Suspended-sediment distribution and certain aspects of phytoplankton production off Georgia, U.S.A.

Abstract

Coastal water of the central Georgia embayment is composed of two distinct zones — the turbid zone and the boundary zone — that are clearly different from the shelf water. The turbid zone is a band of lagoonal and nearshore water that has relatively high concentrations of dissolved and particulate substances. During ebbing tides, contacts between the turbid zone and the boundary zone are well-defined by frontal systems of inlet plumes. In the boundary zone, a gradational transition exists between the turbid zone and the relatively constant but much lower concentrations of dissolved and particulate substances in the shelf water zone. Dispersion of suspended particulates in the lagoonal portion of the turbid zone is primarily influenced by tidal hydraulics. Inlet plumes and wave resuspension are major factors affecting suspended particulate concentrations in the nearshore portion of the turbid zone. The seaward attenuation of particulate and dissolved matter in the boundary zone is primarily the result of dilution by settling and mixing with shelf water. Based on preliminary measurements, the turbid zone appears to be an area of high primary production in the central Georgia embayment. Although photosynthetic processes of phytoplankton are limited to the upper meter of water in this zone, the rapid uptake of relatively high concentrations of nutrients that are available, result in high biomass production. At high tides, production is particularly maximized in the lagoonal portion of the turbid zone, when nutrient-rich water “spills” out of tidal channels and spreads across the extensive marsh surface. Whereas phytoplanktons are dispersed seaward of inlets, resuspended benthic microalgae do not make up a large portion of the organic material ebbing through inlets.