SPATIAL-DISTRIBUTION OF SUSPENDED POLLEN IN THE MISSISSIPPI-RIVER AS AN EXAMPLE OF POLLEN TRANSPORT IN ALLUVIAL CHANNELS

A comparison of pollen concentrations on a velocity profile within a c ross-section of the Mississippi River at St. Francisville, Louisiana i s used to examine processes of pollen suspension and transport. The pr ofile consists of five verticals sampled at six different depths paire d with current velocity measurements, as well as surface samples. Our results show no significant correlation between pollen load and veloci ty. Application of sediment mechanics to pollen grain transport demons trates that such relationships should not be expected in a river. Due to the negligible terminal fall velocities of pollen grains, one shoul d expect a nearly uniform distribution of pollen load with river depth . Differential deposition of pollen grains due to spatial heterogeneit y in a fluvial environment is also an unlikely phenomenon. In the Miss issippi we find that other mechanisms, such as pollen rain and resuspe nsion of grains from the bed, are more likely to control the spatial d istribution of pollen.