Effects of groundwater level decline on soil‐vegetation system in semiarid grassland influenced by coal mining

Although it is well known that groundwater significantly influences the plant communities, there have been few studies on how the soil and plant communities respond to a rapid decline of groundwater in a short time affected by coal mining. This paper focuses on the examination of changes in groundwater depth before and after coal mining and the soil‐vegetation response in a typical semi‐arid grassland coal mine area of Hulunbuir Steppe, Northeastern China. The IsoSource model, based on the dual stable isotopes of δ D and δ18O, was employed to estimate groundwater contributions to shallow soil (0–100 cm) water under different groundwater depths. The results revealed that groundwater was the dominant water source (75.7% ± 17.1%) for shallow soil water when the groundwater depth is less than 4 m, indicating that 4 m is a threshold in groundwater depth, separating groundwater‐dependent, and precipitation‐driven vegetation system in the study area. Secondly, a strong nonlinear response was observed between vegetation species, height, coverage, and the decline in groundwater. The vegetation properties were found to be the lowest in the areas where groundwater depth increased from 1.5–4 m to 4–28 m before and after coal mining. Finally, the groundwater level decline in the mining area significantly influenced the groundwater‐dependent vegetation ecosystem, the soil cation exchange capacity and organic matter reduced lead to the degradation of plant communities and the transition of mesophytes to xerophytes. Besides, the soil‐vegetation system in the non‐groundwater‐dependent area has no obvious response to the groundwater decline. These results suggest that caution should be exercised when mining in groundwater‐dependent ecosystem regions.