Brian Stewart

Associate Professor


Brian Stewart
413 SRCC
4107 O'Hara Street
Pittsburgh, PA 15260


Dr. Stewart received his B.S. in Geology from Brown University and Ph.D. in Geochemistry from UCLA, with a focus on magma chamber processes.  After postdoctoral work on meteorite petrogenesis at Caltech and soil cation cycling at UC Riverside, he joined the Pitt faculty in 1994.  Since that time he has studied geologic and environmental processes using radiogenic and metal isotope systems as tracers. Dr. Stewart served as Department Chair from 2005 to 2008.


  • Research
  • Publications
  • Laboratory Members
  • Teaching

Our group’s research is directed toward understanding geochemical processes in earth and environmental systems.  We approach these problems by using radiogenic and metal stable isotopes as geochronological tools and as tracers for natural physical and chemical processes occurring on all scales.  Our scientific investigations involve field work, high-precision isotopic and geochemical analyses of rock, water and other environmental samples, laboratory experiments, numerical modeling of physical and chemical processes, and geologic interpretation.  Examples of ongoing studies include: (1) development of new isotope tools to determine the origin and fate deep, saline groundwaters from the deep levels of the critical zone; (2) geochemical studies of acidic mine drainage to understand its origin and evolution, and to develop remediation strategies; (3) determining the provenance of soil cations and dust in climate conditions ranging from rain forest to hyperarid; and (4) quantifying contributions of weathering and hydrothermal activity to element fluxes at the watershed scale.

Research Areas

Matecha, R.M., Xiong, W., Heck, W.F., Stewart, B.W., Capo, R.C., Hakala, J.A. (2022) Experimental investigation of barium sources and fluid-rock interaction in unconventional Marcellus Shale wells using Ba isotopes. Energy & Fuels 36, 4470-4478.

Stewart, B.W. and Capo, R.C. (2022) Chapter 10: Metal isotope signatures as tracers for unconventional oil and gas fluids. In Environmental Impacts from the Development of Unconventional Oil and Gas Reserves (eds. J. Stolz, D. Bain, M. Griffin), Cambridge University Press, pp. 246-271; doi:10.1017/9781108774178.013.

Matecha, R.M., Capo, R.C., Stewart, B.W., Thompson, R.L., Hakala, J.A. (2021) A single column separation method for barium isotope analysis of geologic and hydrologic materials with complex matrices. Geochemical Transactions 22:4,

Gardiner, J.B., Capo, R.C., Newell, D.L., Stewart, B.W., Phan, T.T., Keating, E.H., Guthrie, G.D., Hakala, J.A. (2021) Tracking natural CO2 migration through a sandstone aquifer using Sr, U and C isotopes: Chimayó, New Mexico, USA. International Journal of Greenhouse Gas Control 104, 103209.

Hedin, B.C., Hedin, R.S., Capo, R.C., Stewart, B.W. (2020) Critical metal recovery potential of Appalachian acid mine drainage treatment solids. International Journal of Coal Geology 231, 103610.

Tieman, Z.G., Stewart, B.W., Capo, R.C., Phan, T.T., Lopano, C.L., Hakala, J.A. (2020) Barium isotopes track the source of dissolved solids in produced water from the unconventional Marcellus Shale gas play. Environmental Science & Technology 54, 4275-4285.

Wallrich, I.L.R., Stewart, B.W., Capo, R.C., Hedin, B.C., Phan, T.T. (2020) Neodymium isotopes track sources of rare earth elements in acidic mine waters. Geochimica et Cosmochimica Acta 269, 465-483.

Mackey, J.E., Stewart, B.W. (2019) Evidence of anoxia in Late Cambrian Ocean: Paired δ13C and trace element chemostratigraphy of upper Conasauga Group, Central Appalachian Basin. Palaeogeography, Palaeoclimatology, Palaeoecology 528, 160-174.

Hedin, B.C., Capo, R.C., Stewart, B.W., Hedin, R.S., Lopano, C.L., Stuckman, M.Y. (2019) The evaluation of critical rare earth element (REE) enriched treatment solids from coal mine drainage passive treatment systems. International Journal of Coal Geology 208, 54-64.

Phan, T.T., Gardiner, J.B., Capo, R.C., Stewart, B.W. (2018) Geochemical and multi-isotopic (87Sr/86Sr, 143Nd/144Nd, 238U/235U) perspectives of sediment sources, depositional conditions, and diagenesis of the Marcellus Shale, Appalachian Basin, USA. Geochimica et Cosmochimica Acta 222, 187-211.

