CAREER: Generation of Sediment Heterogeneity by Macrophytes and Macrofauna and Consequences for Redox Chemistry and Trace Metal Speciation

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AbstractIntellectual Merit: Coastal and inland wetland areas are enormously impacted by rapidly growing human populations. This typically leads to increased metal and nutrient loading together with significant changes in wetland hydrology, fauna and flora. Sustainable coastal and inland wetland development (and remediation) strategies depend on the development of accurate, predictive models of metal and nutrient speciation, bioavailability and mobility and their dependence on wetland flora and fauna populations. This is particularly true at the sensitive interface between saltmarshes and the coastal ocean or between inland wetlands and freshwater aquifers. Macrophytes and macrofauna inhabiting organic-rich saltmarsh and freshwater wetlands produce significant three-dimensional, temporally varying, geochemical heterogeneity in the surrounding sediments. This has a tremendous influence on benthic fluxes of oxygen, metals and nutrients, internal cycling of redox sensitive chemical species, and organic matter degradation kinetics. The following laboratory and field investigations will be used to assess these influences and to advance the development of sophisticated 3D mathematical models of sediment redox chemistry and trace metal speciation, bioavailability and mobility. (1) Metal adsorption experiments on mixed model mineral assemblages will be used to derive thermodynamic surface complexation stability constants and to assess their applicability to natural sediments. (2) Bulk sediment properties (mineralogy, pore water chemistry, trace metal speciation) in adjacent vegetated and unvegetated sediments will be measured as part of an innovative new field course at WMU. (3) Microscale analyses of mineralogy and trace metal speciation in sediments surrounding roots and burrows will be completed using microelectrodes, SEM/TEM, and laser ablation ICP-MS. (4) Changes in trace metal speciation resulting from chemically versus microbially mediated reductive dissolution of trace-metal doped iron oxides will be quantified. (5) Controlled laboratory mesocosm experiments with artificial roots will be used to assess microscale 3D changes in mineralogy and trace metal speciation resulting from root leakage of oxygen and labile organic compounds. Broader Impacts: This study includes a fully integrated plan of research and education. An innovative 6-week summer course is proposed in which students will have the opportunity to participate in field research at Sapelo Island, Georgia (an NSF-LTER site) and at field sites in Michigan. Students will be recruited for this course from WMU and surrounding institutions, especially those without graduate research programs and from colleges with significant enrollments of traditionally underrepresented groups. In addition, a full week of the course will coincide with a secondary education teacher workshop. The teachers will have a hands-on opportunity to participate in an active scientific research program and will be encouraged to disseminate curricula resulting from this experience at the Michigan Science Teachers Annual Meeting. Projects related to the laboratory portions of the study will be incorporated into an undergraduate geochemistry course. In addition to traditional graduate student mentoring, undergraduate students and highly motivated high school students from the Kalamazoo Area Math and Science Academy will participate in all aspects of the research, presenting results of individual projects at national or international scientific conferences. Equipment funded though this study will be a valuable addition to the research infrastructure available to graduate and undergraduate students at WMU, a rapidly growing doctoral research institution.