Alterations in soil moisture dynamics due to open-pit coal mining semi-arid regions: Perceptions based on soil water stable isotopes and underground water conductivity analysis

Purpose

Over the past three decades, open-pit mining has been expanding in arid and semi-arid areas of China.Open-pit mining profoundly changes the soil environment and has a profound impact on the circulation of soil water in the aeration zone.Therefore, this research explores the impacts of open-pit coal mining on soil moisture processes in the semi-arid grasslands of Eastern Inner Mongolia Autonomous Region, China.

Materials and methods

Soil samples were collected from depths of 0–500 cm at Shengli No. 1 open-pit mine’s inner dump and a nearby natural grassland. These soil samples were analyzed for stable isotope characteristics (\({\delta ^2 H, \delta ^{18} O}\)) and moisture content. Collection of underground water samples inside and outside the mining area for conductivity analysis.

Results and discussion

Soil evaporation loss in the mine’s inner dump was significantly higher than in the grassland, with rates of 22.26% for \({\delta ^{18} O}\) and 6.61% for \({\delta ^2 H}\). The limiting depth of soil evaporation at the mine was found to be 260 cm, compared to 200 cm in the grassland. The increased underground water conductivity in the mine area was linked to heightened soil evaporation loss. Isotopic profiling of the soil indicated that the open-pit mining led to deeper preferential flow infiltration during heavy precipitation, reaching 280 cm in the mine area versus 220 cm in the grassland.

Conclusions

The surface soil moisture content (SMC) increased due to mining activities intensified water-heat exchanges with the atmosphere, leading to more frequent and severe wet-dry cycles. This study provides a comprehensive understanding of open-pit mining’s impact on SMC, evaporation, and infiltration in semi-arid areas, offering critical insights for ecological reclamation and sustainable mine construction.