ABSTRACT Road salt deicers, especially NaCl and CaCl2, are increasingly applied to paved areas th... more ABSTRACT Road salt deicers, especially NaCl and CaCl2, are increasingly applied to paved areas throughout the world. The goal of this study is to investigate the influence of high concentrations of these salts on wetland biogeochemistry. Sediment cores were collected in fall and spring from a freshwater wetland fringing an urban kettle lake (Asylum Lake, Kalamazoo, MI, USA), and incubated for 100 days in deionized water (control) or with treatments of 1 or 5 g/L CaCl2·2H2O or 5 g/L NaCl to simulate addition of road salt deciers. At monthly intervals, cores were sliced into three depths (0–5, 5–10, 10–15 cm) and pore waters extracted for analysis of pH, total alkalinity and dissolved Mn(II), Fe(II), PO 4−3, NH3, H2S, SO4−2, Na, K, Mg, and Ca. Changes in solid phase geochemistry were assessed by measuring the percent organic matter and the distribution of Fe and Mn among four operationally defined sediment fractions (exchangeable, carbonate, reducible, oxidizable) in the control and treatment cores. Addition of NaCl, and especially CaCl2, stimulated significant growth of microbial mats at the core sediment–water interface and led to decreased pH and increased concentrations of Mn(II), Fe(II) and exchangeable cations (Ca, Mg, K, Na) in the sediment pore waters. This study demonstrates that the influx of road salt deciers is likely to have a significant impact on biogeochemical cycling in wetland sediments.
Journal of Colloid and Interface Science, Aug 1, 2009
Cadmium adsorption was measured as a function of ionic strength (0.001-0.1 M NaNO 3), and spannin... more Cadmium adsorption was measured as a function of ionic strength (0.001-0.1 M NaNO 3), and spanning a range of sorbate/sorbent ratios, on pure hydrous ferric oxide (HFO), kaolinite, and quartz and also on binary and ternary mixtures of the three solids. Diffuse-layer surface complexation models (DLMs) were parameterized to fit Cd sorption data for the pure kaolinite and quartz systems. Cd adsorption on kaolinite was modeled using a two-site DLM, with formation of a monodentate Cd complex on a variable charge site and Cd binding to a permanent exchange site; Cd adsorption on quartz was described using a one-site DLM with formation of a mondentate Cd complex on a variable charge site. These DLMs, together with the Dzombak and Morel DLM for HFO, were used to predict Cd adsorption on the binary and ternary mineral mixtures using a simple component additivity approach. In general, the predicted adsorption edges were in good agreement with measured data, with statistically similar goodness of fit compared to that obtained for the pure mineral systems. However, in some cases the model overpredicted Cd sorption, possibly indicating that interaction of the solids may prevent Cd from accessing all of the sorption sites.
Seasonal variations in anaerobic respiration pathways were investigated at three saltmarsh sites ... more Seasonal variations in anaerobic respiration pathways were investigated at three saltmarsh sites using chemical data, sulfate reduction rate measurements, enumerations of culturable populations of anaerobic iron-reducing bacteria (FeRB), and quantification of in situ 16S rRNA hybridization signals targeted for sulfate-reducing bacteria (SRB). Bacterial sulfate reduction in the sediments followed seasonal changes in temperature and primary production of the saltmarsh, with activity levels lowest in winter and highest in summer. In contrast, a dramatic decrease in the FeRB population size was observed during summer at all sites. The collapse of FeRB populations during summer was ascribed to high rates of sulfide production by SRB, resulting in abiotic reduction of bioavailable Fe(III) (hydr)oxides. To test this hypothesis, sediment slurry incubations at 10, 20 and 30°C were carried out. Increases in temperature and labile organic carbon availability (acetate or lactate additions) increased rates of sulfate reduction while decreasing the abundance of culturable anaerobic FeRB. These trends were not reversed by the addition of amorphous Fe(III) (hydr)oxides to the slurries. However, when sulfate reduction was inhibited by molybdate, no decline in FeRB growth was observed with increasing temperature. Addition of dissolved sulfide adversely impacted propagation of FeRB whether molybdate was added or not. Both field and laboratory data therefore support a sulfide-mediated limitation of microbial iron respiration by SRB. When total sediment respiration rates reach their highest levels during summer, SRB force a decline in the FeRB populations. As sulfate reduction activity slows down after the summer, the FeRB are able to recover.
