Organic Matter in Soil of Coal Mine Dumps in Siberia: Quantitative and Qualitative Assessment

Currently, due to the issues related to carbon emissions and sequestration, particular interest is being drawn towards technogenic landscapes represented by coal mine spoil heaps. First, this is due to the significant presence of potential sources of climate-active gases in the form of carbonaceous particles within the spoil heaps. Second, the accumulation of organic carbon in the form of humus substances occurs as a result of soil formation on the surface of technogenic landscapes. Given that the area of disturbed coal mining territories in certain regions amounts to hundreds of thousands of hectares and continues to increase, research on coal mine spoil heaps is necessary for the development of measures to achieve carbon neutrality. The research was conducted on old dumps ( over 30 years old) coal mining enterprises in the Kuznetsk (Kemerovo Oblast), Gorlovka (Novosibirsk Oblast), and Kansk-Achinsk (Krasnoyarsk Krai) coal basins, Minusinsk (Republic of Khakassia) and UluKhem (Republic of Tuva) deposits, within lithogenetic and geographic sequences (see the Table). The dumps comprise fragmented dense sedimentary rocks and clayey rocks. The objects of the study were non-carbonate soils of coal mine spoil heaps - initial, organo-accumulative, soddy, and humus-accumulative embryosols (Spolic and Hyperskeletic Technosols). Field morphological descriptions of embryosol profiles were conducted using conventional soil science methods. The carbon and nitrogen content were determined by dry combustion using a CHN analyzer and by wet combustion method with oxidation of 0.4N K2Cr2O7 in 50% sulfuric acid solution, heated to 150 degrees C in a drying cabinet. The calculation of the ratio of carbon determination results provides an indication of the degree of pedogenic maturity of organic matter. Research results have shown that the content of organic carbon determined by wet and dry combustion methods in embryosols significantly differs in evolutionary, geographical, and lithogenetic sequences of objects (see the Figures). The degree of pedogenic maturity expressed through the ratio of carbon determined by different methods has been applied to assess the qualitative state of organic matter systems and their transformation. It has been demonstrated that the maximum values of pedogenic maturity were found in the studied embryosols of Brown Coal deposits, ranging from 63.8% to 100%. The minimum values were observed in embryosols on the spoil heaps of Anthracite deposits. It has been established that the degree of pedogenic maturity increases in the evolutionary sequence of embryosols, with humus-accumulative embryosols showing values within the range characteristic of zonal black soils (see the Figures). Research results have shown the stability of organic matter to oxidation and its ability to persist unchanged in the substrate of coal spoil heaps for a long time. Along with the processes of organic matter accumulation during soil formation, this allows us to conclude that the Siberian coal spoil heaps do not release carbon, but, on the contrary, sequester it. The article contains 4 Figures, 1 Table, 42 References.