Abstract: Accumulation and Trace-Metal Variability of Estuarine Sediments, St. Bernard Delta Geomorphic Region, Louisiana

Kenneth E. Landrum

Prior to government regulation, little monitoring of metal discharges into the canals, bayous, and rivers that drain estuarine systems occurred. Discharges of trace-metals by industries and municipalities into surface water bodies are presently regulated through the use of Federal and State mandated permit programs. Resource management of economically important estuarine systems has fostered increasing concern over the accumulation of trace-metal pollutants in water, sediments, and biota from these dynamic areas.

The acid-leachable concentrations of fourteen trace-metals were determined for 125 bottom sediment samples and 50 core interval samples by plasma emission analysis. Bottom sediments of the St. Bernard estuarine complex consist predominantly of silty clays and clayey silts 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 areal distribution of the trace-metals is controlled predominantly by the texture and mineralogy of the sediments. Sediment accumulation rates were determined from three cores within the study area using ²¹⁰Pb geochronology. Rates varied from 0.12 to 0.21 cm/yr. Within the 2 cm core intervals, trace-metal concentrations of Ba, Cr, Cd, Pb, and Zn i creased by 10% to 18% in sediments accumulated within the last 75 years. Natural trace-metal variability was examined 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. Elevated concentrations 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.

AAPG Search and Discovery Article #90955©1995 GCAGS 45th Annual Meeting and Gulf Section SEPM, Baton Rouge, Louisiana