Air quality indicators at Lake Merritt, Oakland, California

Dasha Bulatov, Brittany Collins, Jenny Hsiao, Jackson Liang and Anthony Majors

Lake Merritt is significant in its role as both a recreational center for humans, as well as a refuge for migratory wild birds. It is, however, closely surrounded by streets and highways, and even sees a large amount of water traffic by motor-driven boats and pontoons. These two factors contribute to what we suspect is a generally high level of emissions in the atmosphere surrounding the lake. While the harmful components of these emissions can be measured directly using specialized and generally expensive tools, the goal of our research is to explore the use of tree leaves as indicators of air quality. Properties of atmospheric air directly affect the quality of leaves because of plants’ reliance on photosynthesis. In brief, photosynthesis requires the input of sunlight, water, and carbon dioxide to produce oxygen and glucose. The gateways through which many of these inputs and outputs pass are essential to every leaf’s survival and are called stomata. However, water is an exception; since its entry into the plant’s vascular system is through the roots, water generally diffuses outward at stomatal openings rather than inward. Therefore, plants must strike a balance between gaining carbon dioxide and losing water, as well as risk exposure to toxic compounds in the air itself. Primarily, guard cells fulfill this purpose by closing over stomatal openings to conserve water. However, we also believe that over generations of leaves, the absolute number of stomata itself can change to reflect the surrounding environment. That is, increases in carbon dioxide must coincide with higher levels of toxic compounds, which force the number of stomata to decrease over time. Our research examined the relationship between quantitative presence of stomata for several species of trees and the levels of carbon dioxide, oxygen, and wind-speed for ten sites around Lake Merritt. Wind-speed is one of our primary measures because increasing wind velocity leads to water diffusing out of the leaves at a higher rate. Stomata were counted by plating a 0.5 cm2 square of the lower epidermal layer of leaves collected at each of the sites, then examining it through a microscope at 400X. Preliminary data suggests an unexpected direct relationship between carbon dioxide and stomata, although the correlation is not strong � itself suggesting that yet another factor exists. We suspect that wind-speed may be that very factor, though further analysis of our current body of data is required. Overall, the stomata count does indeed seem to reflect properties of the environment.

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