Is the PH of Water Systems Higher in the Evening or in the Morning?
In order to determine if the pH of pond water is higher in the morning or in the evening, we tested the pH levels in eight different park ponds during the morning hours of 0730 and evening hours of 1930 between the dates of October 3rd, 2011 and October 21st 2011. We went to each of the pond sites and took 50 ml of water from five different areas around each of the ponds and waited no more than 30 seconds before comparing the color we saw on the litmus paper to the color levels according to the wide range of pH test paper color scale and recorded our findings. After collecting and comparing the data, we found that on average, the pH levels were significantly higher in the evening hours than in the morning in our study (P=3.95E-09).
In determining whether or not the pH of pond water is higher in the morning or in the evening, we considered a variety of factors. PH is a logarithmic scale that ranges from pH 1, which is very acidic, to pH 14, which is very alkaline or basic. Every unit drop in pH represents an increase in acidity by a base of 10, so pH of 1 is ten times more acidic than pH of 2. Distilled water has a pH of 7, while “normal” rain is slightly acidic due to dissolved CO (West, 1980). Since there was a possibility of us testing the pH of various ponds after or during a period of heavy rain, this was one of the factors we considered in formulating out hypothesis. Another factor that we considered might have an effect on the pH of pond water was the fact that there is vegetation that will be doing photosynthesis throughout the day surrounding each of the ponds (Frazer 2005). After considering these factors, we hypothesized that the pH of the water would rise by nightfall because there will be a larger amount of CO2 in the water in the morning because of the plants doing cellular respiration and releasing CO2 at night and CO2 being taken up by the plants during the day. The CO2 bonds with the water molecules and the pH will be lower in the morning (Witney 1942).
Materials and Methods
Between the dates of October 3rd, 2011 and October 21st, 2011 we took the pH levels of the following eight different park ponds: Greenfield, Holler, Humbolt, Jackson, MaCarty, Saveland, Wilson, and Witnal at 0730 in the morning and 1930 in the evening. For each of the sites we did the following: We began by going to the pond site and recording the time. Then, we would take 50 ml of water from five different locations around each pond and at each of the five locations; we would insert pH litmus paper into the 50 ml of sample water. After waiting no more than 30 seconds we compared the pH color we saw on the litmus paper to the levels according to the wide range of pH test paper color scale and record our findings. Once we had collected all of our samples, we analyzed the data using Microsoft Excel for Windows 2010 to calculate a type 1, 1 tailed t-test.
There was a significant difference in the pH levels taken in our study (P=3.95E-09). We found that on average the pH levels were lower in the morning hours around 0730 am as opposed to the evening hours around 1930 pm which supports our hypothesis.
Figure 1. Average pH of pond water in the morning and evening (P=3.95E-09)
Most of our data were relatively consistent with our hypothesis throughout our study. A factor contributing to the changing levels of pH throughout the day, other than from photosynthesis as stated in our introduction, could be from rain since some of the pH tests we recorded were on days it was raining or had rained the night before. On such days, we often found that there was a lower level of pH that we had recorded in our research. Another factor that we had to take into consideration was the fact that the pH levels that we recorded were our own interpretation of the colors when compared to those of the color scale. It was especially hard to identify the most accurate comparison during the evening hours when it was dark. This could have had an effect on how we perceived color when comparing the color on the litmus paper to that of the color scale; therefore, if we were to do this experiment again we would use a more accurate pH tool such as the pH meter. Something we didn’t take into consideration was the fact that the different algae within each of the ponds each grow at different forms of CO2 and pH levels which could have had a possible affect on the overall pH’s of each of the ponds (Meric and Pokorny 2002). This could be another possible factor we would take into consideration, as well as the pH meter, if we were to do this experiment again. Overall after doing this experiment and learning more about pH, in addition to some of the factors we discussed previously, we agreed that something we would be interested in learning more about is the difference in pH of different aquatic environments after or during heavy rain storms to determine if that factor has a significant effect on water pH.
Frazer, L. (2005). Streamside solution. Environmental Health Perspectives, Vol. 113 (Issue 3), 156. Retrieved September 27, 2011, from EBSCOhost Green File.
Meric, A., Pokorny, J. (2002) Influence of the inorganic carbon addition on photosynthesis of algae and some macrophytes. Turkish Journal of Botany, Vol. 26 (Issue 5), 395-401. Retrieved September 27, 2011, from EBSCOHOST Academic Search Premier.
West, S. (1980). Acid from Heaven. Science News, Vol. 117 (Issue 5), 3. Retrieved October 30, 2011, from Academic Search Premier.
Witney, R. J. (1942). Diurnal fluctuations of oxygen and ph in two small ponds and a stream. Journal of Experimental Biology, May 1942 (Issue 19), 92-99. Retrieved from http://jeb.biologists.org/content/19/1/92.full.pdf+html