Microbial Processes and Populations as Related to Zinc, Cadmium and Sulfur Speciation in Natural Metalliferous Soil Environments

Soil environments are biogeochemical systems under continual modification by biological and chemical processes. This research project involves the study of field soils with elevated levels of heavy metals that resulted from natural biogeochemical processes. The overall hypothesis is that microbial populations involved in sulfur cycling (sulfur oxidizing bacteria, SOB; sulfur reducing bacteria, SRB) determine the solid-phase speciation and distribution of Zn and Cd in organic-matter rich soil environments. The soils to be studied are peat deposits that overlie a mineral bed of Lockport Dolomite extending from Eastern New York State to Guelph (Canada). These peat deposits can concentrate Cd and Zn by biogeochemical processes, and the solubility, mobility and bioavailability of these metals can increase when such deposits are drained, initiating oxidation of organic matter and sulfides under aerobic conditions. We propose that the structure, function, and activity of microbial populations in these soils determine the speciation, solubility, mobility, and bioavailability of Zn and Cd. Among the relationships to be investigated are the spatial distribution (imaging), identity, and co-location of microbes and minerals or elements in soil particles. To do this, soils will be sampled during wet and dry seasons. Vertical profiles of these soils will be studied to assess the involvement of microbial processes in metal mobility. In the laboratory, experiments conducted under oxidizing conditions will be undertaken to investigate the potential effects that changes in microbial community structure and function might have on Zn and Cd dissolution and binding environment and to S oxidation states. A suite of techniques involving wet chemistry, spectroscopy, classic microbiology, molecular biology and fluorescence microscopy at the micro-scale will be employed to test hypotheses about the role of microorganisms in chemical speciation and mobility at macro-scales. We plan to obtain spatially coupled data from confocal laser scanning microscopy (CLSM) and m-XRF and m-XRD, thereby linking the distribution of microbes with Zn and Cd in soil particles. In addition, we will integrate PCR- and non-PCR-based molecular analyses to obtain directed, quantitative information about microbial populations of interest. The intellectual merit of the proposed activity lies in the direct coupling of microbiological and geochemical analyses under controlled conditions, which will help us better understand biogeochemical processes controlling trace metal retention and solubility in complex soil environments. This research project will advance our capabilities for linking micro- and macro-scale processes in pollution prevention, remediation, and environmental management. This proposal will also support a unique blend of interdisciplinary education for students who will be trained in molecular and geochemical techniques. Overall, this research will simultaneously advance basic knowledge of biogeochemical processes and promote significant innovations in interdisciplinary training of environmental scientists.