Laurie S. Balistrieri

Environmental Chemistry, Chemical Thermodynamics, Chemical Kinetics

31.03

Publications

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    ABSTRACT: Aquatic organisms use a variety of biogeochemical reactions to regulate essential and non-essential trace metals. Many of these mechanisms can lead to isotopic fractionation, thus measurement of metal isotopes may yield insights into the processes by which organisms respond to metal exposure. We illustrate these concepts with two case studies, one involving an intra-and the other an extra-cellular mechanism of Zn sequestration. In the first study, the mayfly Neocloeon triangulifer was grown in the laboratory, and fed a diet of Zn-doped diatoms at Zn levels exceeding the requirements for normal mayfly life functions. The N. triangulifer larvae consumed the diatoms and retained their Zn isotopic signature. Upon metamorphosis, the subimago life stage lost Zn mass either in the exuvia or by excretion, and the Zn retained was isotopically enriched. Thus, Zn uptake is non-fractionating, but Zn regulation favors the lighter isotope. Thus the Zn remaining in the subimago was isotopically heavier. In the second study, Zn was adsorbed on the cell walls and exopolysaccharide secretions of cyanobacteria, which favored the heavier Zn isotope. Continued adsorption eventually resulted in nucleation and biomineralization of hydrozincite {Zn 5 (CO 3) 2 (OH) 6 }. These case studies demonstrate the utility of Zn isotopes to provide insights into how aquatic insects respond to metal exposure.
    Full-text · Conference Paper · Sep 2015
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    Full-text · Dataset · Aug 2015
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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.
    Full-text · Article · Jun 2015 · Applied Geochemistry
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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.
    Full-text · Dataset · May 2015
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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.
    Full-text · Article · Mar 2015 · Environmental Toxicology and Chemistry
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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
    No preview · Article · Nov 2014 · Environmental Toxicology and Chemistry
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    Laurie S. Balistrieri · Christopher A. Mebane
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    ABSTRACT: [This describes the 2012 model prototype evaluated by Farley et al, "Metal Mixture Modeling Evaluation project: 2. Comparison of four modeling approaches:"] This work is part of a larger modeling effort that is assessing the toxicity of metal (Cd, Cu, Ni, Pb, and Zn) mixtures to aquatic organisms and evaluating the relative importance of these metals as toxicants in the mixtures. The sponsor of the larger modeling effort, i.e., the International Lead Zinc Research Organization (ILZRO), supplied four modeling groups with seven data sets. These data sets included the composition of freshwaters and associated biological responses (i.e., survival or growth metrics) from laboratory and field studies that had either paired single and multiple metal solutions or just multiple metal solutions. Our tasks were to model the data sets, provide insight into the hierarchy of metal toxicity in the mixtures, summarize our results in a report, and participate in a collaborative workshop to integrate results from the four modeling groups. This document summarizes the modeling results of our group. We evaluated the data sets using an integrated modeling approach (Figure 6), which includes: 1. determining the loading of toxicants on biotic ligands in the solutions using WHAM 7 and a common set of equilibrium constants for biotic-ligand interactions that is incorporated into a multiple-toxicant biotic ligand model (BLM); 2. defining a function called Tox that incorporates the fractional loading of biotic ligands by hydrogen and metal toxicants and weights their relative toxicity to biota through toxicity coefficients; 3. evaluating the relative importance of metal toxicants in the metal mixtures by examining each term in the Tox function; and 4. using the Generalized Logit I equation to relate Tox and biological response (i.e., mortality or growth retardation) of biota. . Overarching Conclusions · The BLM-Tox approach reasonably fits observed biological responses to metal mixtures using a consistent set of weighting coefficients and organism-specific logistic parameters. · The composition of the metal load on the biotic ligand in metal mixtures can vary but still produce the same biological response. · Tox incorporates the effects of solution composition and speciation (in particular, identities and total dissolved concentrations of toxicants); affinities of toxicants for the biotic ligand (KBL-metal); and weighting coefficients for toxicants into a single parameter. · Values of Tox do not depend on the type of organism, but rather the response of an organism is related to Tox with increasing values of Tox producing more adverse responses. · Organisms have different sensitivities to Tox. · Tox provides an evaluation of the relative importance of toxicants in a mixture. That importance depends on the relative concentrations of dissolved metals in the mixture. The relative importance of toxicants in binary or multiple metal mixtures appear to be equal at unique dissolved metal ratios.
    Full-text · Article · Nov 2014 · Environmental Toxicology and Chemistry
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    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.
    Preview · Article · Sep 2014 · Applied Geochemistry
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    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.
    Preview · Article · Sep 2014 · Applied Geochemistry
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    Laurie S Balistrieri · Christopher A Mebane

