A new method to remove biogenic silica from lake sediments by chemical dissolution coupled with sonication

Abstract

The grain-size distribution of lake sediments is a crucial proxy for paleoclimate reconstruction, as it is closely related to the transport dynamics of clastic materials from the surrounding land. However, the presence of biogenic silica, particularly remains of diatom frustules, can significantly bias the grain-size distribution of lake-sediment samples. To remove this component, an alkaline solution, usually consisting of sodium carbonate, is commonly used during sample preparation. However, the efficiency of this method has not been fully verified under the microscope and with statistical tests. This study aims to assess the efficiency of removing diatoms from sediment samples under different concentrations and treatment durations of Na₂CO₃ solution, and with and without sonication. The removal efficiency was assessed using microscope examination. Two sets of sediment samples from Huguang Maar Lake with high contents of diatoms but different species compositions were used. Results show that increasing sodium carbonate concentration and treatment duration improved the removal efficiency. A treatment with 2 mol L⁻¹ Na₂CO₃ solution coupled with ultrasound vibrations for 4 h was found to be the most effective method for removing biogenic silica from the lake-sediment samples that were investigated. Differences in the removal efficiency between the two samples might be due to the different dominant diatom species in the samples. The new method provides a more reliable and effective procedure for removing diatoms from lake-sediment samples.