Hydrological functioning of thawing soil water in a permafrost‐influenced alpine meadow hillslope

Abstract

Abstract The complex variation of the hydrological functioning of soil water has been widely studied using measurements of the stable isotopic composition of either the bulk soil water (BSW) collected by the cryogenic vacuum extraction method or the mobile soil water (MSW) collected by the zero‐tension soil lysimeter method. We collected samples of precipitation, BSW, MSW, and hillslope runoff in an alpine meadow hillslope influenced by permafrost to investigate the hydrological functioning of thawing soil water. The results showed that the δ 2 H values in BSW were generally more negative than those of the MSW, which may be a result of the depleted spring snowmelt that formed the tightly bound soil water. The relatively stable characteristics of δ 2 H in the MSW were related to the dynamic mixing of newly infiltrated precipitation with slightly enriched mobile water held by the low soil matrix potential. The δ 2 H values in the BSW showed higher temporal variations than the values in the MSW, which were mainly related to the mixing of depleted tightly bound soil water and enriched MSW in varying fractions. The MSW better represented the lateral subsurface flow (SSF, which further generated streamflow) than the BSW samples considering the relatively close stable isotopic values between the lateral SSF and the MSW in the same soil layer. The results of this study show the influences of the varying water level maintained by the underlying permafrost on the water and isotopic dynamics of both the soil water pools and streamflow.