Moss Biocrusts Regulate Heavy Metal Speciation and Mobility in Coal Mine Soils

ABSTRACT

On a global scale, coal mining activities often lead to heavy metal(loid) contamination in soils of mine dump sites, posing serious ecological risks. As ecosystem “engineers,” biological soil crusts (biocrusts)—especially moss crust—have shown great potential in remediating heavy metal‐polluted soils, but their roles remain underexplored. In this study, we investigated the effects of moss crusts on the distribution and speciation of heavy metals in soils of an open‐pit coal mining area through field surveys at nine sites and laboratory analyses of soil samples collected from three depth layers (0–5 cm, 5–10 cm, and 10–20 cm), using sequential extraction and ICP‐MS. Results showed that moss crusts significantly improved soil physicochemical properties (particularly by mitigating acidification caused by coal gangue), thereby indirectly influencing heavy metal speciation and distribution. We found that heavy metal(loid)s fractions were significantly correlated with soil properties such as pH, CEC, and OM ( p  < 0.05), although specific elements and fractions exhibited different patterns. Furthermore, moss crusts directly accumulated heavy metal(loid)s via extracellular ion exchange and intracellular uptake, reducing heavy metal(loid)s (Pb, Cr, Ni, As, and Cu) concentrations in surface soils by up to 28.6% in the top 0–5 cm layer and altering their vertical distribution across soil layers. However, the presence of moss crusts also shifted certain heavy metal(loid)s from residual (stable) forms toward more labile fractions in the surface soil, indicating a potential increase in their mobility. These findings elucidate the influence of moss crust on heavy metal speciation in mining soils and provide a theoretical basis for the ecological restoration of contaminated sites worldwide.