Katharine (Kate) Maher

All Publications

• Mountainous Floodplain Connectivity in Response to Hydrological Transitions WATER RESOURCES RESEARCH Babey, T., Perzan, Z., Pierce, S., Rogers, B., Wang, L., Carroll, R. H., Bargar, J. R., Boye, K., Maher, K. 2024; 60 (7)

  View details for DOI 10.1029/2024WR037162

  View details for Web of Science ID 001257399100001

• Sorption of Soil Carbon Dioxide by Biochar and Engineered Porous Carbons. Environmental science & technology Ringsby, A. J., Ross, C. M., Maher, K. 2024

  Abstract

  CO2 is 45 to 50 times more concentrated in soil than in air, resulting in global diffusive fluxes that outpace fossil fuel combustion by an order of magnitude. Despite the scale of soil CO2 emissions, soil-based climate change mitigation strategies are underdeveloped. Existing approaches, such as enhanced weathering and sustainable land management, show promise but continue to face deployment barriers. We introduce an alternative approach: the use of solid adsorbents to directly capture CO2 in soils. Biomass-derived adsorbents could exploit favorable soil CO2 adsorption thermodynamics while also sequestering solid carbon. Despite this potential, previous study of porous carbon CO2 adsorption is mostly limited to single-component measurements and conditions irrelevant to soil. Here, we probe sorption under simplified soil conditions (0.2 to 3% CO2 in balance air at ambient temperature and pressure) and provide physical and chemical characterization data to correlate material properties to sorption performance. We show that minimally engineered pyrogenic carbons exhibit CO2 sorption capacities comparable to or greater than those of advanced sorbent materials. Compared to textural features, sorbent carbon bond morphology substantially influences low-pressure CO2 adsorption. Our findings enhance understanding of gas adsorption on porous carbons and inform the development of effective soil-based climate change mitigation approaches.

  View details for DOI 10.1021/acs.est.4c02015

  View details for PubMedID 38689207

• Transport, dispersion, and degradation of nonpoint source contaminants during flood-managed aquifer recharge VADOSE ZONE JOURNAL Perzan, Z., Maher, K. 2024

  View details for DOI 10.1002/vzj2.20307

  View details for Web of Science ID 001174565100001

• Determination of trace elements in ibuprofen drug products using microwave-assisted acid digestion and inductively coupled plasma-mass spectrometry. Heliyon Holmfred, E., Alrijjal, A., Chamberlain, C. P., Maher, K., Stürup, S. 2024; 10 (1): e23566

  Abstract

  Trace elements are found in most drugs as a result of the drug formulation and drug production methods. An inductively coupled plasma-mass spectrometry method for the determination of 24 trace elements (Mg, Ti, V, Cr, Mn, Cu, Fe, Co, Ni, Zn, As, Se, Mo, Ru, Rh, Pd, Ag, Cd, Sb, Ba, Ir, Pt, Au, and Pb) in solid ibuprofen tablets was established in relation to the ICH Q3D(R1) guideline, to evaluate the possibility of linking trace elemental profiles to drug formulation strategies, and to differentiate between drug products based on the trace elemental profiles. Ten European ibuprofen drug products were evaluated (n=3). The sample preparation was performed by microwave-assisted acid digestion using only 10 mg of homogenized sample and 900 μL of a mix of 65% HNO3, 37% HCl, and 30% H2O2. Solid residuals primarily composed of insoluble SiO2 excipients were removed by centrifugation. Only concentrations of Mg, Fe, Ti, Mn, Cr, and Ni were detected above the limits of detection and did not exceed the ICH Q3D(R1) guideline permitted daily exposure limits. The trace elemental profiles were evaluated through principal component analysis. Three principal components describing 96% of the variance were useful in grouping the ibuprofen drug products, and the detected trace elemental remnants could be related to drug formulation and drug production strategies. An in-house quality control material was used in lack of certified reference materials and was in combination with spike recoveries used for method validation. Good spike recoveries (94-119%) were obtained for all measured trace elements except Mg. Mg showed acceptable spike recoveries (75-155%) for mid and high-spike concentrations, but poor recoveries (30-223%) were detected with low spike concentrations in spike matrices containing high amounts of Mg. Overall, the method is suggested applicable for solid drugs containing insoluble SiO2 excipients and drugs comparable to ibuprofen.

  View details for DOI 10.1016/j.heliyon.2023.e23566

  View details for PubMedID 38205305

  View details for PubMedCentralID PMC10776936

• Controls on flood managed aquifer recharge through a heterogeneous vadose zone: hydrologic modeling at a site characterized with surface geophysics HYDROLOGY AND EARTH SYSTEM SCIENCES Perzan, Z., Osterman, G., Maher, K. 2023; 27 (5): 969-990

  View details for DOI 10.5194/hess-27-969-2023

  View details for Web of Science ID 000943974500001

• The circular nutrient economy of terrestrial ecosystems and the consequences for rock weathering FRONTIERS IN ENVIRONMENTAL SCIENCE Maher, K., von Blanckenburg, F. 2023; 10

  View details for DOI 10.3389/fenvs.2022.1066959

  View details for Web of Science ID 000922774600001

• Rates of carbon and oxygen isotope exchange between calcite and fluid at chemical equilibrium GEOCHIMICA ET COSMOCHIMICA ACTA Harrison, A. L., Schott, J., Oelkers, E. H., Maher, K., Mavromatis, V. 2022; 335: 369-382

  View details for DOI 10.1016/j.gca.2022.06.041

  View details for Web of Science ID 000862791900013

• Simulation of anoxic lenses as exporters of reactivity in alluvial aquifer sediments GEOCHIMICA ET COSMOCHIMICA ACTA Babey, T., Boye, K., Tolar, B., Engel, M., Noel, V., Perzan, Z., Kumar, N., Francis, C. A., Bargar, J. R., Maher, K. 2022; 334: 119-134

  View details for DOI 10.1016/j.gca.2022.07.018

  View details for Web of Science ID 000855258500004

• WEATHERING INTENSITY AND LITHIUM ISOTOPES: A REACTIVE TRANSPORT PERSPECTIVE AMERICAN JOURNAL OF SCIENCE Winnick, M. J., Druhan, J. L., Maher, K. 2022; 322 (5): 647-682

  View details for DOI 10.2475/05.2022.01

  View details for Web of Science ID 000836915700001

• Duration and Intensity of End-Permian Marine Anoxia GEOCHEMISTRY GEOPHYSICS GEOSYSTEMS Pimentel-Galvan, M., Lau, K. V., Maher, K., Mukerji, T., Lehrmann, D. J., Altiner, D., Payne, J. L. 2022; 23 (1)

  View details for DOI 10.1029/2021GC010130

  View details for Web of Science ID 000751308100013

• Local and Global Sensitivity Analysis of a Reactive Transport Model Simulating Floodplain Redox Cycling WATER RESOURCES RESEARCH Perzan, Z., Babey, T., Caers, J., Bargar, J. R., Maher, K. 2021; 57 (12)

  View details for DOI 10.1029/2021WR029723

  View details for Web of Science ID 000735901700042

• Concentration-Discharge Relationships of Dissolved Rhenium in Alpine Catchments Reveal Its Use as a Tracer of Oxidative Weathering WATER RESOURCES RESEARCH Hilton, R. G., Turowski, J. M., Winnick, M., Dellinger, M., Schleppi, P., Williams, K. H., Lawrence, C. R., Maher, K., West, M., Hayton, A. 2021; 57 (11)

  View details for DOI 10.1029/2021WR029844

  View details for Web of Science ID 000723106900017

• Opportunities for large-scale CO2 disposal in coastal marine volcanic basins based on the geology of northeast Hawaii INTERNATIONAL JOURNAL OF GREENHOUSE GAS CONTROL DePaolo, D. J., Thomas, D. M., Christensen, J. N., Zhang, S., Orr, F. M., Maher, K., Benson, S. M., Lautze, N., Xue, Z., Mito, S. 2021; 110

  View details for DOI 10.1016/j.ijggc.2021.103396

  View details for Web of Science ID 000696737000001

• Effective kinetics driven by dynamic concentration gradients under coupled transport and reaction GEOCHIMICA ET COSMOCHIMICA ACTA Le Traon, C., Aquino, T., Bouchez, C., Maher, K., Le Borgne, T. 2021; 306: 189-209

  View details for DOI 10.1016/j.gca.2021.04.033

  View details for Web of Science ID 000667771200010

• Chromium isotope fractionation during reduction of Chromium(VI) by Iron(II/III)-bearing clay minerals GEOCHIMICA ET COSMOCHIMICA ACTA Joe-Wong, C., Weaver, K. L., Brown, S. T., Maher, K. 2021; 292: 235–53

