An Integrated Assessment of Geochemical and Community Structure Determinants of Metal Reduction Rates in Subsurface Sediments

Funding

Funding for this project is from the Office of Science of the US Department of Energy.

Summary

Significant advances have been made in the ability to measure the composition of indigenous subsurface microbial communities. However, fundamental questions still persist concerning the interactive effects of geochemistry and community structure on metal reduction rates in the subsurface. Many microorganisms can change the subsurface geochemical conditions (e.g., cause a drop in redox) so metal reduction becomes an energetically favored reaction. Some microbes can directly catalyze the necessary reactions so that metal reduction occurs at a more rapid rate than without microbial activity. Many microorganisms can accomplish the first role but many fewer can accomplish the second. Physical and geochemical factors such as mass transport, oxygen level, and nitrate concentration will likely dominate the rate of microbial change in the redox potential. Thus, it is possible that the importance of community structure at this stage of metal reduction may be minimal. However, the effect of community composition on the rate of metal reduction may be important. We are using controlled laboratory experiment with sediments and groundwater from the SBR Oak Ridge Field Research Center (ORFRC) to compare the effects of manipulations designed to influence community structure (differences in electron donors) to those designed to influence geochemistry (presence of humics as electron shuttles) on uranium reduction. Also, the effect of carbon:phosphate ratios on community structure and uranium reduction rates will be examined in the context of resource-ratio theory to help predict the nutrient supply rates and ratios that maximize uranium reduction at the ORFRC site. In the final stage we will extend the research to other sites where toxic metals and radionuclides are problematic.

Figure 1. Relationships among planned manipulations and anticipated changes in community structure, geochemistry, and uranium reduction rate.

Project Team

This project is a team effort with investigators from:

  • ORNL - A.V. Palumbo,  C. C. Brandt, C. Schadt, J. C. Schryver
  • FSU - J. Kostka
  • UT - S. M. Pfiffner 

Primary responsibility for microcosm setup and operation is shared between ORNL and UT. Primary responsibility for  geochemical measurements is with ORNL. Primary responsibility for microbial measurements is shared between ORNL and FSU.


Figure 2. Microcosms containing FRC site sediment and groundwater with additions of substrates (methanol, ethanol, and glucose) and unamended control.

Microcosms

We are using laboratory microcosms containing sediments and groundwater collected from the Subsurface Biogeochemical Research (SBR) program Oak Ridge Field Research Center (ORFRC) located at Oak Ridge National Laboratory. The ORFRC is contaminated with uranium and has high levels of nitrate and an acidic pH. Sediment samples are homogenized anaerobically prior to use in the microcosms.

SBR Related Links

Project and Related Publications:

Abstracts

Previous Related Publications

  • Palumbo, A. V., J. C. Schryver, M. W. Fields, C. E. Bagwell, J. Z. Zhou, T. Yan, X. Liu, and C. C. Brandt 2004. Coupling of functional gene diversity and geochemical data from environmental samples Applied and Environmental Microbiology. 70:6525-6534.
  • Brandt, C.C., J.C. Schryver, S.M. Pfiffner, A.V. Palumbo, and D.C. White. 1999. Using artificial neural networks to assess changes in microbial communities. pp. 5(4):1-6. In A. Leeson and B. C. Alleman. [eds.]. Bioremediation of metals and inorganic compounds. Proceedings of The Fifth International Symposium on In Situ and On-Site Bioremediation Symposium , San Diego, CA. Battelle Press, Columbus, OH.
  •  Pfiffner, S.M., C.C. Brandt, J.C. Schryver, A.V. Palumbo, and. J.S. Almeida. 1999. Using artificial neural networks to assess microbial communities. pp. 205-212. In G. A. Uzochukwu and G. B. Reddy. [eds.]. Proceedings of the 1998 National Conference on Environmental Remediation Science and Technology. Battelle Press, Columbus, OH.
  • Schryver, J.C., C.C. Brandt, S.M. Pfiffner, A.V. Palumbo, A.D. Peacock, D.C. White, J.P. McKinley, and P.E. Long. In Press. Application of nonlinear analysis methods for identifying relationships between microbial community structure and groundwater geochemistry. Microbial Ecology.

For more information, contact:
Chris W. Schadt (schadtcw@ornl.gov, 865-576-3982)