AN EXAMINATION OF PROCESSES INFLUENCING HISTORICAL SEDIMENTATION PATTERNS IN THE MOBILE BAY ESTUARINE SYSTEM, ALABAMA (USA)

Over the last century, the interplay between natural processes and anthropogenic activities has had a significant influence on the supply and deposition of sediment to the Mobile Bay Estuarine System. Modern bathymetry and morphology divide the bay into three depositional sub-basins: middle bay, lower bay, and Bon Secour Bay. Lead-210 (²¹⁰Pb) geochronologies of seven box cores constrain the depositional history of the bay and each sub-basin. To verify the assumption of constant rate of supply (CRS) of ²¹⁰Pb, excess ²¹⁰Pb inventories in the box-core sediment were compared to that preserved in marsh sediment. Inventories between the marsh sediment record and box-core sediment record were generally within 10 % of each other, supporting the CRS assumption. At the bay scale, linear sedimentation rates over the last 120 years average 0.4 cm y^-1 which is slightly higher than local sea-level rise (0.298 cm y^-1; Dauphin Island Tide Station, NOAA). However, differences in deposition are observed within and among sub-basins, reiterating the need to understand controls on spatially heterogeneous bay infilling. For example, sedimentation rates for the middle sub-basin east of the shipping channel are three to four times higher than rates west of the shipping channel. This difference is in part controlled by channel dredging and spoil disposal, which have isolated the western middle bay from sediment supplied by the Mobile-Tensaw Rivers.