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Organic substances in streams affect the water quality and uses of the water. To determine the effect of organic substances on water quality, the physical, chemical, and biological processes involved in the transport and degradation of these substances must be understood. Procedures for measuring or estimating the rate coefficients describing these processes must be developed. Models using these coefficients must then be developed for predicting the fate of organic substances in streams and their effect on water quality. Project objectives are: (1) to study the fundamentals of volatilization, dispersion, and sorption on sediments of organic substances in water; (2) to develop sub-models of these processes including...
Categories: Project;
Tags: Organic Compounds
Movement of toxic and radioactive substances in aquifer systems occurs in all three phases and is controlled by both hydrologic and chemical forces. Solute movement can be greatly affected not only by physical dispersion, but by other factors such as exchange sorption, chemical kinetics, and ionic distributions. Movement of gases and particulate material in the unsaturated zone are controlled by many additional factors. Knowledge of how these physical and geochemical factors affect prediction of movement of toxic and radioactive wastes is only generally known for ideal systems. This project's objective is to develop field methods and techniques that will yield values for physical and geochemical factors of regional...
Categories: Project;
Tags: Groundwater Flow and Transport,
Radioisotopes,
Solute Transport,
Unsaturated Zone
a) Developing defensible conceptual models of processes influencing the mass transfer of inorganic contaminants between aqueous and solid phases. b) Translating conceptual models into quantitative models that can be used to predict the influence of mass-transfer processes on contaminant fate and transport in field applications. c) Developing approaches to obtain parameters required to describe contaminant mass transfer in quantitative fate and transport models that are, to the maximum extent possible, independent of field observations. d) Testing these approaches in laboratory experimental studies, field experimental studies, and field-scale plume characterization studies.
My research focuses on the application of remote sensing to rivers as a means of more efficiently characterizing fluvial systems, primarily channel form and behavior. More specifically, I develop, test, and apply methods of measuring various river attributes, such as depth, streambed composition, turbidity, and flow velocity, from different types of remotely sensed data, including multi- and hyperspectral images and near-infrared and green LiDAR. These techniques provide higher resolution, essentially continuous data over larger spatial extents than could be surveyed via conventional field methods and thus could facilitate river research and management. My research involves a combination of numerical radiative...
Stable and radioactive isotopes such as oxygen, hydrogen, carbon, nitrogen and sulfur have proved to be extremely useful tracers of hydrologic pathways, biogeochemical processes, and residence times of waters and solutes. However, use of these isotopes as tracers is presently hampered by our limited understanding of the physical processes and chemical reactions influencing isotopic compositions. The unsaturated zone, particularly the soil zone and the top of the water table, is probably the portion of the hydrologic system most responsible for alteration of the isotopic compositions of potential isotope tracers, this environmental component is also one of the least studied. The overall goal of this project is to...
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;...
Categories: Project;
Tags: Biogeochemistry,
Contaminants,
Ecology,
Metals,
Microbiology (Activity and Transport)
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...
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...
Categories: Project;
Tags: Contaminants,
Groundwater Flow and Transport,
Groundwater-Surface Water Interactions,
Nitrogen Cycling,
Nutrients
Efficient management of ground-water aquifers and geothermal reservoirs requires accurate estimates of the hydraulic properties of water-bearing formations. These are needed to predict water- level changes, aquifer storage capacity, and the rate of movement of chemical species or thermal energy. Analytical models, properly applied, can often be used to estimate the hydraulic and transport properties of complex aquifer systems. This project's objective is to obtain analytical solutions to specific problems of flow and transport in water- bearing formations that can be used for evaluating the hydraulic and transport properties of aquifers and geothermal reservoirs.
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.
Categories: Project;
Tags: Bioaccumulation,
Bioavailability,
Biogeochemistry,
Contaminants,
Ecology,
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...
The overall objective of the MoWS research group is to gain better understanding of the precipitation-runoff processes and use this knowledge to develop improved hydrologic models. The main research topics include: • Add functionality and improvements to the MoWS simulation models being developed and integrate with other hydrologic, hydraulic, and climate models. • Enhance the models to use the best and latest topographic, climate, geologic, and land-use data sets as direct input to process algorithms to increase the physical nature and temporal and spatial resolution of model input. • Develop national model structure and calibration strategy for national model application.
The mechanisms that control the composition of river-borne materials are only imperfectly understood, because both erosion and the subsequent transport of material by rivers are mediated by a wide variety of highly-linked chemical, biological, and physical processes. Moreover, in developed river systems, such as those in the United States, these processes are subject to pervasive human- related perturbations. This project studies weathering, erosion, and atmospheric-exchange processes which are the sources of dissolved and particulate material in rivers and trace substances in the atmosphere; studies chemical partitioning of various phases during transport in rivers and estuaries; describes the dispersal pathways...
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.
Categories: Project;
Tags: Contaminants,
Groundwater Flow and Transport,
Groundwater Hydraulics,
Hydrogeology
To provide useful tools in river hydraulics, sediment transport, and geomorphology that: can be used to predict the impacts of man’s activities in rivers, canals, and reservoirs; can forecast the natural evolution of fluvial courses of water; provide analytic and computational platforms to study hypothesis; and enhance our understanding of fluvial morphodynamics.
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...
Aquatic humic substances and other classes of dissolved organic material present in natural waters can control the biogeochemistry of trace metals and other solutes and can influence ecological processes in lakes and streams. The nature and reactivity of the dissolved organic material is in turn influenced by biological, chemical, and physical processes occurring in the aquatic environment. Recent advances in isolating and characterizing different fractions of the dissoloved organic carbon (DOC) and in measuring rates of microbial processes can be used to advance the understanding of the dynamic relationship between aquatic biota and dissolved organic material and trace metals in different environments. Project...
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...
Categories: Project;
Tags: Biogeochemistry,
Contaminants,
Groundwater Flow and Transport,
Isotopic Tracers,
Nutrients,
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...
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