pH Differences in Pond versus Lake

Samantha Teichmiller

Sara Hernández

Jamie deRuiter

Alverno College





Pond versus Lake pH Differences


            In this lab we tested the pH levels in the pond at Washington Park and at Lake Michigan both located in Milwaukee, Wisconsin.  We hypothesized that the pH levels would be lower in a pond than in a lake; due to it having more vegetation in or near the water.  To test the pH levels we used wide range pH test strips for each location.  Our results showed that in the pond at Washington Park the pH level was 7 and in Lake Michigan the pH varied between 4 and 7.  The P value of Lake Michigan and the pond was 3.55447x10^-5 in the morning and at night the two was 0.0003.  From this information we can conclude that our hypothesis was not supported; this is because Lake Michigan had lower pH than in the pond at Washington Park.


            In lakes the water acidity is measured by pH and pH plays an important part in the carbonate system.  The carbonate system consists of carbon dioxide, carbonic acid, water, bicarbonate and carbonate ions that are in balance and oppose the pH changes in the water.  pH measures the amount of hydrogen ions there are in the water.  This means that when there are more hydrogen ions the water has a lower pH and is more acidic.  A neutral pH is 7, in the water would mean that there is the same quantity of hydroxide ions and hydrogen ions (Shaw et al., 2004). 

Waters that have lower pH levels are more acidic and have increased hydrogen ions.  This is compared to those lakes that have higher pH levels, where the hydrogen ions are decreased.  Lower pH levels in an area may indicate a decrease in plant life; this is because increased acidity.  This is because pH affects the amount of nutrient availability.  There will normally be a higher concentration of hydrogen ions in the water when there are increased amounts of plant life.  When there is a decreased amount of plant life in a given area, the pH levels would show that there is an increased amount of hydrogen ions (Chamier, 1987).  When the water content is more acidic, with lower pH levels, there will be higher carbon dioxide concentration. 

Photosynthesis is critical for the life of the plant and its ecosystem.  Photosynthesis is a chemical reaction in plants that uses light from the sun as energy, water, carbon dioxide, and chlorophyll to make the necessary carbohydrates it needs to survive, the plant then gives off oxygen (Shaw et al. 2004).  During the day photosynthesis produces higher oxygen levels and at night the oxygen levels decrease and carbon dioxide levels are higher.  This is because at night oxygen is being used in cellular respiration which is a reaction independent of light. Therefore, photosynthesis only occurs during the day because it uses light as energy.

pH levels in water are influenced by the amount of plants, the more there are the more carbon dioxide that is taken in and the more oxygen is released.  This ultimately decreases the acidity of the water.  When there is a decrease of plant life the carbon dioxide levels would increase and in the water the acidity levels would also increase (Whitney, 1942).  Therefore, we hypothesized that because there is more vegetation by the pond than by the lake that the pH levels will be lower in the pond in comparison to the lake due to photosynthesis of the nearby vegetation by the lake.

Materials and Methods

We used wide range of pH test paper along with a Taylor thermometer with an attached wire probe to measure the temperature of the air along with the pH of water a pond and Lake Michigan.  We started running our test on October 17, 2008 and ran them for seven days ending on October 23, 2008.  One of us went out to Lake Michigan by the South Shore Park and started at the same point every day, by the boat landing farthest south and took the pH of water there.  Then she walked ten steps and took the pH of the water again.  This was continued for 8 tests and this was done twice daily at 8 am and 8 pm for one week.  The temperature of the air was also measured at the eighth pH test each time.  Another one of us went to a pond in Milwaukee located at Washington Park and did the same tests.  At this site, due to the instability of banks around the pond, the tester was only able to test in haphazard spots until all 8 tests were read.  She also took the temperature of the air after the last pH test strip was read.  Once we had all of our results from both sites for the entire week we analyzed what we found using excel. A t- test was completed on Microsoft Excel which was type 2, 1 tailed.  The P value results for the morning (t test) was 3.55447 X10^-5 and for the night it was 0.0003.  The results show that the hypothesis was not supported. 


 Figure 1: pH averages at 0800 hours in Lake Michigan and Pond in Washington Park


 Figure2:  pH averages at 2000 hours in Lake Michigan and Pond in Washington Park


                The results show that the pH was higher in the pond in Washington Park than Lake Michigan for during both times of the day. The standard deviation for the pond in Washington Park during the morning was 0.18 and during the night was 0.65.  The standard deviation for Lake Michigan in the morning was 0.34 and during the night was 0.65.  The day light hours (0800 hours) had a higher Ph than the night (2000 hours).





The results of our tests did not support our hypothesis; but the results did support the background information in the introduction.  What we found was that the pH levels were actually lower in Lake Michigan and higher in Washington Park pond.  We hypothesized that if there was more vegetation by the pond than by the lake then the pH levels will be lower in the pond in comparison to the lake due to photosynthesis of the nearby vegetation. We could have taken the pH tests three times a day; one at 0800, one at 1200 and one at 1600.  Another way we could have done this is to take the pH measurements in different seasons for example spring versus the summer. 






Literature Cited


Rhodes, T. E., Davis, R. B. (1995). Effects of late Holocene forest disturbance and vegetative change on acidic mud pond. Maine, USA. Ecology 76, n3. P.734(13). Retrieved on September 24, 2008 from Academic On File

Chamier, A -C. (1987).  Effect of pH on microbial degradation of leaf litter in seven streams of the English Lake District. Oecologia, Vol. 71, No. 4, pp. 491-500. Published by Springer Berlin/Heidelberg. Retrieved on November 4, 2008 from the World Wide Web

Shaw, B., Mechenich, C., Klessig, L. (2004). Understanding Lake Data (G3582). Wisconsin Department of Natural Resources. Retrieved from the World Wide Web on October 14, 2008.

Whitney, R., J. (1942). Diurnal Fluctuations of Oxygen and pH In Two Small Ponds and A Stream. Journal of Experimental Biology. Zoology Department, University of Birmingham. Retrieved on November 4, 2008 from the World Wide Web