Monday, 10 July 2006

Phytolith Transport in Sandy Sediments: Experimental Data.

O. Fishkis, J. Ingwersen, K. Pustovoytov, and T. Streck. Univ of Hohenheim, Inst of Soil Science and Land Evaluation, Stuttgart, Germany

Phytoliths are minerals of amorphous silicon dioxide (SiO2*nH2O) forming in living plants. Morphological plant-specificity of phytoliths at least on a family level and their durability in soils make phytoliths a beneficial tool in paleoenvironmental studies. However, the mechanisms and velocities of phytolith transport through the soil profile are poorly understood, causing difficulties in the interpretation of phytolith data in paleoenvironmental research. This paper presents for the first time experimental data on velocities of phytolith transport in sandy sediments. Columns 23-cm length and 11 cm in diameter were filled with phytolith-free homogeneous sandy sediment. Ash of reed (Phragmites australis), known as an abundant phytolith producer, was added to the uppermost one-centimeter layer of each column. The experiment was carried out under two water flux regimes to simulate annual moderate and extra-humid precipitation. After running the experiment for 5 months, the columns were sliced into layers, and phytoliths of each layer were extracted. Particles extracted (4-63 μm) were counted by a particle counter and then, phytolith percentage was determined in the same sample under a polarized microscope. Besides, the absolute phytolith number, the size distribution of phytoliths was also defined by microscopy. Finally, the average depth of phytolith migration and size-dependence of phytolith transport were determined. The average phytolith transfer was 0,27 cm/yr under moderate humid precipitation and 0,37 cm/yr under extra-humid water flux. The Size distribution of phytoliths over depth showed faster transport of smaller phytoliths (5-35 Ám) and slower migration of the large ones (100-300 Ám). Thus, this study revealed that, the labeling of phytoliths with a fluorescent dye that we are currently working on will enable us to study phytolith transport in intact cores.

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