Stratigraphic distribution of lignite-derived atmospheric deposits in forest soils of the upper Lusatian Region, East Germany

Abstract

Atmospheric fly ash emissions from lignite-fired power plantsin the Upper Lusatian and Turowan mining districts stronglyaffected large forest areas along the German-Polish border. Afield study was conducted in old spruce stands (Piceaabies (L.) Karst.) to assess the stratigraphic distributionof fly ash in the forest floor and mineral topsoil in the St. Marienthal forest area in the eastern part of Saxony,Germany. This forest area is subjected to long-termatmospheric depositions by two German and one Polish powerplants since the early 1900s. The three study sites arelocated along a fly ash deposition gradient of 3, 6 and 15 kmfrom the power plant in Turow (Sites Ia, II and III,respectively). An additional site (Site Ib) at a distance of 3 km from Turow was chosen to study the influence of vegetationtype on fly ash deposition intensity in forest soils. Samplesof the humic layer (Oi (L), Oe (F) and Oa (H) horizons) andmineral soil (0–10 cm) were taken in Spring and Fall 1999 andanalysed for their ferromagnetic susceptibility and total ashcontent. Particle size distribution, magnetic susceptibilityof individual size fractions, scanning electron microscopy(SEM), and energy dispersive X-ray microanalysis (EDX) wereperformed on selected samples to evaluate the origin ofmineral particles found in the forest floor. High magneticsusceptibility of the Oa and Oe horizons is a result of thelong-term accumulation of lignite-derived atmospheric depositsin the forest floors of the studied area. Pure conifer stands(year-round filtration of airborne pollutants) resulted inhigher inputs of ferromagnetic fly ash particles in forestsoils. Unusually high total ash contents for humic horizons(up to 77%) were determined in the Oa and Oe horizons atSites Ia and IIb, indicating the need for a new classificationsystems for the organic layer in forest soils near coal-firedpower plants. SEM revealed 4 typical phases of persistent flyash deposits formed by combustion of Lusatian lignite: (1) iron-containing `stable glasses’, (2) aluminium-iron-silicate-minerals,(3) slag fragments and (4) lignite-derived fossilcarbon. Particle size analysis, magnetic susceptibilitymeasurements and SEM-EDX techniques indicated that a greatportion of the mineral particles found in the humic horizonsof forests soils are from atmospheric sources. Fly ashaccumulation consisting of ferromagnetic minerals contributesmainly to the 125–63 and <63 μm fractions in soils. EDXanalysis revealed that atmospheric input of lignite-derivedfly ash increases the contents of the following ecologicalrelevant elements in soils: carbon, iron, aluminium, calcium,potassium, sulphur, titanium and sodium.