S. Aaron Ross and Dr. Nolan F. Mangelson, Chemistry and Biochemistry
Lichens are a symbiotic relationship between a fungus and an alga. They have no root system, so although they grow off rocks and trees, they need to gather their nutrients from the air. Their great dependence on the atmosphere makes them very susceptible to changes in the air. For instance, a high ambient level of pollution particulates could cause the lichens to collect an increased amount of those particles. Because of this sensitivity to the environment, lichens have become a focus point of scientists to determine ambient pollution levels.1
At Brigham Young University, Dr. Larry St. Clair and associates have collected lichens for many years. In recent years over 210 lichens have been analyzed for trace elements using PIXE (Proton Induced X-ray Emissions) analysis. The proton accelerator is located in the underground lab, north of the Eyring Science Center. By bombarding the lichen material with protons, the elements in the lichen give off characteristic x-rays. These x-rays can be detected and analyzed to determine the elemental composition of the lichen.
For each of the over 210 lichens analyzed, 20 elements have been detected and documented. The lichen data set includes over 20 species and two growth forms. The lichens come from 15 different federal sites in the Rocky Mountain states. The sites range from Canada to Mexico.
I began this project by preparing the data from the lichen set to be read by the statistics department. This required not only reformatting of the data, but various decision calls on values that were reported as too low for the analysis to be accurate. I then gave the data to the statistics department who ran a multivariate factor analysis program on it that is similar to one used by a research group in Portugal.2
This program allowed all of the lichens to be graphed in ways that would group similar lichen compositions together. Then, the task of interpreting the values began. The attempt to translate the statistical data into physical meaning was the most difficult aspect of my project, and I was aided by Dr. Mangelson, Dr. Reese, Dr. St. Clair, and Brett Clark.
The groupings of the lichens displayed several preliminary characteristics. First, preliminary factor analysis of the lichen element data showed that the lichens separated into two groups identified as the growth forms. There were two growth forms included in this research: foliose, a flat lichen that attaches to hard surfaces like rocks; and fruticose an elongated lichen that hangs from a point on a hard surface like tree bark. B. M. Clark et. al., have already reported large differences in the content of iron and titanium between the two growth forms.3
Second, we needed to know if the lichens from one site differ statistically from lichens of another site. Preliminary data from Clark et. all indicated that there is a modest separation of lichens by site, and the graphs produced from my experiment supported that find.
Third, tentative connections between site conditions and lichen compositions have been made. These comparisons may help determine if lichens can be reliably used as pollution monitors.
Many problems arose during this project. After having run the data set through the computer, we realized we had improperly calculated some composition values. Also, many of the values were below the limit of detection for the PIXE analyzer; therefore, we need to decide whether to change these values to a low concentration or to zero. Of course there were numerous problems inherent in analyzing such a complex system, and the connections made from the graphs need to be further proved through more data and more analysis.
While I was completing this project, I continued to aid the research group in enlarging the data set. I participated in the enlargement of the data set in three ways. First, I prepared the lichens for PIXE analysis by preparing sample targets. Second, I ran a spectral analysis program called “GUPIX” on the PIXE data, which translates numerical x-ray data to elemental concentrations. Third, I trained a new laboratory assistant to continue these procedures.
Another run on the data set is almost ready, and will more accurately help us to determine how the lichens differ. It is hoped that the data will show that the lichens’ compositions differ depending on the pollution levels of the area.4
- Ahmadjian, Vernon, The lichen symbiosis. John Wiley & Sons, New York, New York, 1993, pp. 142-3.
- Reis, M. A., L. C. Alves, H. Th. Wolterbeek, T. Verburg, M. C. Freitas, and A. Gouveia, Main atmospheric heavy metal sources in Portugal by biomonitor analysis. Nuclear Instruments and Methods in Physics Research B, 109 (1996) 493.
- Clark, B. M., N. F. Mangelson, L. L. St. Clair, K. T. Anderson, and L. B. Rees, Analysis of rocky mountain lichens using PIXE: Characteristics of iron and titanium. Application of Accelerators in Research and Industry: Proceedings of the Fourteenth International Conference, 1 (1996) 561.
- Project made possible by Dr. St. Clair, Dr. Larry Reese, Dr. Mangelson, and Brett Clark.