  View details for DOI 10.1016/j.gca.2020.09.034

  View details for Web of Science ID 000590782100014

• Global Sensitivity Analysis of a Reactive Transport Model for Mineral Scale Formation During Hydraulic Fracturing Environmental Engineering Science Li, Q., Wang, L., Perzan, Z., Caers, J., Brown Jr., G. E., Bargar, J. R., Maher, K. 2021

  View details for DOI 10.1089/ees.2020.0365

• Thicknesses of Chemically Altered Zones in Shale Matrices Resulting from Interactions with Hydraulic Fracturing Fluid (vol 33, pg 6878, 2019) ENERGY & FUELS Li, Q., Jew, A. D., Kohli, A., Maher, K., Brown, G. E., Bargar, J. R. 2020; 34 (12): 16981

  View details for DOI 10.1021/acs.energyfuels.0c03982

  View details for Web of Science ID 000600407600159

• Uranium reduction and isotopic fractionation in reducing sediments: Insights from reactive transport modeling GEOCHIMICA ET COSMOCHIMICA ACTA Lau, K., Lyons, T. W., Maher, K. 2020; 287: 65–92

  View details for DOI 10.1016/j.gca.2020.01.021

  View details for Web of Science ID 000570270000005

• Soil Respiration Response to Rainfall Modulated by Plant Phenology in a Montane Meadow, East River, Colorado, USA JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES Winnick, M. J., Lawrence, C. R., McCormick, M., Druhan, J. L., Maher, K. 2020; 125 (10)

  View details for DOI 10.1029/2020JG005924

  View details for Web of Science ID 000586701500016

• Integrating airborne remote sensing and field campaigns for ecology and Earth system science METHODS IN ECOLOGY AND EVOLUTION Chadwick, K., Brodrick, P. G., Grant, K., Goulden, T., Henderson, A., Falco, N., Wainwright, H., Williams, K. H., Bill, M., Breckheimer, I., Brodie, E. L., Steltzer, H., Williams, C., Blonder, B., Chen, J., Dafflon, B., Damerow, J., Hancher, M., Khurram, A., Lamb, J., Lawrence, C. R., McCormick, M., Musinsky, J., Pierce, S., Polussa, A., Hastings Porro, M., Scott, A., Singh, H., Sorensen, P. O., Varadharajan, C., Whitney, B., Maher, K. 2020

  View details for DOI 10.1111/2041-210X.13463

  View details for Web of Science ID 000572262300001

• ` Stability of Floodplain Subsurface Microbial Communities Through Seasonal Hydrological and Geochemical Cycles FRONTIERS IN EARTH SCIENCE Tolar, B. B., Boye, K., Bobb, C., Maher, K., Bargar, J. R., Francis, C. A. 2020; 8

  View details for DOI 10.3389/feart.2020.00338

  View details for Web of Science ID 000566258600001

• Persistence of soil organic carbon caused by functional complexity NATURE GEOSCIENCE Lehmann, J., Hansel, C. M., Kaiser, C., Kleber, M., Maher, K., Manzoni, S., Nunan, N., Reichstein, M., Schimel, J. P., Torn, M. S., Wieder, W. R., Koegel-Knabner, I. 2020

  View details for DOI 10.1038/s41561-020-0612-3

  View details for Web of Science ID 000552918600002

• Reactive Transport Modeling of Shale-Fluid Interactions after Imbibition of Fracturing Fluids ENERGY & FUELS Li, Q., Jew, A. D., Brown, G. E., Bargar, J. R., Maher, K. 2020; 34 (5): 5511–23

  View details for DOI 10.1021/acs.energyfuels.9b04542

  View details for Web of Science ID 000537407200035

• A model for kinetic isotope fractionation during redox reactions GEOCHIMICA ET COSMOCHIMICA ACTA Joe-Wong, C., Maher, K. 2020; 269: 661–77

  View details for DOI 10.1016/j.gca.2019.11.012

  View details for Web of Science ID 000502332400035

• Lithologic and redox controls on hexavalent chromium in vadose zone sediments of California's Central Valley GEOCHIMICA ET COSMOCHIMICA ACTA McClain, C. N., Fendorf, S., Johnson, S. T., Menendez, A., Maher, K. 2019; 265: 478–94

  View details for DOI 10.1016/j.gca.2019.07.044

  View details for Web of Science ID 000488959900028

• Sources of Blood Lead Exposure in Rural Bangladesh ENVIRONMENTAL SCIENCE & TECHNOLOGY Forsyth, J. E., Weaver, K. L., Maher, K., Islam, M., Raqib, R., Rahman, M., Fendorf, S., Luby, S. P. 2019; 53 (19): 11429–36

  Abstract

  Lead (Pb) exposure is a major public health problem worldwide. Although high levels of Pb in blood in Bangladesh have been documented, the dominant Pb sources contributing to human exposure in rural Bangladesh have not been determined. Here, we first obtained blood from pregnant women from three rural Bangladeshi districts who were previously assessed by a case-control and sampling study, and we then conducted semistructured in-depth interviews to understand Pb exposure behavior and finally collected samples of the suspected Pb sources. We measured the Pb isotopic composition of both potential Pb sources and 45 blood samples in order to understand which of three sources predominate: (1) food from Pb-soldered cans, (2) turmeric, or (3) geophagous materials (clay, soil, or ash). The Pb isotope ratios of the three sources are distinct (p = 0.0001) and blood isotope ratios are most similar to turmeric. Elevated lead and chromium (Cr) concentrations in turmeric and a yellow pigment used in turmeric processing are consistent with reported consumption behavior that indicated turmeric as a primary contributor to blood Pb. The Pb isotopic composition analyses combined with a case-control and sampling approach provides evidence that turmeric adulterated with the yellow Pb-bearing pigment is the main Pb exposure source in these districts and illustrates the need to assess drivers and practices of turmeric adulteration, as well as the prevalence of adulteration across South Asia.

  View details for DOI 10.1021/acs.est.9b00744

  View details for Web of Science ID 000488993500041

  View details for PubMedID 31525910

• Thicknesses of Chemically Altered Zones in Shale Matrices Resulting from Interactions with Hydraulic Fracturing Fluid ENERGY & FUELS Li, Q., Jew, A. D., Kohli, A., Maher, K., Brown, G. E., Bargar, J. R. 2019; 33 (8): 6878–89

  View details for DOI 10.1021/acs.energyfuels.8b04527

  View details for Web of Science ID 000481569100004

• Modeling Transient Soil Moisture Limitations on Microbial Carbon Respiration JOURNAL OF GEOPHYSICAL RESEARCH-BIOGEOSCIENCES Liu, Y., Lawrence, C. R., Winnick, M. J., Hsu, H., Maher, K., Druhan, J. L. 2019; 124 (7): 2222–47

  View details for DOI 10.1029/2018JG004628

  View details for Web of Science ID 000481443800029

• Isotopic Fingerprint of Uranium Accumulation and Redox Cycling in Floodplains of the Upper Colorado River Basin ENVIRONMENTAL SCIENCE & TECHNOLOGY Lefebvre, P., Noel, V., Lau, K. V., Jemison, N. E., Weaver, K. L., Williams, K. H., Bargar, J. R., Maher, K. 2019; 53 (7): 3399–3409

  View details for DOI 10.1021/acs.est.8b05593

  View details for Web of Science ID 000463679600007

• Tracking Diverse Minerals, Hungry Organisms, and Dangerous Contaminants Using Reactive Transport Models ELEMENTS Maher, K., Mayer, K. 2019; 15 (2): 81–86

  View details for DOI 10.2138/gselements.15.2.81

  View details for Web of Science ID 000465457000003

• THE ART OF REACTIVE TRANSPORT MODEL BUILDING ELEMENTS Maher, K., Mayer, K. 2019; 15 (2): 117–18

  View details for DOI 10.2138/gselements.15.2.117

  View details for Web of Science ID 000465457000010

• Alteration depths from the shale surface into the matrix Li, Q., Jew, A., Kohli, A., Brown, G., Maher, K., Bargar, J. AMER CHEMICAL SOC. 2019

  View details for Web of Science ID 000478861200803

• Isotopic Fingerprint of Uranium Accumulation and Redox Cycling in Floodplains of the Upper Colorado River Basin. Environmental science & technology Lefebvre, P., Noel, V., Lau, K. V., Jemison, N. E., Weaver, K. L., Williams, K. H., Bargar, J. R., Maher, K. 2019

  Abstract

  Uranium (U) groundwater contamination is a major concern at numerous former mining and milling sites across the Upper Colorado River Basin (UCRB), USA, where U(IV)-bearing solids have accumulated within naturally reduced zones (NRZs). Understanding the processes governing U reduction and oxidation within NRZs is critical for assessing the persistence of U in groundwater. To evaluate the redox cycling of uranium, we measured the U concentrations and isotopic compositions (delta238U) of sediments and pore waters from four study sites across the UCRB that span a gradient in sediment texture and composition. We observe that U accumulation occurs primarily within fine-grained (low-permeability) NRZs that show active redox variations. Low-permeability NRZs display high accumulation and low export of U, with internal redox cycling of U. In contrast, within high-permeability NRZs, U is remobilized under oxidative conditions, possibly without any fractionation, and transported outside the NRZs. The low delta238U of sediments outside of defined NRZs suggests that these reduced zones act as additional U sources. Collectively, our results indicate that fine-grained NRZs have a greater potential to retain uranium, whereas NRZs with higher permeability may constitute a more-persistent but dilute U source.

