The proposed research will examine the role of microbial influences on metal cycling in four stratified lakes in the McMurdo Dry Valleys: Lake Fryxell, Hoare, Joyce and Miers. These lakes are characterized by unusually stable redox transition zones and are especially amenable to a finely spaced sampling regime. Collectively, they represent a broad range of water chemistries. The proposed research will test the following hypotheses: (1) Instratified water columns there will be a clear spatial difference between the onset of manganese reduction and the onset of iron reduction. Heavy metals and rare earth elements will be seen to undergo co-cycling with manganese rather than with iron. (2) In all four lakes, manganese reduction will be associated with the presence of carnobacteria or with other manganese-reducing organisms. In brief, the study will explore the link between microbial activity and the cycling and fate of a large suite of chemical elements at key redox boundaries. Dissolved and particulate metal profiles will be examined as a function of depth from the ice-water interface to the sediments. Profiles will be correlated with microbial manganese-reduction assays and the presence of manganese reducers as detected by screening with Mn-oxide overlay agar plates and nucleic acid hybridizations with probes for known manganese reducers. The research will include significant involvement of undergraduates.
