Collaborative Research: Biogeochemical Transformations of Manganese and Toxic Metals in a Changing Riparian System

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This award in the Environmental Geochemistry and Biogeochemistry Program supports collaborative research by Martha Conklin, University of Arizona, Bradley Tebo, University of California at San Diego (Scripps Institute), and Christopher Fuller and Judson Harvey of the U. S. Geological Survey. The award is jointly made by the Divisions of Chemistry, Earth Sciences, and Ocean Sciences, and the MPS Office of Multidisciplinary Activities. The team will study the movement of manganese and other toxic metals (Zn, Ni, Co, and Cu) in a riparian system that contains a stream that receives contaminated ground water. Of particular concern are the biogeochemical constraints on the attenuation of Mn(II), the role of Mn(II)-oxidizing bacteria, and the effect of remediation methods on these processes. Both laboratory and field studies will be carried out and the system will be modeled. The field site is Pinal Creek, Arizona. Streamwater (hyporheic zone) recharges shallow groundwater flow paths with dissolved oxygen, metals, nutrients, and biologically active sediment coatings. The goal of this research is to understand the process of bacterial Mn(II) oxidation and precipitation along with co-precipitation of other metals under these conditions. Remediation activities may change local environments and cause long-term release of metals already deposited in the system. The results of the study will indicate how removal of other metals is coupled to removal of Mn, identify differences between optimal zones for Mn removal and sorption/coprecipitation of other trace metals, and determine the stability of other metals in the Mn-oxides. In addition, the study will identify the diverse Mn-oxidizing bacteria present, the relationships among different strains, and the underlying mechanisms involved in microbial utilization of manganese.This is a collaborative effort involving faculty, scientists, research specialists, and graduate and undergraduate students in four disciplines: water chemistry, hydrology, geochemistry, and microbiology. The reseach will elucidate the role of manganese in the biogeochemical cycling of metals in a manganese-dominated environmental system.