Weathered bedrock converts hydrological processes in loess hilly-gully critical zone

Abstract

Weathered bedrock ecohydrology is indispensable for terrestrial ecosystem stability; however, the influence on the hydrological processes is poorly understood in loess hilly-gully critical zone. Using simulation experiments and in-suit observations, this study evaluated the intervention of weathered bedrock particles on profile infiltration and evaporation, investigated rock core sample characteristics and detected the spatiotemporal water variation in hillslopes of woodland and shrubland. Results showed that adding weathered bedrock particles interfered with infiltration and evaporation processes. Infiltration simulation discovered that stable infiltration rates increased linearly with weathered bedrock thicknesses, which accelerated by 0.5–5.7 times more than bulk soil layers. Interestingly, due to water separation at soil-rock interface, there existed nonlinear initial and average infiltration intensity fluctuations. Evaporation simulation demonstrated that cumulative evaporation presented a linear decrease with weathered bedrock, while the initial daily evaporation intensity increased, reaching a maximum of 15.4 ± 2.2 mm d−1. Moreover, borehole investigations manifested that weathered bedrock layers presented a thickness of more than 5.0 m, and the weathering intensity gradually decreased with depth, which was related to terrains and locations in hillslopes. Furthermore, profile water movement monitoring between woodland and shrubland slopes demonstrated that weathered bedrock optimized profile hydrological allocation. The average rock moisture reached about twofold than soil moisture, with average soil and rock moisture of 0.07 ± 0.04 cm3 cm−3 and 0.15 ± 0.05 cm3 cm−3 in woodland, 0.08 ± 0.03 cm3 cm−3 and 0.15 ± 0.03 cm3 cm−3 in shrubland, respectively. Besides, the profile water storage changed dynamically in equilibrium and escalated linearly with weathering layer thickness. Fundamentally, a conceptual structure model covering soil and rock water balance, vegetation dynamics, and climate change was constructed and discussed throughout the Earth’s critical zone, which was then applied in describing water circulation participating by rock moisture under relative water shortage and abundance scenarios in loess hilly-gully regions. This study would furnish insights for improving and deepening the water cycle in shallow soils, and provide new horizons for enriching water resources utilization under climate change.