  View details for PubMedID 30807121

• Cr(VI) reduction by Fe(II) sorbed to silica surfaces. Chemosphere Nelson, J. n., Joe-Wong, C. n., Maher, K. n. 2019; 234: 98–107

  Abstract

  The reaction kinetics of groundwater contaminants are integral to evaluating the fate and transport of toxic metals in the environment. For redox sensitive contaminants, such as chromium, the kinetics of different reaction pathways can vary by orders of magnitude. Species-specific rate constants for iron-chromium oxidation-reduction reactions are unknown for many systems, especially in the presence of sorbing surfaces. We investigate the role of quartz and amorphous silica (SiO2(am)) surfaces in mediating abiotic reduction of Cr(VI)aq by aqueous and sorbed Fe(II) using batch sorption and redox experiments. Sorption edges indicate outer-sphere (Fe(II)ads,OS) and inner-sphere (Fe(II)ads,IS) complexes are present on both silica surfaces, and their abundance depends on pH, ionic strength, and surface disorder. The rate constants for Cr(VI)aq reduction by Fe(II) species increase in the following order: kaq ≪ kads,OS,quartz < kads,OS,SiO2(am) < kads,IS,quartz < kads,IS,SiO2(am), suggesting that increasing proximity of Fe(II) to the negatively charged silica surface enhances the rate of reduction of Cr(VI)aq. However, we observe that experiments with larger amounts of sorbed Fe(II) reduce less total Cr(VI)aq over time, which we attribute to a portion of the sorbed Fe(II) being sequestered into the Cr(III)-Fe(III)-oxyhydroxide precipitates forming on the silica surface. Therefore, the balance between increases in the rate and decreases in the total amount of Cr(VI)aq reduction by various sorbed Fe(II) species must be considered when devising remediation strategies.

  View details for DOI 10.1016/j.chemosphere.2019.06.039

  View details for PubMedID 31203046

• Reactive Transport Processes that Drive Chemical Weathering: From Making Space for Water to Dismantling Continents REACTIVE TRANSPORT IN NATURAL AND ENGINEERED SYSTEMS Maher, K., Navarre-Sitchler, A., Druhan, J. L., Tournassat, C. 2019; 85: 349–80

  View details for DOI 10.2138/rmg.2018.85.12

  View details for Web of Science ID 000534267900013

• Ten-million years of activity within the Eastern California Shear Zone from U–Pb dating of fault-zone opal Earth and Planetary Science Letters Nuriel, P., Miller, D. M., Schmitt, K. M., Coble, M. A., Maher, K. 2019; 521: 37-45

  View details for DOI 10.1016/j.epsl.2019.05.047

• The sensitivity of terrestrial δ18O gradients to hydroclimate evolution Journal of Geophysical Research: Atmospheres Kukla, T., Winnick, M. J., Maher, K., Ibarra, D. E., Chamberlain, C. 2019; 124 (2): 563-582

  View details for DOI 10.1029/2018JD029571

• Thermodynamic controls on redox-driven kinetic stable isotope fractionation Geochemical Perspectives Letters Joe-Wong, C., Weaver, K. L., Brown, S. T., Maher, K. 2019: 20-25

  View details for DOI 10.7185/geochemlet.1909

• Multimodal imaging and stochastic percolation simulation for improved quantification of effective porosity and surface area in vesicular basalt ADVANCES IN WATER RESOURCES Zahasky, C., Thomas, D., Matter, J., Maher, K., Benson, S. M. 2018; 121: 235–44

  View details for DOI 10.1016/j.advwatres.2018.08.009

  View details for Web of Science ID 000447617000017

• Shale Kerogen: Hydraulic Fracturing Fluid Interactions and Contaminant Release ENERGY & FUELS Dustin, M. K., Bargar, J. R., Jew, A. D., Harrison, A. L., Joe-Wong, C., Thomas, D. L., Brown, G. E., Maher, K. 2018; 32 (9): 8966–77

  View details for DOI 10.1021/acs.energyfuels.8b01037

  View details for Web of Science ID 000445711700006

• Nanopore, surface disorder, and sorption controls on reactivity of the silica-water interface Nelson, J., Zalles, L., Maher, K. AMER CHEMICAL SOC. 2018

  View details for Web of Science ID 000447609100847

• Relationships between CO2, thermodynamic limits on silicate weathering, and the strength of the silicate weathering feedback EARTH AND PLANETARY SCIENCE LETTERS Winnick, M. J., Maher, K. 2018; 485: 111–20

  View details for DOI 10.1016/j.epsl.2018.01.005

  View details for Web of Science ID 000425070200011

• Global perturbation of the marine calcium cycle during the Permian-Triassic transition Geological Society of America Bulletin Silva-Tamayo, J., Payne, J. L., Wignall, P. B., Newton, R. J., Eisenhauer, A., DePaolo, D. J., Brown, S., Lau, K. V., Maher, K., Lehrmann, D. J., Altiner, D., Yu, M., Richoz, S., Paytan, A., Kump, L. R. 2018

  View details for DOI 10.1130/B31818.1

• The Earth Resources Challenge QUANTIFYING UNCERTAINTY IN SUBSURFACE SYSTEMS Vilhelmsen, T., Maher, K., Da Silva, C., Hermans, T., Grujic, O., Park, J., Yang, G., Scheidt, C., Li, L., Caers, J. 2018; 236: 1–27

  View details for Web of Science ID 000481474600002

• Quantifying Uncertainty in Subsurface Systems QUANTIFYING UNCERTAINTY IN SUBSURFACE SYSTEMS Vilhelmsen, T., Maher, K., Da Silva, C., Hermans, T., Grujic, O., Park, J., Yang, G., Scheidt, C., Li, L., Caers, J. 2018; 236: 217–62

  View details for Web of Science ID 000481474600009

• Effects of nano-confinement on Zn(II) adsorption to nanoporous silica Geochimica et Cosmochimica Acta Nelson, J., Bargar, J. R., Wasylenki, L., Brown Jr., G. E., Maher, K. 2018; 240: 80-97

  View details for DOI 10.1016/j.gca.2018.08.017

• Growing new generations of critical zone scientists EARTH SURFACE PROCESSES AND LANDFORMS Wymore, A. S., West, N. R., Maher, K., Sullivan, P. L., Harpold, A., Karwan, D., Marshall, J. A., Perdrial, J., Rempe, D. M., Ma, L. 2017; 42 (14): 2498–2502

  View details for DOI 10.1002/esp.4196

  View details for Web of Science ID 000414348200022

• Kinetics and Products of Chromium(VI) Reduction by Iron(II/III)-Bearing Clay Minerals ENVIRONMENTAL SCIENCE & TECHNOLOGY Joe-Wong, C., Brown, G. E., Maher, K. 2017; 51 (17): 9817–25

  Abstract

  Hexavalent chromium is a water-soluble pollutant, the mobility of which can be controlled by reduction of Cr(VI) to less soluble, environmentally benign Cr(III). Iron(II/III)-bearing clay minerals are widespread potential reductants of Cr(VI), but the kinetics and pathways of Cr(VI) reduction by such clay minerals are poorly understood. We reacted aqueous Cr(VI) with two abiotically reduced clay minerals: an Fe-poor montmorillonite and an Fe-rich nontronite. The effects of ionic strength, pH, total Fe content, and the fraction of reduced structural Fe(II) [Fe(II)/Fe(total)] were examined. The last variable had the largest effect on Cr(VI) reduction kinetics: for both clay minerals, the rate constant of Cr(VI) reduction varies by more than 3 orders of magnitude with Fe(II)/Fe(total) and is described by a linear free energy relationship. Under all conditions examined, Cr and Fe K-edge X-ray absorption near-edge structure spectra show that the main Cr-bearing product is a Cr(III)-hydroxide and that Fe remains in the clay structure after reacting with Cr(VI). This study helps to quantify our understanding of the kinetics of Cr(VI) reduction by Fe(II/III)-bearing clay minerals and may improve predictions of Cr(VI) behavior in subsurface environments.

