Indicative properties of fly-ash affected forest soils in Northeastern Germany

Many forest ecosystems in Germany are strongly influenced by emissions of p ollutants like SO2 and alkaline dusts. To quantify and evaluate the consequ ences of long-term fly ash deposition on forest soils, a study was conducte d in pine stands (Pinus sylvestris) in the Dubener Heide in Northeastern Ge rmany. This forest area has been influenced mainly by emissions from coal-f ired power plants and the chemical industry of the industrial region Bitter feld-Wolfen-Zschornewitz since the early 1900. The study sites are located along a fly ash deposition gradient of 8, 16, 14, 18, and 25 km away from t he main emission source in Bitterfeld (sites 1, 2, 3, 4, and 5, respectivel y). Samples of the organic horizons (Oi, Oe, and Oa) and mineral topsoil (0 -10 cm) were taken in fall 1998 and analyzed for their ferromagnetic suscep tibility and total ash content. Scanning electron microscopy (SEM) and ener gy dispersive X-ray microanalysis (EDX) were performed on selected samples to differentiate between the pedogenic and atmospheric origin of the minera l components in the organic horizons. As a result of the long-term depositi on. ferromagnetic fly ash components are mainly accumulated in the Oe and O a horizons of the forest soils studied. Ferromagnetic susceptibility was si gnificantly higher (p less than or equal to 0.05) in the Oe horizon of site s 1 and 2 compared to sites 3, 4, and 5. Unusually high total ash contents for organic horizons of > 74 % were determined in the Oa at all sites. SEM revealed 3 distinct features of persistent fly ash deposits from coal-fired power plants within the organic horizons that can be defined as "stable gl asses" with magnetic properties, aluminum-silicate-minerals, and slag fragm ents. SEM and EDX indicated that a great portion of the mineral particles f ound in the organic horizons of forests soils influenced by fly ash are fro m atmospheric sources. For detection of atmospheric lignite-derived deposit ion into forest soils, the Oe and Oa horizons have to be considered as spec ific diagnostic horizons because they show indicative properties for such s oils.