My research focuses on the intricate coupling of geochemical and biological processes controlling element cycling within near-surface environments, across multiple temporal and spatial scales, which is essential to understanding naturally occurring processes as well as contaminated systems. I am particularly interested in examining the cycling of nutrients and contaminants in variably saturated systems and at redox interfaces. Understanding these systems, on a molecular level, is essential to developing a full understanding of the mechanisms responsible for carbon mineralization, in addition to the retention and/or biotransformation of metals and nutrients. To approach this problem, my research group uses laboratory-scale and model biogeochemical systems, coupled with molecular spectroscopic techniques, to determine possible mechanisms responsible for nutrient and contaminant retention and release. In addition, my research examines biogeochemical cycling in field-scale systems to determine if the laboratory observations are consistent with real-world systems.
Characterization of Ra Contaminated Groundwater in Wisconsin
There are many wells in the Midwestern Cambrian-Ordovician aquifer with Ra concentration measuring at or above the Maximum Contaminant Level (MCL). Various municipalities across the state of Wisconsin have had install Ra removal systems or reconstruct wells to maintain total Ra concentrations below the MCL. Some municipalities have achieved lower Ra concentrations through well reconstruction. The specific goals of my research are to (1) identify geographically distributed wells with elevated groundwater Ra concentrations and collect geologic and hydrologic characterization data, (2) determine the Ra leaching potential of aquitard materials associated with wells that have elevated dissolved Ra, and (3) provide geochemically and geographically driven recommendations to minimize Ra concentration during well construction and operation. The overarching goal of our work is the development of a conceptual understanding of primary sources of Ra to groundwater throughout the Cambrian-Ordovician aquifer system in Wisconsin. This understanding will provide a scientific basis for cost effective strategies to minimize dissolved Ra concentration in produced groundwater. Our research has been funded by the Wisconsin Department of Natural Resources and the Wisconsin Groundwater Research Management Program. Results from this research were recently published in Applied Geochemistry and AWWA Water Science.
Organic Contaminant Transformation by Mn(IV) Oxides
Naturally occurring and synthetic manganese oxides (e.g., MnO2) are among the strongest, naturally occurring oxidants and can oxidize hazardous organic compounds containing amine or phenolic groups to potentially less hazardous species. These target organic compounds are widespread aqueous pollutants and include many endocrine disrupting compounds, biologically active hormones, and antibiotics. These chemicals are generally not removed nor significantly degraded by traditional primary and secondary wastewater treatment technologies, resulting in their discharge to, and presence in, drinking water sources, including surface and ground waters. In this work, I aim to assess the reactivity of target organic compounds with manganese oxides and investigate the impact of environmental conditions on Mn oxide reactivity. This unique approach combines solution phase chemistry (i.e., rates and transformation mechansims of the target organic compounds) with a thorough assessment of changes in solid-phase Mn oxide chemistry using synchrotron-based techniques. This work uses both pure Mn oxides and minerals generated during drinking water treatment; these waste materials could potentially be used to treat urban stormwater through reactive media filtration. This collaborative research is supported by the Wisconsin Groundwater Research and Monitoring Program (WGRMP) and twice by the National Science Foundation. Results from this research have recently been published in Environmental Science and Technology, Environmental Science Processes & Impacts, Environmental Science: Water Research & Technology.
Production and Migration of High pH Leachate from Recycled Concrete Aggregate
Recycled concrete aggregate (RCA) provides excellent mechanical properties for use as base course aggregate in pavement applications. Additionally, use of RCA has significant life-cycle benefits, such as reduction of greenhouse gas emissions, energy demand, and virgin aggregate consumption. However, since RCA is a reactive, cement-based material, there are concerns relating to the production and migration of high pH and alkalinity leachate into surface and groundwater. There have been many laboratory studies of the chemistry of leachate produced from recycled concrete aggregate; however, the results of many of these studies are contradicted by field observations. This research utilizes a comprehensive approach to reconcile the contradictory results of previous studies of leachate pH and alkalinity in field and laboratory settings. Inclusion of field, laboratory and computational components provides fundamental and in situ information to normalize the expected variance of leachate pH and identify when it is or is not a behavior or condition of environmental concern. This research has been funded by the Portland Cement Association, the Ready-Mix Concrete Research and Education Foundation and the Recycled Materials Research Center. Results from this work were recently published in the Journal of Materials in Civil Engineering, Journal of Hazardous Materials and Journal of Environmental Quality. Ginder-Vogel group members involved in these studies include Robin Ritchey, Morgan Sanger, and Bharat Madras Natarajan.
Refining our understanding of methylmercury production and bioavailability in the St. Louis River Estuary
The St. Louis River Estuary (SLRE) lies at the mouth of the St. Louis River, just prior to its discharge into the western tip of Lake Superior. The diverse and abundant habitats in the estuary make it a valuable fish spawning ground for the western arm of Lake Superior and a valuable recreational resource for northeastern Minnesota and northwestern Wisconsin. Methylmercury (MeHg), the bioaccumulative form of mercury, is primarily produced by microbial activity in anaerobic wetlands, soils, and sediments that are abundant in estuarine environments, such as the SLRE. Preliminary Hg stable isotope data collected from fish in the SLRE suggests that higher Hg levels are found in walleye that feed within the SLRE as opposed to those that feed in Lake Superior. Although the underlying cause of elevated mercury levels in fish tissue in the SLRE is presently unknown, it is likely due to a combination of biogeochemical factors including solid-phase Hg speciation, coupled with variations in water chemistry (e.g., dissolved sulfate and organic carbon). These factors control both Hg bioavailability and methylation and hence its entry to the base of the SLRE food web. Developing an understanding of these fundamental biogeochemical processes is critical to the ability of state and federal resource management agencies to make effective management decisions concerning the beneficial use of future dredging materials and habitat restoration in the SLRE. Out proposed work aims to address these uncertainties by relating mercury methylation potential to the speciation of mercury in solid and dissolved phases of SLRE sediments, and its subsequent bioavailability to the base of the food web. To assess spatial variability, we will evaluate samples collected from several distinct settings and geochemical conditions (e.g., estuary flats, sheltered bays, near-shore wetlands, clay-influenced river mouths).
Coupled Fe and C Biogeochemistry
Soil organic matter (SOM) is one of the largest carbon pools on the Earth’s surface, in fact it’s larger than the amount in the biosphere and atmosphere combined. Despite the obvious importance of soil organic matter in relatively little is understood about the biogeochemical processes controlling its mobility and speciation, particularly in cyclically anaerobic environments. Recent studies have shown that the cycling between Fe(II) and Fe(III), which occurs in many near-surface environments promotes the transformation, dissolution and mobilization of soil organic matter (SOM). Currently, global climate models assign SOM residence times without taking these underlying biogeochemical processes into account, resulting in large uncertainties in the residence time of SOM and in projections of its response to a changing climate.
The chemical nature of OM can dictate the amount and chemical components of OM released during Fe(III) reduction, and consequently the microbial oxidation of OM under aerobic conditions. However, the exact nature of interactions between organic carbon and iron under redox fluctuating conditions remains unclear. Additionally, the use of solid-state OM as an electron source for Fe(III) reduction has not been extensively studied. We are investigating the molecular-level changes in chemical nature of soil OM and OM-iron oxide interactions upon the reduction of Fe(III).