Distribution of silicon in soils and sediments of a small catchment area: similarities and differences.

The uptake and transformation of silicon (Si) by terrestrial plants is of importance for both the plants themselves and for the transport of Si from the watershed. The occurrence and transport of potentially bioavailable Si pools from soil in the drainage area to rivers, lakes and the sea may significantly influence the phytoplankton composition and ecological state of the receiving water body due to complicated ecological interactions. The distribution of biogenic Si in soil, seston (suspended particles), and sediment in samples from a small watershed in Southern Finland was studied and the different compartments compared to each other and to environmental variables. The biogenic Si content in the different parts of the watershed varied, and biogenic Si produced by diatom algae in the aquatic part of the watershed appeared to be more important than the transformation of dissolved Si into phytoliths by terrestrial plants in the soil. More information on the variability of the biogenic Si (phytolith) content in different types of soil and on the differentiation between diatom and phytolith Si in waters are needed.