Effects of biological soil crusts on soil hydrological processes

Abstract

Biological soil crusts (BSCs) are widely distributed in the sandy land east of the Yellow River in Ningxia, China, where they alter the original hydrological processes and form unique eco-hydrological dynamics distinct from those of the original desert ecosystem. While the effects of BSCs on individual hydrological processes have been documented in various arid regions worldwide, the integrated assessment of infiltration, evaporation, condensation, and their net implications for water balance, remains poorly understood, particularly in areas where BSCs have spontaneously developed following large-scale desertification control efforts. In this study, we investigated the effects of bare sand and different successional stage BSCs (algae crusts, moss crusts, herb and moss mixed crusts) on soil physicochemical properties, soil infiltration, water condensation, and evaporation under arid climatic conditions on the southwestern edge of the Mu Us Desert. The results showed that BSCs significantly altered surface soil properties: compared with bare sand, the sand content of the underlying soil was decreased by 2.0%–5.1%, and soil organic matter content increased by 5–6 times. BSCs exhibited strong infiltration resistance in later successional stages, while herb and moss mixed crusts promoted infiltration. Furthermore, BSCs significantly affected the formation of condensation and soil evaporation. The ability to capture condensed water was as follows: moss crusts > herb and moss mixed crusts > bare sand > algae crusts. Notably, although moss crusts, herb and moss mixed crusts enhanced both condensation capture and evaporation, the enhanced condensation partially offset the increased evaporative losses, suggesting a nuanced role in the near-surface water balance. Soil condensation water constituted the primary source of total condensation, accounting for 52.90% to 58.46% of the total. The 15-day total evaporation and daily evaporation rate followed the order: herb and moss mixed crusts > moss crusts > bare sand > algae crusts. In conclusion, the successional transition from algae crusts to moss crusts to herb and moss mixed crusts shifts the hydrological function, from inhibition of both infiltration and evaporation to enhanced infiltration with increased evaporative exchange, providing new insights into the eco-hydrological mechanisms underlying water redistribution mediated by BSCs in dryland ecosystems.