  View details for PubMedID 28783317

• Element release and reaction-induced porosity alteration during shale-hydraulic fracturing fluid interactions APPLIED GEOCHEMISTRY Harrison, A. L., Jew, A. D., Dustin, M. K., Thomas, D. L., Joe-Wong, C. M., Bargar, J. R., Johnson, N., Brown, G. E., Maher, K. 2017; 82: 47–62

  View details for DOI 10.1016/j.apgeochem.2017.05.001

  View details for Web of Science ID 000403734000005

• Impact of Organics and Carbonates on the Oxidation and Precipitation of Iron during Hydraulic Fracturing of Shale (vol 31, pg 3643, 2017) ENERGY & FUELS Jew, A. D., Dustin, M. K., Harrison, A. L., Joe-Wong, C. M., Thomas, D. L., Maher, K., Brown, G. E., Bargar, J. R. 2017; 31 (7): 7700

  View details for DOI 10.1021/acs.energyfuels.7b01721

  View details for Web of Science ID 000406356600110

• Effects of nano-confinement and crystallinity on Zn isotope fractionation during adsorption onto silica surfaces Nelson, J., Wasylenki, L., Bargar, J., Brown, G., Maher, K. AMER CHEMICAL SOC. 2017

  View details for Web of Science ID 000430569101804

• Spectroscopic investigation of the mechanism and kinetics of the sulfidation of FeIII-(oxyhydr)oxide nanoparticles Kumar, N., Noel, V., Pacheco, J., Maher, K., Brown, G. AMER CHEMICAL SOC. 2017

  View details for Web of Science ID 000430569100676

• Molecular investigation of soil organic carbon composition, spatial variability, and depth distribution across a subalpine catchment Hsu, H., Lawrence, C., Winnick, M., Druhan, J., Williams, K., Maher, K. AMER CHEMICAL SOC. 2017

  View details for Web of Science ID 000430569102073

• Factors affecting the sorption of uranyl at mineral-aqueous solution interfaces Brown, G., Dublet, G., Noel, V., Fendorf, S., Bargar, J., Maher, K. AMER CHEMICAL SOC. 2017

  View details for Web of Science ID 000430569104797

• Snowmelt controls on concentration-discharge relationships and the balance of oxidative and acid-base weathering fluxes in an alpine catchment, East River, Colorado Winnick, M., Carroll, R., Williams, K., Maxwell, R., Dong, W., Maher, K. AMER CHEMICAL SOC. 2017

  View details for Web of Science ID 000430569101832

• Insights into mineral-water interface dynamics through coupled stable isotope and spectroscopic investigations Maher, K., Nelson, J. AMER CHEMICAL SOC. 2017

  View details for Web of Science ID 000430569101803

• Impact of Organics and Carbonates on the Oxidation and Precipitation of Iron during Hydraulic Fracturing of Shale ENERGY & FUELS Jew, A. D., Dustin, M. K., Harrison, A. L., Joe-Wong, C. M., Thomas, D. L., Maher, K., Brown, G. E., Bargar, J. R. 2017; 31 (4): 3643-3658

  View details for DOI 10.1021/acs.energyfuels.6b03220

  View details for Web of Science ID 000400039800031

• Snowmelt controls on concentration-discharge relationships and the balance of oxidative and acid-base weathering fluxes in an alpine catchment, East River, Colorado WATER RESOURCES RESEARCH Winnick, M. J., Carroll, R. W., Williams, K. H., Maxwell, R. M., Dong, W., Maher, K. 2017; 53 (3): 2507-2523

  View details for DOI 10.1002/2016WR019724

  View details for Web of Science ID 000400160500042

• Expanding the role of reactive transport models in critical zone processes EARTH-SCIENCE REVIEWS Li, L., Maher, K., Navarre-Sitchler, A., Druhan, J., Meile, C., Lawrence, C., Moore, J., Perdrial, J., Sullivan, P., Thompson, A., Jin, L., Bolton, E. W., Brantley, S. L., Dietrich, W. E., Mayer, K. U., Steefel, C. I., Valocchi, A., Zachara, J., Kocar, B., McIntosh, J., Tutolo, B. M., Kumar, M., Sonnenthal, E., Bao, C., Beisman, J. 2017; 165: 280-301

  View details for DOI 10.1016/j.earscirev.2016.09.001

  View details for Web of Science ID 000394395800012

• The influence of mixing on stable isotope ratios in porous media: A revised Rayleigh model WATER RESOURCES RESEARCH Druhan, J. L., Maher, K. 2017; 53 (2): 1101-1124

  View details for DOI 10.1002/2016WR019666

  View details for Web of Science ID 000398568800007

• An evaluation of paired delta O-18 and (U-234/U-238)(0) in opal as a tool for paleoclimate reconstruction in semi-arid environments CHEMICAL GEOLOGY Oster, J. L., Kitajima, K., Valley, J. W., Rogers, B., Maher, K. 2017; 449: 236-252

  View details for DOI 10.1016/j.chemgeo.2016.12.009

  View details for Web of Science ID 000393001800019

• Uranium isotope evidence for temporary ocean oxygenation in the aftermath of the Sturtian Snowball Earth EARTH AND PLANETARY SCIENCE LETTERS Lau, K. V., Macdonald, F. A., Maher, K., Payne, J. L. 2017; 458: 282-292

  View details for DOI 10.1016/j.epsl.2016.10.043

  View details for Web of Science ID 000392685100027

• Quantifying Cr(VI) Production and Export from Serpentine Soil of the California Coast Range ENVIRONMENTAL SCIENCE & TECHNOLOGY McClain, C. N., Fendorf, S., Webb, S. M., Maher, K. 2017; 51 (1): 141-149

  Abstract

  Hexavalent chromium (Cr(VI)) is generated in serpentine soils and exported to surface and groundwaters at levels above health-based drinking water standards. Although Cr(VI) concentrations are elevated in serpentine soil pore water, few studies have reported field evidence documenting Cr(VI) production rates and fluxes that govern Cr(VI) transport from soil to water sources. We report Cr speciation (i) in four serpentine soil depth profiles derived from the California Coast Range serpentinite belt and (ii) in local surface waters. Within soils, we detected Cr(VI) in the same horizons where Cr(III)-minerals are colocated with biogenic Mn(III/IV)-oxides, suggesting Cr(VI) generation through oxidation by Mn-oxides. Water-extractable Cr(VI) concentrations increase with depth constituting a 7.8 to 12 kg/km(2) reservoir of Cr(VI) in soil. Here, Cr(VI) is produced at a rate of 0.3 to 4.8 kg Cr(VI)/km(2)/yr and subsequently flushed from soil during water infiltration, exporting 0.01 to 3.9 kg Cr(VI)/km(2)/yr at concentrations ranging from 25 to 172 μg/L. Although soil-derived Cr(VI) is leached from soil at concentrations exceeding 10 μg/L, due to reduction and dilution during transport to streams, Cr(VI) levels measured in local surface waters largely remain below California's drinking water limit.

  View details for DOI 10.1021/acs.est.6b03484

  View details for Web of Science ID 000391346900016

  View details for PubMedID 27935688

• The influence of diagenesis, mineralogy, and seawater changes on calcium isotope variations in Lower-Middle Triassic carbonate rocks Chemical Geology Lau, K. V., Maher, K., Brown, S., Jost, A. B., Altiner, D., DePaolo, D. J., Eisenhauer, A., Kelley, B. M., Lehrmann, D. J., Paytan, A., Silva-Tamayo, J., Yu, M., Payne, J. L. 2017; 471: 13-37

  View details for DOI 10.1016/j.chemgeo.2017.09.006

• Effects of surface structural disorder and surface coverage on isotopic fractionation during Zn(II) adsorption onto quartz and amorphous silica surfaces Geochimica et Cosmochimica Acta Nelson, J., Wasylenki, L., Bargar, J. R., Brown Jr., G. E., Maher, K. 2017; 215: 354-376

  View details for DOI 10.1016/j.gca.2017.08.003

• Critical zone structure controls concentration-discharge relationships and solute generation in forested tropical montane watersheds Water Resources Research Wymore, A. S., Brereton, R. L., Ibarra, D. E., Maher, K., McDowell, W. H. 2017; 53 (7): 6279-6295

  View details for DOI 10.1002/2016WR020016

• Concentration–discharge patterns of weathering products from global rivers Acta Geochimica Ibarra, D. E., Moon, S., Caves, J. K., Chamberlain, C., Maher, K. 2017

  View details for DOI 10.1007/s11631-017-0177-z

• Surface ages and weathering rates from Be-10 (meteoric) and Be-10/Be-9: Insights from differential mass balance and reactive transport modeling CHEMICAL GEOLOGY Maher, K., von Blanckenburg, F. 2016; 446: 70-86

  View details for DOI 10.1016/j.chemgeo.2016.07.016

  View details for Web of Science ID 000389396200006

• Geochemistry of CO2-rich waters in Iceland CHEMICAL GEOLOGY Thomas, D. L., Bird, D. K., Arnorsson, S., Maher, K. 2016; 444: 158-179

  View details for DOI 10.1016/j.chemgeo.2016.09.002

  View details for Web of Science ID 000388776800014

• Clumped-isotope thermometry of magnesium carbonates in ultramafic rocks GEOCHIMICA ET COSMOCHIMICA ACTA del Real, P. G., Maher, K., Kluge, T., Bird, D. K., Brown, G. E., John, C. M. 2016; 193: 222-250

