Resolution of sedimentation rates in impacted coastal environments using 137Cs and 210Pb markers: Dog River and Fowl River embayments

J.M. Sanders, D.W. Haywick, and M.L. Fearn

The rate of sedimentation and the change in rate of sedimentation are two of the most important parameters by which to interpret the depositional history and health of coastal environments. Sedimentation rates have traditionally been estimated by using sediment traps or through various biological (e.g., pollen, diatoms, wood) and physical markers (e.g., chronostratigraphic horizons such as volcanic ash beds). More recently, short-lived radioactive markers such as 210Pb and 137Cs have been used. The object of this research is to determine the average rate of sedimentation over the least 50 years at various points in two southern Alabama coastal embayments, Dog River and Fowl River, by using 137Cs and 210Pb dating. Portions of Dog River have been heavily impacted by run-off sediment due to its headwaters being affected by Mobile's urban sprawl. Fowl River has been much less impacted as most of its drainage is derived from non-developed areas in southern Mobile County. The proposed dating techniques will allow sedimentation rates to be determined for each river and for different tributaries within a watershed to investigate the effects of development on sedimentation in the two river systems. Cores will also be extracted from Big Creek Lake, a reservoir which was filled between 1950 and 1955 to serve as the water supply for the city of Mobile. Although it is a completely different environment to the two embayments to be studied, the cores from the lake will serve as references by which to evaluate the nature of the 137Cs and 210Pb flux in the Mobile area.