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(38-58) Natural Processes that Concentrate Mn in Rural and Urban Soil Environments of the Lower Mississippi River Delta. Howard, Mielke1, Gonzales, Christopher1, Powell, Eric1, Shah, Aila1, Welt, Marc*,1, 1 Xavier University of Louisiana, New Orleans, Louisiana, USA ABSTRACT- Unlike other metals, about the same amounts of Mn are found in rural as in urban environments of metropolitan New Orleans. This observation motivated the study of natural processes of Mn accumulation in alluvia and sediments of the lower Mississippi River Delta. Three hypotheses were tested, the "railroad manganese," the "industrial manganese" and the "dynamic aquifer-stream transfer of Mn". The results support the hypothesis that friction between Mn-rich steel wheels and rails contribute Mn to the environment. Sediment loads of Mn upstream and downstream from the Mississippi River industrial corridor in Louisiana were similar (P-value = 0.77) and the hypothesis that industrial use of manganese contaminates the sediments is not supported. The Bonnet Carré Spillway is a gateway that can be opened to relieve floodwater pressure on the control structures that protect inhabited areas of New Orleans. The gates to the Spillway were last opened in the spring of 1997, and the alluvium in the spillway was scoured and fresh sediment deposited during that time. There is an increasing enrichment of Mn, with medians of 59 mg/kg, 159 mg/kg and 513 mg/kg respectively, from the alluvium surface to the 20-30 cm depth of the aquifer, and to the aquifer discharge zone along the where Mn rich riverbank clay precipitates. This supports the aquifer-stream transfer hypothesis for Mn accumulation. The process of Mn enrichment is facilitated by the change from insoluble oxidized Mn+4 to the water-soluble reduced Mn+2 form in the anoxic aquifer. Microorganisms mediate redox processes as part of the biogeochemical cycle of Mn. Funded by ATSDR/MHPF cooperative agreement # U50/ATU398948 to Xavier University of Louisiana. Key words: Dynamic aquifer-stream transfer , Mn biogeochemistry |