  View details for DOI 10.1016/j.gca.2016.08.003

  View details for Web of Science ID 000385507900013

• Aluminous gneiss derived by weathering of basaltic source rocks in the Neoarchean Storo Supracrustal Belt, southern West Greenland CHEMICAL GEOLOGY Szilas, K., Maher, K., Bird, D. K. 2016; 441: 63-80

  View details for DOI 10.1016/j.chemgeo.2016.08.013

  View details for Web of Science ID 000384057800006

• Differential weathering of basaltic and granitic catchments from concentration-discharge relationships GEOCHIMICA ET COSMOCHIMICA ACTA Ibarra, D. E., Caves, J. K., Moon, S., Thomas, D. L., Hartmann, J., Chamberlain, C. P., Maher, K. 2016; 190: 265-293

  View details for DOI 10.1016/j.gca.2016.07.006

  View details for Web of Science ID 000388802600015

• Cenozoic carbon cycle imbalances and a variable weathering feedback EARTH AND PLANETARY SCIENCE LETTERS Caves, J. K., Jost, A. B., Lau, K. V., Maher, K. 2016; 450: 152-163

  View details for DOI 10.1016/j.epsl.2016.06.035

  View details for Web of Science ID 000381535600015

• Chromium(VI) reduction by mixed iron(II/III)-bearing clay minerals Joe-Wong, C., Maher, K., Brown, G. AMER CHEMICAL SOC. 2016

  View details for Web of Science ID 000431460400076

• Isotopic Evidence for Reductive Immobilization of Uranium Across a Roll-Front Mineral Deposit ENVIRONMENTAL SCIENCE & TECHNOLOGY Brown, S. T., Basu, A., Christensen, J. N., Reimus, P., Heikoop, J., Simmons, A., WoldeGabriel, G., Maher, K., Weaver, K., Clay, J., DePaolo, D. J. 2016; 50 (12): 6189-6198

  Abstract

  We use uranium (U) isotope ratios to detect and quantify the extent of natural U reduction in groundwater across a roll front redox gradient. Our study was conducted at the Smith Ranch-Highland in situ recovery (ISR) U mine in eastern Wyoming, USA, where economic U deposits occur in the Paleocene Fort Union formation. To evaluate the fate of aqueous U in and adjacent to the ore body, we investigated the chemical composition and isotope ratios of groundwater samples from the roll-front type ore body and surrounding monitoring wells of a previously mined area. The (238)U/(235)U of groundwater varies by approximately 3‰ and is correlated with U concentrations. Fluid samples down-gradient of the ore zone are the most depleted in (238)U and have the lowest U concentrations. Activity ratios of (234)U/(238)U are ∼5.5 up-gradient of the ore zone, ∼1.0 in the ore zone, and between 2.3 and 3.7 in the down-gradient monitoring wells. High-precision measurements of (234)U/(238)U and (238)U/(235)U allow for development of a conceptual model that evaluates both the migration of U from the ore body and the extent of natural attenuation due to reduction. We find that the premining migration of U down-gradient of the delineated ore body is minimal along eight transects due to reduction in or adjacent to the ore body, whereas two other transects show little or no sign of reduction in the down-gradient region. These results suggest that characterization of U isotopic ratios at the mine planning stage, in conjunction with routine geochemical analyses, can be used to identify where more or less postmining remediation will be necessary.

  View details for DOI 10.1021/acs.est.6b00626

  View details for Web of Science ID 000378469900010

  View details for PubMedID 27203292

• Chromium fluxes and speciation in ultramafic catchments and global rivers CHEMICAL GEOLOGY McClain, C. N., Maher, K. 2016; 426: 135-157

  View details for DOI 10.1016/j.chemgeo.2016.01.021

  View details for Web of Science ID 000371214700012

• Regional importance of organic-rich sediments to uranium mobility in the upper Colorado River Basin Noel, V., Boye, K., Bargar, J., Lefebvre, P., Maher, K., Bone, S., Lezama, J., Carderelli, E., Dam, W., Johnson, R. AMER CHEMICAL SOC. 2016

  View details for Web of Science ID 000431905701331

• Marine anoxia and delayed Earth system recovery after the end-Permian extinction. Proceedings of the National Academy of Sciences of the United States of America Lau, K. V., Maher, K., Altiner, D., Kelley, B. M., Kump, L. R., Lehrmann, D. J., Silva-Tamayo, J. C., Weaver, K. L., Yu, M., Payne, J. L. 2016; 113 (9): 2360-2365

  Abstract

  Delayed Earth system recovery following the end-Permian mass extinction is often attributed to severe ocean anoxia. However, the extent and duration of Early Triassic anoxia remains poorly constrained. Here we use paired records of uranium concentrations ([U]) and (238)U/(235)U isotopic compositions (δ(238)U) of Upper Permian-Upper Triassic marine limestones from China and Turkey to quantify variations in global seafloor redox conditions. We observe abrupt decreases in [U] and δ(238)U across the end-Permian extinction horizon, from ∼3 ppm and -0.15‰ to ∼0.3 ppm and -0.77‰, followed by a gradual return to preextinction values over the subsequent 5 million years. These trends imply a factor of 100 increase in the extent of seafloor anoxia and suggest the presence of a shallow oxygen minimum zone (OMZ) that inhibited the recovery of benthic animal diversity and marine ecosystem function. We hypothesize that in the Early Triassic oceans-characterized by prolonged shallow anoxia that may have impinged onto continental shelves-global biogeochemical cycles and marine ecosystem structure became more sensitive to variation in the position of the OMZ. Under this hypothesis, the Middle Triassic decline in bottom water anoxia, stabilization of biogeochemical cycles, and diversification of marine animals together reflect the development of a deeper and less extensive OMZ, which regulated Earth system recovery following the end-Permian catastrophe.

  View details for DOI 10.1073/pnas.1515080113

  View details for PubMedID 26884155

  View details for PubMedCentralID PMC4780601

• A spatially resolved surface kinetic model for forsterite dissolution GEOCHIMICA ET COSMOCHIMICA ACTA Maher, K., Johnson, N. C., Jackson, A., Lammers, L. N., Torchinsky, A. B., Weaver, K. L., Bird, D. K., Brown, G. E. 2016; 174: 313-334

  View details for DOI 10.1016/j.gca.2015.11.019

  View details for Web of Science ID 000368819800021

• THE NEW EARTH AND ENVIRONMENTAL NANOSCIENCE AND TECHNOLOGYCENTERS SPONSORED BY NSF ELEMENTS Hochella, M., Mogk, D., Maher, K. 2016; 12 (1): 77–78

  View details for DOI 10.2113/gselements.12.1.77

  View details for Web of Science ID 000370987700012

• The imprint of climate and geology on the residence times of groundwater GEOPHYSICAL RESEARCH LETTERS Maxwell, R. M., Condon, L. E., Kollet, S. J., Maher, K., Haggerty, R., Forrester, M. M. 2016; 43 (2): 701-708

  View details for DOI 10.1002/2015GL066916

  View details for Web of Science ID 000372056400027

• Physico-Chemical Heterogeneity of Organic-Rich Sediments in the Rifle Aquifer, CO: Impact on Uranium Biogeochemistry ENVIRONMENTAL SCIENCE & TECHNOLOGY Janot, N., Pacheco, J. S., Pham, D. Q., O'Brien, T. M., Hausladen, D., Noel, V., Lallier, F., Maher, K., Fendorf, S., Williams, K. H., Long, P. E., Bargar, J. R. 2016; 50 (1): 46-53

  Abstract

  The Rifle alluvial aquifer along the Colorado River in west central Colorado contains fine-grained, diffusion-limited sediment lenses that are substantially enriched in organic carbon and sulfides, as well as uranium, from previous milling operations. These naturally reduced zones (NRZs) coincide spatially with a persistent uranium groundwater plume. There is concern that uranium release from NRZs is contributing to plume persistence or will do so in the future. To better define the physical extent, heterogeneity and biogeochemistry of these NRZs, we investigated sediment cores from five neighboring wells. The main NRZ body exhibited uranium concentrations up to 100 mg/kg U as U(IV) and contains ca. 286 g of U in total. Uranium accumulated only in areas where organic carbon and reduced sulfur (as iron sulfides) were present, emphasizing the importance of sulfate-reducing conditions to uranium retention and the essential role of organic matter. NRZs further exhibited centimeter-scale variations in both redox status and particle size. Mackinawite, greigite, pyrite and sulfate coexist in the sediments, indicating that dynamic redox cycling occurs within NRZs and that their internal portions can be seasonally oxidized. We show that oxidative U(VI) release to the aquifer has the potential to sustain a groundwater contaminant plume for centuries. NRZs, known to exist in other uranium-contaminated aquifers, may be regionally important to uranium persistence.

