Prof. Johnson's group focuses on environmental geochemistry, isotope geochemistry, and hydrogeology. The group is working to better understand several redox-sensitive contaminant elements, including chromium, selenium, uranium, and mercury. They develop and use methods for measurement of the stable isotopes of these and other elements as indicators of key geochemical reactions, contamination sources, and past environments on Earth.
The group uses the department's multicollector ICP-MS laboratory constantly to make these measurements and often develops or improves measurement methods.
Ph.D., University of California at Berkeley
- GEOL 117: The Oceans
- GEOL 118: Natural Disasters
- GEOL 370/GEOG 370/ESE 320: Water Planet/Water Crisis
- GEOL 470: Hydrogeology
- GEOL 562: Isotope Geochemistry
- GEOL 579: Isotope Hydrogeology
Wang, X., & Johnson, T. M. (2021). Factors Affecting the Robustness of Data Inversion for Stable Isotope Measurement Using the Double Spike Method: Insights from Chromium Isotope Analysis. Analytical Chemistry, 93(20), 7449-7455. https://doi.org/10.1021/acs.analchem.1c00434
Wang, Y., Bartov, G., Wang, T., Reinfelder, J. R., Johnson, T. M., & Yee, N. (Accepted/In press). Rapid Attainment of Isotopic Equilibrium after Mercury Reduction by Ferrous Iron Minerals and Isotopic Exchange between Hg(II) and Hg(0). ACS Earth and Space Chemistry. https://doi.org/10.1021/acsearthspacechem.1c00026
Wasserman, N. L., Schilling, K., Johnson, T. M., & Pallud, C. (2021). Selenium Isotope Shifts during the Oxidation of Selenide-Bearing Minerals. ACS Earth and Space Chemistry, 5(5), 1140-1149. https://doi.org/10.1021/acsearthspacechem.1c00036
Basu, A., Wanner, C., Johnson, T. M., Lundstrom, C. C., Sanford, R. A., Sonnenthal, E. L., Boyanov, M. I., & Kemner, K. M. (2020). Microbial U Isotope Fractionation Depends on the U(VI) Reduction Rate. Environmental Science and Technology, 54(4), 2295-2303. https://doi.org/10.1021/acs.est.9b05935
Jemison, N. E., Bizjack, M. T., Johnson, T. M., & Druhan, J. L. (2020). Influence of physical and chemical hydrology on bioremediation of a U-contaminated aquifer informed by reactive transport modeling incorporating 238U/235U ratios. Geochimica et Cosmochimica Acta, 269, 303-328. https://doi.org/10.1016/j.gca.2019.10.031