Testing a statistical curve-fitting procedure for quantifying sediment populations within multi-modal particle-size distributions

This paper describes a series of tests designed to evaluate the capacity of a personal computer (PC) based statistical curve-fitting program called MIX to quantify composite populations within multi-modal particle-size distributions. Three natural soil samples were analysed by a Coulter Multisizer, and their particle-size distributions analysed using MIX software to identify the modes, standard deviations and proportions of their composite populations. The particle-size distributions of the three natural soil samples were then numerically combined in equal proportions using a spreadsheet program to create synthetic particle-size distributions of known populations. MIX was then tested on the synthetic particle-size distributions to see if the modes and proportions it identified were similar to those modes and proportions known to characterize the synthetic particle-size distributions. The main outcome is that MIX can very accurately describe the modal particle size and proportions of the major composite populations within a particle-size distribution. However MIX has difficulty in identifying small populations (those contributing <10 per cent of a total particle-size distribution), particularly when they are located in the central sections of particle-size distributions, overlain by larger populations, or when positioned in the fine tails of distributions. Despite these minor shortcomings, MIX is a valuable tool for the examination and interpretation of particle-size data.