The effect of desertification on frozen soil on the Qinghai-Tibet plateau

Sci Total Environ. 2020 Apr 1;711:134640. doi: 10.1016/j.scitotenv.2019.134640. Epub 2019 Nov 20.

Abstract

Under the influences of climate change and human activities, desertification has become widespread on the Qinghai-Tibet Plateau (QTP). However, the effect of desertification on frozen soil is still debated. Here, soil temperatures are observed through 14 boreholes at Honglianghe River Basin on the QTP to study the relationship between desertification and frozen soil. The results showed soil temperatures change with the thickness of sand cover. With increasing sand thickness, maximum soil temperatures at shallow depths (0.05-6.00 m) increase by 0.25-1.57 °C, but minimum temperatures decrease by 0.21-1.49 °C, on average. Temperatures at deep depth (≥6.00 m) exhibit a rising trend that temperatures increase by 0.01-0.05 °C on average with each increment of 10 cm in sand thickness. Furthermore, aeolian sand enhances seasonal thawing processes, resulting in an increase of 7.70-9.50 cm in active layer thickness with each increment of 10 cm in sand thickness. Meanwhile, aeolian sand weakens seasonal freezing processes, resulting in a decrease of 1.07-13.00 cm in seasonal freezing depth with each increment of 10 cm in sand thickness. Moisture contents of aeolian sand and vegetation coverages on the sand cover surface influence energy state and thermal regime of frozen soil. Annual heat budgets of soil under aeolian sand increase from -57.97 MJ m-2 to -26.28 MJ m-2 as water content of sand layer decreases from 13.42% to 3.61%. Annual range of ground temperatures of soil at shallow depths (0.05-1.60 m) increase by 2.19-6.17 °C on average as vegetation coverage increases from 5% to 20%. Due to the effects of aeolian sand on frozen soil, desertification accelerates, and can even cause, the degradation of frozen soil on the QTP. Our study provides an important reference for future research about the interaction between desertification and frozen soil in other regions.

Keywords: Aeolian sand; Permafrost; Qinghai-Tibet Plateau; Seasonally frozen ground; Thermal regime of soil.