| Summary: | The goal of this study was to determine the sediment history of the Cedar and Ortega River estuaries, part of the lower St. Johns River (LSJR) in northeastern Florida. Sedimentation rate data based on 210Pb and 137Cs analyses, combined with the profiles of bulk sediment properties, reveal how natural and anthropogenic factors have altered the quantity and character of sediments in this urbanized estuary. This investigation also provides a chronology for future contaminant studies. Knowledge of the timing of contaminant input to the sediments is useful in controlling the future introduction of contaminants. An additional goal of this study was to test the applicability of two sedimentation models, the Constant Initial Concentration (CIC) and the Constant Rate of Supply (CRS) models, to estuarine sedimentation. === Forty-seven cores collected from the Cedar and Ortega Rivers were analyzed for percent water, percent organics, percent fines, bulk density, color, and sedimentary structure by x-radiography. A subset was analyzed for historic sedimentation rate using 210Pb analysis, and a smaller subset of cores was analyzed for short-term (~50 years) sedimentation rate using 137Cs. These measurements provide a record of historic changes in the geological and land-use conditions of the estuary. Additionally, several sets of bridge borings were examined to investigate longer-term trends in sedimentation in the estuary, and to establish the history of sedimentation during late Quaternary time. The large set of dated cores analyzed in this study provide a unique insight into the sedimentation history of a large estuary. In addition to being significant in its own right, this history provides a chronology for contaminant studies. Continuing studies of organic and trace metal pollutants--performed in the Cedar and Ortega Rivers on these and other cores--will employ the results of this investigation to determine the history of contamination in the lower St. Johns River. === by Michael O. O'Sullivan. === Advisor: Joseph F. Donoghue, Florida State University, College of Arts and Sciences, Dept. of Geological Sciences. === Thesis (M.S.)--Florida State University, 2001. === Includes bibliographical references.
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