Reduction of raindrop kinetic energy by moss crust on rare earth tailings and its potential impact on soil erosion

Water erosion of rare earth tailings poses significant ecological risks, while moss crusts are widely distributed across these tailings. However, their role in erosion mitigation remains poorly understood. Using a single-raindrop simulation experiment, this study quantified the kinetic energy reduction capacity of moss crusts at four developmental stages (I: bare soil; II–IV: increasing cover, biomass, and height). Key results include: (1) Moss crusts markedly increased the accumulated kinetic energy required to disrupt the surface ( E moss ). At 1 cm thickness, E moss values for developmental stages II, III, and IV were 0.04, 0.18, and 4.61 J, respectively—stage IV exhibited 363-fold greater resistance than bare soil (stage I). (2) After moss removal, the underlying soil's resistance ( E under ) dropped sharply (averaging 0.01 J across stages), with no differences between developmental stages. Moss crusts reduced raindrop kinetic energy by 65.04% (stage II), 92.79% (stage III), and 99.72% (stage IV). (3) Resistance correlated strongly with slope and soil moisture: air-dried crusts exhibited higher E moss (0.35 J) than wet samples, and steeper slopes (25°–30°) increased E mos s by 10-fold compared to flat terrain. These findings demonstrate that moss crusts act as effective physical barriers against splash erosion, offering a scalable strategy for ecological restoration of degraded rare earth tailings in subtropical regions.