The ability to accurately measure organic carbon (OC) in marine sediments or soils is overall taken for granted in scientific communities, yet this seemingly mundane task remains a methodological challenge when the soil matrix contains calcium carbonate (CaCO₃), creating inaccuracies in Blue Carbon estimates. Here, we compared five common methods combining acidification, combustion, and wet oxidation pre-treatments for determination of OC in sediments and soils containing CaCO₃ based on the analyses of artificial soil mixtures made of different OC and CaCO₃ contents, and multiple soils from Australian seagrass cores. The results obtained showed that methods involving acidification pre-treatment entailed −17 ± 0.2% (mean ± SE) underestimation of OC content (ranging from −8% to −26%), whereas the combustion-based method was accurate for samples with high CaCO₃ content but entailed 32–47% overestimation in samples with low CaCO₃ content. The Heanes method (wet oxidation method) showed <5% deviation from the known OC content, but this method is not suitable for soil samples containing reduced iron, sulfur and potentially manganese compounds. The differences observed among methods have significant impacts on local, regional, and global Blue Carbon storage calculations. We provide key methodological guidelines for the analysis of OC in soils with high and low CaCO₃ contents, aiming at improving accuracy in current Blue Carbon science.

中文翻译：

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海草蓝碳土壤有机碳分析方法的缺陷

准确测量海洋沉积物或土壤中有机碳 (OC) 的能力在科学界总体上被认为是理所当然的，但当土壤基质含有碳酸钙 (CaCO ₃ ) 时，这项看似平凡的任务仍然是方法上的挑战，从而导致 Blue Carbon 中的不准确估计。在这里，我们通过对不同 OC 和 CaCO ₃含量的人造土壤混合物以及多种土壤的分析，比较了酸化、燃烧和湿式氧化预处理相结合的五种常用方法，用于测定含 CaCO ₃的沉积物和土壤中的 OC。澳大利亚海草芯。获得的结果表明，涉及酸化预处理的方法需要低估 OC 含量 -17 ± 0.2%（平均值 ± SE）（范围为 -8% 至 -26%），而基于燃烧的方法对于高浓度样品是准确的。 CaCO _{3含量，但在 CaCO 3}含量低的样品中高估了 32–47% 。Heanes 法（湿式氧化法）显示与已知 OC 含量的偏差 <5%，但该方法不适用于含有还原铁、硫和潜在锰化合物的土壤样品。不同方法之间观察到的差异对当地、区域和全球蓝碳储存计算有重大影响。_{我们为高和低 CaCO 3}含量土壤中的 OC 分析提供了关键方法指南，旨在提高当前蓝碳科学的准确性。