Laurie S. Balistrieri

Environmental Chemistry, Chemical Thermodynamics, Chemical Kinetics

30.61

Publications

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    Kathleen S. Smith, Laurie S. Balistrieri, Andrew S. Todd
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    ABSTRACT: The biotic ligand model (BLM) is a numerical approach that couples chemical speciation calculations with toxicological information to predict the toxicity of aquatic metals. This approach was proposed as an alternative to expensive toxicological testing, and the U.S. Environmental Protection Agency incorporated the BLM into the 2007 revised aquatic life ambient freshwater quality criteria for Cu. Research BLMs for Ag, Ni, Pb, and Zn are also available, and many other BLMs are under development. Current BLMs are limited to ‘one metal, one organism’ considerations. Although the BLM generally is an improvement over previous approaches to determining water quality criteria, there are several challenges in implementing the BLM, particularly at mined and mineralized sites. These challenges include: (1) historically incomplete datasets for BLM input parameters, especially dissolved organic carbon (DOC), (2) several concerns about DOC, such as DOC fractionation in Fe- and Al-rich systems and differences in DOC quality that result in variations in metal-binding affinities, (3) water-quality parameters and resulting metal-toxicity predictions that are temporally and spatially dependent, (4) additional influences on metal bioavailability, such as multiple metal toxicity, dietary metal toxicity, and competition among organisms or metals, (5) potential importance of metal interactions with solid or gas phases and/or kinetically controlled reactions, and (6) tolerance to metal toxicity observed for aquatic organisms living in areas with elevated metal concentrations.
    Applied Geochemistry 06/2015; 57:55-72. DOI:10.1016/j.apgeochem.2014.07.005 · 2.02 Impact Factor
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    Kathleen S. Smith, Laurie S. Balistrieri, Andrew S. Todd
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    ABSTRACT: Supplementary Material for: Smith, K.S., Balistrieri, L.S., and Todd, A.S., 2015, Using biotic ligand models to predict metal toxicity in mineralized systems (review paper): Applied Geochemistry, v. 57, p. 55-72, http://dx.doi.org/10.1016/j.apgeochem.2014.07.005.
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    ABSTRACT: A modeling approach that was used to predict the toxicity of dissolved single and multiple metals to trout is extended to stream benthic macroinvertebrates, freshwater zooplankton, and daphnia magna. The approach predicts the accumulation of toxicants (h, al, cd, cu, ni, pb, and zn) on organisms using three equilibrium accumulation models that define interactions between dissolved cations and biological receptors (biotic ligands). These models differ in the structure of the receptors and include a 2-site biotic ligand model, a bidentate biotic ligand or 2-pka model, and a humic acid (ha) model. The predicted accumulation of toxicants is weighted using toxicant-specific coefficients and incorporated into a toxicity function called tox, which is then related to observed mortality or invertebrate community richness using a logistic equation. All accumulation models provide reasonable fits to metal concentrations in tissue samples of stream invertebrates. Despite the good fits, distinct differences in the magnitude of toxicant accumulation and biotic ligand speciation exist among the models for a given solution composition. However, predicted biological responses are similar among the models because there are interdependencies among model parameters in the accumulation-Tox models. To illustrate potential applications of the approaches, the three accumulation-Tox models for natural stream invertebrates are used in Monte Carlo simulations to (1) predict the probability of adverse impacts in catchments of differing geology in central Colorado (USA), (2) link geology, water chemistry, and biological response, and (3) demonstrate how this approach can be used to screen for potential risks associated with resource development. This article is protected by copyright. All rights reserved. This article is protected by copyright. All rights reserved.