Pfister, S., Capo, R.C., Stewart, B.W., Macpherson, G.L., Phan, T.T., Gardiner, J.B., Diehl, J.R., Lopano, C.L., Hakala, J.A. (2017) Geochemical and lithium isotope tracking of dissolved solid sources in Permian Basin carbonate reservoir and overlying aquifer waters at an enhanced oil recovery site, northwest Texas, USA. Applied Geochemistry 87, 122-135.

Stewart, B.W., Capo, R.C., Hedin, B.C., Hedin, R.S. (2017) Rare earth element resources in coal mine drainage and treatment precipitates in the Appalachian Basin, USA. International Journal of Coal Geology 169, 28-39.

Wolfe, A.L., Stewart, B.W., Capo, R.C., Dzombak, D.A., Liu, R., Gordon, G., Anbar, A.D. (2016) Iron isotope investigation of hydrothermal and sedimentary pyrite and their aqueous dissolution products. Chemical Geology 427, 73-82.

Phan, T.T., Capo, R.C., Stewart, B.W., Macpherson, G.L., Rowan, E.L., Hammack R.W. (2016) Factors controlling Li concentration and isotopic composition in formation waters and host rocks of Marcellus Shale, Appalachian Basin. Chemical Geology 420, 162-179.

Macpherson, G.L., Phan, T.T., Stewart, B.W. (2015) Direct determination (without chromatographic separation) of lithium isotopes in saline fluids using MC-ICPMS:  establishing limits on water chemistry. Journal of Analytical Atomic Spectroscopy 30, 1673-1678.

Phan, T.T., Capo, R.C., Stewart, B.W., Graney, J.R., Johnson, J.D., Sharma, S., Toro, J. (2015) Trace metal distribution and mobility in drill cuttings and produced waters from Marcellus shale gas extraction: uranium, arsenic, barium. Applied Geochemistry 60, 89-103.

Stewart, B.W., Chapman, E.C., Capo, R.C., Johnson, J., Graney, J., Kirby, C.S., Schroeder, K.T. (2015) Origin of brines, salts and carbonate from shales of the Marcellus Formation: Evidence from geochemical and Sr isotope study of sequentially extracted fluids. Applied Geochemistry 60, 78-88.

Johnson, J.D., Graney, J.R., Capo, R.C., Stewart, B.W. (2015) Identification and quantification of regional brine and road salt sources in watersheds along the New York/Pennsylvania border, U.S.A. Applied Geochemistry 60, 37-50.

Newell, D.L., Perkins, G., Larson, T., Pugh, J.D., Stewart, B.W., Capo, R.C., and Trautz, R. (2014) Tracing CO2 leakage into groundwater using carbon and strontium isotopes during a controlled CO2 release field test. International Journal of Greenhouse Gas Control 29, 200-208.

Kolesar Kohl, C.A., Capo, R.C., Stewart, B.W., Wall, A.J., Schroeder, K.T., Hammack, R.W., Guthrie, G.D. (2014) Strontium isotopes test long-term zonal isolation of injected and Marcellus Formation water after hydraulic fracturing. Environmental Science & Technology 48, 9867-9873.

Macpherson, G.L., Capo, R.C., Stewart, B.W., Phan, T.T., Schroeder, K.T., Hammack, R.W. (2014) Temperature-dependent Li isotope ratios in Appalachian Plateau and Gulf Coast Sedimentary Basin saline water. Geofluids 14, 419-429.

Capo, R.C., Stewart, B.W., Rowan, E.L., Kolesar, C.A., Wall, A.J., Chapman, E.C., Hammack, R.W., Schroeder, K.T. (2014) The strontium isotopic evolution of Marcellus Formation produced waters, southwestern Pennsylvania. International Journal of Coal Geology 126, 57-63.

Soeder, D.J., Sharma, S., Pekney, N., Hopkinson, L., Dilmore, R., Kutchko, B.G., Stewart, B.W., Carter, C., Hakala, J.A., Capo, R.C. (2014) An approach for assessing engineering risk from shale gas wells in the United States. International Journal of Coal Geology 126, 4-19.

Wall, A.J., Capo, R.C., Stewart, B.W., Phan, T.T., Jain, J.C., Hakala, J.A., Guthrie, G.D. (2013) High throughput method for Sr extraction from variable matrix waters and 87Sr/86Sr isotope analysis by MC-ICP-MS. Journal of Analytical Atomic Spectrometry 28, 1338-1344.

