EXTENSIVE OXYGEN DEPLETION IN MOBILE BAY, ALABAMA1

Extensive areas of bottom water in Mobile Bay, Alabama, one of the largest estuaries on the Gulf of Mexico, suffer oxygen depletion in summer because of salinity stratification in sinks created by shoals in the lower bay and by spoil from construction of the Mobile Ship Channel. When these water masses low in dissolved oxygen are occasionally forced against the beach demersal fishes and crustaceans migrate shoreward in a depressed or moribund state. In the absence of technical data these popular occurrences called “jubilees” provide over a century of historical evidence of oxygen depletion. Oxygen depletion and jubilees occurred in the bay before man physically modified the basin but the conditions responsible for oxygen depletion are worse than in the past. Because of bathymetric changes and modifications which have restricted water circulation, Mobile Bay has exceeded its capacity to assimilate its oxygen demand in summer, which has severely affected the biota of the estuary.