    Environmental Toxicology and Chemistry 03/2015; DOI:10.1002/etc.2824 · 2.83 Impact Factor
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    ABSTRACT: As part of the Metal Mixture Modeling Evaluation (MMME) project, models were developed by the National Institute of Advanced Industrial Science and Technology (Japan), the U.S. Geological Survey (USA), HDR׀HydroQual, Inc. (USA), and the Centre for Ecology and Hydrology (UK) to address the effects of metal mixtures on biological responses of aquatic organisms. A comparison of the 4 models, as they were presented at the MMME Workshop in Brussels, Belgium (May 2012), is provided herein. Overall, the models were found to be similar in structure (free ion activities computed by WHAM; specific or non-specific binding of metals/cations in or on the organism; specification of metal potency factors and/or toxicity response functions to relate metal accumulation to biological response). Major differences in modeling approaches are attributed to various modeling assumptions (e.g., single versus multiple types of binding site on the organism) and specific calibration strategies that affected the selection of model parameters. The models provided a reasonable description of additive (or nearly additive) toxicity for a number of individual toxicity test results. Less-than-additive toxicity was more difficult to describe with the available models. Because of limitations in the available datasets and the strong inter-relationships among the model parameters (log KM values, potency factors, toxicity response parameters), further evaluation of specific model assumptions and calibration strategies is needed. This article is protected by copyright. All rights reserved
    Environmental Toxicology and Chemistry 11/2014; 34(4). DOI:10.1002/etc.2820 · 2.83 Impact Factor
  • D.N. Castendyk, L.E. Eary, L.S. Balistrieri
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    ABSTRACT: Pit lakes are permanent hydrologic/landscape features that can result from open pit mining for metals, coal, uranium, diamonds, oil sands, and aggregates. Risks associated with pit lakes include local and regional impacts to water quality and related impacts to aquatic and terrestrial ecosystems. Stakeholders rely on predictive models of water chemistry to prepare for and manage these risks. This paper is the first of a two part series on the modeling and management of pit lakes. Herein, we review approaches that have been used to quantify wall-rock runoff geochemistry, wall-rock leachate geochemistry, pit lake water balance, pit lake limnology (i.e. extent of vertical mixing), and pit lake water quality, and conclude with guidance on the application of models within the mine life cycle. The purpose of this paper is to better prepare stakeholder, including future modelers, mine managers, consultants, permitting agencies, land management agencies, regulators, research scientists, academics, and other interested parties, for the challenges of predicting and managing future pit lakes in un-mined areas.
    Applied Geochemistry 09/2014; 57. DOI:10.1016/j.apgeochem.2014.09.004 · 2.02 Impact Factor
  • D.N. Castendyk, L.S. Balistrieri, C. Gammons, N. Tucci
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    ABSTRACT: Pit lakes, a common product of open pit mining techniques, may become long-term, post-mining environmental risks or long-term, post-mining water resources depending upon management decisions. This study reviews two published pit lake modeling studies and one pit lake monitoring program in order to increase the transparency of approaches used in pit lake prediction and management. The first model is a two-year limnological simulation of the existing Dexter pit lake, Nevada, USA that accurately modeled temperature profiles, salinity profiles, and turnover events observed between 1999 and 2000. The second model is a 55-year prediction of a future pit lake in the Martha Mine, New Zealand that identified the need for additional mitigation and evaluated potential effects of cost-effective mitigation options. The final study reviews eight years of monitoring data collected from the Berkeley pit lake, Montana, USA, from 2004 to 2012. This study identifies changes in the physical limnology and water quality of the pit lake that resulted from metal recovery operations, and highlights the value of monitoring programs in general. Whereas these pit lakes are different in many ways, the management tools discussed herein maximized the value and understanding of the post-mining resources.
    Applied Geochemistry 09/2014; 57. DOI:10.1016/j.apgeochem.2014.09.003 · 2.02 Impact Factor
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    Laurie S Balistrieri, Christopher A Mebane
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    Laurie S Balistrieri, Christopher A Mebane
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    ABSTRACT: The toxicity of single and multiple metal (Cd, Cu, Pb, and Zn) solutions to trout is predicted using an approach that combines calculations of: (1) solution speciation; (2) competition and accumulation of cations (H, Ca, Mg, Na, Cd, Cu, Pb, and Zn) on low abundance, high affinity and high abundance, low affinity biotic ligand sites; (3) a toxicity function that accounts for accumulation and potency of individual toxicants; and (4) biological response. The approach is evaluated by examining water composition from single metal toxicity tests of trout at 50% mortality, results of theoretical calculations of metal accumulation on fish gills and associated mortality for single, binary, ternary, and quaternary metal solutions, and predictions for a field site impacted by acid rock drainage. These evaluations indicate that toxicity of metal mixtures depends on the relative affinity and potency of toxicants for a given aquatic organism, suites of metals in the mixture, dissolved metal concentrations and ratios, and background solution composition (temperature, pH, and concentrations of major ions and dissolved organic carbon). A composite function that incorporates solution composition, affinity and competition of cations for two types of biotic ligand sites, and potencies of hydrogen and individual metals is proposed as a tool to evaluate potential toxicity of environmental solutions to trout.
