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The AAPG/Datapages Combined Publications Database

GCAGS Transactions


Gulf Coast Association of Geological Societies Transactions
Vol. 45 (1995), Pages 365-370

Trace Metal Variability of Estuarine Sediments, St. Bernard Geomorphic Region, Louisiana

Kenneth E. Landrum


Bottom sediments of the St. Bernard Delta Geomorphic Region estuarine complex consist predominantly of silty clays derived from the erosion of the St. Bernard lobe of the Mississippi River delta and sediments associated with historic crevasses along the Mississippi River. The acid-leachable concentrations of fourteen trace metals were determined for 125 bottom sediment samples and 40 core interval samples by plasma emission analysis. The areal distribution of the trace metals is controlled predominantly by the texture and mineralogy of the sediments. Elevated trace metal concentrations present reflect the significant correlations which exists with smaller grain-size sediments. Trace metal concentrations were plotted against aluminum, iron, clay, and total carbon contents. The most significant correlations exist between the trace metal concentrations and the aluminum and iron content of the sediment samples. Of the fourteen trace metals analyzed, As, Ba, Cd, Pb, and Zn are the least correlatable and may represent those with greater anthropogenic influence. Natural trace metal variability was determined through the use of an aluminum normalization model based on Florida and Louisiana estuarine sediments, basinwide and Gulf Coast trace metal comparisons, sediment geochronology, and grain-size corrected data. Trace metal concentrations from sediments of the study area tend to have greater mean concentrations than Florida estuarine sediments due to their finer grain size, lack of CaCO3, and higher clay and carbon content. Anthropogenic trace metal inputs of As, Ba, Cd, Pb, V and Zn were noted from sediments associated with oil and gas drilling and production, sandblasting and shipbuilding, dredging, and stormwater, municipal, and industrial discharges. Although evidence of trace metal contributions within the study area exists, comparisons of average trace metal concentrations with those of other Gulf Coast estuaries and with the average shale concentration reveal that only isolated industrialized and nonpoint sources within the St. Bernard Geomorphic Region have been impacted.

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