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
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
Xu, W., Zhu, J. M., Johnson, T. M., Wang, X., Lin, Z. Q., Tan, D., & Qin, H. (2020). Selenium isotope fractionation during adsorption by Fe, Mn and Al oxides. Geochimica et Cosmochimica Acta, 272, 121-136. https://doi.org/10.1016/j.gca.2020.01.001
Jemison, N. E., Shiel, A. E., Johnson, T. M., Lundstrom, C. C., Long, P. E., & Williams, K. H. (2018). Field Application of 238U/235U Measurements to Detect Reoxidation and Mobilization of U(IV). Environmental Science and Technology, 52(6), 3422-3430. https://doi.org/10.1021/acs.est.7b05162
Wang, X., Planavsky, N. J., Hofmann, A., Saupe, E. E., De Corte, B. P., Philippot, P., ... Konhauser, K. O. (2018). A Mesoarchean shift in uranium isotope systematics. Geochimica et Cosmochimica Acta, 238, 438-452. https://doi.org/10.1016/j.gca.2018.07.024
Basu, A., Schilling, K., Brown, S. T., Johnson, T. M., Christensen, J. N., Hartmann, M., ... DePaolo, D. J. (2016). Se Isotopes as Groundwater Redox Indicators: Detecting Natural Attenuation of Se at an in Situ Recovery U Mine. Environmental Science and Technology, 50(20), 10833-10842. https://doi.org/10.1021/acs.est.6b01464