Environmental Transformations and Interactions Science Area Lead
Environmental Transformations and Interactions Science Area Lead

Biography

Dr. John Bargar is the Environmental Transformations and Interactions Science Area group leader at the Environmental Molecular Sciences Laboratory (EMSL), a Department of Energy (DOE), Office of Science user facility located at the Pacific Northwest National Laboratory (PNNL). His research interests focus on understanding and modeling biogeochemical processes across scales, from molecular to continental. He has extensive experience leveraging community science to generate molecular data at unprecedented scale to transform our understanding and prediction of Earth Systems.

For more than 28 years, Bargar has led projects focused on basic and applied energy research. Before joining PNNL in 2022, Bargar led the SLAC National Accelerator Laboratory geosciences program, including the DOE-Biological and Environmental Research-funded Floodplain Hydro-Biogeochemistry Sciences Focus Area (SFA), a SLAC-led multi-laboratory synchrotron nuclear forensics research program, and the SLAC deep subsurface geochemistry project program.

Bargar’s work on the behavior of essential metal micronutrients and contaminants in soils and natural waters has improved our understanding and prediction of metal behavior in soils and groundwater. At systems scales, his research has focused on understanding how, where, and when molecular reactions occur and interact across larger distances, from floodplains to regions. Bargar’s SFA team’s work demonstrated that soil organic matter controls uranium accumulation and release in shallow sediments across the upper Colorado River Basin. This behavior is significant because it moderates the dissolved concentrations of persistent regional uranium groundwater contamination. Similarly, Bargar’s deep subsurface team’s work on hydraulically stimulated unconventional reservoirs provided critical new insights and modeling tools to understand geochemical reaction networks and predict the impact of fluid additives on fracture permeability and water quality. At PNNL, Bargar has led the launch of the Molecular Observation Network (MONet), a community science activity within EMSL’s user program. MONet is generating high-volume, high-quality, AI-ready molecular data on biogeochemical and atmospheric processes at continental scale across the U.S.

Bargar has participated as a reviewer for numerous geochemistry, hydrology, and chemistry journals, has chaired and organized numerous committees and symposia, and has been published in more than 195 scholarly articles.

Research Interests

  • Soil molecular processes across molecular to pore to field scales
  • Biogeochemistry, genesis, and transport of natural colloids
  • Metal micronutrient and contaminant biogeochemistry and reactive transport in soils
  • Water–rock interactions

Education

  • PhD in Geology, The Ohio State University
  • BS in Geological and Environmental Sciences, Stanford University
  • National Research Council Postdoctoral Fellowship, U.S. Geological Survey
  • SLAC Managerial Skill Development Series

Publications

2025

  • Shi C., M. Mudunuru, M.M. Bowman, Q. Zhao, J.G. Toyoda, W.R. Kew, and Y. Eberlim de Corilo, et al. 2025. "Scaling High-resolution Soil Organic Matter Composition to Improve Predictions of Potential Soil Respiration Across the Continental United States." Geophysical Research Letters 52, no. 4:Art. No. e2024GL113091. PNNL-SA-199762. doi:10.1029/2024GL113091

2024

  • Babey T., Z. Perzan, S. Pierce, B. Rogers, L. Wang, R. Carroll, and J.R. Bargar, et al. 2024. "Mountainous Floodplain Connectivity in Response to Hydrological Transitions." Water Resources Research 60, no. 7:e2024WR037162. PNNL-SA-200026. doi:10.1029/2024WR037162

2023

  • Bowman M.M., A.E. Heath, T. Varga, A. Battu, R.K. Chu, J.G. Toyoda, and T. Cheeke, et al. 2023. "One thousand soils for molecular understanding of belowground carbon cycling." Frontiers in Soil Science 3. PNNL-SA-183617. doi:10.3389/fsoil.2023.1120425
  • Engel M., V. Noel, S. Pierce, L. Kovarik, R.K. Kukkadapu, J.S. Lezama Pacheco, and O. Qafoku, et al. 2023. "Structure and composition of natural ferrihydrite nano-colloids in anoxic groundwater." Water Research 238. PNNL-SA-181172. doi:10.1016/j.watres.2023.119990

2022

  • Engel M., V. Noel, R.K. Kukkadapu, K.E. Boye, J.R. Bargar, and S. Fendorf. 2022. "Nitrate controls on the extent and type of metal retention in fine-grained sediments of a simulated aquifer." Environmental Science & Technology 56, no. 20:14452-14461. PNNL-SA-172685. doi:10.1021/acs.est.2c03403

2017

  • Noel V., K.E. Boye, R.K. Kukkadapu, S.E. Bone, J.S. Lezama Pacheco, E. Cardarelli, and N. Janot, et al. 2017. "Understanding the controls on redox processes in floodplain sediments of the Upper Colorado River Basin." Science of the Total Environment 603-604. PNNL-SA-121839. doi:10.1016/j.scitotenv.2017.01.109
  • Stubbs J., C.A. Biwer, A.M. Chaka, E.S. Ilton, Y. Du, J. Bargar, and P. Eng. 2017. "Oxidative Corrosion of the UO2 (001) Surface by Nonclassical Diffusion." Langmuir 33, no. 46:13189-13196. PNNL-SA-130086. doi:10.1021/acs.langmuir.7b02800