  View details for DOI 10.1021/acs.est.5b03208

  View details for Web of Science ID 000367866300006

• Physico-Chemical Heterogeneity of Organic-Rich Sediments in the Rifle Aquifer, CO: Impact on Uranium Biogeochemistry. Environmental science & technology Janot, N., Lezama Pacheco, J. S., Pham, D. Q., O'Brien, T. M., Hausladen, D., Noël, V., Lallier, F., Maher, K., Fendorf, S., Williams, K. H., Long, P. E., Bargar, J. R. 2016; 50 (1): 46-53

  Abstract

  The Rifle alluvial aquifer along the Colorado River in west central Colorado contains fine-grained, diffusion-limited sediment lenses that are substantially enriched in organic carbon and sulfides, as well as uranium, from previous milling operations. These naturally reduced zones (NRZs) coincide spatially with a persistent uranium groundwater plume. There is concern that uranium release from NRZs is contributing to plume persistence or will do so in the future. To better define the physical extent, heterogeneity and biogeochemistry of these NRZs, we investigated sediment cores from five neighboring wells. The main NRZ body exhibited uranium concentrations up to 100 mg/kg U as U(IV) and contains ca. 286 g of U in total. Uranium accumulated only in areas where organic carbon and reduced sulfur (as iron sulfides) were present, emphasizing the importance of sulfate-reducing conditions to uranium retention and the essential role of organic matter. NRZs further exhibited centimeter-scale variations in both redox status and particle size. Mackinawite, greigite, pyrite and sulfate coexist in the sediments, indicating that dynamic redox cycling occurs within NRZs and that their internal portions can be seasonally oxidized. We show that oxidative U(VI) release to the aquifer has the potential to sustain a groundwater contaminant plume for centuries. NRZs, known to exist in other uranium-contaminated aquifers, may be regionally important to uranium persistence.

  View details for DOI 10.1021/acs.est.5b03208

  View details for PubMedID 26651843

• Multi-phase flow simulation of CO2 leakage through a fractured caprock in response to mitigation strategies INTERNATIONAL JOURNAL OF GREENHOUSE GAS CONTROL Vialle, S., Druhan, J. L., Maher, K. 2016; 44: 11-25

  View details for DOI 10.1016/j.ijggc.2015.10.007

  View details for Web of Science ID 000368753500002

• Stable runoff and weathering fluxes into the oceans over Quaternary climate cycles NATURE GEOSCIENCE von Blanckenburg, F., Bouchez, J., Ibarra, D. E., Maher, K. 2015; 8 (7): 538-U146

  View details for DOI 10.1038/NGEO2452

  View details for Web of Science ID 000357404200016

• Isotopic and Geochemical Tracers for U(VI) Reduction and U Mobility at an in Situ Recovery U Mine. Environmental science & technology Basu, A., Brown, S. T., Christensen, J. N., DePaolo, D. J., Reimus, P. W., Heikoop, J. M., WoldeGabriel, G., Simmons, A. M., House, B. M., Hartmann, M., Maher, K. 2015; 49 (10): 5939-5947

  Abstract

  In situ recovery (ISR) uranium (U) mining mobilizes U in its oxidized hexavalent form (U(VI)) by oxidative dissolution of U from the roll-front U deposits. Postmining natural attenuation of residual U(VI) at ISR mines is a potential remediation strategy. Detection and monitoring of naturally occurring reducing subsurface environments are important for successful implementation of this remediation scheme. We used the isotopic tracers (238)U/(235)U (δ(238)U), (234)U/(238)U activity ratio, and (34)S/(32)S (δ(34)S), and geochemical measurements of U ore and groundwater collected from 32 wells located within, upgradient, and downgradient of a roll-front U deposit to detect U(VI) reduction and U mobility at an ISR mining site at Rosita, TX, USA. The δ(238)U in Rosita groundwater varies from +0.61‰ to -2.49‰, with a trend toward lower δ(238)U in downgradient wells. The concurrent decrease in U(VI) concentration and δ(238)U with an ε of 0.48‰ ± 0.08‰ is indicative of naturally occurring reducing environments conducive to U(VI) reduction. Additionally, characteristic (234)U/(238)U activity ratio and δ(34)S values may also be used to trace the mobility of the ore zone groundwater after mining has ended. These results support the use of U isotope-based detection of natural attenuation of U(VI) at Rosita and other similar ISR mining sites.

  View details for DOI 10.1021/acs.est.5b00701

  View details for PubMedID 25909757

• Sedimentary reservoir oxidation during geologic CO2 sequestration GEOCHIMICA ET COSMOCHIMICA ACTA Lammers, L. N., Brown, G. E., Bird, D. K., Thomas, R. B., Johnson, N. C., Rosenbauer, R. J., Maher, K. 2015; 155: 30-46

  View details for DOI 10.1016/j.gca.2015.02.001

  View details for Web of Science ID 000351732800003

• Adsorption and precipitation of Zn and Ni in nanoporous silica Nelson, J., Bargar, J., Brown, G., Maher, K. AMER CHEMICAL SOC. 2015

  View details for Web of Science ID 000411186500729

• Steering of westerly storms over western North America at the Last Glacial Maximum NATURE GEOSCIENCE Oster, J. L., Ibarra, D. E., Winnick, M. J., Maher, K. 2015; 8 (3): 201-205

  View details for DOI 10.1038/NGEO2365

  View details for Web of Science ID 000350770900017

• Numerical simulation of reactive barrier emplacement to control CO2 migration Carbon Dioxide Capture for Storage in Deep Geologic Formations: Results from the CO2 Capture Project. Vol. 4 Druhan, J. J., Vialle, S., Beson, S., Maher, K. 2015
• Rise and fall of late Pleistocene pluvial lakes in response to reduced evaporation and precipitation: Evidence from Lake Surprise, California GEOLOGICAL SOCIETY OF AMERICA BULLETIN Ibarra, D. E., Egger, A. E., Weaver, K. L., Harris, C. R., Maher, K. 2014; 126 (11-12): 1387-1415

  View details for DOI 10.1130/B31014.1

  View details for Web of Science ID 000343759600001

• The impact of neogene grassland expansion and aridification on the isotopic composition of continental precipitation GLOBAL BIOGEOCHEMICAL CYCLES Chamberlain, C. P., Winnick, M. J., Mix, H. T., Chamberlain, S. D., Maher, K. 2014; 28 (9): 992-1004

  View details for DOI 10.1002/2014GB004822

  View details for Web of Science ID 000343752900006

• Modeling the influence of organic acids on soil weathering GEOCHIMICA ET COSMOCHIMICA ACTA Lawrence, C., Harden, J., Maher, K. 2014; 139: 487-507

  View details for DOI 10.1016/j.gca.2014.05.003

  View details for Web of Science ID 000339176400027

• Uranium Incorporation into Amorphous Silica ENVIRONMENTAL SCIENCE & TECHNOLOGY Massey, M. S., Lezama-Pacheco, J. S., Nelson, J. M., Fendor, S., Maher, K. 2014; 48 (15): 8636-8644

  Abstract

  High concentrations of uranium are commonly observed in naturally occurring amorphous silica (including opal) deposits, suggesting that incorporation of U into amorphous silica may represent a natural attenuation mechanism and promising strategy for U remediation. However, the stability of uranium in opaline silicates, determined in part by the binding mechanism for U, is an important factor in its long-term fate. U may bind directly to the opaline silicate matrix, or to materials such as iron (hydr)oxides that are subsequently occluded within the opal. Here, we examine the coordination environment of U within opaline silica to elucidate incorporation mechanisms. Precipitates (with and without ferrihydrite inclusions) were synthesized from U-bearing sodium metasilicate solutions, buffered at pH ∼ 5.6. Natural and synthetic solids were analyzed with X-ray absorption spectroscopy and a suite of other techniques. In synthetic amorphous silica, U was coordinated by silicate in a double corner-sharing coordination geometry (Si at ∼ 3.8-3.9 Å) and a small amount of uranyl and silicate in a bidentate, mononuclear (edge-sharing) coordination (Si at ∼ 3.1-3.2 Å, U at ∼ 3.8-3.9 Å). In iron-bearing synthetic solids, U was adsorbed to iron (hydr)oxide, but the coordination environment also contained silicate in both edge-sharing and corner-sharing coordination. Uranium local coordination in synthetic solids is similar to that of natural U-bearing opals that retain U for millions of years. The stability and extent of U incorporation into opaline and amorphous silica represents a long-term repository for U that may provide an alternative strategy for remediation of U contamination.

