshes around a third (22 % ± 10.2 and 6.0 % ± 3.1 % CI 95 %). The results provide useful data from underrepresented regions, and, reiterates the need to consider both BC and PIC for more reliable blue carbon mitigation assessments to ensure that greenhouse gas emitters do not exceed the ecosystems’ capacity.

作为 CO ₂缓解服务的总有机碳 (TOC) 沉积物储量需要排除外来黑 (BC) 和针对水-大气平衡校正的颗粒无机碳 (PIC _eq )。我们第一次解决了对代表马来西亚和澳大利亚两种不同蓝碳生态系统的 BC 热点地区的温带盐沼和沿海热带海草的这种偏见。海草 TOC 储量与土壤深度 < 1 m 的盐沼相似（分别为 59.3 ± 11.3 和 74.9 ± 18.9 MgC ha ^{- 1}，CI 95 %）。两个生态系统都显示出比原始生态系统更大的 BC 约束。然而，海草草甸的缓解服务在很大程度上受到较高的 BC/TOC 和 PIC _{eq 的限制}/TOC 部分（38.0 % ± 6.6 和 43.4 % ± 5.9 %，CI 95 %）和大约三分之一的盐沼（22 % ± 10.2 和 6.0 % ± 3.1 % CI 95 %）。结果提供了来自代表性不足地区的有用数据，并重申需要同时考虑 BC 和 PIC 以进行更可靠的蓝碳减排评估，以确保温室气体排放者不会超过生态系统的能力。