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We tested the hypothesis that runoff of uranium-bearing particles from mining waste disposal areas was a significant mechanism for redistribution of uranium in the northeastern part of the Upper Puerco River watershed (New Mexico). However, our results were not consistent with this hypothesis. Analysis of >100 sediment and suspended sediment samples collected adjacent to and downstream from uranium source areas indicated that uranium levels in the majority of the samples were not elevated above background. Samples collected within 50 m of a known waste disposal site were subjected to detailed geochemical characterization. Uranium in these samples was found to be highly soluble; treatment with synthetic pore water...
Specific UV absorbance (SUVA) is defined as the UV absorbance of a water sample at a given wavelength normalized for dissolved organic carbon (DOC) concentration. Our data indicate that SUVA, determined at 254 nm, is strongly correlated with percent aromaticity as determined by 13C NMR for 13 organic matter isolates obtained from a variety of aquatic environments. SUVA, therefore, is shown to be a useful parameter for estimating the dissolved aromatic carbon content in aquatic systems. Experiments involving the reactivity of DOC with chlorine and tetra- methylammonium hydroxide (TMAH), however, show a wide range of reactivity for samples with similar SUVA values. These results indicate that, while SUVA measurements...
Processes that reduce the productivity of arid and semi-arid lands, collectively known as desertification, affect more than 3 billion hectares or more than 80% of such lands. The degradation process results in redistribution of water and nutrients, loss of find soil fractions and replacement of palatable plants with undesirable plants. These changes frequently uncouple rainfall and productivity on a temporal scale. This uncoupling is probably due to modification of the nitrogen cycle as a result of the desertification processes. Changes in vegetation can produce changes in fluxes of radiatively active gasses and a variety of organic volatiles to the atmosphere. Redistribution of soil and water may produce "hot"...
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 a function of pH, U(VI), Ca, and dissolved carbonate concentration. Batch adsorption experiments were performed using <2 mm size sediment fractions, a sand-sized fraction, and artificial groundwater solutions prepared to simulate the field groundwater composition. To encompass the geochemical conditions of the alluvial aquifer at the site, the experimental conditions ranged from 6.8 x 10(-8) to 10(-5) M in [U(VI)](tot), 7.2 to 8.0 in pH, 3.0 x 10(-3) to 6.0 x 10(-3) M in [Ca(2+)], and 0.05 to 2.6% in partial pressure of carbon dioxide. Surface area normalized...
Although aquatic mosses are widely used as metal biomonitors in rivers, there are few effective models to describe metal uptake and loss by these plants. To fill this gap, we exposed the aquatic moss Fontinalis dalecarlica for 28 d to three Cd concentrations (âˆ&frac14;5−50 nM) in a flow-through laboratory system. Cadmium accumulation by F. dalecarlica was rapid during the first few days of exposure and slowed thereafter but did not reach a steady state within our 1-month long experiment. This lack of a plateau in moss concentrations suggests that, for biomonitoring purposes, the duration of moss exposure should be considered either through a model of the type that we tested or by standardizing the exposure time...
In the Rocky Mountains, there is uncertainty about the source areas and emission types that contribute to nitrate (NO3) deposition, which can adversely affect sensitive aquatic habitats of high-elevation watersheds. Regional patterns in NO3 deposition sources were evaluated using NO3 isotopes in five National Parks, including 37 lakes and 7 precipitation sites. Results indicate that lake NO3 ranged from detection limit to 38 Î&frac14;eq/L, δ18O (NO3) ranged from −5.7 to +21.3‰, and δ15N (NO3) ranged from −6.6 to +4.6‰. δ18O (NO3) in precipitation ranged from +71 to +78‰. δ15N (NO3) in precipitation and lakes overlap; however, δ15N (NO3) in precipitation is more depleted than δ15N (NO3) in lakes,...
A reactive transport model based on one-dimensional transport and equilibrium chemistry is applied to synoptic data from an acid mine drainage stream. Model inputs include streamflow estimates based on tracer dilution, inflow chemistry based on synoptic sampling, and equilibrium constants describing acid/base, complexation, precipitation/dissolution, and sorption reactions. The dominant features of observed spatial profiles in pH and metal concentration are reproduced along the 3.5-km study reach by simulating the precipitation of Fe(III) and Al solid phases and the sorption of Cu, As, and Pb onto freshly precipitated iron(III) oxides. Given this quantitative description of existing conditions, additional simulations...
We measured the dielectric permittivity of dry and fluid saturated Green River oil shale samples over a frequency range of 1 MHz to 1.8 GHz. Dry sample measurements were carried out between room temperature and 146 °C; saturated sample measurements were carried out at room temperature. Samples obtained from the Green River formation of Wyoming and from the Anvil Points Mine in Colorado were cored both parallel and perpendicular to layering. The samples, which all had organic richnesses in the range of 0.04−0.19 L/kg (10−45 gal/ton), showed small variations between samples and a relatively small level of anisotropy of dielectric properties when dry. The real and imaginary part of the relative dielectric permittivity...
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We collected and analyzed 2,707 large fish from 626 stream/river sites in 12 western U.S. states using a probability design to assess the regional distribution of whole fish mercury (Hg) concentrations. Large (>120 mm total length) fish Hg levels were strongly related to both fish length and trophic guild. All large fish that we sampled exceeded the wet weight detection limit of 0.0024 ?g�g-1, and the mean Hg concentration in piscivores (0.260 ?g�g-1) was nearly three times that of nonpiscivores (0.090 ?g�g-1). Fish tissue Hg levels were not related to local site disturbance class. After partialing out the effects of fish length, correlations between Hg and environmental variables were low (r < 0.3) for the most...


    map background search result map search result map The Western Airborne Contaminant Assessment Project (WACAP): an interdisciplinary evaluation of the impacts of airborne contaminants in western U.S. National Parks. Mercury Concentration in Fish from Streams and Rivers Throughout the Western United States Modeling Cadmium Exchange by an Aquatic Moss ( Fontinalis dalecarlica ) Rapid Dissolution of Soluble Uranyl Phases in Arid, Mine-Impacted Catchments near Church Rock, NM Rapid Dissolution of Soluble Uranyl Phases in Arid, Mine-Impacted Catchments near Church Rock, NM Mercury Concentration in Fish from Streams and Rivers Throughout the Western United States The Western Airborne Contaminant Assessment Project (WACAP): an interdisciplinary evaluation of the impacts of airborne contaminants in western U.S. National Parks.