Quantifyting research on the protection effect of a desert‒oasis ecotone in Dunhuang, Northwest China

Abstract

A desert‒oasis ecotone is an important barrier for an oasis, although few studies have attempted to investigate and quantify the protection that it offers. In this paper, a portable wind-monitoring system, fixed automatic weather-monitoring instrument, and eight-directional sand-collecting instrument were used to study the protection benefits offered by a desert‒oasis ecotone in Dunhuang, Northwest China. The data showed that a desert–oasis ecotone can effectively reduce regional wind speed, sand-driving wind speed, drift potential, and wind-blown sand activity, while also increasing the aerodynamic roughness length in order to prevent erosion driven by surface winds. When passing through the ecotone, the percentage of sand-driving wind reduced from 21.0% to 2.98%, and the resultant drift potential was reduced from 135.67 to 14.94 VU. In the study area, the resultant sand-driving wind mainly traveled southwards, and the frequency of sand-driving winds decreased commensurately with increases in vegetation cover and desert–oasis ecotone width. In 2015, the total wind-blown sand fluxes were 3.90 kg m−1 d−1 in the desert environment, 1.09 kg m−1 d−1 in the desert‒oasis ecotone, and 1.08 kg m−1 d−1 in the oasis. The wind-blown material's grain size in the desert region was dominated by medium sand, which comprised 47–60% of the total; by contrast, wind-blown materials in the desert‒oasis ecotone and oasis were dominated by fine sand, with proportions of 51–63% and 52–70%, respectively. The protection offered by a desert‒oasis ecotone is related to aerodynamic roughness length, distance of airflow across the ecotone, and wind speed. Among them, aerodynamic roughness length and distance of airflow across the ecotone were positively correlated with the level of protection offered, while wind speed showed a negative correlation. We also present a mathematical relationships between these variables that can provide a scientific basis for determining the optimum width to develop desert–oasis ecotones in arid regions.