    Science of The Total Environment 08/2013; 466-467C:788-799. DOI:10.1016/j.scitotenv.2013.07.034 · 4.10 Impact Factor
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    Laurie S Balistrieri, David A Nimick, Christopher A Mebane
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    ABSTRACT: Evaluating water quality and the health of aquatic organisms is challenging in systems with systematic diel (24 h) or less predictable runoff-induced changes in water composition. To advance our understanding of how to evaluate environmental health in these dynamic systems, field studies of diel cycling were conducted in two streams (Silver Bow Creek and High Ore Creek) affected by historical mining activities in southwestern Montana. A combination of sampling and modeling tools was used to assess the toxicity of metals in these systems. Diffusive Gradients in Thin Films (DGT) samplers were deployed at multiple time intervals during diel sampling to confirm that DGT integrates time-varying concentrations of dissolved metals. Site specific water compositions, including time-integrated dissolved metal concentrations determined from DGT, a competitive, multiple-toxicant biotic ligand model, and the Windemere Humic Aqueous Model Version 6.0 (WHAM VI) were used to determine the equilibrium speciation of dissolved metals and biotic ligands. The model results were combined with previously collected toxicity data on cutthroat trout to derive a relationship that predicts the relative survivability of these fish at a given site. This integrative approach may prove useful for assessing water quality and toxicity of metals to aquatic organisms in dynamic systems and evaluating whether potential changes in environmental health of aquatic systems are due to anthropogenic activities or natural variability.
    Science of The Total Environment 04/2012; 425:155-68. DOI:10.1016/j.scitotenv.2012.03.008 · 4.10 Impact Factor
  • Suzan Aranda, David M Borrok, Richard B Wanty, Laurie S Balistrieri
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    ABSTRACT: The pollution of natural waters with metals derived from the oxidation of sulfide minerals like pyrite is a global environmental problem. However, the metal loading pathways and transport mechanisms associated with acid rock drainage reactions are often difficult to characterize using bulk chemical data alone. In this study, we evaluated the use of zinc (Zn) isotopes to complement traditional geochemical tools in the investigation of contaminated waters at the former Waldorf mining site in the Rocky Mountains, Colorado, U.S.A. Geochemical signatures and statistical analysis helped in identifying two primary metal loading pathways at the Waldorf site. The first was characterized by a circumneutral pH, high alkalinity, and high Zn/Cd ratios. The second was characterized by acidic pHs and low Zn/Cd ratios. Zinc isotope signatures in surface water samples collected across the site were remarkably similar (the δ(66)Zn, relative to JMC 3-0749-L, for most samples ranged from 0.20 to 0.30‰±0.09‰ 2σ). This probably suggests that the ultimate source of Zn is consistent across the Waldorf site, regardless of the metal loading pathway. The δ(66)Zn of pore water samples collected within a nearby metal-impacted wetland area, however, were more variable, ranging from 0.20 to 0.80‰±0.09‰ 2σ. Here the Zn isotopes seemed to reflect differences in groundwater flow pathways. However, a host of secondary processes might also have impacted Zn isotopes, including adsorption of Zn onto soil components, complexation of Zn with dissolved organic matter, uptake of Zn into plants, and the precipitation of Zn during the formation of reduced sulfur species. Zinc isotope analysis proved useful in this study; however, the utility of this isotopic tool would improve considerably with the addition of a comprehensive experimental foundation for interpreting the complex isotopic relationships found in soil pore waters.
