AGGREGATE DISTRIBUTION AND ORGANIC CARBON MINERALIZATION OF RECONSTRUCTED SOILS FILLED WITH COAL GANGUE IN A HUAINAN COAL MINING AREA, CHINA

Coal mining areas typically use coal gangue to infill mined areas. The effect of adding coal gangue to the overall soil characteristics in these areas is an area of research which is often not investigated. The distribution of aggregates and organic carbon mineralization in a soil are importance indices for examining the improvement of the soil, indices which may have detrimental effects on soil organic carbon (SOC) dynamics and soil aggregate stability. However, few investigations have been undertaken on the distribution of aggregates and organic carbon mineralization in reconstruction soil. Thus, soils from the Huainan mining area were investigated. Surface soils (0-10 cm) from normal land and reconstruction soil that the overburden depths are 15-40 cm, 40-60 cm, 60-80 cm and 80-100 cm were collected. The soils were classified according to aggregate size (2, 1, 0.5, 0.25, 0.1 and 0.053 mm) and SOC content of the aggregates, and they were subjected to a 30-day soil carbon mineralization incubation experiment. The normal soil contains more SOC content, C mineralization potential and better aggregate stability as it contains more aggregates greater than 2 mm in size than the reconstruction soil. The presence of coal gangue exerts significant influence on SOC accumulation, aggregate distribution, SOC content in the aggregates and C mineralization of the topsoil. The SOC content in the macro-aggregate has a significant negative correlation with the mineralization rate and SOC is beneficial to the formation of macro-aggregates and the stability of soil aggregates. As a general rule, the greater the SOC content, the greater is the macro-aggregate and the higher is the stability of the soil aggregates. This study demonstrated that the effects of coal gangue on topsoil decreases with an increasing thickness of covering soil. The optimum thickness of soil cover for the reconstructed soil is >80 cm.