Quantifying simulated fine sand fraction in muddy sediment using laser diffraction

Abstract

The objective of this study is to verify whether low amounts of fine sand added to a muddy sediment matrix can be detected and quantified with accuracy using a Mastersizer 3000 (Malvern Panalytical) laser diffraction particle-size analyzer equipped with a Hydro LV large volume liquid dispersion module. To achieve this goal, a postglacial sediment sample was sieved to recover naturally co-occurring sand and clay–silt fractions. Sand in the range of 1%–7% by weight was added to the clay–silt at three concentrations (88, 132, and 276 mg dry weight) and each sample was duplicated. A very strong linear relationship was found between the measured % volume of sand added and the actual weight of sand added to the mud. Sand representing as low as 1% by weight could be detected. On average, there was only a 0.7% absolute difference between the measured and actual % sand values (range 0.02%–1.65%). Sample concentration had a negligible impact on the measured % sand. A range of plausible values for the refractive and absorption indexes, essential parameters for the Mie theory calculation of the size distribution from the measured light scattering, also had very small impact on the measured % sand. The demonstrated possibility of detecting a small input of fine sand to muddy sediment provides a basis for studies using grain-size data to reconstruct past and modern detrital inputs and sediment transport variations.