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

Abstract

Prior to government regulation, little monitoring of metal discharges into the canals, bayous, and rivers that drain estuarine systems occured. 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 estuarom 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. Within the 2 cm core intervals, trace-metal concentrations of Ba, Cr, Cd, Pb, and Zn increased by 10% to 18% in sediments accumulated within the last 75 years. Trace-metal concentrations from sediments for the study area tend to have greater mean concentrations than Florida estuarine sediments, basinwide and Gulf Coast trace-metal comparisons, sediment geochronology. Rates varied from 0.12 to 0.21 cm/yr. Within the 2 cm core intervals, trace-metalmore » concentrations of Ba, Cr, Cd, Pb, and Zn increased 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. 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.« less