The influence of climatic conditions on the permeability and hydraulic properties of the L5–S5 layers in the Loess Plateau, North Qinling Mountains

Abstract

ABSTRACT A better understanding of the role of Quaternary-era climate change in the development of regional hydrology in the Loess Plateau and the impact on regional ecosystems is needed. In particular, a thorough examination of the permeability and recharge under different conditions in the fifth loess–palaeosol layer is required. The fifth loess–palaeosol layer is located at the southern edge of the Jinghe River in the Guanzhong Basin, and was examined to better understand these conditions. A constant head permeability test was conducted at 11 points that covered different stratum of loess–palaeosol, and 55 corresponding undisturbed soil samples were analysed for porosity, magnetic susceptibility, and grain size. Results showed that: (1) with an increase in hydraulic gradient, the permeability coefficient of the upper part of the loess and the lower part of the palaeosol showed contrasting characteristics – this phenomenon was closely related to climatic conditions during the sedimentary period, post-sedimentary microbial activity, and to certain properties relating to permeability in the strata under similar monsoon effects; (2) the Loess Plateau, alternately dominated by the East Asian summer and winter monsoons, exhibited different grain-size compositions in the sedimentary layer, which, in turn, made the permeability in the loess noticeably more stable than that in the palaeosol; and (3) different aquifer characteristics and recharge conditions between the loess–palaeosol layers can be primarily explained by the intensity of the pedogenesis, which depended on extreme dry-old glacial climates and relatively humid-warm interglacial climates. These findings show that climate change played an important role in influencing hydrological systems in the loess–palaeosol sequence.