| The exploitation of coal mining had damaged lots of land resources, which caused the surface subsidence, the depress the erosion resistance of soil, the decrease of soil fertility consists of, the depress of soil nutrient, the depress of soil enzyme activity, the depress of the diversity of soil fauna and so on. Restoration of soil fertility quality in coal mining subsidence area was intensively concerned. To analyze the relations between soil physical and chemical properties, soil animals, and soil enzyme activities of coal mines in different collapse types to evaluate the soil fertility of ecologically which were significant for comprehensive treatment of coal mining subsidence region and its reclamation later.Three types of subsidence from coal mine in Huainan were collected for evaluation, including unstable subsidence region, stable subsidence region and restoration region. The typical characteristics of different types of subsidence soil were selected, including soil physical and chemical properties, soil enzyme activities, soil animals and so on. The spatial distributive traits of soil physical chemical properties and soil enzyme were analyzed. The spatial distributive traits of soil animal were analyzed. The effects of heavy metal pollution on soil animal community structure were analyzed. The main findings of this study were summarized as follows:(1). In the studied region, the soil layer at a depth of 0-30cm was mainly composed of powder particles and sand grains, while having the lowest proportion clay particles. The soil layer in the unstable subsidence region had an increasing amount of clay particles from top to bottom at a proportion in unstable subsidence region> stable subsidence region> restoration region. Total nitrogen content varied in different types of subsidence land. The soil layer at depth of 0～10cm in unstable subsidence region had the highest proportion of total nitrogen, significantly greater than that in stable subsidence region and restoration region. The total nitrogen content showed a similar law in soil layers at depth of 10-20cm and 20-30cm. And contents of soil available phosphorus, alkali hydrolyzable nitrogen and organic matter shared the same trend. In the studied region, the content of soil organic matters had highly significant negative correlation with soil pH and soil layer depth, but had highly significant positive correlation with the content of moisture, alkali hydrolyzable nitrogen, total nitrogen, and total potassium, indicating that the content of soil organic matters had highly significant correlation with the content of nitrogen, and affected the balance of carbon and nitrogen.(2) As the coal mine transforms from unstable subsidence region to stable subsidence region, soil sucrase activity showed a decreasing trend, while that was somewhat higher in restoration region than in stable subsidence region. As the soil layer deepens, the soil sucrase activity was decreasing constantly, and it showed a similar law in different soil layers in all the regions. In the studied region, the activity of soil urease, catalase and dehydrogenation had the same variation characteristics enzyme basically as that of the soil sucrase, manifested as unstable subsidence region> restoration region> stable subsidence region, with the enzyme activities decreasing as the soil layer deepens. The soil urease, sucrase and soil physics and chemistry properties had a fair correlation with other activity indexes, so the soil urease and sucrase could be used as effectiveness indexes to assess the changes of soil fertility in the coal mining subsidence region.(3) Dominant families of soil animals in the studied region consisted of collembola, diplura, nematode and enchytraeidae, accounting for 78.5% of all the catched soil animals, among where the common groups were formicidae, muscidae, and hemipteran, accounting for 16.4% of all the catched soil animals; The other four species were rare groups which were only 5.1% of all catched animals; The species number and individual number presented as unstable subsidence region> stable subsidence region> restoration region.(4) Heavy metal pollution constitutes certain degree of influence on community structures of soil animals. The numbers of groups and individuals went down of with aggravation of the pollution. With the increased heavy metal pollution index, both diversity index and evenness index of soil animals went down but the dominance index tends to increase. The soil animal community structural index maight provide a scientific basis for monitoring heavy metal pollution of soils, and also could be used as an indirect index to assess the soil environment quality.(5) Integrated Fertility Index (IFI) and Soil Enzyme Index (ISE) were calculated which were based on soil physics and chemistry properties and enzyme activities, the result showed that the IFI and the ISE were the highest in unstable subsidence region, and higher in restoration region than in stable subsidence region. The soil biological fertility had changing characteristics of decrease along with increase of soil layer depth. Soil physical and chemical properties and soil enzyme activities can be used as scientific indexes to assess the soil biological fertility in the coal mining subsidence region. |
