PHYTOLITH DEPTH FUNCTIONS IN SURFACE REGOLITH MATERIALS

Abstract

Phytoliths are microscopic opaline silica particles that are common in many soils, forming a vital part of the global biogeochemical silica cycle (Alexandre et al. 1997, Conley 2002). Most are placed on the surface of the soil within litter and are released from their enclosing plant material by a combination of decay and digestion by soil fauna. Most studies of the distribution of phytoliths with depth in soils find a concentration of phytoliths in the topsoil with a decline in abundance with depth. A concentration at depth within a sediment has often been used as evidence for environmental change; however other interpretations have been suggested which change the basis of this explanation. In considering this issue we have recognized three distinct types of depth functions which are used as a framework to evaluate the contributing processes. The focus of this note is the distribution of phytoliths as reported in the Handbook of Australian Soils (Stace et al. 1968), which provides estimates of the relative abundance of phytoliths in each depth interval examined in sixty-nine profiles. These data are sufficient to describe phytolith depth distribution diagrams or Phytolith Depth Functions (PDFs) that can be evaluated in terms of site variables and soil type (Great Soil Group of Stace et