The Effect of Acid Rain Photosynthesis in Elodea anacharis


Colby Campbell, Mickey Ellenwood, and Tucker Hinchliffe


CU Boulder, Fall 2009


We tested the effects that different pH levels in a solution have on the rates of photosynthesis. This is important because due to pollution in the air, acid rain is becoming a serious problem in more heavily populated area and is affecting the environment. We hypothesized that the concentration of HCl in a solution will determine the rate of photosynthesis.

For our experiment, we made three different solutions of HCl and water to represent three levels of acidity (pH 7, pH 5, pH 3). We placed samples of Elodea anacharis in the solutions and allowed them to acclimate in front of a light lamp for several minutes before collecting data. Since O2 production is an indicator of photosynthesis, we used dissolved oxygen probes to collect data on O2 production in three different trials for each pH. We recorded the data over a 2 minute period and recorded the rate of O2 production for each trial. Since there was a slight decrease in O2 production in the plants placed in the most acidic solution, we predicted that the rate of photosynthesis would be highest in the neutral solution.

            Our results indicated that the rate of photosynthesis was not significantly different between any of the pH levels. Although photosynthesis appeared to be somewhat higher in a neutral solution (mean = -.202 ppm O2/min/g) than in an acidic solution (mean = -.883 ppm O2/min/g), the t-test showed that there was no significant difference (P = 0.093) gave us a P value that was greater than .05 (t = .093).

            The results were inconsistent with our predictions based on our hypothesis. The data we collected may not have been accurate since the results were so different between all the trials. We did not calibrate the instrument before collecting data in our trials. In the future, we could use a different method for measuring the rate of photosynthesis. A similar study by Egle et al. (2005) yielded the same results showing that there were no significant differences in rates of photosynthesis of E. anacharis between the different solutions of HCl. However in their experiment, they transferred the Elodea samples between solutions instead of using different plants in each solution. Yu et al. (2002) found a significant reduction in the rate of photosynthesis in seedless cucumbers affected by acid rain. Hindawi et al. (1980) also ran an experiment that yielded the same result: significant reductions in chlorophyll content as pH decreased. Because other experiments show a significant reduction in the rate of photosynthesis in plants affected by acid rain, we would not change our hypothesis, but we would change our methods. For a modified experiment, we would use a different method for measuring the rate of photosynthesis. Rate of photosynthesis can be determined by measuring the rate of CO2 uptake or by O2 production. Egle et al. measured production of O2 by counting the number of oxygen bubbles released by the Elodea over a period of time.