    Full-text · Dataset · Aug 2014
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    ABSTRACT: Natural resource planning at all scales demands methods for assessing the impacts of resource development and use, and in particular it requires standardized methods that yield robust and unbiased results. Building from existing probabilistic methods for assessing the volumes of energy and mineral resources, we provide an algorithm for consistent, reproducible, quantitative assessment of resource development impacts. The approach combines probabilistic input data with Monte Carlo statistical methods to determine probabilistic outputs that convey the uncertainties inherent in the data. For example, one can utilize our algorithm to combine data from a natural gas resource assessment with maps of sage grouse leks and piñon-juniper woodlands in the same area to estimate possible future habitat impacts due to possible future gas development. As another example: one could combine geochemical data and maps of lynx habitat with data from a mineral deposit assessment in the same area to determine possible future mining impacts on water resources and lynx habitat. The approach can be applied to a broad range of positive and negative resource development impacts, such as water quantity or quality, economic benefits, or air quality, limited only by the availability of necessary input data and quantified relationships among geologic resources, development alternatives, and impacts. The framework enables quantitative evaluation of the trade-offs inherent in resource management decision-making, including cumulative impacts, to address societal concerns and policy aspects of resource development.
    Full-text · Article · Mar 2014 · Natural Resources Research
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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.
    Full-text · Article · Aug 2013 · Science of The Total Environment
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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.
    Full-text · Article · Apr 2012 · Science of The Total Environment
  • 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.
    No preview · Article · Mar 2012 · Science of The Total Environment
  • S. Hayes · A. L. Foster · L. S. Balistrieri
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    ABSTRACT: Increased use of tellurium, a toxic metalloid, in CdTe-based solar panels and other high-tech applications highlights the need for improved understanding of the geochemical controls over Te released in the near-surface environment. Many ore minerals and industrially important Te species are reduced (e.g., AuTe, BixTey, Te metal, CdTe) making them vulnerable to oxidation under surface conditions to tellurate (TeO42-) and tellurite (TeO32-) oxyanions. Understanding the geochemistry of Te oxyanions is an important first step understanding Te behavior in the near-surface environment. As with the geochemically similar selenium, our geochemical sorption models for tellurium oxyanions indicate a strong affinity for ferrihydrite. In addition, we used X-ray absorption spectroscopy to examine the sorption geometry of a tellurite-ferrihydrite complex, which yielded a Te-O bond distance of 1.97 Å. We also examined tellurium speciation in copper mine tailings and determined that, while most of the Te is in a bismuth telluride (Te-Bi bond distance is 3.07 Å), a small fraction of Te is bonded to oxygen, indicating that Te in these tailings is beginning to oxidize. These types of analysis are important to understanding the fundamental geochemistry of Te as well as determining what forms of Te occur in the natural environment.
    No preview · Article · Dec 2011
  • Laurie S. Balistrieri · Robert S. Seal · Michael J. Pribil · Nadine M. Piatak
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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.
    No preview · Conference Paper · Oct 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.
    Full-text · Article · Jan 2011 · Limnology and Oceanography
  • 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.
    No preview · Conference Paper · Aug 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.
    No preview · Article · Dec 2008 · Applied Geochemistry
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    Laurie S. Balistrieri · David M. Borrok · Richard B. Wanty · W. Ian Ridley
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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).
    Full-text · Article · Jan 2008 · Geochimica et Cosmochimica Acta

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