Effect of solid to solution ratio on biogenic silica determination in coastal sediments

Abstract

The method of DeMaster (1981) for measuring biogenic silica (BSi) in marine sediments was modified. We found a considerable effect of the solid to solution (S/S) ratio on BSi determination in coastal sediments. The BSi contents determined by DeMaster’s method were overestimated due to the contribution of clay mineral-derived extractable Si at a low S/S ratio (<1 g l⁻¹), and incomplete recovery of BSi was observed due to incomplete extraction when using a high S/S ratio (>2 g l⁻¹). For BSi analysis of coastal sediment samples, the BSi content of representative samples must be measured using various S/S ratios to determine the appropriate S/S ratio in order to minimize the contribution of extractable Si derived from clay minerals and to obtain sufficiently efficient extraction with 1% Na₂CO₃ before actual sample measurement. One way to determine the appropriate S/S ratio is to use artificial sediment which has a theoretical Si and clay mineral content similar to the sediment sample composition. Using artificial sediment, the S/S ratio of 2 g l⁻¹ seems appropriate for measuring the BSi content of the coastal sediments investigated in this study, because 99.6% recovery can be achieved.