Characteristics of long-term freshwater transport in Apalachicola Bay

Long-term freshwater transport is an important factor affecting estuarine a quatic ecosystems. In this study, a primitive equation, prognostic, three-d imensional, hydrodynamic model was applied to Apalachicola Bay, Florida, fo r the summer and fall seasons of 1993. In response to the river freshwater discharge, tide, and wind forces, the model simulations were used to charac terize the long-term freshwater transport processes in the bay. Analysis of spatial distributions of seasonal average salinity and currents shows that the long-term freshwater transport was strongly affected by the forcing fu nctions of wind and density gradient in the bay. Average freshwater input w as approximately the same in the summer and fall seasons of 1993. However, in the summer season, more freshwater moved to the east direction due to th e predominant wind from the west, while in the fall season more freshwater moved to the west in response to the wind primarily from the east. The wate r column was strongly stratified near the river mouth, and it gradually cha nged to well mixing near the ocean boundaries. Vertical stratification in t he bay changed due to wind-induced mixing and mass transport. Due to the de nsity gradient effect, surface residual currents carrying fresher water wer e in the direction from the river toward the Gulf, while the bottom residua l currents with saltier water entered the bay from the Gulf of Mexico.