Comparing pH in Lakes and Ponds

In the Milwaukee Area

Arahseris Cerna

and

Sarah Imp

Alverno College

Abstract

In this research lab, we tested to see if there was a difference in pH in ponds in the Milwaukee area and Lake Michigan. The test was performed all over the Milwaukee area. We choose to look at eight ponds in Milwaukee, and eight different locations on Lake Michigan to test at. There seemed to be a slight difference in the pH of ponds and lakes, with the ponds having a more neutral pH and the lake having a more acidic level. However, the P-value is 0.051779, which indicates the difference is insignificant.

Keywords: pH, acidic, neutral, lake, pond

Introduction

We hypothesized that Lake Michigan will have a lower pH than ponds in the Milwaukee area; based on research about ponds and lakes. We found that most lakes are acidic naturally. The average pH in lakes is between six and eight in the United States (Bronmark and Hansson, 2005). There are several different reasons why lakes are slightly acidic from the precipitation to the amount of vegetation in the water that is performing photosynthesis and cellular respiration.

The importance of pH in water is great since different levels can determine whether or not life can exist. pH measures how acidic, neutral or basic something is. pH of water is the measurement of hydrogen ion concentration. The reason for the correlation of pH with photosynthesis is due to the use of hydrogen molecules. During photosynthesis hydrogen molecules get used up. During this process the concentration of hydrogen ions will decrease which means the pH will increase.

pH can affect organisms negatively when the levels are either too high or too low. If a body of water has a low buffering capacity then a change in pH can cause death in aquatic life. For example “fish have an average blood pH of 7.4” therefore if a body of water had a pH level of about 4.0, this level would be unacceptable and would most likely cause mortality in fish population (Stevens 2009). We also found that photosynthesis and cellular respiration are two processes that can affect pH levels due to the change of carbon dioxide in the water. The process of photosynthesis in the case of aquatic environments is when the vegetation in the body of water uses energy from the sun to convert carbon dioxide into oxygen.

Acid rain is a factor that can negatively affect lakes. If lakes receive too much acid rain, then the lakes’ buffering capacity can eventually reach a certain point where a “small bit of rain” can cause the pH to change which would cause a lake to become more acidic (Michaud 1991).

Materials and Methods

The test performed on October 31^st, 2009 began at 9am until 2:49pm. The ponds we choose to test were Jackson Park pond, McCarthy Park Pond, the pond connected to the Wehr Nature Center, the Witnall Park pond, Arlington Park Cemetery’s pond, Wilson Park pond, Humboldt Park pond, and Kosciuszko Park pond. The eight locations on Lake Michigan was chosen with the starting point in the South Shore Park, we then drove north to the next location, which was chosen haphazardly. The criteria in which we used to pick a location were the ability to access the lake, and at least 0.40 kilometers away from last location.

To test the pH of that water we used pH paper test strips. Once we arrived to a location we chose a spot on the pond or lake that we could access the water. We used a Garmin Nüvi 250, to get the exact coordinates of the test site. We then used the pH test strips to test the pH of the water. We recorded the pH, time, coordinates, and address in a log book. The sample size was eight ponds and eight locations on Lake Michigan. Once we collected all of the data we analyzed the data using Microsoft Office© Excel 2007. A t-test was performed and we got a P-value of 0.051776. With a P-value of 0.5 or higher the data is insignificant, our P-value is slightly higher that this so the results are insignificant.

Results

Figure 1. Comparison of pH in ponds and Lake Michigan in the Milwaukee area.

The data indicated that the pH in Lake Michigan (mean=5.5, S.D.= 0.756) was slightly higher than ponds(Mean=6, S.D. = 0.0) in the area, the P-value shows there is no real difference in the two site types (Fig. 1, P=.051779).

Discussion

Overall, the data shows that there was no significant difference between ponds and lakes in the Milwaukee Area; therefore our hypothesis was not supported. But we had some confounding variables that could have affected our results. One issue was the time of day. We know that at different times in the day plants can carry out photosynthesis differently, so this could affect the pH of the water. We did all of the ponds in the morning, before the noon hour, and the lake closer to noon. Because we collected the data at different times in the day, it is possible that the measurements collected closer to the noon hour had more photosynthesis occurring compared to earlier in the day.

A variable to take into account that potentially affected the pH in both bodies of water is that it had rained a lot the night before. As mentioned earlier acid rain can affect lakes especially by causing the pH to decrease to levels that can be dangerous to aquatic life (Michaud, 1991). For the most part the pH levels of both bodies of water were acceptable in order to sustain aquatic life (Stevens 2009).

If doing this again we would have to find a better way to collect our data so that it is in about the same time frame. This also could have been an interesting experiment to test, the relationship between pH and the time of day. Another confounding variable was that it was sometimes difficult to read the test strips. If we were to conduct this experiment again, it would be helpful to have a more accurate way of collecting the pH, such as a pH meter. This way human error would be eliminated from reading the pH levels.

Resources

Bronmark, Christer, and Lars-Anders Hansson. (2005). The Biology of Lakes and Ponds. 2nd ed. Oxford New York: Oxford University Press

Stevens, Russell. (2009) Fish Pond water quality: As simple as chemistry 101. Retrieved November 8, 2009 from: http://noble.org/AG/Wildlife/Fish-Pond-Water/index.html

Michaud, P. Joy. (1994). A citizens Guide to understanding and monitoring Lakes and Streams. Department of Ecology. Retrieved on November 8, 2009 from: http://ecv.wa.gov/programs/wg/plants/management/jovsmanual/ph.html