    Science of The Total Environment 03/2012; 420:202-13. DOI:10.1016/j.scitotenv.2012.01.015 · 4.10 Impact Factor
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    ABSTRACT: The Callahan Zn-Cu-Pb Mine in Brooksville, Maine produced ore enriched in pyrite, chalcopyrite, and sphalerite from an open pit in a dammed tidal estuary (Goose Cove) during 1968-1972. The pit was about 180-300 m wide and 97 m deep. The dam was breached in 1972 and the pit filled with seawater. To understand the seasonal hydrodynamics and geochemistry of the pit lake, temperature sensors were deployed at multiple depths and continuous temperature records were obtained from April 2007 to June 2008. The water column was sampled in April and August 2007 and June 2008. Water samples were analyzed for acid-soluble and dissolved constituents, including stable metal isotopes of Cu, Fe, and Zn. Profiles of temperature, dissolved oxygen, and dissolved sulfide indicated that the pit lake is permanently stratified, and that the redox boundary became shallower (from 63 to 47 m) during the study period. Concentrations of dissolved oxygen between 10 and 60 m decreased by 150 µM between the April and August 2007 samplings, whereas a mixing event ventilated depths between 10 and 35 m between the August 2007 and June 2008 samplings. Dissolved sulfide reached a maximum of 315 µM in the bottom water, and values of pH decreased from 7.3-7.8 in the surface water to 6.7 in the bottom water. Dissolved concentrations of Cu were < 50 pM in the surface water, increased to 75-130 pM at 20 m, and then decreased to < 2 pM below 60 m. Preliminary isotopic data from June 2008 indicated that dissolved δ65Cu decreased from 1.6 ‰ at 10-40 m to -0.7 ‰ at 80 m. Dissolved concentrations of Fe were low in the surface water and reached a maximum of 10 µM at 50 m in June 2008, and then decreased to about 3 µM as sulfide increased. Values of dissolved δ56Fe were about -1.6 ‰ at depths < 40 m and increased to -0.7 ‰ at depths below 60 m. Like Cu, dissolved Zn was lower (< 1.2 µM) in the surface water, increased to a maximum of 6.5 µM at 20 m in June 2008, and then decreased to < 0.03 µM below 60 m. Isotopic data from June 2008 indicated that dissolved δ66Zn decreased from 0.4 ‰ at 40 m to ~ 0 ‰ below 65 m. Seasonal changes in metal concentrations and isotopic signatures with depth likely are due to a combination of mixing, scavenging by particles, and dissolution and precipitation of mineral phases across the redox boundary.
    GSA Annual Meeting and Exposition, Minneapolis, Mn; 10/2011
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    ABSTRACT: We used a hydrodynamics model to assess the consequences of climate warming and contemporary geomorphic evolution for thermal conditions in a large, shallow Alaskan lake. We evaluated the effects of both known climate and landscape change, including rapid outlet erosion and migration of the principal inlet stream, over the past 50 yr as well as future scenarios of geomorphic restoration. Compared to effects of air temperature during the past 50 yr, lake thermal properties showed little sensitivity to substantial (similar to 60%) loss of lake volume, as the lake maximum depth declined from 6 m to 4 m driven by outlet erosion. The direction and magnitude of future lake thermal responses will be driven largely by the extent of inlet stream migration when it occurs simultaneously with outlet erosion. Maintaining connectivity with inlet streams had substantial effects on buffering lake thermal responses to warming climate. Failing to account for changing rates and types of geomorphic processes under continuing climate change may misidentify the primary drivers of lake thermal responses and reduce our ability to understand the consequences for aquatic organisms.
    Limnology and Oceanography 01/2011; 56(1-1):193-205. DOI:10.4319/lo.2011.56.1.0193 · 3.62 Impact Factor
  • Jennifer R. Grififths, Daniel E. Schindler, Laurie S. Balistrieri
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    ABSTRACT: Background/Question/Methods Research investigating the effects of climate change on freshwater species and ecosystems frequently assumes a static landscape. Yet landscapes are dynamic and, especially in areas of recent glacial and volcanic activity, can evolve on temporal scales relevant for understanding ecosystem responses to global change. On the Alaska Peninsula, climate warming is occurring simultaneously with rapid geomorphic evolution of the upper Chignik watershed, which has substantially altered rearing habitat for juvenile sockeye salmon (Oncorhynchus nerka). A large, shallow, isothermal lake has lost 23% of its volume since 1960 and volume continues to decline. Fry emigrating during mid-summer have shown evidence of thermal stress and overwintering life histories strategies have changed. We used a hydrodynamics model to assess whether further volume loss can lead to a substantial shift in lake thermal regimes. We investigated the effects of two potential restoration strategies for improving sockeye salmon rearing habitat: an outlet control structure and a tributary diversion. Additionally, we assessed the potential efficacy of these restoration strategies given projections of future climate regimes. Results/Conclusions Model simulations demonstrate that a decline in maximum depth alters the lake thermal environment by increasing the magnitude of cooling periods. If a decline in lake volume also decreases connectivity to some lake tributaries, there is an overall increase in stressful thermal conditions for juvenile sockeye. However, a river diversion strategy maintains tributary connectivity and results in cooler lake temperatures as volume declines. Alternatively, restoration to restore historic water levels using an outlet control structure will not decrease summer thermal stress for juvenile sockeye salmon under current climate conditions. The restoration consequences for lake thermal regimes under future climate are quite different. There are large magnitude effects of predicted air temperature increases on lake temperatures leading to a more stressful thermal rearing environment for juvenile sockeye salmon. Neither restoration strategy is likely to mitigate lake temperature response to increasing air temperatures. Rapid landscape evolution has the potential to amplify or dampen the response of ecosystems to climate change. Our understanding of ecosystem responses to climate change and the creation of successful management strategies may be enhanced by considering the role of landscape evolution.
