SUITMA 2003 Nancy - Soil development and classification of anthrosols with vitric/andic properties from lignite ash (Germany)
SUITMA 2003 Nancy
| This abstract is about one of the papers of the Methodology for the study of urban soils and classification theme of the SUITMA 2003 Nancy symposium. |
| Reinhold Jahn,i | Sabine Zikeli,i |
| Michael Kastler.i |
- i - Institute of Soil Science and Plant Nutrition - Martin-Luther-University Halle-Wittenberg.
Introduction
Lignite ash derived substrates cover an area of approximately 6000 ha in Saxony – Anhalt, Germany. Even larger areas have been contaminated by eolian distributed ash particles. Coal burning refuses from power plants have been either sluiced to settling ponds or have been deposited in stock piled landfills, which are no longer in use since 1990. These disposal sites are now exposed to weathering which induces changes in their chemical properties and mineralogical constitution. All sites carry plants, show biological activity and other soil forming processes as e.g. degypsification and enrichment of pedogenic carbon.
Until now it is not possible to classify soils derived from technogenic materials successfully according to the FAO-Legend, Soil Taxonomy or WRB. Many anthropogenic soils key out as Regosols and do not reflect the specificity of the parent material. For practical uses, soil classification is supposed to be (i) ecologically meaningful, (ii) convey information relevant for land use planning and (iii) facilitate land evaluation. The task at hand creates a strong urge to properly represent ecologically relevant soil characteristics and to avoid misleading taxonomic interpretations even for anthropogenic soils. With these examples of soils we propose a way to open the WRB for soils deriving and derived on technogenic-anthropogeomorphic materials.
Materials and method
For our current research work we have chosen 69 ashy layers from 5 disposal sites of different age (5 to 30 years) and different methods of disposal (landfilling and sluicing to settling ponds) as well as one site with eolian deposits. The A-horizons were sampled in the depths of 0-2 cm, 2-4 cm and 4-10 cm to detect changes in those horizons which are the most exposed to weathering. From 10 cm to 100 cm the samples were taken in 10 cm intervals, as far as stratification and changes in substrate made it possible.
Soil samples were sieved to <2 mm. Bulk densities were determined by the core method with five replicates. Ct and Nt were determined on ground samples by dry combustion (vario EL). CaCO3 was measured by dissolution in 42 % phosphoric acid. The evolving CO2 was detected by IR. Gypsum content was determined by precipitation in acetone, followed by dissolution in deionized water and measurement of Ca by ICPAES (Buurman et al. 1996). The calculation of gypsum content was based on CaSO4 ·2H2O. Oxalate extraction of iron (Feo), silica (Sio) and aluminium (Alo) was performed according to Blakemore (1987). The samples were shaken for four hours in the dark, then Feo, Sio and Alo were determined by ICP-AES. pH was measured in 0.01 CaCl2, 1 M KCl and deionized water applying a soil:water-ratio of 1:2.5.
Results and discussion
Lignite ash soils show properties similar to soils derived from younger volcanoclastic materials. In the field they display andic properties like thixotropy, dark colours and high porosity. They are characterised by low bulk densities (0.3 to 0.9 g cm-3), high contents of organic carbon (max. 52%) with a very wide C/N-ratio (max. 122), high cation exchange capacities (max. 157 cmolc kg-1) and high contents of ammonium oxalate soluble compounds consisting of Si, Al and Fe (Zikeli et al. 2002).
Moreover, they exhibit certain soil properties which are uncommon for soils of temperate regions like Saxony–Anhalt. They are characterised by high contents of gypsum (max. 27 %), calcium carbonate (max. 46 %) and high pH values (7-9).
Cation exchange properties of lignite ashes, bulk density, P-retention and oxalate soluble elements resemble those of Andosols. There is a strong correlation between the content of organic carbon (TOC, consisting of unburned lignite particles and pedogenic organic carbon) and the cation exchange capacity (CEC) in most of the investigated profiles. Furthermore, the size of coal particles influences the CEC. Sand-sized coal particles result in high amount of TOC, but comparatively low CEC. A rise of CEC is also induced by a rising content of silt and clay. In medium-textured sluiced lignite ashes with Alo-contents of 3.5 - 4 % CEC is significantly lowered after oxalate treatment. The difference in CEC calculated to Alo and clay results in values of 270 - 500 cmolc kg-1 Alo and 120 - 340 cmolc kg-1 clay respectively. The CECo for the organic matter remains with values of 250 - 360 cmolc kg-1 TOC still high. A high P-retention is also present in the investigated layers. Out of 69 sampled layers, 65 have a bulk density <0.90 kg dm-3. All layers have an Alo+0.5 Feo-content >0.4 % and out of 37 sluiced layers 33 have an Alo+0.5 Feo-content >2 % and fulfil therefore the requirements for vitric or andic horizons.
Conclusions
These soils currently after FAO (1998) key out as Regosols and Arenosols and as such do not reflect the specificity of the technogenic parent material which dominates the properties of these very young soils. To classify those soils more precisely, we suggest to widen the WRB-rules of FAO (1998) and (i) to include technogenic materials into the list of "anthropogeomorphic soil materials", (ii) to include soils from mainly technogenic materials into the group of "Anthrosols" (as Technogenic Anthrosols) and (iii) to recognise other characteristics and properties at the third and fourth level according to the groups of related natural soils. Such soils, fulfilling the requirements of andic properties as the soils derived from sluiced lignite ashes, will than key out as Vitri- or Andi-Technogenic Anthrosols (Regic) if finer than loamy sand or -(Arenic) if loamy sand or coarser. The soils derived from tipped lignite ashes will key out as Areni-Technogenic Anthrosols (Calcareous) or (Gypsiric).
References
- Blakemore L.C., P.L. Searle and B.K. Daly 1987. Methods of chemical analysis of soils. New Zealand Bureau Scientific Report 80, New Zealand Soil Bureau, Department of Scientific and Industrial Research Lower Hutt, New Zealand
- Buurman P., B. van Lagen and E.J. Velthorst 1996. Manual for soil and water analysis. p. 311 Leiden, The Netherlands
- FAO (1998): World Reference Base for Soil Resources. World Soil Resources Report 84. Rome
- Zikeli S., R. Jahn and M. Kastler 2002. Initial soil development in lignite ash fills and settling ponds in Saxony-Anhalt, Germany. J. Plant Nutr. Soil Sci. 165, 530-536
