FY 1993

A model for estuarine sedimentation involving marine snow

Lavelle, J.W.

In Nearshore and Estuarine Cohesive Sediment Transport, A. Mehta (ed.), Coastal and Estuarine Study Series, American Geophysical Union, Springer-Verlag, Washington, D.C., 148–166 (1993)

Fine particles, which make up the bulk of the suspended particle mass in estuaries, are assumed to be scavenged by and settle as part of larger fragile aggregates (marine snow). The large settling velocity of those aggregates and their scavenging rate lead to the rapid vertical transport of the smaller particles. Macroaggregates also release fine particles back into the water column during transit to the seafloor. Modeling the two particle populations and their interaction permits a description of suspended particle concentrations and fluxes that a single settling class model cannot provide. Model results are compared to observations in Puget Sound, Washington, of both suspended particles and UCM, a petroleum hydrocarbon mixture having a high affinity for fine particles. The results together show the dominance of fine particles in determining concentration and macroaggregates in determining flux. The effects of resuspension on concentrations and on flux into sediment traps are also made apparent. A time dependent solution to the model shows that fine particles from surface events (e.g. plankton blooms) begin to arrive at the seafloor in a time corresponding to the depth of the water column divided by the settling velocity of the macroaggregates. Overall, the analysis supports the existing view that marine snow is important in regulating the vertical distribution and transport of particles and particulate-borne contaminants.