Spatial distribution of suspended pollen in the Mississippi River as an example of pollen transport in alluvial channels

Abstract

A comparison of pollen concentrations on a velocity profile within a cross-section of the Mississippi River at St. Francisville, Louisiana is used to examine processes of pollen suspension and transport. The profile consists of five verticals sampled at six different depths paired with current velocity measurements, as well as surface samples. Our results show no significant correlation between pollen load and velocity. Application of sediment mechanics to pollen grain transport demonstrates that such relationships should not be expected in a river. Due to the negligible terminal fall velocities of pollen grains, one should expect a nearly uniform distribution of pollen load with river depth. Differential deposition of pollen grains due to spatial heterogeneity in a fluvial environment is also an unlikely phenomenon. In the Mississippi we find that other mechanisms, such as pollen rain and resuspension of grains from the bed, are more likely to control the spatial distribution of pollen.