About tmjohnsn@illinois.edu

Prof. Johnson's group works on water quality, environmental contaminants, and deep-time environmental history of the earth. They apply the tools of geochemistry, with a focus on isotope geochemistry, in this work.

Lead stable isotope ratios as indicators of soil age and human impacts

Lead (Pb) isotope ratios can often be used to trace sources of Pb in soils and water.   207Pb/206Pb and other Pb isotope ratios differ between the various sources of Pb in the environment.  For example, Pb deposited during the use of Pb gasoline additives often has distinctive Pb isotope ratios that can used to distinguish it from ordinary, naturally occurring Pb in soils.

This project aims to use Pb isotopes to trace the appearance of industrial Pb in soils close to Champaign-Urbana (in the “Critical Zone Observatory”).  The focus is not on Pb contamination; we seek to use the appearance of industrial Pb as an indicator of soil and sediment age- to distinguish pre-1940 soils from more recent ones.

This project involves:

  1. Lab work to implement methods for extracting and purifying Pb from soils and measuring Pb isotope ratios using the Multicollector ICP-MS.
  2. Measuring a series of soils.
  3. Interpreting results using information in the scientific literature regarding Pb isotopes in industrial emissions over time.

This could be either a senior thesis project or an undergraduate research project.

Supervisors:  Dr. David Grimley (ISGS), Prof. Tom Johnson, Dr. Gideon Bartov (Lab Manager)   contact:  tmjohnsn@illinois.edu

Geochemical tracers in archaeology: Preparation of samples from the Cahokia complex

Cahokia Mounds, in southwestern Illinois, was the site of a major “city” from ca. A.D. 1050 to 1350 with an estimated population of 40,000.  It was the largest prehistoric mound center in North America and is considered the center of what archaeologists call the Mississippian culture. Archaeological investigations aim to reveal the diet, health, demography, and biological relationships. The Illinois State Archaeological Survey (ISAS) Cahokia Project is a long-term, multi-disciplinary research project that seeks to identify factors that contributed to the rise and fall of the Cahokian polity.  ISAS is part of the Prairie Research Institute here at the U of I:
http://www.isas.illinois.edu/

This project will contribute to an effort that uses geochemical analyses (mainly stable isotope measurements) of both recently excavated and museum-derived human and animal remains from Cahokia and related regions, to offer new information on the health, diet, geographic origins, and genetic relationships of individuals living in, and interacting with, Cahokia.  See more about the Cahokia project at:
http://www.isas.illinois.edu/transportation_research/totc.shtml

This research project will involve working with ISAS archaeologists to extract small samples of teeth and bone using micro-drilling techniques, and prepare them for geochemical analyses.  The prepared samples will then be analyzed for carbon and strontium isotope ratios and, possibly, other geochemical variables.  The project will involve some training in these methods and ability to take part in analysis of samples.  The strontium isotope analyses are carried out in the Dept. of Geology geochemical laboratory; the carbon isotope analyses are done at the Illinois State Geological Survey.

Advisors:  
Dr. Kris Hedman, Assistant Director, Program on Ancient Technologies and Archaeological Materials, Illinois State Archaeological Survey (khedman@illinois.edu)
Dr. Tom Johnson, Professor of Geology (tmjohnsn@illinois.edu)