Influence of Atchafalaya River discharge and Winter frontal passage on suspended sediment concentration and flux in Fourleague Bay, Louisiana

Suspended sediment concentrations and fluxes between Fourleague Bay, Louisiana and the northern Gulf of Mexico were sampled every 3 h for 3 months to examine the importance of atmospheric cold fronts and riverine forcing on the functioning of this estuarine system. A cold front index was developed and used to identify major winter frontal passages likely to have the largest effects on material concentrations and transport. Suspended sediment concentrations ranged from 11 to 1527 mg l(-1); the highest values occurred during winter frontal passages and the lowest during calm periods. High concentrations are generated by a continuous source of sediment from the Atchafalaya River and resuspension of benthic sediment via high intensity winds associated with cold fronts along with sufficient duration to keep the sediment in suspension. Spring peak discharge of the Atchafalaya River increased water levels and sediment concentrations in the bay leading to strong seasonal net exports of water (1.02 x 10(9) m(3)) and sediment (1.72 x 10(8) kg) into the Gulf of Mexico through Oyster Bayou over the 89-day study. Net fluxes associated with tidal forcing were nearly balanced with a small net export due to freshwater input. The combination of high volumes of water originating from the northern bay and the restricted outlet to the Gulf often cause increased water levels and inundation of the surrounding marshes and potential advection of sediments onto the marsh surface. The results suggest that marsh drainage often increases the particulate organic carbon export as a result of marsh flushing. (C) 2000 Academic Press.