A comparison of pH in rural and urban bodies of water in Wisconsin
Jessica De Santis
We collected two water samples from eight bodies of water in a rural area, Langlade County, WI, and eight bodies of water in an urban area, Milwaukee County, WI. Determination of rural and urban water sources was based on population density by county (person per square mile). Samples of water from each site were chosen haphazardly from different coasts. We determined that there is no significant difference in pH between rural and urban water sources (P = 0.43).
Keywords: water chemistry, pH, rural, urban, water ecology
The pH of a body of water can be affected by many different factors, such as rainfall, runoff, location, climate, and microbial populations. Higher levels of air pollution increase the acidity of rainwater, and this acid rain, seen in more urban areas, runs off into bodies of water. This lowers pH levels and harms aquatic life (Khemani et al., 1967). This can cause aquatic macro and micro-invertebrate ecosystem alterations, making water chemistry an important role in ecosystem biodiversity (Vermonden et al., 2009).
Urban areas are also home to sewer systems. These drainage systems can be an altering factor in microbial populations. This can, in turn, cause a change in the flora and fauna of that body of water, which can also modify the water chemistry. Due to this information, we hypothesized that urban bodies of water would have a lower pH level than rural bodies of water in Wisconsin. We distinguished urban from rural areas based on the population density of the area, where our rural county had a population density of less than 100 people per square mile.
Methods and Materials
On September 27, 2009 from the hours of 1308 to 1500, eight different rural bodies of water were sampled. Two 100 ml samples were taken from each location at different shores. These samples were retrieved from Langlade County in Wisconsin (Fig. 1). The bodies of water collected from were Upper Post Lake, Lower Post Lake, Post Dam, Lost Lake, Summit Lake, Jack Lake, Wolf River, and Moccasin Lake. Each sample was collected about three feet from shore, near the surface. The samples were collected in GladWare® Mini Round 113g containers. Once collected, each sample was immediately placed in the freezer at -20 oC.
On Saturday October 10th, 2009 between the hours of 1430 and 1700 eight different urban bodies of water were sampled (Fig. 1). The process was repeated as with the rural bodies of water. The same type of container was used for this collection process as well. The eight urban locations were as follows: the Wind Lake Channel a waterway between two bodies of water, a residential Champions Pond, Wind Lake, Scout Lake, Waubeesee Lake, Lake Denoon, Long Lake, and Showtime Pond, just off a private business. These samples were also frozen immediately after collection.
On November 4, 2009 from the hours of 1000 to 1100 the samples were tested for pH with Edmund ScientificÒ litmus paper on a scale of 1 - 14. The water samples were allowed to thaw for 24 hours before being tested. Averages were calculated for each body of water as were averages for urban versus rural bodies of water on a whole. Statistical analysis was performed using a Tails 1, Type 2, t test on Microsoft Excel.
Fig. 1: This is a map of Wisconsin showing the locations of the sampled counties. The rural area in which the water samples were taken from is outlined in red. The urban area is outlined in green.
There was no significant difference in the pH of urban and rural bodies of water (Fig 2, P = 0.43). The results did not support our hypothesis that urban water sources would have a lower pH than rural water sources.
Fig 2: Comparison of pH in eight urban bodies of water (Mean = 6.34, S. D. = 0.48), Milwaukee County, and eight rural bodies of water (Mean = 6.31, S. D. = 0.26), Langlade County, in Wisconsin. There was no significant difference between rural and urban water pH (P = 0.43).
During this experiment we found no significant difference between rural water and urban water pH values. This did not support our hypothesis that urban bodies of water would have a lower pH than rural bodies of water. Our results, however, may have been altered by our procedure. Once the water samples were attained, they were immediately frozen to prevent microbial pH alterations. We decided that the water would increase in microbial population over time within the sample containers, causing a reduction of pH from microbial cellular respiration taking place. In an attempt to prevent this we stored our samples in the freezer at -20 oC. However, we did not realize that the process of freezing the water could be just as much a factor in altering the pH of the samples.
When water is frozen gases are trapped, and when the water is thawed gases are able to escape. By freezing and thawing our samples, we allowed Nitrogen and Carbon dioxide gases to escape the water, which are the main contributors to water pH levels (Bar-nun et al., 1985). Through this process we ultimately changed our sample pH levels. If we were to repeat this experiment, we would take the pH at the water source instead of retrieving a sample for later pH readings. This would have given us the exact pH on site rather than allowing room for possible contamination in our sample containers or releasing of gases during the freezing and thawing process.
One thing to keep in mind, however, is that it has been studied that urban drainage systems can be a resource for biodiversity if specific conditions are achieved, pH levels being among those factors. In previous research it was found that when pH values were between 7.1 and 9.2, a significant difference could not be determined in biodiversity (Vermonden et al. 2009). Thawing and freezing of samples would not be a factor in our experiment if this were the case. Urban and rural water sources may be a well enough designed buffering system to resist a high or low pH change, or sewer systems are not polluting urban water enough to alter the water chemistry overall.
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