Pore water and solid phase samples were collected from the upper 50 cm of a peat profile at four ... more Pore water and solid phase samples were collected from the upper 50 cm of a peat profile at four sites within a 10 m 2 area in Kleinstuck Marsh, a minerotropic fen located in Kalamazoo, MI. Although the chosen sites are in close proximity to each other, they differ with respect to vegetation species and density. Pore water analyses for a suite of redox sensitive species (pH, alkalinity, dissolved Mn(II), Fe(II), Fe(III), sulfide, sulfate), together with Fe and Mn distributions inferred from operationallydefined sequential extractions, demonstrate that Fe(III) and Mn(IV) reduction occurs in the shallow peat at three of the four sites. At the fourth site, the only site containing the invasive purple loosestrife (Lythrum salicaria), accumulation of dissolved sulfide in the pore waters and increased levels of oxidizable phases in the shallow peat point to increased net sulfate reduction relative to the other three sites. Speciation calculations indicate that pore water concentrations of phosphate, especially below *10 cm depth, are largely controlled by the solubility of phases such as strengite or hydroxylapatite, and that at all but the loosestrife site, dissolved Ca and Mg are likely determined by carbonate solubility. Fe and Mn distribution among operationally defined solid phase fractions are consistent with reductive dissolution of FMO in the uppermost peat, leading to precipitation of Fe sulfides and Mn carbonates deeper in the peat profile. Zn, Co, Cr and Ni distributions are consistent with release from FMO to form sulfides or organic associations deeper in the peat. Pb and Cu may also be released by reductive dissolution of FMO, or more likely, shift from primary association with organic matter to increased association with sulfides under more sulfidic conditions. This study highlights the existence of extreme lateral variations in peat pore water and solid phase geochemical profiles, even over quite small areas.
Spatial and temporal trends in pore water geochemistry and sediment microbial community structure... more Spatial and temporal trends in pore water geochemistry and sediment microbial community structure are compared at three intertidal sites of a saltmarsh on Sapelo Island, GA. The sites include a heavily bioturbated, unvegetated creek bank, a levee with dense growth of Spartina ...
A combined modeling and spectroscopic approach is used to describe Cd(II), Cr(VI), and Pb(II) ads... more A combined modeling and spectroscopic approach is used to describe Cd(II), Cr(VI), and Pb(II) adsorption onto nanomaghemite and nanomaghemite coated quartz. A pseudo-second order kinetic model fitted the adsorption data well. The sorption capacity of nanomaghemite was evaluated using a Langmuir isotherm model, and a diffuse double layer surface complexation model (DLM) was developed to describe metal adsorption. Adsorption mechanisms were assessed using X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. Pb(II) adsorption occurs mainly via formation of inner-sphere complexes, whereas Cr(VI) likely adsorbs mainly as outer-sphere complexes and Cd(II) as a mixture of inner- and outer-sphere complexes. The simple DLM describes well the pH-dependence of single adsorption edges. However, it fails to adequately capture metal adsorption behavior over broad ranges of ionic strength or metal-loading on the sorbents. For systems with equimolar concentrations of Pb(II), Cd(II), and Cr(VI). Pb(II) adsorption was reasonably well predicted by the DLM, but predictions were poorer for Cr(VI) and Cd(II). This study demonstrates that a simple DLM can describe well the adsorption of the studied metals in mixed sorbate-sorbent systems, but only under narrow ranges of ionic strength or metal loading. The results also highlight the sorption potential of nanomaghemite for metals in complex systems.
Little research regarding student conceptions of complex environmental systems and biogeochemical... more Little research regarding student conceptions of complex environmental systems and biogeochemical cycles has been published. We investigate the nature of student ideas about such systems and cycles in a newly developed a field course for upper level undergraduate Geoscience and Environmental Studies majors in which students engage in problem-based learning and work collaboratively to investigate a real-world environmental system - eutrophication of an urban lake in Kalamazoo, MI. Classroom work focuses on a weekly pre-instruction ``question of the day'' (QED). After answering QEDs individually, students gather in groups to create and illustrate consensus answers. The instructor then typically presents a ``mini-lecture'' to address the QED's content. Students spend a substantial amount of class time outside the classroom in both lab and field settings. Once they have gained familiarity with relevant lab and field techniques, students design and execute a field sam...
