Seasonal Changes in Zooplankton Biomass and Grazing in a Temperate Estuary, South Africa

Suspended sediment transport and sedimentation dynamics in the sub-tropical Richmond River estuary were investigated between July 1994 and June 1996. During low flow months the estuary received net sediment inputs from the continental shelf; during high flow the estuary exported sediment to the continental shelf depending on the magnitude of floods. Flow-weighted sampling along with a one-dimensional unsteady flow hydrodynamic model of the estuary estimated that about fifty percent of the flood-borne suspended sediment was transported through the estuary to the continental shelf during two minor floods (with a 2year return period), whereas, one hundred percent of the flood-borne sediment was transported to the continental shelf during a moderate flood (with a 5-year return period). Marker horizons confirmed a net accumulation of sediment in the Richmond River estuary at the salt-fresh water interface during all post flood recovery stages.