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The project focuses on the use of analytical techniques that we have developed to support a wide range of studies in water-rock interaction, integrating solid phase mineralogy and elemental chemistry and clay mineralogy into hydrologic and contaminant studies.
Categories: Project; Tags: Contaminants, Mineralogy
Watershed-scale water quality and water availability are affected by the interaction between the landscape and surface and subsurface flows at multiple scales. Wide-spread agriculture leads to diffuse non-point sources of contamination by agricultural chemicals. Localized exchanges of surface water and groundwater through highly reactive streambeds can attenuate the impact of agricultural chemicals on water quality. Thus, understanding the patterns and trends in water quality within a watershed requires analyses at multiple scales to understand hydrologic processes and the integration of hydrology and water quality information. The main objective of my research is to develop a better understanding of the role of...
The goal of my biodegradation research is to understand the processes controlling the rate of biodegradation of contaminants in the subsurface. This understanding will form the basis of methods to increase degradation rates without causing further degradation of groundwater quality. Recent work has focused on the fate of crude oil and agricultural nitrate contamination in the subsurface. Specific objectives for the crude oil research include: (a) determine the rate that contaminants are transported from the source zone; (b) provide an estimate of how long the spilled oil will continue to pollute the groundwater; and (c) determine the fate of products of biodegradation or so-called “secondary water quality impacts”...
To study the mechanisms, pathways, and rates of transformation of carbon and nitrogen compounds (natural and contaminant) mediated by microorganisms in aquatic habitats and identify factors controlling these transformations and to examine the effect that these transformations have upon other biogeochemical processes.
Much work has been done to track spilled oil and study its fate and its effect on the environment. Our studies involved developing and applying methods to identify and track spilled oil as it weathers, as well as to differentiate it from other petrogenic hydrocarbon input sources, as well as differentiating petrogenic sources. This work in identifying petroleum sources, both natural and anthropogenic, has a great deal of transfer value to other estuarine systems.
Categories: Project; Tags: Contaminants, Organic Compounds
I conduct research focused on understanding the role of microorganisms on both contaminated and pristine ecosystems. I carry out this work using a polyphasic approach that combines microbiology, molecular biology, and biogeochemistry to understand microbial processes. My work specifically aims to (1) assess the impact of microorganisms on the fate of organic and inorganic contaminants; (2) to investigate the microbial role in metal cycling, e.g., iron, uranium, and manganese cycling; (3) evaluate the potential of microbial populations to contribute to energy resources, either through coal bed methane production or mitigating contaminants due to nuclear energy production or unconventional oil and gas production;...
My research is concerned broadly with the use of stable isotopes, primarily hydrogen, carbon and oxygen, to examine the dynamics of hydrological systems and associated geochemical problems. I perform studies in the identification and quantification of ground-water recharge, discharge, surface-water/ground-water interaction, redox processes in contaminated aquifers, as well as source identification of stray methane gas in drinking water wells. I develop new sample- preparation techniques in the laboratory including inlet systems for continuous- flow isotope- ratio analytical techniques , such as EA, TC/EA, GPI, Gasbench, GCC, TC/GCC, and TIC/TOC and publish Sandard Operating Procedures in the U.S. Geological Survey...
Categories: Project; Tags: Contaminants, Isotopic Tracers
Evaluate the hydrologic and geochemical processes that control nitrate fluxes in agricultural settings. Important questions remain about the overall regional and global importance of groundwater nitrogen fluxes, denitrification (microbial reduction of NO 3 − to N 2), and the sources of electron donors contributing to this microbial reaction. Studies are needed that apply robust methods for measuring nitrogen fluxes and denitrification among multiple sites to evaluate important factors affecting N fluxes. These results, in combination with novel methods for efficient estimation of fluxes in groundwater, facilitate estimates of N fluxes in across large regions such as the Corn Belt. Quantify the effects of complex...
Robin Stewart's research is focused on identifying and understanding processes influencing the fate and bioavailability of selenium and mercury in food webs across a range of aquatic environments including estuaries, rivers, lakes and reservoirs.
Humic substances are the predominant form of natural organic matter (NOM) in soil and water and comprise the major pools of biologically refractory organic carbon and nitrogen in the biosphere. Humic substances play a role in almost all geochemical processes affecting soil and water. Knowledge of the formation and mineralization pathways of soil and aquatic humic substances is therefore critical to an understanding of the biogeochemical cycles of carbon and nitrogen, and climate change. Humic substances act as electron donor-acceptor systems and thus participate in oxidation –reduction processes with transition metal ions and biological systems in soil and water environments. Chlorination and chloramination of...
