In saltmarsh soils, humic acids (HA) are involved in geochemically important redox processes. The electron donating capacity (EDC) of HA depends on their molecular structure, but also reflects the intensity of biological reduction in tidal environments. We examined twelve soils in three saltmarshes located along a geographical gradient and applied a specific sequential extraction procedure for the isolation of HA fractions bound (BHA) or not (FHA) to the mineral matrix by Ca²⁺ bridges, and investigated the relationships of their properties, in particular their EDC, with the biogeochemical characteristics of the soils. Spectroscopic assessment was carried out by UV–vis, FTIR and ¹³C NMR, quantification and characterization of radicals was performed by electron paramagnetic resonance (EPR) spectroscopy. The EDC was determined by using the 2,2′-azinobis-(3-ethylbenzothiazolinesulfonic acid) (ABTS) decolorization assay and experimental data were fitted to a biphasic model to calculate the contributions of the fast and slow reactions to electron transfer. The results confirmed that the two HA fractions possess different structural characteristics and that BHA present higher EDC values compared to FHA. The EDC of both fractions is strongly related to the geochemical characteristics of soils, and represents an easily measured and highly informative parameter to understand mechanisms affecting redox processes in transitional environments.

在盐沼土壤中，腐植酸 (HA) 参与地球化学重要的氧化还原过程。HA 的给电子能力 (EDC) 取决于其分子结构，但也反映了潮汐环境中生物还原的强度。^{我们检查了位于沿地理梯度的三个盐沼中的 12 种土壤，并应用特定的顺序提取程序来分离通过 Ca 2+}桥与矿物基质结合 (BHA) 或未结合 (FHA) 的 HA 部分，并研究了它们的关系。特性，特别是它们的 EDC，与土壤的生物地球化学特征。^{通过 UV-vis、FTIR 和13}进行光谱评估通过电子顺磁共振 (EPR) 光谱进行 C NMR、自由基的量化和表征。通过使用 2,2'-azinobis-(3-ethylbenzothiazolinesulfonic acid) (ABTS) 脱色测定法测定 EDC，并将实验数据拟合到双相模型以计算快速和慢速反应对电子转移的贡献。结果证实，两种 HA 级分具有不同的结构特征，并且与 FHA 相比，BHA 具有更高的 EDC 值。这两个部分的 EDC 与土壤的地球化学特征密切相关，并且代表了一个易于测量且信息量很大的参数，以了解影响过渡环境中氧化还原过程的机制。