    94th ESA Annual Convention 2009; 08/2009
  • Laurie S. Balistrieri, Richard G. Blank
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    ABSTRACT: In order to evaluate thermodynamic speciation calculations inherent in biotic ligand models, the speciation of dissolved Cd, Cu, Pb, and Zn in aquatic systems influenced by historical mining activities is examined using equilibrium computer models and the diffusive gradients in thin films (DGT) technique. Several metal/organic-matter complexation models, including WHAM VI, NICA-Donnan, and Stockholm Humic model (SHM), are used in combination with inorganic speciation models to calculate the thermodynamic speciation of dissolved metals and concentrations of metal associated with biotic ligands (e.g., fish gills). Maximum dynamic metal concentrations, determined from total dissolved metal concentrations and thermodynamic speciation calculations, are compared with labile metal concentrations measured by DGT to assess which metal/organic-matter complexation model best describes metal speciation and, thereby, biotic ligand speciation, in the studied systems. Results indicate that the choice of model that defines metal/organic-matter interactions does not affect calculated concentrations of Cd and Zn associated with biotic ligands for geochemical conditions in the study area, whereas concentrations of Cu and Pb associated with biotic ligands depend on whether the speciation calculations use WHAM VI, NICA-Donnan, or SHM. Agreement between labile metal concentrations and dynamic metal concentrations occurs when WHAM VI is used to calculate Cu speciation and SHM is used to calculate Pb speciation. Additional work in systems that contain wide ranges in concentrations of multiple metals should incorporate analytical speciation methods, such as DGT, to constrain the speciation component of biotic ligand models.
    Applied Geochemistry 12/2008; DOI:10.1016/j.apgeochem.2008.06.031 · 2.02 Impact Factor
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    ABSTRACT: Fractionation of Cu and Zn isotopes during adsorption onto amorphous ferric oxyhydroxide is examined in experimental mixtures of metal-rich acid rock drainage and relatively pure river water and during batch adsorption experiments using synthetic ferrihydrite. A diverse set of Cu- and Zn-bearing solutions was examined, including natural waters, complex synthetic acid rock drainage, and simple NaNO3 electrolyte. Metal adsorption data are combined with isotopic measurements of dissolved Cu (65Cu/63Cu) and Zn (66Zn/64Zn) in each of the experiments. Fractionation of Cu and Zn isotopes occurs during adsorption of the metal onto amorphous ferric oxyhydroxide. The adsorption data are modeled successfully using the diffuse double layer model in PHREEQC. The isotopic data are best described by a closed system, equilibrium exchange model. The fractionation factors (αsoln–solid) are 0.99927 ± 0.00008 for Cu and 0.99948 ± 0.00004 for Zn or, alternately, the separation factors (Δsoln–solid) are −0.73 ± 0.08‰ for Cu and −0.52 ± 0.04‰ for Zn. These factors indicate that the heavier isotope preferentially adsorbs onto the oxyhydroxide surface, which is consistent with shorter metal–oxygen bonds and lower coordination number for the metal at the surface relative to the aqueous ion. Fractionation of Cu isotopes also is greater than that for Zn isotopes. Limited isotopic data for adsorption of Cu, Fe(II), and Zn onto amorphous ferric oxyhydroxide suggest that isotopic fractionation is related to the intrinsic equilibrium constants that define aqueous metal interactions with oxyhydroxide surface sites. Greater isotopic fractionation occurs with stronger metal binding by the oxyhydroxide with Cu > Zn > Fe(II).
