A mathematical model is developed to investigate the exchange of natural trace sediments between an estuary and an adjacent continental shelf, assuming that the tracer originates from the shelf. The model is run for four cases representing various landward-seaward sediment transport patterns at the entrance to the estuary. The results show that landward flux of the tracer takes place independent of net sediment transport direction. This observation implies that there is some transport from the source but that the mere presence of the tracer in the estuary is not necessarily indicative of net landward sediment transport. The model also suggests that the magnitude of the tracer concentration in any estuarine stratigraphic record is controlled by 1) sediment discharge associated with the river input, 2) tracer concentration at the source, 3) processes of dispersion, 4) patterns of landward-seaward net sediment transport, and 5) the amount of time required for equilibrium to occur. Hence, net transport pathways can be defined on the basis of the magnitude of the tracer concentration in estuarine sediments, when compared against a critical level.

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