Measure soil resilience after reclamation of open pit dump in semi-arid area

The main work of soil reclamation in coal mine area is to recover the structure and function of soil, which is the key factor for the restoration of mine damaged ecosystem. The calculation of soil resilience is an index to measure the stability of ecosystem, which provides guidance for the sustainability of soil management. As the case of Heidaigou open pit mine in Mongolia, the soil restoration of waste dump in 1995, 2000, 2008 and 2015 is taken as the research objects. The field investigation and soil quality experiment data are used to compare and analyze between the reclamation soil and original soil. The soil resilience of waste dump of open pit mine is measured by principal component analysis and structural equation model. The results showed:  (1) The volume density of reclaimed soil was larger, and the soil particle size did not show obvious vertical layered distribution. The degradation of soil nutrients, the low level of soil fertility, the accumulation of soil alkaline hydrolysis nitrogen content and organic matter, and the utilization of plant roots to nutrients were low. The biodiversity and activity of soil decreased. (2) Quantitative evaluation of soil resilience was divided into four dimensions: soil structure stability, soil water retention capacity, soil fertilizer retention capacity, and soil biological activity. Soil clay particles, silt particles, median diameter, and sand particles contributed 81.609% to main component for soil structure stability. Surface water content, deep water content, bulk density, calcium carbonate contributed 82.379% to main component for soil water retention capacity. Soil organic, alkaline nitrogen, total nitrogen, pH, total potassium, total phosphorus, available phosphorus contributed 85.39% to main component for soil fertilizer retention capacity. Soil urease, alkaline phosphatase, invertase activity, microbial diversity Simpson index, richness Chao index, litter quality, pH contributed 87.373% to main component for soil biological activity. (3) Soil resilience was measured by four aspects: soil structure stability, soil water holding capacity, soil fertilizer holding capacity and soil biological activity. The average soil resilience value was 0.37, 0.33, 0.26, 0.18 in 1995, 2000, 2008, 2015, respectively. The average soil resilience was 0.75 in original soil. Soil biological activity had the positive impact on soil resilience, with an influence coefficient of 0.66. The water retention capacity and fertilizer retention capacity had coefficient of 0.44 and 0.37 on soil resilience.