Moss biocrusts enhance hydrological functionality on engineered slopes: pore restructuring, water retention, and hydrophobicity compensation in humid subtropical ecosystems

Abstract

Although biological soil crusts (BSCs) are known to regulate hydrology in arid ecosystems, their effects on pore structure, water retention, and infiltration in humid subtropical engineered slopes with high rainfall and erosion risk remains poorly understood. This study compares the hydrological functions of moss-dominated BSCs and bare soil at different slope positions on phosphogypsum-covered slopes (Hubei, China). Using in situ infiltration data, X-ray μCT pore analysis, and van Genuchten modeling, we identified three slope-dependent mechanisms that explain BSCs’ functionality: (1) Pore restructuring: BSCs increased macroporosity (>50 μm) by 100.8 %, enhanced pore connectivity to 98.25 % (compared to 92.3 % in bare soil), and enlarged pore-throat radii by 39.85 %. These changes created efficient water-transport networks, doubling saturated hydraulic conductivity. (2) Water retention: BSCs reduced bulk density, increased capillary porosity, and boosted soil organic matter, raising volumetric water content across matric potentials (0 to 􀀀 15,000 kPa) by 32.0–39.6 %. This improved plant-available water by 7.9–14.3 % and sustained soil moisture during drought conditions. (3) Hydrophobicity compensation: Although surface ydrophobicity limited unsaturated hydraulic conductivity to 30 %, structural modifications favored preferential flow. Hydrophobic surface features and BSC-induced roughness slowed overland flow, increased infiltration time, and reduced erosion energy. Slope-specific conditions caused spatial differences. These findings highlight BSCs as an “ecological lock” for slope stabilization, providing a theoretical and practical framework for restoring engineered slopes.