August 7, 2012
This past Thursday we finally were able to take the soil samples from our plots on the Deer Valley Trail to USC’s University Park campus and start testing them. This marked the first step in collecting real data from our plots that will go toward our experiment.
Our experiment looks at the effects of invasive plant species on soil health and quality. To measure the overall health of the soil, we need to get accurate reads on the nitrogen, total carbon, and organic carbon in the soil. As stated before, upon removal of invasives from the plots, we hope to see a decrease in nitrogen level. When the health of the soil increases with declining invasives, and with the eventual return of native plants, we hope to see the carbon content in the soil increase.
Before we trekked back to the mainland to analyze our samples, we decided to take more samples to use comparatively with the samples from our plots. To see what a more “healthy” soil profile should look like, we took two samples from beneath two different native plants, Toyon (Heteromeles arbutifolia) and sagebrush (Artemisia californica). Along with these samples, we also samples from each of the three potential sites for our restoration project, to get an idea of soil health in these areas.
Using a geology lab on campus with the help of our professor Dr. Lisa Collins, we weighed approximately 10 mg from each soil sample, and packaged them accordingly to be analyzed by an elemental analysis. To weigh 10 mg, it required a great deal of precision, and quite a few practice runs between the four of us to not spill at all and to keep the samples neat and organized. Soon enough, we were able to measure out the samples so that they could be analyzed.
Above: Intern Judy Fong carefully measures out 10 mg of a soil sample. Photo by Justin Bogda.
The elemental analysis uses standard curves to interpret how much of a substance is in a sample. For total carbon, the 10 mg samples, packaged in small, flexible tin cups, are burned at 900 °C, and reduced to carbon monoxide. This then runs through a mass spectrometer that detects the amount of carbon monoxide released, and this value is compared to a standard curve to detect the amount of carbon in the soil. Similarly, nitrogen gas is read by the mass spectrometer and compared to a standard curve. In order to measure the organic carbon in the soil, we had to measure separately another 10 mg from each sample, and instead put them in small silver cups. In order to just measure organic carbon, rather than total carbon, a small amount of hydrochloric acid is added to the cups. By doing this, calcium carbonate, the main component of the inorganic carbon in the sample, is released from the sample, and only the organic carbon is left.
Above: Soil samples after they have been measure, ready to be analyzed by the elemental analysis. Photo by Justin Bogda.
Within the next week, our first sample results should be complete, and we can finally begin collecting quantitative data for our project.