Influence of environmental conditions on the ecological quality of wood biomass growing on different soils and geological background

Abstract

The aim of this study was to evaluate the influence of environmental factors, particularly the geological substrate, soil properties, and atmospheric pollution, on the elemental composition of ash produced from wood biomass combustion. The study also assessed the implications of these factors for the use of wood biomass as a high-quality energy resource and for the safe utilization or disposal of the resulting ash. The study was conducted in six forest areas in Poland, differing in soil types (natural and technogenic), geological substrates (sands, ultrabasic rocks, post-industrial waste), and historical dust deposition rates. Two coniferous and two deciduous tree species were selected from each area, from which samples of wood, bark, and small twigs were collected. Soil samples were collected as cores to a depth of 30 cm. Biomass samples were dried, crushed, and combusted in stages at controlled temperatures. The elemental composition of the ash was analyzed using ICP-OES and ICP-MS, determining macro- and microelements as well as potentially toxic elements. The results were verified against reference materials and repeated three times. The elemental composition of the soil was determined using XRF, and its pH was measured potentiometrically. The chemical composition of wood biomass ash varies depending on species, plant part, and location. In most cases, Ca was the dominant element, with K and Mg occurring in variable proportions. Bark and twigs often contained more Fe, Al, and trace elements than wood. High concentrations of Zn were noted particularly in birch, while Cd and Pb were elevated in many samples, especially in contaminated areas and on technogenic soils, with Cd accumulating more readily in wood than Pb. Environmental conditions and tree species determine the quality of biomass as fuel and the potential use of ash for soil fertilization. Wood reflects soil composition, while bark, twigs, and needles accumulate air pollutants, particularly in coniferous species. Anthropogenic elements (Pb, Cd, Sn, Sb) accumulate primarily in above-ground parts, but can also originate from the soil. Cd is more mobile than lead and accumulates more readily. Birch hyperaccumulates Zn, which makes its ash unsuitable for use as a fertilizer. Most ash samples did not meet fertilization standards.