    Geochimica et Cosmochimica Acta 01/2008; 72(2-72):311-328. DOI:10.1016/j.gca.2007.11.013 · 4.25 Impact Factor
  • Laurie S. Balistrieri, Robert R. Seal, Nadine M. Piatak, Barbara Paul
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    ABSTRACT: The authors determine the composition of a river that is impacted by acid-mine drainage, evaluate dominant physical and geochemical processes controlling the composition, and assess dissolved metal speciation and toxicity using a combination of laboratory, field and modeling studies. Values of pH increase from 3.3 to 7.6 and the sum of dissolved base metal (Cd + Co + Cu + Ni + Pb + Zn) concentrations decreases from 6270 to 100 μg/L in the dynamic mixing and reaction zone that is downstream of the river’s confluence with acid-mine drainage. Mixing diagrams and PHREEQC calculations indicate that mixing and dilution affect the concentrations of all dissolved elements in the reach, and are the dominant processes controlling dissolved Ca, K, Li, Mn and SO4 concentrations. Additionally, dissolved Al and Fe concentrations decrease due to mineral precipitation (gibbsite, schwertmannite and ferrihydrite), whereas dissolved concentrations of Cd, Co, Cu, Ni, Pb and Zn decrease due to adsorption onto newly formed Fe precipitates.The uptake of dissolved metals by aquatic organisms is dependent on the aqueous speciation of the metals and kinetics of complexation reactions between metals, ligands and solid surfaces. Dissolved speciation of Cd, Cu, Ni and Zn in the mixing and reaction zone is assessed using the diffusive gradients in thin films (DGT) technique and results of speciation calculations using the Biotic Ligand Model (BLM). Data from open and restricted pore DGT units indicate that almost all dissolved metal species are inorganic and that aqueous labile or DGT available metal concentrations are generally equal to total dissolved concentrations in the mixing zone. Exceptions occur when labile metal concentrations are underestimated due to competition between H+ and metal ions for Chelex-100 binding sites in the DGT units at low pH values. Calculations using the BLM indicate that dissolved Cd and Zn species in the mixing and reaction zone are predominantly inorganic, which is consistent with the DGT results. Although the DGT method indicates that the majority of aqueous Cu species are inorganic, BLM calculations indicate that dissolved Cu is inorganic at pH < 5.5 and organic at pH > 5.5.Integrated dissolved labile concentrations of Cd, Cu and Zn in the mixing and reaction zone are compared to calculated acute toxicity concentrations (LC50 values) for fathead minnows (Pimephales promelas) (Cd, Cu and Zn) and water fleas (Ceriodaphnia dubia) (Cd and Cu) using the BLM, and to national recommended water quality criteria [i.e., criteria maximum concentration (CMC) and criterion continuous concentration (CCC)]. Observed labile concentrations of Cd and Zn are below LC50 values and CMC for Cd, but above CCC and CMC for Zn at sites <30 m downstream of the confluence. In contrast, labile Cu concentrations exceed LC50 values for the organisms as well as CCC and CMC at sites <30 m downstream of the confluence. These results suggest that environmental conditions at sites closest to the confluence of the river and acid-mine drainage should not support healthy aquatic organisms.
    Applied Geochemistry 05/2007; DOI:10.1016/j.apgeochem.2007.02.005 · 2.02 Impact Factor
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    ABSTRACT: Uncertainties in the determinations of particulate organic carbon flux from measurements of the disequilibrium between 234Th and its mother isotope uranium depend largely on the determination of the organic carbon to 234thorium (OC : 234Th) ratio. The variability of the OC : 234Th ratio in different size fractions of suspended matter, ranging from the truly dissolved (< 3 or 10 kDa) fraction to several millimeter sized marine snow, as well as from sediment trap material was assessed during an eight-day cruise off the coast of California in Spring 1997. The affinity of polysaccharide particles called TEP (transparent exopolymer particles) and inorganic clays to 234Th was investigated through correlations. The observed decrease in the OC : 234Th ratio with size, within the truly dissolved to small particle size range, is consistent with concepts of irreversible colloidal aggregation of non-porous nano-aggregates. No consistent trend in the OC : 234Th ratio was observed for particles between 1 or 10 to 6000 μm. Origin and fate of marine particles belonging to this size range are diverse and interactions with 234Th too complex to expect a consistent relationship between OC : 234Th ratio and size, if all categories of particles are included. The relationship between OC and 234Th was significant when data from the truly dissolved fraction were excluded. However, variability was very large, implying that OC flux calculations using different collection methods (e.g. sediment trap, Niskin bottles or pumps) would differ significantly. Therefore a large uncertainty in OC flux calculations based on the 234Th method exist due to individual decisions as to which types or size classes of particles best represent sinking material in a specific area. Preferential binding of 234Th to specific substance classes could explain the high variability in the relationship between OC and 234Th. At 15 m, in the absence of lithogenic material, the OC : 234Th ratio was a function of the fraction of TEP or TEP-precursors in OC, confirming that acidic polysaccharides have a high affinity for 234Th and that TEP carry a ligand for 234Th. Preferential binding to TEP might change distribution patterns of 234Th considerably, as TEP may sink when included in large aggregates, or remain suspended or even ascend when existing as individual particles or microaggregates. In the presence of lithogenic matter, at depths below 30 m, the ratio between 234Th and OC was linearly related to the ratio between alumino silicates and C. The affinity of inorganic substances to 234Th is known to be relatively low, suggesting that a coating of acidic polysaccharides was responsible for the apparently high affinity between 234Th and lithogenic material. Overall, OC : 234Th ratios of all material collected during this investigation can best be explained by differential binding of 234Th to both TEP and TEP-precursors, as well as to lithogenic minerals, which were very abundant in an intermediate nepheloid layer between 50 and 90 m.