Brubaker, T.M., Stewart, B.W., Capo, R.C., Schroeder, K.T., Chapman, E.C., Spivak-Birndorf, L.J., Vesper, D.J., Cardone, C.R., Rohar, P.C. (2013) Coal fly ash interaction with environmental fluids: Geochemical and strontium isotope results from combined column and batch leaching experiments. Applied Geochemistry 32, 184-194.

Chapman, E.C., Capo, R.C., Stewart, B.W., Hedin, R.S., Weaver, T.J., Edenborn, H.M. (2013) Strontium isotope quantification of siderite, brine, and acid mine drainage contributions to abandoned gas well discharges in the Appalachian Plateau. Applied Geochemistry 31, 109-118.

Amundson, R., Dietrich, W., Bellugi, D., Ewing, S., Nishiizumi, K., Chong, G., Owen, J., Finkel, R., Heimsath, A., Stewart, B., and Caffee, M. (2012) Geomorphologic evidence for the late Pliocene onset of hyperaridity in the Atacama Desert. Geological Society of America Bulletin 124, 1048-1070.

Schatzel, S.J. and Stewart, B.W. (2012) A provenance study of mineral matter in coal from Appalachian Basin coal mining regions and implications regarding the respirable health of underground coal workers: A geochemical and Nd isotope investigation. International Journal of Coal Geology 94, 123-136.

Chapman, E.C., Capo, R.C., Stewart, B.W., Kirby, C.S., Hammack, R.W., Schroeder, K.T., Edenborn, H.M. (2012) Geochemical and strontium isotope characterization of produced waters from Marcellus Shale natural gas extraction. Environmental Science & Technology 46, 3545-3553.

Spivak-Birndorf, L.J., Stewart, B.W., Capo,  R.C., Chapman, E.C., Schroeder, K.T., Brubaker, T.M. (2012) Strontium isotope study of coal utilization byproducts interacting with environmental waters. Journal of Environmental Quality 41, 144-154.

Hamel, B.L., Stewart, B.W. and Kim, A.G. (2010) Tracing the interaction of acid mine drainage with coal utilization byproducts in a grouted mine: Strontium isotope study of the inactive Omega Coal Mine, West Virginia (USA). Applied Geochemistry 25, 212-223.

Liu, R., Wolfe, A.L., Dzombak, D.A., Horwitz, C.P., Stewart, B.W., and Capo, R.C. (2009) Controlled electrochemical dissolution of hydrothermal and sedimentary pyrite. Applied Geochemistry 24, 836-842.

Cole, R.B. and Stewart, B.W. (2009) Continental margin volcanism at sites of spreading ridge subduction:  Examples from southern Alaska and western California. Tectonophysics 464, 118-136.

Liu, R., Wolfe, A.L., Dzombak, D.A., Horwitz, C.P., Stewart, B.W., and Capo, R.C. (2008) Electrochemical study of hydrothermal and sedimentary pyrite dissolution. Applied Geochemistry 23, 2724-2734.

Liu, R. Wolfe, A.L., Dzombak, D.A., Stewart, B.W., and Capo, R.C. (2008). Comparison of dissolution under oxic acid drainage conditions for eight sedimentary and hydrothermal pyrite samples.  Environmental Geology 56, 171-182.

Ewing, S., Yang, W., DePaolo, D.J., Michalski, G., Kendall, C., Stewart, B.W., Thiemens, M. and Amundson, R. (2008) Non-biological fractionation of stable Ca isotopes in soils of the Atacama Desert, Chile. Geochimica et Cosmochimica Acta 72, 1096-1110.

Wolfe, A.L., Liu, R., Stewart, B.W., Capo, R.C. and Dzombak, D.A. (2007) A method for generating uniform size-segregated pyrite particle fractions, Geochemical Transactions 8:9 doi:10.1186/1467-4866-8-9; 8p.

Watanabe, Y., Stewart, B.W. and Ohmoto, H. (2004) Organic- and carbonate-rich soil formation ~2.6 billion years ago at Schagen, East Transvaal district, South Africa. Geochimica et Cosmochimica Acta 68, 2129-2151.

Doran, P.T., Clifford, S.M.,  Forman, S.L., Nyquist, L., Papanastassiou, D.A., Stewart, B.W., Sturchio, N.C., Swindle, T.D., Cerling, T., Kargel, J., McDonald, G., Nishiizumi, K., Poreda, R., Rice, J. & Tanaka, K. (2004) Mars chronology:  assessing techniques for  quantifying surface processes. Earth Science Reviews 67, 313-337.