  View details for DOI 10.1021/es501064m

  View details for Web of Science ID 000340080600039

  View details for PubMedID 24984107

• Olivine dissolution and carbonation under conditions relevant for in situ carbon storage CHEMICAL GEOLOGY Johnson, N. C., Thomas, B., Maher, K., Rosenbauer, R. J., Bird, D., Brown, G. E. 2014; 373: 93-105

  View details for DOI 10.1016/j.chemgeo.2014.02.026

  View details for Web of Science ID 000334737200009

• URANIUM ISOTOPES IN SOILS AS A PROXY FOR PAST INFILTRATION AND PRECIPITATION ACROSS THE WESTERN UNITED STATES AMERICAN JOURNAL OF SCIENCE Maher, K., Ibarra, D. E., Oster, J. L., Miller, D. M., Redwine, J. L., Reheis, M. C., Harden, J. W. 2014; 314 (4): 821-857

  View details for DOI 10.2475/04.2014.01

  View details for Web of Science ID 000345105100001

• Hydrologic regulation of chemical weathering and the geologic carbon cycle. Science Maher, K., CHAMBERLAIN, C. P. 2014; 343 (6178): 1502-1504

  Abstract

  Earth's temperature is thought to be regulated by a negative feedback between atmospheric CO2 levels and chemical weathering of silicate rocks that operates over million-year time scales. To explain variations in the strength of the weathering feedback, we present a model for silicate weathering that regulates climatic and tectonic forcing through hydrologic processes and imposes a thermodynamic limit on weathering fluxes, based on the physical and chemical properties of river basins. Climate regulation by silicate weathering is thus strongest when global topography is elevated, similar to the situation today, and lowest when global topography is more subdued, allowing planetary temperatures to vary depending on the global distribution of topography and mountain belts, even in the absence of appreciable changes in CO2 degassing rates.

  View details for DOI 10.1126/science.1250770

  View details for PubMedID 24625927

• Probing the mechanisms of pore size dependent geochemistry: Effects of meso-confinement on Zn sorption in mesoporous silica Nelson, J. M., Bargar, J. R., Brown, G. E., Maher, K. AMER CHEMICAL SOC. 2014

  View details for Web of Science ID 000348457600705

• Uranium isotopes in soils as a proxy for past infiltration and precipitation across the western United States AMERICAN JOURNAL OF SCIENCE Maher, K., Ibarra, D. E., Oster, J. L., Miller, D. M., Redwine, J. L., Reheis, M. C., Harden, J. C. 2014; 314: 821-857
• A reactive transport model for geochemical mitigation of CO2 leaking into a confined aquifer Druhan, J. L., Vialle, S., Maher, K., Benson, S., Dixon, T., Herzog, H., Twinning, S. ELSEVIER SCIENCE BV. 2014: 4620–29

  View details for DOI 10.1016/j.egypro.2014.11.495

  View details for Web of Science ID 000361211504082

• Abiotic/Biotic Coupling in the Rhizosphere: A Reactive Transport Modeling Analysis Lawrence, C., Steefel, C., Maher, K., Gaillardet, J. ELSEVIER SCIENCE BV. 2014: 104–8

  View details for DOI 10.1016/j.proeps.2014.08.037

  View details for Web of Science ID 000345407200018

• Modeling coupled chemical and isotopic equilibration rates Steefel, C. I., Druhan, J. L., Maher, K., Gaillardet, J. ELSEVIER SCIENCE BV. 2014: 208–17

  View details for DOI 10.1016/j.proeps.2014.08.022

  View details for Web of Science ID 000345407200038

• Relationships between the transit time of water and the fluxes of weathered elements through the critical zone Geochemistry of the Earth's Surface (GES) Meeting Maher, K., Druhan, J. ELSEVIER SCIENCE BV. 2014: 16–22

  View details for DOI 10.1016/j.proeps.2014.08.004

  View details for Web of Science ID 000345407200003

• A model linking stable isotope fractionation to water flux and transit times in heterogeneous porous media Geochemistry of the Earth's Surface (GES) Meeting Druhan, J. L., Maher, K. ELSEVIER SCIENCE BV. 2014: 179–188

  View details for DOI 10.1016/j.proeps.2014.08.054

  View details for Web of Science ID 000345407200033

• Rise and fall of late Pleistocene pluvial lakes in response to reduced evaporation and precipitation: Evidence from Lake Surprise, California GEOLOGICAL SOCIETY OF AMERICA BULLETIN Ibarra, D. E., Egger, A. E., Weaver, K. L., Harris, C. R., Maher, K. 2014; 126 (11-12): 1387-1415

  View details for DOI 10.1130/B31014.1

• Uranium incorporation into amorphous silica ENVIRONMENTAL SCIENCE AND TECHNOLOGY Massey, M., Lezama-Pacheco, J. S., Nelson, J. M., Fendorf, S., Maher, K. 2014; (in press)
• (Submitted) Thermal Fracturing of Crustal Ultramafic Rocks for Geologic CO2 Sequestration na Garcia del Real, P., Maher, K., Brown, Jr., G. E., Bird, D. K. 2014
• A Teaching Exercise To Introduce Stable Isotope Fractionation of Metals into Geochemistry Courses JOURNAL OF CHEMICAL EDUCATION Weiss, D. J., Harris, C., Maher, K., Bullen, T. 2013; 90 (8): 1014-1017

  View details for DOI 10.1021/ed300370d

  View details for Web of Science ID 000323462900010

• Environmental Speciation of Actinides INORGANIC CHEMISTRY Maher, K., Bargar, J. R., Brown, G. E. 2013; 52 (7): 3510-3532

  Abstract

  Although minor in abundance in Earth's crust (U, 2-4 ppm; Th, 10-15 ppm) and in seawater (U, 0.003 ppm; Th, 0.0007 ppm), light actinides (Th, Pa, U, Np, Pu, Am, and Cm) are important environmental contaminants associated with anthropogenic activities such as the mining and milling of uranium ores, generation of nuclear energy, and storage of legacy waste resulting from the manufacturing and testing of nuclear weapons. In this review, we discuss the abundance, production, and environmental sources of naturally occurring and some man-made light actinides. As is the case with other environmental contaminants, the solubility, transport properties, bioavailability, and toxicity of actinides are dependent on their speciation (composition, oxidation state, molecular-level structure, and nature of the phase in which the contaminant element or molecule occurs). We review the aqueous speciation of U, Np, and Pu as a function of pH and Eh, their interaction with common inorganic and organic ligands in natural waters, and some of the common U-containing minerals. We also discuss the interaction of U, Np, Pu, and Am solution complexes with common Earth materials, including minerals, colloids, gels, natural organic matter (NOM), and microbial organisms, based on simplified model system studies. These surface interactions can inhibit (e.g., sorption to mineral surfaces, formation of insoluble biominerals) or enhance (e.g., colloid-facilitated transport) the dispersal of light actinides in the biosphere and in some cases (e.g., interaction with dissimilatory metal-reducing bacteria, NOM, or Mn- and Fe-containing minerals) can modify the oxidation states and, consequently, the behavior of redox-sensitive light actinides (U, Np, and Pu). Finally, we review the speciation of U and Pu, their chemical transformations, and cleanup histories at several U.S. Department of Energy field sites that have been used to mill U ores, produce fissile materials for reactors and weapons, and store high-level nuclear waste from both civilian and defense operations, including Hanford, WA; Rifle, CO; Oak Ridge, TN; Fernald, OH; Fry Canyon, UT; and Rocky Flats, CO.

  View details for DOI 10.1021/ic301686d

  View details for Web of Science ID 000317094300009

  View details for PubMedID 23137032

• The role of Neogene grassland expansion and aridification on the isotopic composition of continental precipitation na Chamberlain, C. P., Winnick, M., Mix, H. T., Chamberlain, S. D., Maher, K. 2013
• Uranium comminution ages: Sediment transport and deposition time scales COMPTES RENDUS GEOSCIENCE DePaolo, D. J., Lee, V. E., Christensen, J. N., Maher, K. 2012; 344 (11-12): 678-687

  View details for DOI 10.1016/j.crte.2012.10.014

  View details for Web of Science ID 000312926000013

• Influence of eolian deposition and rainfall amounts on the U-isotopic composition of soil water and soil minerals GEOCHIMICA ET COSMOCHIMICA ACTA Oster, J. L., Ibarra, D. E., Harris, C. R., Maher, K. 2012; 88: 146-166

  View details for DOI 10.1016/j.gca.2012.04.004

  View details for Web of Science ID 000304765200011

• The role of fluid residence time and topographic scales in determining chemical fluxes from landscapes EARTH AND PLANETARY SCIENCE LETTERS Maher, K. 2011; 312 (1-2): 48-58

  View details for DOI 10.1016/j.epsl.2011.09.040

  View details for Web of Science ID 000298456200006

• Evolution of hillslope soils: The geomorphic theater and the geochemical play APPLIED GEOCHEMISTRY Yoo, K., Weinman, B., Mudd, S. M., Hurst, M., Attal, M., Maher, K. 2011; 26: S149-S153