    Marine Chemistry 08/2006; DOI:10.1016/j.marchem.2005.10.020 · 3.20 Impact Factor
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    ABSTRACT: This paper examines the seasonal cycling of temperature and salinity in Dexter pit lake in arid northern Nevada, and describes an approach for modeling the physical processes that operate in such systems. The pit lake contains about 596,200m3 of dilute, near neutral (pHs 6.7–9) water. Profiles of temperature, conductivity, and selected element concentrations were measured almost monthly during 1999 and 2000. In winter (January–March), the pit lake was covered with ice and bottom water was warmer (5.3°C) with higher total dissolved solids (0.298g/L) than overlying water (3.96°C and 0.241g/L), suggesting inflow of warm (11.7°C) groundwater with a higher conductivity than the lake (657 versus 126–383μS/cm). Seasonal surface inflow due to spring snowmelt resulted in lower conductivity in the surface water (232–247μS/cm) relative to deeper water (315–318μS/cm). The pit lake was thermally stratified from late spring through early fall, and the water column turned over in late November (2000) or early December (1999). The pit lake is a mixture of inflowing surface water and groundwater that has subsequently been evapoconcentrated in the arid environment. Linear relationships between conductivity and major and some minor (B, Li, Sr, and U) ions indicate conservative mixing for these elements.Similar changes in the elevations of the pit lake surface and nearby groundwater wells during the year suggest that the pit lake is a flow-through system. This observation and geochemical information were used to configure an one-dimensional hydrodynamics model (Dynamic Reservoir Simulation Model or DYRESM) that predicts seasonal changes in temperature and salinity based on the interplay of physical processes, including heating and cooling (solar insolation, long and short wave radiation, latent, and sensible heat), hydrologic flow (inflow and outflow by surface and ground water, pumping, evaporation, and precipitation), and transfers of momentum (wind stirring, convective overturn, shear, and eddy diffusion). Inputs to the model include the size and shape of the lake, daily meteorological data (short wave radiation, long wave radiation or cloud cover, air temperature, vapor pressure, wind speed, and rainfall), rates for water inputs and outputs, the composition of inflowing water, and initial profiles of temperature and salinity. Predicted temperature profiles, which are influenced by seasonal changes in the magnitude of solar radiation, are in good agreement with observations and show the development of a strong thermocline in the summer, erosion of the thermocline during early fall, and turnover in late fall. Predicted salinity profiles are in reasonable agreement with observations and are affected by the hydrologic balance, particularly inflow of surface and groundwater and, to a lesser degree, evaporation. Defining the hydrodynamics model for Dexter pit lake is the first step in using a coupled physical – biogeochemical model (Dynamic Reservoir Simulation Model-Computational Aquatic Ecosystem Dynamics Model or DYRESM-CAEDYM) to predict the behavior of non-conservative elements (e.g., dissolved O2, Mn, and Fe) and their effect on water quality in this system.
