Dissolved Organic Matter Composition and Mineral Characteristics Jointly Control Adsorption Processes

Abstract

Adsorption of dissolved organic matter (DOM) onto mineral surfaces plays a critical role in the global carbon cycle, influencing carbon stability and sequestration across terrestrial and aquatic ecosystems. Currently, it remains unclear if mineral properties or DOM composition are more relevant for predicting adsorption. Previous studies have only tested the influence of soil particles or DOM on adsorption. Here, we quantified the maximum adsorption capacity (Q_max) of five mineral materials (podzol Bs horizon, agricultural topsoil, glacial stream sediment, kaolinite-dominated clay, synthetic goethite) exposed to five DOM sources (humic lake, peat, leaf litter, algae, and pyrogenic matter). Adsorption characteristics were determined using a modified Langmuir model. Q_max values spanned 31–28,630 mg C kg⁻¹, exceeding previously reported ranges. The results showed that both DOM composition and mineral properties strongly influenced the adsorption capacity. Even for strongly adsorbing mineral materials, such as goethite and a commercial reference clay, Q_max varied widely among DOM sources, with the highest values for peat and the lowest for algae. Likewise, DOM from different sources varied in their adsorption affinities for the different mineral surfaces. One treatment evaluated the effect of removing pre-existing organic matter, showing increased DOM adsorption and highlighting the importance of accounting for mineral-associated organic matter when predicting Q_max. In summary, carbon adsorption on minerals is co-dependent on the characteristics of both the minerals and the DOM. These findings suggest that soil models that do not account for DOM characteristics are limited in predicting the carbon sequestration potentials in soils and aquatic ecosystems.