Subsurface structure regulates water storage in the alpine critical zone on the Qinghai-Tibet Plateau

Abstract

The subsurface critical zone (CZ) structure in alpine regions has a profound influence on water storage that is not well understood due to a lack of available accurate spatiotemporal measurements. This work is to reveal that the organic layer (A), leaching-deposit layer (B), saprolite layer (C) and freeze–thaw processes regulate changes in subsurface liquid water storage (CSWS). We performed in situ field surveys, ground-penetrating radar (GPR) and electrical resistivity tomography (ERT) along an elevation gradient (4221–3205 m) in the Qinghai Lake Basin Critical Zone Observatory (QLBCZO) on the Qinghai-Tibet Plateau. The results showed that the saprolite layer (thickness of 0.84–41.85 m) and the liquid water storage (SWS) increased along the decreasing elevation. The saprolite layer was the main subsurface liquid water storage reservoir, with average value of 595.49 ± 729.87 mm, which occupied 76.10 % of the total water storage of layers A, B and C. The SWS of the saprolite layers increased the most, by 39.41 mm and 45.88 mm in the thawing and nonfreezing periods, respectively, and that of layer B decreased maximally by 52.50 mm in the freezing period. The subsurface layer and elevation had the contribution to SWS at 68.07 % during the nonfreezing period. Comparing other climate and environmental factors, the seasonal frozen thickness (SFT) and precipitation contributed most to CSWS during the thawing and freezing period (27.95 % and 19.87 %), respectively. This study contributes to advancing the mechanistic understanding of the interactions between the subsurface CZ structure and water storage processes and provides high-quality data with which coupled ecohydrological models can be developed.