    Applied Geochemistry 07/2006; 21(7):1184-1203. DOI:10.1016/j.apgeochem.2006.03.013 · 2.02 Impact Factor
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    Erin J. Breckel, Steven Emerson, Laurie S. Balistrieri
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    ABSTRACT: We evaluated authigenic changes of Fe, Mn, V, U, Mo, Cd and Re in suboxic, periodically remobilized, tropical shelf sediments from the Amazon continental shelf and the Gulf of Papua. The Cd/Al, Mo/Al, and U/Al ratios in Amazon shelf sediments were 82%, 37%, and 16% less than those in Amazon River suspended sediments, respectively. Very large depletions of U previously reported in this environment were not observed. The Cd/Al ratios in Gulf of Papua sediments were 76% lower than measurements made on several Papua New Guinea rivers, whereas U/Al ratios in the shelf sediments were enriched by approximately 20%. Other metal/Al ratios in the Papua New Guinea river suspended sediments and continental shelf sediments were not distinguishably different. Comparison of metal/Al ratios to grain size distributions in Gulf of Papua samples indicates that our observations cannot be attributed to differences in grain size between the river suspended sediments and continental shelf sediments. These two shelves constitute a source of dissolved Cd to the world ocean equal to 29–100% of the dissolved Cd input from rivers, but only 3% of the dissolved Mo input and 4% of the dissolved U input. Release of Cd, Mo, and U in tropical shelf sediments is likely a result of intense Fe and Mn oxide reduction in pore waters and resuspension of the sediments. Since we do not observe depletions of particulate Fe and Mn in the shelf sediments most of these dissolved metals must reoxidize in the overlying waters and reprecipitate. As Cd exhibits the largest losses on these tropical shelves, we examined the ability of newly formed Fe and Mn oxides to adsorb dissolved Cd using a geochemical diffuse double-layer surface complexation model and found the oxide surfaces are relatively ineffective at readsorbing Cd in seawater due to surface-site competition by Mg and Ca. If the remobilization and reoxidation of Fe and Mn occurs frequently enough before sediment is buried significant amounts of Cd may be removed from the oxide surfaces. Because a much greater percentage of Mn than Fe becomes remobilized in these shelf sediments, metals closely associated with Mn oxides (like Cd) are more likely to show losses during deposition.
    Continental Shelf Research 07/2005; DOI:10.1016/j.csr.2005.02.001 · 2.12 Impact Factor
  • Jennifer W. Tonkin, Laurie S. Balistrieri, James W. Murray
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    ABSTRACT: Manganese oxides are important scavengers of trace metals and other contaminants in the environment. The inclusion of Mn oxides in predictive models, however, has been difficult due to the lack of a comprehensive set of sorption reactions consistent with a given surface complexation model (SCM), and the discrepancies between published sorption data and predictions using the available models. The authors have compiled a set of surface complexation reactions for synthetic hydrous Mn oxide (HMO) using a two surface site model and the diffuse double layer SCM which complements databases developed for hydrous Fe (III) oxide, goethite and crystalline Al oxide. This compilation encompasses a range of data observed in the literature for the complex HMO surface and provides an error envelope for predictions not well defined by fitting parameters for single or limited data sets. Data describing surface characteristics and cation sorption were compiled from the literature for the synthetic HMO phases birnessite, vernadite and δ-MnO2. A specific surface area of 746 m2g−1 and a surface site density of 2.1 mmol g−1 were determined from crystallographic data and considered fixed parameters in the model. Potentiometric titration data sets were adjusted to a pHIEP value of 2.2. Two site types (≡XOH and ≡YOH) were used. The fraction of total sites attributed to ≡XOH (α) and pKa2 were optimized for each of 7 published potentiometric titration data sets using the computer program FITEQL3.2. pKa2 values of 2.35±0.077 (≡XOH) and 6.06±0.040 (≡YOH) were determined at the 95% confidence level. The calculated average α value was 0.64, with high and low values ranging from 1.0 to 0.24, respectively. pKa2 and α values and published cation sorption data were used subsequently to determine equilibrium surface complexation constants for Ba2+, Ca2+, Cd2+, Co2+, Cu2+, Mg2+, Mn2+, Ni2+, Pb2+, Sr2+ and Zn2+. In addition, average model parameters were used to predict additional sorption data for which complementary titration data were not available. The two-site model accounts for variability in the titration data and most metal sorption data are fit well using the pKa2 and α values reported above. A linear free energy relationship (LFER) appears to exist for some of the metals; however, redox and cation exchange reactions may limit the prediction of surface complexation constants for additional metals using the LFER.
    Applied Geochemistry 01/2004; DOI:10.1016/S0883-2927(03)00115-X · 2.02 Impact Factor

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