Rapid fines assessment: A quantitative volumetric method to assess fines content in marine soft sediments

Abstract

Methods for sediment classification commonly use particle size analysis (PSA) by weight to describe sediment size fractions and other physical sediment properties. For many applications, the sediment parameter controlling the physical, chemical, and biological processes associated with the seabed is determined by the volume of aggregated fine particles. For example, the apparent weight of the fines fraction in multiple sediment samples across an area can be similar, but there can be large variations in the volume this fine fraction occupies. The volumetric percentage of fines can affect sediment porosity, tortuosity, and permeability and hence biogeochemistry, e.g., the oxygen penetration depth or diffusion rates. Development and testing of the rapid fines assessment (RFA) has shown that this simple method of measuring the ratio of fines to sand volume layers within a settled sediment sample can give high accuracy estimates of percentage fines by volume. Data presented here demonstrate that a volumetric approach can better describe variations and discriminate between sample differences at low percentage fines by weight. This is key to defining the boundary between sediments dominated by diffusion and those which have pore-water advection in the upper layers. The increased resolution which the method provides is useful in tracking site changes caused by human impacts and over various spatial or temporal scales. It is a rapid, inexpensive, and simple technique to implement in the laboratory, and one which can be used in the field to aid or guide sampling site selection.