Quantitative analysis of the relationship between vegetation and groundwater buried depth: A case study of a coal mine district in Western China

Studying the interdependence between vegetation and the buried depth of groundwater is key to revealing the ecological and hydrological processes affecting vegetation in arid and semi-arid areas. The study area, the Yushen coal mine district, is located in the Mu Us Desert, which is the typical arid and semi-arid transition zone in Western China. There are a large number of areas with shallow with shallow groundwater depths in the region, which provides favorable growing conditions for vegetation growth. Due to sparse precipitation and rapid evaporation of water in the region, vegetative growth is tied closely to the depth of groundwater table. Given the widespread and intensive exploitation of the region's abundant coal resources, the decline of groundwater table poses a threat to surface vegetation ecology health inevitably. Therefore, study of the ecological effects of large-scale changes to the depth of groundwater is of great significance for guiding exploitation of coal resources, eco-environmental conservation and future rehabilitation efforts. Using Yushen coal mine district as a study area, the quantitative relationship between groundwater buried depth and vegetation development is determined in different ecological and geological (eco-geological) environments by combining MODIS remote sensing with measured groundwater buried depth data as well as supplementing with other on-site investigations and collection of data. Using ArcGIS 10.5 and MATLAB R2018a, we divided the study area into 3 eco-geological environments: (1) phreatic water desert shallows oasis; (2) surface runoff (loess) gully; and (3) surface water river-valley oasis. The vegetation types, growth status, and diversity differed within the eco-geological environments. Based on the sensitivity of vegetation to the buried depth of groundwater in each of the three eco-geological environments, we further classified areas within the eco-geological environments as either type-1 sensitive, either type-2 sensitive or non-sensitive. We found that sensitivity class was related to the groundwater buried depth. Vegetative ecology improved with groundwater buried depth drawdown, while it deteriorated in type-2 sensitive areas. Vegetative ecology generally exhibited little dependence on groundwater buried depth in non-sensitive areas, where climate and soil moisture content were the predominant influences.