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Key Findings Tree swallows were sampled at 6 locations in the Maumee River watershed, as part of a collaborative four-agency study on ecosystem effects of contaminants of emerging concern (CECs) on biota. This study involved samples of sediment, benthic invertebrates, and an insectivorous bird, the tree swallow. Endpoints include assessment of changes in both the tree swallow metabolome and transcriptome to determine whether perturbations can be traced from ToxCaste, an in vitro water sample assessment through mussels/clams, fish, and birds. Avian tissues and food will be analyzed for CECs with an emphasis on agricultural pesticides. Other Great Lakes’ landscape types will be sampled in future years. Products...
To elucidate and quantitatively explain the behavior of hydrogeologic systems typically characterized by hydrogeologic and physics-based complexity and data scarcity, for purposes of developing theory when needed, and with a focus on practical management (use and preservation) of water-resource systems to benefit humankind.
Research goals are (1) to develop reaction-transport models with varying levels of complexity and data requirements, providing guidelines for the appropriate application of these models given field conditions and limited resources; (2) to incorporate the effects of surface-chemistry phenomena into reaction-transport modeling; (3) to develop methods to identify and quantify important chemical and biological reactions affecting transport of inorganic and organic substances; and (4) to compile estimates of reaction rates and reaction-rate laws for chemical and biological reactions. In addition to model development, the project undertakes field, laboratory, and theoretical studies to investigate field-scale chemical...
Improve understanding of physical and biogeochemical processes affecting water quality of groundwater and surface water. Research focus includes multidisciplinary field and laboratory studies to determine factors affecting sources, movement, and fate of nutrients and reactive inorganic contaminants in the hydrologic cycle. Improve the usefulness of stable isotopes and other environmental tracers in hydrology and biogeochemistry by developing new techniques and approaches. Research topics include analytical techniques for stable isotopes in compounds separated from groundwater and surface water, stable isotope forensics, enriched isotope tracer experiments to quantify transport and reaction rates, field and...
Uranium mill tailings and related forms of low-level radioactive waste contain elevated contents of naturally occurring radionuclides that have been brought to the surface, processed for the recovery of uranium and/or other components and then disposed of in near-surface impoundments. The long-term fate of the tailings and their constituents will be determined by surficial earth processes. Project objectives are to study the chemical form in which radionuclides and selected stable elements are retained in surficial earth materials, particularly uranium mill tailings, and to identify processes operating in natural aqueous and terrestrial systems that may influence the transport of these constituents from these earth...
Human activities from climate change to waste discharges to water management are modifying ecosystems across the earth, often in ways that are not well understood. This project addresses the problem of better understanding changes in aquatic ecosystems as driven by human disturbances interacting with natural processes. More specifically, the project studies a) the mechanisms of biological and ecological response to stressors such as metal contamination, nutrient enrichment, physical habitat alteration, climate change, and introduced species, and b) the influence of species, communities, and ecosystem processes on the distribution, transport, and fate of chemical contaminants (e.g., metals, nutrients). Most studies...
The objective of this research is to study and quantitatively describe the factors that influence the response of macroinvertebrates to both anthropogenic and natural environmental factors and assess the effects macroinvertebrates have on the physical, chemical, and biological quality of aquatic systems. This involves 1) studying macroinvertebrate distributions across a range of spatial and temporal scales representing a variety of environmental settings and influences, 2) identifying and measuring the effects of stressors that are macroinvertebrate-specific, 3) identifying the effects macroinvertebrates have on the physical, chemical, and biological environment, 4) developing and applying statistical models that...
The overarching objective of my research is to integrate hydrology, pedology, chemistry, and physics to develop an improved process-level understanding of fluid, solute, and heat transport in unsaturated zones with applications ranging from geologic hazards to carbon storage in soils. I try to develop multi-disciplinary understanding of unsaturated zones in diverse settings with respect to groundwater-recharge and contaminant-transport determining processes, soil formation, and soil-water-plant-atmospheric interactions. I lead teams and work with others to generate individual and multidisciplinary synthesis products that address long-standing problems of fundamental importance to water resources, such as groundwater...
I conduct research on the transport and fate of organic contaminants in aquatic systems (terrestrial and marine). This entails field investigations and laboratory experiments that are designed to advance our understanding of natural processes and the effects of these processes on the behavior, mobility, and geochemical fate of organic chemicals of concern. I develop and apply new sampling and analytical techniques, identify potential molecular tracers, and develop models to predict contaminant fate. The laboratory I supervise houses analytical instrumentation that is used for detailed characterization of complex mixtures of organic chemicals as well as quantitative determination of targeted substances at ultra-trace...
Human activities from climate change to waste discharges to water management are modifying ecosystems across the earth, often in ways that are not well understood. This project addresses the problem of better understanding changes in aquatic ecosystems as driven by human disturbances interacting with natural processes. More specifically, the project studies a) the mechanisms of biological and ecological response to stressors such as metal contamination, nutrient enrichment, physical habitat alteration, climate change, and introduced species, and b) the influence of species, communities, and ecosystem processes on the distribution, transport, and fate of chemical contaminants (e.g., metals, nutrients). Most studies...