Stratigraphic and spatial differentiation of chemical properties in long-term fly ash influenced forest soils in the Dubener Heide region, NE Germany

摘要

Long-term effects of fly ash depositions on soil chemical properties and humus morphology were investigated in samples from the Oi (L), Oe (F) and Oa. (H) horizons and mineral topsoils (0-10 cm) in pine stands (Pinus sylvestris L.) near the industrial center of Bitterfeld (Dubener Heide, NE Germany). Along a deposition gradient of 5 sites (8, 16, 14, 18 and 25 kin in distance from Bitterfeld, sites 1, 2, 3, 4 and 5, respectively), organic horizons and mineral soil samples were taken in fall 1998 and analysed for pH (H2O and CaCl2), electrical conductivity, amounts of water- and NH4Cl-extractable cations, and carbon and nitrogen pools. In order to evaluate the temporal development of fly ash affected forest soils, data of this work were compared with results from studies in 1967 and 1988. About 8 years after the last major deposition events, soil chemical properties and humus morphology of the 5 studied sites showed a distinct differentiation along the deposition gradient. Within the relatively short distance of 17 km (i.e. distance between sites 1 and 5), the pH((H2O)) values decreased from 6.3 to 3.9, the portion of basic cations on the sum of NH4Cl-extractable cations decreased from 99 to 31% in the humic horizons, and from 94 to 21% in the mineral topsoil (0 - 10 cm). In general, the sod acidification potential (i.e. the difference between pH((H2O)) and PH(CaCl2)) decreased with increasing distance from the emission center. Pools of OC and Nt in the forest floor generaIly decreased along the investigated gradient, while OC:Nt ratio significantly increased within the diagnostic horizons (i.e. Oe and Oa) from 19 to 24 at sites 1 and 5, respectively. Comparing the concentrations of NH4Cl-extractable basic cations found in 1998 with die results of 1967 and 1988, a loss of basic cations from the forest floor was observed. This trend was particularly evident at the most effected sites (i.e. sites 1 and 2) and during the past decade from 1988 to 1998. Chemical properties and macro-morphology of organic horizons in soils in the Dubener Heide forest area showed a disharmony, implying the need for specific indicative parameters and critical values for chemical properties for forest soils in emission regions.