Spatial distribution characteristics and environmental significance of phytoliths in surface sediments of Qingshitan Lake in Southwest China

Abstract

Fossil phytolith assemblages in lake sediments are widely used to reconstruct past vegetation patterns and dynamics, especially in subtropical environments. However, our understanding of how hydrodynamic conditions (river input and lake basin sedimentological processes) influence the transportation and taphonomy of phytoliths in lacustrine sediments is limited. The aim of this study is to use phytolith assemblage and grain size analyses of Qingshitan Lake surface sediments to identify the distribution characteristics and main transportation modes of phytoliths in lakes. Our results show that the grain size of surface sediments changes across different lacustrine areas of Qingshitan Lake. The median diameter (Md) and volume moment mean diameter (D(4,3)) of surface sediments gradually decreases with distance from the inlet river mouth. The phytolith assemblages of surface sediments vary between sampling locations in the lake. The percentage of woody dicotyledon phytoliths decreases from the estuary delta to the central lake basin, and correlates with the Md and D(4,3) of lake sediments. We find that phytolith assemblages in the riverine delta are mainly influenced by hydrodynamic (river input) processes and record the vegetation cover of the Gongping River catchment. Assemblages in the central lake basin are affected not only by riverine influences but also by eolian transport and similarly reflect the local vegetation. Investigating the relationships between the phytolith assemblages and sediment grain sizes in lakes may make it possible to identify the phytolith source area, which is crucial information to interpret assemblages and indices.