Northeastern Section (45th Annual) and Southeastern Section (59th Annual) Joint Meeting (13-16 March 2010)

Paper No. 5
Presentation Time: 9:25 AM


ISPHORDING, Wayne C., Earth Sciences, University of South Alabama, Mobile, AL 36688,

Mobile Bay is the second largest estuary in the United States and serves as the terminus for the Nation’s sixth largest watershed system. The average discharge of rivers emptying into the bay amounts to some 79,300 cubic feet/second, a quantity exceeded only by the Mississippi, Columbia, and Yukon Rivers.

A number of investigations have been carried out over the past half century documenting changes that have taken place in the chemistry, mineralogy, and texture of the bay’s bottom sediments. These changes have resulted, in part, from major storm events (hurricanes) but can also be traced to the activities of man. Dams and other water control structures (e.g. the Tennessee-Tombigbee Waterway completed December, 1984), as well as other urban and industrial construction activities throughout the watershed, have left their imprint on the bay’s sediments. Within the bay itself, the widespread practice of bulkhead/shoreline armoring has exacerbated erosion and markedly reduced the ability of the shoreline to withstand and recover from wave stresses that accompany major storm events. Further, the presence of the Mobile Delta complex at the head of the bay (the largest inland delta system in North America), combined with the bay’s wind and circulation patterns, generally shallow depth (approximately 9 feet), and restricted opening to the Gulf of Mexico results in most sediments (~70%) remaining in the bay for extended periods of time. As a consequence, and because of the extensive industrial development in the watershed, abundant contaminants have entered the bay and have become adsorbed by Smectite Group clays that are the dominant species in the bay. Major efforts have been directed toward ameliorating many of the bay’s problems, however it is apparent that Hurricane Frederic (1979), which wreaked devastating surficial effects on the Mobile, Alabama area, probably did more to"undo" some of the worst problems visited on the bay by man.