Physical and chemical properties in reclaimed soils in a stand of Robinia pseudoacacia from Mini Maritsa Iztok basin in Southern Bulgaria

Toma Shishkov, Emil Dimitrov and Irena Atanasova

Abstract: The paper examines physical and chemical properties in reclaimed soils result of restoration practices took place in the surface mining industry in the region of the “Mini Maritsa Iztok”, Stara Zagora district in Southern Bulgaria. In brown-coal surface mining, the overburden (the earth and rock sediments lying above the coal seam) is first removed, and the exposed brown-coal (lignite) is then extracted. Priority task for post mining operations is the environmental protection aiming at the sustainable development, restoration and improvement of the environmental conditions. To fulfill this aim, a systematic survey as well sampling was done of overburden terrains including two soil profiles and three additional surface sites in a stand of Robinia pseudoacacia. Samples were analyzed for particle size distribution, content and composition of organic substances, cation excange capacity, soil bulk density, soil moisture content at field sampling, soil particle density, porosity and soil moisture content at different matric potentials. In reclaimed soils the different sized mineral mechanical elements are inherited during the technical activities of excavated materials. The organic matter in the investigated reclaimed soils was not directly dependent on the local environmental conditions but was result of technology of reclamation of landscape. The studied reclaimed soils under Robinia pseudoacacia contain an amount of ancient organic substances that cannot be decomposed, due to the nature of stable carbon. Despite the high content of organic substances, soil particle density was identified also as high particularly in the profile 1 at the depth 68-97 cm. This specific feature related to the physical properties of reclaimed soils is probably due to the presence of brown-coal particles involved in the mixed mineral materials have deposited in the East Dump Site. The manifold relationship of bulk density and organic matter, total porosity, gravimetric water content and hygroscopic water content was faint and irregular. The intrinsic peculiarity of high mobility of organic substances was identified and the specific relationship within different fractions of extractable organic carbon. Probably the relationship with bulk density is not clearly expressed in case of labile organic matter not bound to the soil mineral part where content of extractable carbon was extremely very high. Humic acids by their molecular weight and structure are very similar to those of fulvic acids being low molecular and with predominance of aliphatic over aromatic moieties in their molecules. Soil pH (H2O) was diverse from acidic to neutral. Soil adsorbent was affected by acidification so there was evidence of initial destructive processes of the soil adsorption complex. Reclaimed soils were characterized by relatively high degree of saturation with bases (67-82%) in profile 1 and very high saturation (81-95%) in profile 2.

Keywords: lignite; Mini Maritsa Iztok; physical and chemical properties; reclaimed soils; surface mining; sustainability

Date published: 2022-12-09