Complexation reactions at the mineral–water interface affect the transport and transformation of ... more Complexation reactions at the mineral–water interface affect the transport and transformation of metals and organic contaminants, nutrient availability in soils, formation of ore deposits, acidification of watersheds and the global cycling of elements. Such reactions can be understood by quantifying speciation reactions in homogeneous aqueous solutions, characterizing reactive sites at mineral surfaces and developing models of the interactions between aqueous
ABSTRACT Road salt deicers, especially NaCl and CaCl2, are increasingly applied to paved areas th... more ABSTRACT Road salt deicers, especially NaCl and CaCl2, are increasingly applied to paved areas throughout the world. The goal of this study is to investigate the influence of high concentrations of these salts on wetland biogeochemistry. Sediment cores were collected in fall and spring from a freshwater wetland fringing an urban kettle lake (Asylum Lake, Kalamazoo, MI, USA), and incubated for 100 days in deionized water (control) or with treatments of 1 or 5 g/L CaCl2·2H2O or 5 g/L NaCl to simulate addition of road salt deciers. At monthly intervals, cores were sliced into three depths (0–5, 5–10, 10–15 cm) and pore waters extracted for analysis of pH, total alkalinity and dissolved Mn(II), Fe(II), PO 4−3, NH3, H2S, SO4−2, Na, K, Mg, and Ca. Changes in solid phase geochemistry were assessed by measuring the percent organic matter and the distribution of Fe and Mn among four operationally defined sediment fractions (exchangeable, carbonate, reducible, oxidizable) in the control and treatment cores. Addition of NaCl, and especially CaCl2, stimulated significant growth of microbial mats at the core sediment–water interface and led to decreased pH and increased concentrations of Mn(II), Fe(II) and exchangeable cations (Ca, Mg, K, Na) in the sediment pore waters. This study demonstrates that the influx of road salt deciers is likely to have a significant impact on biogeochemical cycling in wetland sediments.
Journal of Colloid and Interface Science, Aug 1, 2009
Cadmium adsorption was measured as a function of ionic strength (0.001-0.1 M NaNO 3), and spannin... more Cadmium adsorption was measured as a function of ionic strength (0.001-0.1 M NaNO 3), and spanning a range of sorbate/sorbent ratios, on pure hydrous ferric oxide (HFO), kaolinite, and quartz and also on binary and ternary mixtures of the three solids. Diffuse-layer surface complexation models (DLMs) were parameterized to fit Cd sorption data for the pure kaolinite and quartz systems. Cd adsorption on kaolinite was modeled using a two-site DLM, with formation of a monodentate Cd complex on a variable charge site and Cd binding to a permanent exchange site; Cd adsorption on quartz was described using a one-site DLM with formation of a mondentate Cd complex on a variable charge site. These DLMs, together with the Dzombak and Morel DLM for HFO, were used to predict Cd adsorption on the binary and ternary mineral mixtures using a simple component additivity approach. In general, the predicted adsorption edges were in good agreement with measured data, with statistically similar goodness of fit compared to that obtained for the pure mineral systems. However, in some cases the model overpredicted Cd sorption, possibly indicating that interaction of the solids may prevent Cd from accessing all of the sorption sites.
Seasonal variations in anaerobic respiration pathways were investigated at three saltmarsh sites ... more Seasonal variations in anaerobic respiration pathways were investigated at three saltmarsh sites using chemical data, sulfate reduction rate measurements, enumerations of culturable populations of anaerobic iron-reducing bacteria (FeRB), and quantification of in situ 16S rRNA hybridization signals targeted for sulfate-reducing bacteria (SRB). Bacterial sulfate reduction in the sediments followed seasonal changes in temperature and primary production of the saltmarsh, with activity levels lowest in winter and highest in summer. In contrast, a dramatic decrease in the FeRB population size was observed during summer at all sites. The collapse of FeRB populations during summer was ascribed to high rates of sulfide production by SRB, resulting in abiotic reduction of bioavailable Fe(III) (hydr)oxides. To test this hypothesis, sediment slurry incubations at 10, 20 and 30°C were carried out. Increases in temperature and labile organic carbon availability (acetate or lactate additions) increased rates of sulfate reduction while decreasing the abundance of culturable anaerobic FeRB. These trends were not reversed by the addition of amorphous Fe(III) (hydr)oxides to the slurries. However, when sulfate reduction was inhibited by molybdate, no decline in FeRB growth was observed with increasing temperature. Addition of dissolved sulfide adversely impacted propagation of FeRB whether molybdate was added or not. Both field and laboratory data therefore support a sulfide-mediated limitation of microbial iron respiration by SRB. When total sediment respiration rates reach their highest levels during summer, SRB force a decline in the FeRB populations. As sulfate reduction activity slows down after the summer, the FeRB are able to recover.
