Colvin Winner Sara Nason ’12 Examines Impact of CO2 on Metal Concentrations in Plants

Carol Peters ・ High Meadows Environmental Institute

In May 2011, geosciences major Sara Nason ’12, was awarded the Becky Colvin Memorial Award by the Princeton Environmental Institute (PEI) and the Colvin family. During the following summer, the Colvin funds supported the research she conducted – analyzing tree samples from California – at the Brookhaven National Laboratory in Upton New York. Her thesis title is “The Effects of Elevated Soil Carbon Dioxide on Plant Uptake of Metals.” Below, Nason describes her research project, how the Colvin award made such an ambitious project possible, and her plan to continue this type of research in the fall as a graduate student at the University of Wisconsin-Madison.

Please describe your senior thesis project.

One of the ways that humans are trying to combat global warming is by taking carbon dioxide (CO2) out of the atmosphere and putting it underground. Although CO2 has been injected into geological formations for various purposes, the long term storage of CO2 is a relatively new concept. A major concern with this process is whether an earthquake or an improperly sealed well may cause large amounts of stored gas to leak. Since large amounts of carbon dioxide are already being pumped into the ground, it is important to understand what will happen if leaks occur.

From sites like Mammoth Mountain, California, where carbon dioxide is leaking into the soil naturally, scientists have been concerned that excess amounts of soil CO2 may be killing trees and other plants.

My project helped to piece together why the plants die. Knowing this could help create CO2 storage site selection criteria, or simply provide a strong argument against underground CO2 storage altogether.

When excess amounts of CO2 enter the soil, it changes soil chemistry. CO2 dissolves in water to form carbonic acid, lowering the soil pH and changing the solubility of many metals in the soil. Some metals, such as aluminum, can be harmful to plants. My project tested whether or not CO2 has an effect on metal concentrations in certain plants and trees.

The first part of my project dealt with field samples from Mammoth Mountain, California, where an earthquake caused natural CO2 to enter the soil from underground and an area of tree kill has developed. I tested four tree cores from the edge of the tree kill area. I used x-ray spectroscopy at the Brookhaven National Laboratories National Synchrotron Light Source to analyze the length of the tree cores for metal concentrations. This allowed me to construct a record of how the trees’ metal uptake changed over the past 50 years. Because of the funding provided by the Colvin Award, I was able to travel to Brookhaven National Laboratories over the summer to perform my tree core analysis.

Sara Nason’s bean plants, in 12-inch soil cores, were connected to a CO2 flow in the lab. This simulated the CO2 flowing from underground into the soil. Sara controlled the CO2 level in each core to determine the effects of concentration on plant health.

The second part of my project was based in the lab. I grew bean plants in 12 inch soil cores that were connected to a CO2 flow. This simulated the situation of CO2 flowing from underground into the soil. I controlled the CO2 level in each core to determine the effects of concentration on plant health. After the plants were harvested, they were tested for metal concentrations.

In the end, my data did not support my hypothesis that increased CO2 concentrations increased metal poisoning. The lead soil contamination in my bean plant experiment had a large effect on several metal concentrations in the plants (notably iron, sodium, and potassium), but the CO2 levels did not cause an increase in any metal concentrations. In addition, an increase in CO2 did not seem to have affected metal concentrations in the sampled tree cores from Mammoth Mountain.

How did the Colvin Award support your research?

The funding provided by the Colvin award was extremely important to my thesis. Having my own source of money allowed me to go in my own direction and have a project that was independent of what the other people in my adviser’s group were doing. (Satish Myneni, geosciences professor, was my adviser.) The award also enabled me to purchase needed lab equipment. Without the Colvin award, I would not have been able to complete such an ambitious and complicated project.

Did your project change once you began the research?

While I had to make some minor changes to my research plan, the main idea stayed the same. I kept both parts of my project and I pursued the same main question. The big thing that I had to cancel was my field trip to Mammoth Mountain. While it would have been great to be able to collect fresh samples, time constraints just did not allow that to happen. Instead, I worked with samples collected by a freshman seminar class that I was a part of in 2008, called “Earth’s Changing Surface and Climate,” taught by geosciences professors Adam Maloof and Frederick Simons. I have seen the site, and I was there helping to collect the cores so it still felt like I was working with my own samples. I also made a few other changes to fit my project into a year. I grew bean plants instead of using tree saplings and I used potting soil for my lab experiment instead of collecting soil cores from Mammoth Mountain or another field site.

What surprised you the most and what lessons did you learn?

The biggest surprise for me was how difficult it was to get my lab set up to work. I had problems every step of the way – from my supplies getting back ordered, a broken gas tank regulator, frustrating conversations with customer service, and seeds deciding to rot instead of grow. Everything took at least twice as long to complete as I thought it would. I think this is also the biggest lesson I have learned – research is messy and unpredictable, and not always in your control. Even though my thesis was very frustrating, I still enjoyed the process of developing a project and seeing my plans through to completion.

Has this project influenced your plans post graduation?

My experience with my thesis will be extremely valuable as I finalize my plans. I hope to continue researching the relationship between plants and soil metals and contaminants at the University of Wisconsin – Madison, in the Environmental Chemistry and Technology program. From there, I plan to find a research job or go into academia.

What advice would you give this year’s Colvin winner?

My advice to the next Colvin award winner is to choose a project that really interests you because that’s what will keep you working on it, even when everything starts going wrong. Also, give yourself more time than you think you will need.

This is one of two articles covering PEI’s 2011 Colvin Award winners. In addition to Sara Nason, ecology and evolutionary biology major Maddy Case ’12 was also awarded Colvin funds last spring. Both students will graduate with certificates in environmental studies. Case’s research was featured by PEI in April.

The Becky Colvin Award supports summer field research projects following the junior year, in support of the senior thesis. The award was established in 1995 by Dr. and Mrs. Robert Colvin in memory of their daughter, Becky Colvin ’95. Becky was an ecology and evolutionary biology major who was very interested in field research.