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The purpose of my research group is to develop new methods and applications of environmental isotopes to solve problems of national importance. In specific, the overall goal is to use environmental isotopes, combined with other biogeochemical measurements and hydrologic and biogeochemical modeling, to increase our understanding of biogeochemical and hydrological processes, nutrient and organic matter sources, subsurface flowpaths, and water age distributions in diverse environments. Many of our studies piggyback on the sampling efforts of major monitoring programs to investigate causes of hypoxia and food web problems. Our work provides critical scientific support for these monitoring programs. A long-term career...
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...
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...
Categories: Project; Tags: Isotopic Tracers, Radioisotopes
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...
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...
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...
A study using multiple techniques provided insight into tectonic influences on ground water systems; the results can help to understand ground water systems in the tectonically active western United States and other parts of the world. Ground water in the San Bernardino Valley (Arizona, United States and Sonora, Mexico) is the main source of water for domestic use, cattle ranching (the primary industry), and the preservation of threatened and endangered species. To improve the understanding of ground water occurrence, movement, and sustainability, an investigation was conducted using a number of complementary methods, including major ion geochemistry, isotope hydrology, analysis of gases dissolved in ground water,...
<p>The overall objective of my research is to understand the movement and quality of surface and groundwater using geochemical approaches. Some key issues that are considered in this research are the environmental aspects of energy and mineral resources, climate change, and carbon cycling and sequestration. The geochemical approaches that are used in this research include the use of isotopic tracers, trace elements, and radioisotopes. My research has focused on the sampling and analysis of produced waters from geologic carbon sequestration studies, geochemical characterization of sediment transport in the coastal zone, the environmental chemistry of mercury in coastal regions, and water quality analysis for samples...
The objectives of my work are to better understand nutrient sources and cycling in specific environments to aid in resource management and pollution abatement and to improve and develop isotopic analytical methodologies.
Aqueous chemical models have become popular tools for the interpretation of natural water chemistry. Unfortunately, these models have deficiencies because of (1) incorrect or inconsistent thermodynamic data, (2) invalid assumption regarding the equilibrium state, (3) inappropriate or invalidated corrections for nonideality, (4) inadequate expressions for temperature dependence, (5) invalidated limitations for ionic strength, composition and temperature, and (6) lack of data on solid solution solubility. The plethora of models and databases has prompted federal agencies, especially hazardous waste and nuclear waste managers, to request geochemical code validation. Acid mine waters are a major source of water pollution...
The goal of my research is to develop innovative approaches for the detection trace gases and expanding our understanding of their environmental cycles. Dissolved gases can be used as age tracers and climate markers, provide information about biological activity and recharge conditions, and provide unique fingerprints of superficial activity in aquifer systems. This sort of information is valuable to both scientific and resource management communities, and there are many benefits to enhancing our knowledge of the class of compounds.
Metals and metalloids occur in the environment both as natural constituents of water and as contaminants. The focus of my research is to identify and develop geochemical and particularly isotopic approaches to identifying the sources, transport mechanisms and fates of those metals and metalloids, and to use these novel tracer tools to study hydrologic and biogeochemical processes in varied field and laboratory situations. Examples of current research objectives are: 1) to use isotopes of the alkaline earth elements (Ca, Sr, Ba) to determine water flowpaths and solute sources in headwater catchments; 2) to use isotopes of Cr to understand Cr transport and contaminant remediation at industrial sites and in rivers;...
The focus of my research is to characterize the processes and mechanisms of metal sorption reactions with surfaces of natural solid phases (aquifer and stream sediments) through field studies and lab experiments with solid materials from the field and with model sorbent phases. Molecular scale characterization of sorbed metal speciation is needed for confirmation of reaction mechanisms to improve reaction terms in transport models, to assess long-term fate of attenuated metals in response to changing hydrologic and geochemical conditions, and to better understand the bioavailability of metal contaminants. In conjunction with lab and field experiments, my investigations utilize X-ray absorption spectroscopic (EXAFS)...
Categories: Project; Tags: Contaminants, Metals, Radioisotopes