Chemical and physical characteristics of substrate material for plant growth on coal wastes in rangelands of Kiasar, Sari, Mazandaran province

Background and objectives Mining results in degradation of rangelands ecosystem structure and function. Coal mining in rangelands produces significant quantities of waste dumps in mining area which are considered as the main environmental pollutants in the site and surrounding ecosystems. Vegetation restoration in mining area could reduce soil pollution and could be of great help in restoring the landscape. The aim of this study was to assess the physical and chemical properties of abandoned coal wastes in rangelands of Kiasar, Mazandaran province, Iran. This information could benefit the vegetation restoration on coal mine waste by identifying the factors that limit plant growth and establishment on coal wastes. Methodology This study was carried out in Kiasar coal mine in Sari, Mazandaran province, Iran. The mine site was founded in 1983. This area has an elevation of 1030 m above sea level characterized by an average rainfall of 520 mm and mean temperature of 13.2 C°. A total of 10 coal waste dumps were abandoned in the area during last three decades. We found six age classes according to the time since these wastes were abandoned in surrounding area of the mine site. The identification was done with the help of experienced engineers and local workers. The age classes were 4-6, 8-12, 15-18, 19-21, 22- 24 and 25-27 years since abandonment. Natural rangelands around the mine site were selected as the control site which are currently under livestock grazing. Waste and soil samples were collected using random-systematical method from 0-20 cm depth. Then samples were put in plastic bags until chemical analysis. The soil samples were air-dried at room temperature. Then texture, moisture, pH, EC, OC, CaCO3, N, P, K, Cu, Fe, Cd, Ni, and Pb were measured in the laboratory. Data were analyzed using one-way ANOVA and means were compared using Duncan multiple tests.   Results The analysis of variance showed that all measured parameters of soil and coal except nitrogen and potassium were statistically different among coal wastes and nearby rangelands. Coal wastes were found with lower percentage of silt, clay, moisture and lime than those in surrounding rangelands. However, these properties were not significantly different between abandoned coal wastes. Most of the abandoned wastes were neutral or alkaline with EC less than 1.5 ds/m. An exception was found in waste which were abandoned 22-24 years ago that its pH was acidic and EC was more than 1.5 ds/m. Organic matter in all coal wastes and available phosphor were greater only in 22-24 years abandoned waste compared with those in surrounding rangelands. There was no significant effect for Cd and Ni while for other heavy metals the coal wastes had greater Cu and Pb concentrations than those in the soil of surrounding rangelands. The concentration of Fe in the soil of nearby rangelands was significantly greater than that in abandoned coal wastes. We found that some physical and chemical properties of abandoned coal wastes changed during the time since abandonment resulting from increase in the organic matter, phosphorus and Pb in older waste dumps in this site. Conclusion Our findings showed that the amount of moisture is one of the limiting factors for plant growth on coal wastes. This is because of the sandy and sandy-loamy texture, unstable slop of coal dumps, and high porosity. The waste dump under erosion and leaching had high EC and low pH. The amount of organic matter and available phosphor were observed to be less than the range needed for plant growth. The concentration of heavy metals were in normal range even after a long time since abandonment of coal wastes. Remediation treatments are recommended in similar restoration projects to promoting plant growth and establishment.