Schatzel, S.J. and Stewart, B.W. (2003) Rare earth element sources and modification in the Lower Kittanning coal bed, Pennsylvania:  implications for the origin of coal mineral matter and rare earth element exposure in underground mines. International Journal of Coal Geology 54, 223-251.

Pretti, V.A. and Stewart, B.W. (2002) Solute sources and chemical weathering in the Owens Lake watershed, eastern California. Water Resources Research 38, 2.1-2.18, doi:10.1029/2001WR000370.

Stewart, B.W., Capo, R.C., and Chadwick, O.A. (2001) Effects of rainfall on weathering rate, base cation provenance, and Sr isotope composition of Hawaiian soils. Geochimica et Cosmochimica Acta 65, 1087-1099.

Whipkey, C.E., Capo, R.C., Chadwick, O.A., and Stewart, B.W. (2000) The importance of sea spray to the cation budget of a coastal Hawaiian soil: a strontium isotope approach. Chemical Geology 168, 37-48.

Stewart, B.W., Capo, R.C. and Chadwick, O.A. (1998) Quantitative strontium isotope models for weathering, pedogenesis and biogeochemical cycling.  Geoderma 82, 173-195.

Capo, R.C., Stewart, B.W. and Chadwick, O.A. (1998) Strontium isotopes as a tracer of earth surface processes: Theory and methods.  Geoderma 82, 197-225.

Stewart, B.W., Papanastassiou, D.A. and Wasserburg, G.J. (1996) Sm-Nd systematics of a silicate inclusion from the Caddo IAB iron meteorite.  Earth and Planetary Science Letters 143, 1-12.

Stewart, B.W. and DePaolo, D.J. (1996) Isotopic studies of processes in mafic magma chambers: III.  The Muskox intrusion, Northwest Territories, Canada. In S.R. Hart and A.R. Basu, eds., Earth Processes:  Reading the Isotopic Code. Geophysical Monograph 95.  New York, American Geophysical Union, 277-292.

Stewart, B.W., Papanastassiou, D.A. and Wasserburg, G.J. (1994) Sm-Nd chronology and petrogenesis of mesosiderites. Geochimica et Cosmochimica Acta 58, 3487-3509.

Stewart, B.W. and DePaolo, D.J. (1992) Diffusive isotopic contamination of mafic magma by coexisting silicic liquid in the Muskox intrusion.  Science 255, 708-711.

Stewart, B.W. and DePaolo, D.J. (1990) Isotopic studies of processes in mafic magma chambers: II.  The Skaergaard intrusion, East Greenland.  Contributions to Mineralogy and Petrology 104, 125-141.

GEOL 0800 Geology           

General introduction to geology for non-majors and majors with no previous geology course; covers all fields of geology, emphasizing the major geodynamic processes that shape the Earth’s surface and interior, and the coevolution of life and the Earth’s surface/ocean/atmosphere.  One hour of recitation each week designed to give students hands-on activities in small groups with teaching assistants.

Offered every Spring Term.  Lecture, 2 hours; recitation, 1 hour

GEOL 1001 Mineralogy

Introduction to mineral structures, chemistry, petrogenesis, and analytical techniques, including optical microscopy.  Intensive laboratory section (with teaching assistant) introduces students to identification of minerals and interpretation of micro- and macroscopic structures using the petrographic microscope.

Offered every Fall Term.  Lecture, 3 hours; laboratory, 3 hours

GEOL 1003 Igneous and Metamorphic Petrology

Petrogenesis of igneous and metamorphic rocks for Geology majors; overview of theory and tectonic environment for the major igneous/metamorphic rock types; phase diagrams, fractional crystallization, partial melting, mineral reactions.  Intensive laboratory section (with teaching assistant) on interpretation of hand samples and this sections using the petrographic microscope.

Offered every Spring Term.  Lecture, 3 hours; laboratory, 3 hours

GEOL 2520 Radiogenic Isotope Geochemistry and Geochronology

Fundamentals of isotope geology including nucleosynthesis, geochronology, and the use of radiogenic and stable isotopes as tracers for a variety of geological, biological, planetary, and environmental systems.  Student homework problem sets, term papers, and oral presentations.

Offered Fall Term on alternate years; Lecture, 3 hours

GEOL 3908, 3953  Topics in Geology, Topics in Geochemistry

Courses focused on a range of topics of interest to students and the research community.  Recent topics include shale gas exploration, the application of metal stable isotopes, geochemical tracers for weathering, and the evolution of Earth’s earliest atmosphere. .  Combination of lectures, readings, and student-led discussions.

Offered Fall Term on alternate years; Lecture, 3 hours