Analysis of the effect of organic matter content on the architecture and sinking of sediment aggregates

Analysis of 52 data sets totaling 1226 points of the size and settling velocity of suspended sediment collected in various ecosystems worldwide allowed the establishment of relations between sediment density and fractal parameters for a wide range of organic matter contents. While the fractal dimension showed some nonlinearities against sediment density and organic matter content for sizes smaller than 1mm and larger than 10mm, more than 50% of the average settling velocities were nearly invariant and ranged only between 1 and 4mm/s regardless of size spanning nearly 4 orders of magnitude and organic matter fraction ranging between about 0 and 1. Analyses suggested that settling invariance was the result of a trade-off between the aggregate bulk (excess) density and its fractal architecture. An analysis of the governing quantities of the aggregate fractal scaling (i.e., the primary particle size and fractal dimension as well as its rate of change over the aggregate size) explained how these ultimately affected the settling rate. [Display omitted] •The fractal dimension of biomineral aggregates is affected by the organic matter.•This effect is nonlinear with the content and quality of organic matter.•Size- and density-dependent fractal scaling can be used to describe biomineral aggregates.•The settling rate of biomineral aggregates is nearly invariant with the aggregate properties.