Pore water and solid phase samples were collected from the upper 50 cm of a peat profile at four ... more Pore water and solid phase samples were collected from the upper 50 cm of a peat profile at four sites within a 10 m 2 area in Kleinstuck Marsh, a minerotropic fen located in Kalamazoo, MI. Although the chosen sites are in close proximity to each other, they differ with respect to vegetation species and density. Pore water analyses for a suite of redox sensitive species (pH, alkalinity, dissolved Mn(II), Fe(II), Fe(III), sulfide, sulfate), together with Fe and Mn distributions inferred from operationallydefined sequential extractions, demonstrate that Fe(III) and Mn(IV) reduction occurs in the shallow peat at three of the four sites. At the fourth site, the only site containing the invasive purple loosestrife (Lythrum salicaria), accumulation of dissolved sulfide in the pore waters and increased levels of oxidizable phases in the shallow peat point to increased net sulfate reduction relative to the other three sites. Speciation calculations indicate that pore water concentrations of phosphate, especially below *10 cm depth, are largely controlled by the solubility of phases such as strengite or hydroxylapatite, and that at all but the loosestrife site, dissolved Ca and Mg are likely determined by carbonate solubility. Fe and Mn distribution among operationally defined solid phase fractions are consistent with reductive dissolution of FMO in the uppermost peat, leading to precipitation of Fe sulfides and Mn carbonates deeper in the peat profile. Zn, Co, Cr and Ni distributions are consistent with release from FMO to form sulfides or organic associations deeper in the peat. Pb and Cu may also be released by reductive dissolution of FMO, or more likely, shift from primary association with organic matter to increased association with sulfides under more sulfidic conditions. This study highlights the existence of extreme lateral variations in peat pore water and solid phase geochemical profiles, even over quite small areas.
Spatial and temporal trends in pore water geochemistry and sediment microbial community structure... more Spatial and temporal trends in pore water geochemistry and sediment microbial community structure are compared at three intertidal sites of a saltmarsh on Sapelo Island, GA. The sites include a heavily bioturbated, unvegetated creek bank, a levee with dense growth of Spartina ...
A combined modeling and spectroscopic approach is used to describe Cd(II), Cr(VI), and Pb(II) ads... more A combined modeling and spectroscopic approach is used to describe Cd(II), Cr(VI), and Pb(II) adsorption onto nanomaghemite and nanomaghemite coated quartz. A pseudo-second order kinetic model fitted the adsorption data well. The sorption capacity of nanomaghemite was evaluated using a Langmuir isotherm model, and a diffuse double layer surface complexation model (DLM) was developed to describe metal adsorption. Adsorption mechanisms were assessed using X-ray photoelectron spectroscopy and X-ray absorption spectroscopy. Pb(II) adsorption occurs mainly via formation of inner-sphere complexes, whereas Cr(VI) likely adsorbs mainly as outer-sphere complexes and Cd(II) as a mixture of inner- and outer-sphere complexes. The simple DLM describes well the pH-dependence of single adsorption edges. However, it fails to adequately capture metal adsorption behavior over broad ranges of ionic strength or metal-loading on the sorbents. For systems with equimolar concentrations of Pb(II), Cd(II), and Cr(VI). Pb(II) adsorption was reasonably well predicted by the DLM, but predictions were poorer for Cr(VI) and Cd(II). This study demonstrates that a simple DLM can describe well the adsorption of the studied metals in mixed sorbate-sorbent systems, but only under narrow ranges of ionic strength or metal loading. The results also highlight the sorption potential of nanomaghemite for metals in complex systems.
Little research regarding student conceptions of complex environmental systems and biogeochemical... more Little research regarding student conceptions of complex environmental systems and biogeochemical cycles has been published. We investigate the nature of student ideas about such systems and cycles in a newly developed a field course for upper level undergraduate Geoscience and Environmental Studies majors in which students engage in problem-based learning and work collaboratively to investigate a real-world environmental system - eutrophication of an urban lake in Kalamazoo, MI. Classroom work focuses on a weekly pre-instruction ``question of the day'' (QED). After answering QEDs individually, students gather in groups to create and illustrate consensus answers. The instructor then typically presents a ``mini-lecture'' to address the QED's content. Students spend a substantial amount of class time outside the classroom in both lab and field settings. Once they have gained familiarity with relevant lab and field techniques, students design and execute a field sam...
Complexation reactions at the mineral–water interface affect the transport and transformation of ... more Complexation reactions at the mineral–water interface affect the transport and transformation of metals and organic contaminants, nutrient availability in soils, formation of ore deposits, acidification of watersheds and the global cycling of elements. Such reactions can be understood by quantifying speciation reactions in homogeneous aqueous solutions, characterizing reactive sites at mineral surfaces and developing models of the interactions between aqueous
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Papers by Carla Koretsky