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The acquisition and meaningful interpretation of sediment data from areas disturbed by land-use activities or natural processes are two of the most deficient areas of recognizing nonpoint-source pollution in the United States. The comparison of sediment data from disturbed and undisturbed areas provides a means to (1) evaluate the effects that land-use activities cause, (2) investigate the geomorphic processes that regulate the detachment and transport of sediment, and (3) develop strategies for remedial action to reduce excessive sediment discharges. This information is especially necessary to minimize sediment discharges and sorbed chemical loads from surface-mine, industrial, agricultural, and urban areas. Objectives...
There are two major questions being addressed at study sites of this research project. (1) To what degree is the phosphorus in sediment at a study site bioavailable? (2) Will the phosphorus in the sediment be retained or released to the water column over time? The objectives of my research are (1) to determine the geochemical associations of nutrients (in particular phosphorus) and metals in sedimentary environments (2) determine what these associations mean with respect to bioavailability or release of nutrients or metals to the water column. Bottom sediment is a major control over the concentrations of nutrients and metals in the water column because sediment can retain nutrients and metals or release nutrients...
The development of models of hydrologic systems requires the description of individual processes in mathematical terms and the solution of sets of complex equations in differential form. This project is focused on developing mathematical descriptions of flow and water-quality processes that can be linked together to form such models. Research is needed on application of mathematical theory to the modeling of transport of sediments, including mudflows and hyperconcentrations such as occur after natural disasters such as volcanic eruptions or dam failures. This project is focused on developing mathematial description of flow and water-quality processes that can be linked together to form models of hydrologic systems...
Categories: Project
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;...
In collaboration with scientists from other agencies and academic institutions, studies focus on quantifying the importance of benthic sources of biologically reactive inorganic solutes (for example, dissolved macronutrients and trace metals). The importance is quantified and compared to other solute transport processes (for example, advective transport) and biological requirements for primary production in a wide range of oligotrophic to hypereutrophic aquatic systems. Such results provide critical input to the development and refinement of water-quality (e.g., TMDL) models that must evaluate alternative management scenarios.
Categories: Project; Tags: Contaminants, Ecology, Metals
Quantify the effect of aquatic and floodplain vegetation on sediment and nutrient budgets along several dimensions of hydrologic connectivity (longitudinally, laterally, and temporally) in the Difficult Run floodplain watershed; Determine if long term trends in anthropogenic nutrients are linked to improvements in submerged aquatic vegetation (SAV) diversity and abundance in other less urban estuaries, as they were in the highly urban, Potomac River; and Habitat evaluation and restoration of coastal wetlands and estuaries in the face of climate change and other stressors such as exotic species and eutrophication.
Most of my current efforts are committed to multi-catchment investigations designed to distinguish the roles of vegetation, climate, and land-cover change and to put these in a hydrologic and biogeochemical framework as well as to examine ecosystem costs and services focusing on water, carbon, and biodiversity. Two projects consume most of my efforts: (1) Work related to the Luquillo USGS Water, Energy, and Biogeochemical Budget (WEBB) Project in eastern Puerto Rico and parallel work in Panama is in the modeling and write-up phase (60% time). The objective is a comprehensive assessment of catchment hydrology and biogeochemistry in a humid-tropical landscape. In Puerto Rico we compare two rock types, quartzose and...
My primary research objective is to evaluate ecosystem health in freshwater systems using biologically meaningful measures of metal exposure. Resident aquatic organisms accumulate metal into their tissue by integrating the metal from their environment (dissolved and diet). Using physiological parameters derived from earlier experiments, I am developing a model to predict biomonitor tissue concentrations under various exposure conditions. The goal of this research is to link biological responses to changes in environmental condition (e.g., remediation and physical disturbances associated with floods). While this work was developed from the Clark Fork River study, the model is applicable to other impaired rivers and...
Apply reactive transport models in groundwater to gain understanding of the processes controlling the fate of geochemical species. Develop and apply methods to incorporate small scale information into large scale simulations of groundwater transport in order to formulate more robust modeling approaches and results. Quantify the uncertainty inherent in reactive transport models including both the uncertainty of model parameters as well as the uncertainty in conceptualization of the problem.
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
There are two objectives of my current research. The first objective is the generic problem of groundwater monitoring-network design. This research aims to develop statistically-sound and simulation-based methods for groundwater monitoring network design. The goal is to develop techniques that unify stochastic groundwater flow and contaminant transport simulation with optimization to develop groundwater monitoring strategies and to explore the capabilities and limitations of various monitoring-network design methods. Examples include: (1) Determining the state of groundwater and detecting or predicting changes in the groundwater environment. I am currently developing a sampling-design model for a subarea of the...
Ground-Water solute-transport simulation modeling is an important tool that aids in the analysis of ground-water contamination problems, both actual and potential. Accidental spills, leakage, and waste disposal operations can lead to ground-water contamination. The ability to analyze and predict the movement of solutes in ground-water systems is necessary to assess the effects of a contamination situation or properly design a waste-disposal operation. Laboratory experiments are essential to understanding geochemical reactions in the field and for obtaining the necessary reaction coefficients and rate constants used in transport models. Simulation modeling also is used to compare alternative strategies for aquifer...
My 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...
The energy potential of geothermal waters from geopressured systems is enormous. Geochemical data are necessary for delineating favorable exploration areas, estimating the recoverable geothermal resources from a given reservoir, and identifying potential pollution, waste disposal, and corrosion problems. The project's objectives are to study the chemistry and controls on the chemistry of water in geothermal and other subsurface systems; to provide basic data needed to estimate the geothermal energy and other resources; and to identify potential pollution, waste disposal, and corrosion problems associated with extraction of energy and other resources from these systems.
Categories: Project; Tags: Geothermal Resources
Satisfactory formulations and solutions of equations approximately describing (1) movement of fluids and components contained in fluids through consolidated and unconsolidated rocks, and (2) interactions of the fluids and rocks accompanying fluid movement, are needed for proper understanding and management of ground-water resources. Such formulations and solutions of equations that apply for general field situations where the flow system is complex and hydrologic data are inexact are not, in general, available. Project objectives are to: (1) reformulate where necessary, the equations describing the flow of fluids through porous or fractured rock to include stochastic processes, emphasizing equations that are suitable...