  View details for DOI 10.1016/j.apgeochem.2011.03.054

  View details for Web of Science ID 000297788100043

• ISOTOPIC APPROACHES FOR QUANTIFYING THE RATES OF MARINE BURIAL DIAGENESIS REVIEWS OF GEOPHYSICS Fantle, M. S., MAHER, K. M., DePaolo, D. J. 2010; 48

  View details for DOI 10.1029/2009RG000306

  View details for Web of Science ID 000282328000001

• The dependence of chemical weathering rates on fluid residence time EARTH AND PLANETARY SCIENCE LETTERS Maher, K. 2010; 294 (1-2): 101-110

  View details for DOI 10.1016/j.epsl.2010.03.010

  View details for Web of Science ID 000278506200012

• Climatic and vegetation control on sediment dynamics during the last glacial cycle GEOLOGY Dosseto, A., Hesse, P. P., Maher, K., Fryirs, K., Turner, S. 2010; 38 (5): 395-398

  View details for DOI 10.1130/G30708.1

  View details for Web of Science ID 000277220900003

• Uranyl-chlorite sorption/desorption: Evaluation of different U(VI) sequestration processes GEOCHIMICA ET COSMOCHIMICA ACTA Singer, D. M., Maher, K., Brown, G. E. 2009; 73 (20): 5989-6007

  View details for DOI 10.1016/j.gca.2009.07.002

  View details for Web of Science ID 000273416500003

• Combined ecological and geologic perspectives in ecosystem studies Preface CHEMICAL GEOLOGY Holloway, J. M., Ewing, S. A., Maher, K. 2009; 267 (1-2): 1-2

  View details for DOI 10.1016/j.chemgeo.2009.05.001

  View details for Web of Science ID 000270631000001

• The role of reaction affinity and secondary minerals in regulating chemical weathering rates at the Santa Cruz Soil Chronosequence, California GEOCHIMICA ET COSMOCHIMICA ACTA Maher, K., Steefel, C. I., White, A. F., Stonestrom, D. A. 2009; 73 (10): 2804-2831

  View details for DOI 10.1016/j.gca.2009.01.030

  View details for Web of Science ID 000265669300007

• Chemical weathering of a marine terrace chronosequence, Santa Cruz, California. Part II: Solute profiles, gradients and the comparisons of contemporary and long-term weathering rates GEOCHIMICA ET COSMOCHIMICA ACTA White, A. F., Schulz, M. S., Stonestrom, D. A., Vivit, D. V., Fitzpatrick, J., Bullen, T. D., Maher, K., Blum, A. E. 2009; 73 (10): 2769-2803

  View details for DOI 10.1016/j.gca.2009.01.029

  View details for Web of Science ID 000265669300006

• Fluid-Rock Interaction: A Reactive Transport Approach 19th Annual V M Goldschmidt Conference Steefel, C. I., Maher, K. MINERALOGICAL SOC AMER. 2009: 485–532

  View details for DOI 10.2138/rmg.2009.70.11

  View details for Web of Science ID 000268929000011

• High-resolution paleoclimate records from soils using SIMS approaches Maheri, K., Harden, J., Stock, J., Reheis, M. PERGAMON-ELSEVIER SCIENCE LTD. 2008: A586

  View details for Web of Science ID 000257301601434

• Field evidence for strong chemical separation of contaminants in the Hanford vadose zone VADOSE ZONE JOURNAL Conrad, M. E., DePaolo, D. J., Maher, K., Gee, G. W., Ward, A. L. 2007; 6 (4): 1031-1041

  View details for DOI 10.2136/vzj2007.0007

  View details for Web of Science ID 000252596100032

• Control of chemical weathering rates by secondary mineral precipitation: a reactive transport approach for understanding soil genesis Maher, K., Steefel, C. I., Stonestrom, D. A., White, A. F. PERGAMON-ELSEVIER SCIENCE LTD. 2007: A613

  View details for Web of Science ID 000248789901441

• Th-230-U dating of surficial deposits using the ion microprobe (SHRIMP-RG): A micro stratigraphic perspective Conference on Dating Quaternary Sediments and Landforms in Drylands Maher, K., Wooden, J. L., Paces, J. B., Miller, D. M. PERGAMON-ELSEVIER SCIENCE LTD. 2007: 15–28

  View details for DOI 10.1016/j.quaint.2007.01.003

  View details for Web of Science ID 000247166400003

• U-Sr isotopic speedometer: Fluid flow and chemical weathering rates in aquifers GEOCHIMICA ET COSMOCHIMICA ACTA Maher, K., DePaolo, D. J., Christensen, J. N. 2006; 70 (17): 4417-4435

  View details for DOI 10.1016/j.gca.2006.06.1559

  View details for Web of Science ID 000240601800009

• Sediment transport time measured with U-series isotopes: Results from ODP North Atlantic drift site 984 EARTH AND PLANETARY SCIENCE LETTERS DePaolo, D. J., Maher, K., Christensen, J. N., McManus, J. 2006; 248 (1-2): 394-410

  View details for DOI 10.1016/j.epsl.2006.06.004

  View details for Web of Science ID 000240851400032

• Paleoenvironmental information from U-series measurements of pedogenic opal Maher, K., Redwine, J., Mazdab, F. K., Wooden, J. L. PERGAMON-ELSEVIER SCIENCE LTD. 2006: A384

  View details for DOI 10.1016/j.gca.2006.06.776

  View details for Web of Science ID 000241374201019

• Dissolution rates and vadose zone drainage from strontium isotope measurements of groundwater in the Pasco Basin, WA unconfined aquifer JOURNAL OF HYDROLOGY Singleton, M. J., Maher, K., DePaolo, D. J., Conrad, M. E., Dresel, P. E. 2006; 321 (1-4): 39-58

  View details for DOI 10.1016/j.jhydrol.2005.07.044

  View details for Web of Science ID 000237099500004

• The mineral dissolution rate conundrum: Insights from reactive transport modeling of U isotopes and pore fluid chemistry in marine sediments GEOCHIMICA ET COSMOCHIMICA ACTA Maher, K., Steefel, C. I., DePaolo, D. J., Viani, B. E. 2006; 70 (2): 337-363

  View details for DOI 10.1016/j.gca.2005.09.001

  View details for Web of Science ID 000235124000006

• Rates of silicate dissolution in deep-sea sediment: In situ measurement using U-234/U-238 of pore fluids GEOCHIMICA ET COSMOCHIMICA ACTA Maher, K., DePaolo, D. J., Lin, J. C. 2004; 68 (22): 4629-4648

  View details for DOI 10.1016/j.gca.2004.04.024

  View details for Web of Science ID 000224980000009

• Identifying the sources of subsurface contamination at the Hanford Site in Washington using high-precision uranium isotopic measurements ENVIRONMENTAL SCIENCE & TECHNOLOGY Christensen, J. N., Dresel, P. E., Conrad, M. E., Maher, K., DePaolo, D. J. 2004; 38 (12): 3330-3337

  Abstract

  In the mid-1990s, a groundwater plume of uranium (U) was detected in monitoring wells in the B-BX-BY Waste Management Area at the Hanford Site in Washington. This area has been used since the late 1940s to store high-level radioactive waste and other products of U fuel-rod processing. Using multiple-collector ICP source magnetic sector mass spectrometry, high-precision uranium isotopic analyses were conducted of samples of vadose zone contamination and of groundwater. The isotope ratios 236U/238U, 234U/238U, and 238U/235U are used to distinguish contaminant sources. On the basis of the isotopic data, the source of the groundwater contamination appears to be related to a 1951 overflow event at tank BX-102 that spilled high-level U waste into the vadose zone. The U isotopic variation of the groundwater plume is a result of mixing between contaminant U from this spill and natural background U. Vadose zone U contamination at tank B-110 likely predates the recorded tank leak and can be ruled out as a significant source of groundwater contamination, based on the U isotopic composition. The locus of vadose zone contamination is displaced from the initial locus of groundwater contamination, indicating that lateral migration in the vadose zone was at least 8 times greater than vertical migration. The time evolution of the groundwater plume suggests an average U migration rate of approximately 0.7-0.8 m/day showing slight retardation relative to a groundwater flow of approximately 1 m/day.

  View details for DOI 10.1021/es034700q

  View details for Web of Science ID 000222051400028

  View details for PubMedID 15260332

• Evaporation effects on oxygen and hydrogen isotopes in deep vadose zone pore fluids at Hanford, Washington VADOSE ZONE JOURNAL DePaolo, D. J., Conrad, M. E., Maher, K., Gee, G. W. 2004; 3 (1): 220-232

  View details for Web of Science ID 000227397800019

• Vadose zone infiltration rate at Hanford, Washington, inferred from Sr isotope measurements WATER RESOURCES RESEARCH Maher, K., DePaolo, D. J., Conrad, M. E., Serne, R. J. 2003; 39 (8)

  View details for DOI 10.1029/2002WR001742

  View details for Web of Science ID 000184712400003