A5014895219- Radioactive element chemistry and processing
- Groundwater flow and contamination studies
- Groundwater and Isotope Geochemistry
- Geochemistry and Geologic Mapping
- Mine drainage and remediation techniques
- Radioactive contamination and transfer
- Soil and Water Nutrient Dynamics
- Hydrocarbon exploration and reservoir analysis
- Atmospheric and Environmental Gas Dynamics
- Geochemistry and Elemental Analysis
- Wastewater Treatment and Nitrogen Removal
- Hydrology and Watershed Management Studies
- Heavy metals in environment
- Nuclear and radioactivity studies
- Geological formations and processes
- Additive Manufacturing Materials and Processes
- Peatlands and Wetlands Ecology
- Geology and Paleoclimatology Research
- Water Quality and Resources Studies
- Radioactivity and Radon Measurements
- Constructed Wetlands for Wastewater Treatment
- Soil and Unsaturated Flow
- Water Quality Monitoring Technologies
- Welding Techniques and Residual Stresses
- Insect and Pesticide Research
Lawrence Berkeley National Laboratory
2014-2024
Arizona State University
2001-2020
United States Geological Survey
2004-2013
Pacific Northwest National Laboratory
2009
University of Michigan–Ann Arbor
2009
University of Liverpool
2004
University of California, Berkeley
1990-2003
Forest Products Laboratory
1990
SUNY Brockport
1975-1976
York University
1975-1976
Abstract To understand how redox processes influence carbon, nitrogen, and iron cycling within the intrameander hyporheic zone, we developed a biotic abiotic reaction network incorporated it into reactive transport simulator PFLOTRAN. Two‐dimensional flow simulations were performed (1) to evaluate transient hydrological conditions control lateral zonation an region of East River in Colorado (2) quantify impact single meander on subsurface exports carbon other geochemical species river. The...
In this study, we report the results of in situ U(VI) bioreduction experiments at Integrated Field Research Challenge site Rifle, Colorado, USA. Columns filled with sediments were deployed into a groundwater well and, after period conditioning groundwater, amended mixture soluble U(VI), and acetate to stimulate growth indigenous microorganisms. Individual reactors collected as various redox regimes column achieved: (i) during iron reduction, (ii) just onset sulfate (iii) later reduction. The...
Critical Zone processes encompass interactions among rock, soil, water, air, and living organisms, essential for quantifying water nutrient fluxes predicting downstream river quality. High-fidelity reactive transport models (RTMs) are important understanding but typically computationally expensive, which limits their applicability across large catchments. To address these challenges, we developed a scale-adaptive simulation framework that balances process fidelity with computational...
A tracer test was performed at the Rifle Integrated Field Research Challenge site to assess effect of addition bicarbonate on U(VI) desorption from contaminated sediments in aquifer and compare equilibrium rate‐limited reactive transport model descriptions mass transfer limitations desorption. The consisted injection a 37 mM NaHCO 3 solution containing conservative tracers followed by down‐gradient sampling groundwater various elevations distances point injection. Breakthrough curves show...
Abstract Hydrologic extremes dominate chemical exports from riparian zones and dictate water quality in major river systems. Yet, changes land use ecosystem services alongside growing climate variability are altering hydrologic their coupled impacts on riverine quality. In the western U.S., warming temperatures intensified aridification increasingly paired with expanding range of American beaver—and dams, which transform biogeochemical cycles Here, we show that beaver dams overshadow...
We examined the chemical reactions influencing dissolved concentrations, speciation, and transport of naturally occurring arsenic (As) in a shallow, sand gravel aquifer with distinct geochemical zones resulting from land disposal dilute sewage effluent. The principal were: (1) uncontaminated zone above plume [350 μM oxygen (DO), pH 5.9]; (2) suboxic (5 DO, 6.2, elevated concentrations sewage-derived phosphate nitrate); (3) anoxic [dissolved iron(II) 100–300 μM, 6.5–6.9, phosphate]. Sediments...
A study of U(VI) adsorption by aquifer sediment samples from a former uranium mill tailings site at Rifle, Colorado, was conducted under oxic conditions as function pH, U(VI), Ca, and dissolved carbonate concentration. Batch experiments were performed using <2 mm size fractions, sand-sized fraction, artificial groundwater solutions prepared to simulate the field composition. To encompass geochemical alluvial site, experimental ranged 6.8 × 10−8 10−5 M in [U(VI)]tot, 7.2 8.0 3.0 10−3 6.0...
Recent studies in snowmelt-dominated catchments have documented changes nitrogen (N) retention over time, such as declines watershed exports of N, though there is a limited understanding the controlling processes driving these trends. Working mountainous headwater East River Colorado watershed, we explored effects riparian hollows N-cycling hotspots and important small-scale controls on observed Using modeling-based approach informed by remote sensing situ observations, simulated N-retention...
Microorganisms have evolved several mechanisms to mobilize and mineralize occluded insoluble phosphorus (P), thereby promoting plant growth in terrestrial ecosystems. However, the linkages between microbial P-solubilization traits preponderance of P natural ecosystems are not well known. We tested solubilization hundreds culturable bacteria representative rhizosphere from a gradient where concentration bioavailability decline as soil becomes progressively more weathered. Aluminum, iron...
ABSTRACT This study was undertaken to determine the fate of As, Mo, and V (trace elements, TEs) in sediments a constructed wetland use for remediation potentially toxic trace element–contaminated agricultural drainwater. After three years operation, sediment cores were collected changes TE concentrations as function depth effects varying water column depth. All highest top 2 4 cm decreased with Molybdenum accumulated sediments, up levels 32.5 ± 4.6, 30.2 8.9, 59.3 26.1 mg kg −1 1 at depths...
Abstract Shales contain high levels of organic carbon (OC) and represent a large fraction the Earth's reduced stocks. While recent evidence suggests that shale‐derived OC may be actively cycled in riverine systems, this process is poorly understood not currently considered global C models. Through use sediment density fractionations, extractions, radiocarbon measurements, chemical characterization, we provide information on abundance, chemistry, mobility floodplain sediments shale‐rich...
Water quality transformations during soil aquifer treatment at the Mesa Northwest Reclamation Plant (NWWRP) were evaluated by sampling a network of groundwater monitoring wells located within reclaimed water plume. The has used (SAT) since it began operation in 1990 and recovery from impacted been minimal. Groundwater samples obtained represent travel times several days to greater than five years. Samples analyzed for wide range organic inorganic constituents. Sulfate was as tracer estimate...
Extraction techniques utilizing high pH and (bi)carbonate concentrations were evaluated for their efficacy in determining the oxidation state of uranium (U) reduced sediments collected from Rifle, CO. Differences dissolved between oxic anoxic extractions have been proposed as a means to quantify U(VI) U(IV) content sediments. An additional step was added using strong anion exchange resin separate U(VI). X-ray spectroscopy showed that present polymerized precipitates similar uraninite and/or...
Abstract Sulfur (S) is an essential macronutrient and important component of the earth’s crust, its cycling has critical impacts on trace metal mobility, water quality, human health. Pyrite weathering primary pathway by which sulfur enters surface waters. However, biogeochemical in soils river corridor mediates sulfate exports. In this study, we identified major forms across multiple compartments scales a pristine mountainous watershed, including shale bedrock profiles, hillslope soils,...