Soil-water retention behavior of a loess-paleosol sequence and its significance for hydrology and paleoclimate: a case study from the Luochuan profile of the Loess Plateau, China

The soil water retention behavior of the loess-paleosol sequence has important significance for hydrology and paleoclimate. This report examines the soil-water retention curves and microstructures of the Luochuan loess-paleosol sequence, which has a thickness of around 43.7 m and includes the S-0-L-6 layers. The experimental results demonstrated that as burial depth increases, there is a significant change in the soil-water retention curve of loess-paleosol sequence. Simultaneously, the saturated volumetric water content and water loss rate gradually decrease, while the air entry value and residual water content increase. As a whole, the loess layer has a lower water-holding capacity than the adjacent paleosol layer. Accordingly, the microstructure of the loess-paleosol sequence changes considerably with the burial depth. The microstructure changes from overhead structure to matrix structure, the particle contact relationship changes from direct point contact to indirect surface contact, the degree of cementation changes from slight cementation to complete cementation, and the volumes of all pore types decrease. The results suggest that the loess layer deposited in cold and dry climate conditions can act as an aquifer, which is related to weak pedogenic weathering. In contrast, paleosol layers that were formed in warm, humid climates underwent significant pedogenic weathering and can behave as an aquiclude. Based on the previously mentioned results, the link between paleoclimate changes and the current hydrological system has been explored. This offers a theoretical foundation and guidance for future engineering and ecological construction operations, as well as water resources management in loess areas.