|
Environments |
1 Department of Environmental Science, University of Stirling, Stirling FK9 4LA, UK
2 Headland Archaeology, Albion Business Centre, 78 Albion Road, Edinburgh EH7 5QZ, UK
3 Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, UK
Pedological, palynological, soil-micromorphological, geochemical and soil-faunal data are presented for a weakly developed free-draining ferric podsol soil profile in which three securely dated, known-age inputs (non-native tree pollen, spheroidal carbonaceous particles, 137Cs) have been added to the soil surface and incorporated over the last c. 150 years, from c. 1840 AD. We can thus observe the mechanisms of particle incorporation over time-spans appropriate to those of pedogenic processes, and analyse the rates, depth, extent and significance of mixing processes in a soil type that has often been seen as providing secure stratigraphic contexts for subfossil pollen analysis.
Our data indicate that pollen and other particles are thoroughly and completely mixed within the L/F horizon of podsols. Mixing occurs predominantly by ingestion and bioturbation by large near-surface feeding invertebrates. Mixing is also very rapid. Transfer of pollen to lower organic horizons occurs through the liberation of pollen as large invertebrate excrement is itself ingested by enchytraeid populations, but bioturbation in these lower horizons is insufficient to move further the already-mixed pollen assemblages. The absence of earthworm populations in these acid soils means that subsequent vertical transfer to mineral horizons does not occur in any significant way. This ability of organic horizons in podsols to store pollen, the complete mixing of particles in near-surface horizons, and the prolonged time-spans over which these mixing processes can operate, indicate that resultant pollen stratigraphies are normally probably too coarse in temporal resolution to be of value in palaeoecological interpretation.
