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 1 mm and larger than 10 mm, more than 50% of the average settling velocities were nearly invariant and ranged only between 1 and 4 mm/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.