Effects of coal mining subsidence on soil microorganisms and enzyme activities in different landform types of northern Shaanxi

A profound understanding of the derivative ecological damage effects of coal mining subsidence has become a key basic scientific issue and research hotspot for repairing ecological environment damage caused by mining in western coal mining areas. Grasping how coal mining subsidence in different geomorphic units affects soil microorganisms and enzyme activities is beneficial for the ecological environment protection and restoration of coal mining subsidence areas in the western region. The typical subsidence slope soil of the Yushuwan mine field (aeolian landform) and the north wing of the Ningtiaota mine field (loess landform) in northern Shaanxi coal mine area were selected as the research objects, while the soil samples from different slope parts (vertical depth of 0~60 cm) were collected, respectively. Absolute quantitative PCR and enzyme-linked immunosorbent assay (ELISA) methods were used to determine the number of soil bacteria, actinomycetes and fungi, as well as the activities of sucrase, catalase, urease and phosphatase, respectively. The spatial variation characteristics of soil microbial quantity and enzyme activity on subsidence slope were thoroughly analyzed, while the main physical and chemical soil properties were comprehensively integrated to reveal the impact of coal mining subsidence on soil microorganism and enzyme activity under different landform types. The results showed that: ① Coal mining subsidence in both aeolian landform and loess landform type unit could significantly reduce the number of soil microorganisms and enzyme activity on the subsidence slope. The decrease in soil microbial quantity reached 8.27%-42.39% and 11.53%-45.95%, respectively, while the decrease in soil enzyme activity reaches 6.52%-39.83% and 9.09%-42.42%, respectively. With the transition from the top of the slope to the middle of the slope and then to the foot of the slope, the reduction effect exhibited different variation characteristics for three soil microorganisms and four enzymes; ② The coal mining subsidence of loess landform type unit performed the most significant reduction effect on various soil microbial quantity and enzyme activity in “middle part of slope 0~10 cm soil layer”. Meanwhile, the coal mining subsidence of aeolian landform unit presented the most significant reduction effects on the soil actinomycetes quantity and invertase, urease and phosphatase activities in “middle part of slope 0~10 cm soil layer”, and soil bacteria and fungi quantity in “middle part of slope 10~20 cm soil layer”, as well as soil catalase activity in “middle part of slope 20~40 cm soil layer”. Therefore, it can be served as a targeted area for slope soil microbial remediation in coal mining subsidence areas of northern Shaanxi; ③ Whether in the units of aeolian landform or loess landform, the number of soil fungi and urease activity were the most sensitive indicators to coal mining subsidence, with decreases of 23.28%-45.95% and 22.78%-42.42%, respectively. Moreover, the two indicators can be used as markers to analyze the microbial characteristics of soil damaged by coal mining subsidence in northern Shaanxi mining area; ④ The correlation coefficients between soil available phosphorus and organic matter content and soil microbes and enzyme activities were the highest, exceeding 0.8 and 0.7, respectively, on both wind-sand and loess subsidence slopes. They can be served as key indicator factors for coal mining subsidence affecting soil microbial characteristics.