Submitted to: Laboratory Publication
Publication Type: Government Publication
Publication Acceptance Date: 8/13/2003
Publication Date: 8/13/2003
Citation: BEARD, W.C., DAVIDSON, G., BENNETT, S.J., RHOTON, F.E. EVALUATION OF THE POTENTIAL FOR TRACE ELEMENT MOBILIZATION RESULTING FROM OXYGENATING SEDIMENTS FROM A SMALL MISSISSIPPI RESERVOIR. USDA-ARS NATIONIAL SEDIMENTATION LABORATORY RESEARCH REPORT. 2003. NO. 37. 69 PP. Interpretive Summary: Many of the Nation's 11,000 USDA-NRCS flood control reservoirs are filling with sediment. One way to extend the service life of these reservoirs is to dredge the impounded sediment. Yet this action may mobilize elements from the sediment and the concentrations of these elements may increase in local water bodies. To assess this potential water quality problem, sediment cores were collected from a small USDA-NRCS reservoir in west-central Mississippi and analyzed to determine the potential for mobilization of trace elements following dredging. Twenty cores were collected from Hubbard-Murphree Reservoir, near Charleston, MS. Two cores were processed for bulk chemical analysis. Chemical leaching experiments were conducted on sediment samples under oxygen-rich and oxygen-free conditions to determine their effects on the concentrations of specific trace elements. Calcium, iron, magnesium, sodium, strontium, aluminum, manganese, and potassium under oxygen-rich conditions were at least 20% less more concentrated than under oxygen-free conditions. Thus, these elements became more immobile when exposed to the air. This study suggests that dredging reservoir sediments may be a viable option for extending the service life of flood control structures.
Technical Abstract: Sediment cores were collected from a small Mississippi reservoir and analyzed to determine the potential for mobilization of trace elements following dredging. Twenty cores were collected from Hubbard-Murphree Reservoir, near Charleston, MS, in May and August 2001. Two cores were processed for bulk chemistry analysis at a resolution of 2 cm. Leaching experiments conducted on splits of homogenized sediment samples under oxidizing and reducing conditions were used to determine how the solubilities of specific trace elements would be affected by an increase in redox potential. The aqueous concentrations of Ca, Fe, Mg, Na, Sr, Al, Mn, and K under oxidizing conditions were at least 20% less than under reducing conditions. Coprecipitation and adsorption with Fe and Mn oxides likely caused the decrease in mobility following oxygenation. Immobilization rather than mobilization would likely occur for the detected trace elements if the sediments were to be dredged.