Variations in Water Quality between Various Urban and Rural Locations along Lake Michigan

Samantha Gauger & Elsa Janusiak

Abstract

We tested water samples from various locations along the Lake Michigan shoreline in the greater Milwaukee and surrounding area, with a focus on comparing water quality of urban and rural areas. To test water quality, we took measurements of CO₂, pH, chlorine, bromine, and nitrates. We found that while pH, chlorine, bromine, and nitrate levels remained consistent at each location, CO₂ levels varied greatly (with a range of 91 ppm in the most urban location, and 247 ppm in the most rural location). The difference in CO₂ levels was found to be statistically significant (P-value = 8.1x 10^-4) and our coefficient of determination was found to be statistically significant as well (R²=0.957511216).

Keywords: Water Quality, Carbon Dioxide, Photosynthesis

Introduction

Lake Michigan spans along the entire eastern shoreline of Wisconsin, along rural areas as well as extremely urban, high traffic areas. Lake Michigan provides a major source for drinking water, fishing, and recreational activity for residents of Milwaukee, Wisconsin. In addition, treated wastewater from over one million people in Southeastern Wisconsin is pumped into Lake Michigan. Water quality of these areas may be affected by various factors, such as street traffic, water treatment, surrounding plant and animal life, and elevation. Rural areas are further away from industrial activity which makes the area less likely to experience contaminated runoff (Wilson, Johnson, & Keith, 2003). Water runoff that is contaminated can lead to high contamination and poor water quality for lakes, rivers, and groundwater. These factors can affect water quality by influencing various factors, such as pH levels, carbon dioxide, chlorine, and oxygen content (Dorris & Wilhm, 2008). As these levels vary, they may or may not be within the optimal range for local aquatic plant and animal life, and may also be dangerous for humans to drink, come in contact with, or fish in (Lee et al., 2002). When CO₂ is combined with water the end result is carbonic acid; carbonic acid is a weak acid. Carbonic acid is capable of maintaining homeostasis within waterways or it can be responsible for increasing the acidity (Talling, 1976). When there is a high pH present within a water system carbonic acid can act as a neutralizer by balancing the pH back to normal. If there is a low pH, this could lead to a substantial problem by making the water more acidic, or less than the normal range of 6.5-7.8.

CO₂ in the water can be used by organisms such as phytoplankton for photosynthesis. For photosynthesis to take place there also needs to be adequate sunlight to complete the process; when there are days with heavy clouding or during the night, the ability for phytoplankton and other organisms that need to photosynthesize are reduced. This can lead to detrimental effects as fish and plant life can become harmed by high levels of CO₂ in combination with high levels of O₂; organisms that live underwater are not able to undergo respiration well without taking up O_2.

Because there is an increased amount of street traffic, boat traffic, and runoff from concrete structures and streets in urban locations of Milwaukee and Lake Michigan, we hypothesized that urban locations of Lake Michigan would have much lower water quality than rural locations of Lake Michigan. More specifically, we hypothesized that urban locations would have increased CO₂ levels, decreased pH, and increased amounts of chlorine and bromine, when compared to rural areas of the same water source. We hypothesized that CO2 would be higher in urban areas and lower in rural areas, that pH would be lower in urban areas and higher in rural areas, and that there would be a difference in the amount of bromine and chlorine found in urban water versus rural water .

Materials and Methods

On Thursday, October 14^th, 2010, we went to various waterfront locations along the Lake Michigan Shoreline, in Milwaukee, WI, to test pH, CO₂, chlorine, bromine, and nitrate levels of water samples. Locations selected included the Milwaukee Port, Veteran’s Park, Milwaukee Yacht Club, Lake Park, South Milwaukee Waste Water Treatment Facility, Big Bay Park, Klode Park, and Oak Creek Water Treatment Facility. Our initial location set was the Milwaukee Port. This location was determined as the most central downtown location. We measured the distance from the Milwaukee Port to each additional location in order to determine the distance of the location from downtown. Criterion used to classify urban and rural locations was how many km traveled away from the Milwaukee Port; locations less than 5 km from the Milwaukee port were considered urban locations, and locations more than 5 km from the Milwaukee port were considered rural. At each location, general observations were made, such as the type of shoreline, visible appearance of water, apparent plant and animal life in the surrounding area, and level of traffic. After general observations were made we measured pH, CO₂, chlorine, bromine, and nitrate levels at each location. To measure pH, chlorine, and bromine, a ArchChemical HTH 3-way test kit was used (model number 01070), that included OTO (hydrochloric acid and orthotolidine) to measure chlorine and bromine, and phenol red indicator to measure pH, and a water chamber color comparator which was used to read results. To test for chlorine and bromine, a water sample was obtained in the comparator vial. Five drops of OTO were added to the water sample and the sample was capped and inverted. The water sample changed to a yellow color, and was compared to the color standard vial. Numbers were recorded as parts per million (ppm) bromine and chlorine. To obtain a pH reading, a separate water sample was taken in the pH comparator vial. To this sample, five drops of phenol red were added. The vial was capped and inverted. The water color of the water sample was compared with the pH red color standard vial. CO₂ was measured using a LaMotte Company carbon dioxide test kit (model PCO-DR code 7297-DR). To measure CO₂, the titration tube was filled to the water line. The reagent B titrator was inserted into the center hole of the titration tube cap. The tube was gently swirled as carbon dioxide reagent B (code 4253DR-H) was slowly added one drop at a time, until a faint color was produced and persisted for at least thirty seconds. Results were read by finding the difference between initial volume in titrator and current volume remaining in titrator. CO₂ levels were recorded in parts per million. Lastly, Nitrate levels were measured using a LaMotte Nitrate Test Kit (model NPL code 3119). A water sample was obtained in the test tube to the 2.5 mL line. The sample was diluted to 5 mL using the mixed acid reagent (V-6278). The dilution was capped, mixed and allowed to sit for two minutes. One level measure of nitrate reducing reagent (V-6279) was added to the dilution, capped, and inverted. The mixture was allowed to sit for ten additional minutes. The test tube was placed into the nitrate comparator and the sample color was compared to a color standard. Results were recorded in parts per million. The recorded measurements were analyzed using Microsoft Excel © for Windows XP©, version 2007. To analyze all results comparing urban and rural locations, t-tests were used and a p-value was calculated. A correlation was calculated between CO2 levels and distance from the most downtown urban location.

Results

The overall water quality of urban areas was not much lower than the water quality of more rural areas. While the pH, chlorine, bromine, and nitrate levels remained stable, the CO₂ levels varied greatly between the various locations (Figure 1 & Figure 2). The pH among the eight sites ranged from 7.6 to 7.9, chlorine values were observed as less than 0.5 ppm at each site, bromine values were all found to be less than 1 ppm, and nitrate levels ranged from 0.1 to 0.44 ppm, with no consistent pattern relating to location and nitrate level. The areas with the lowest CO₂ levels were the most urban locations such as the Milwaukee Port and Veteran’s Park. Areas with highest CO₂ levels were locations further away from the Milwaukee Port Klode Park and the Oak Creek Water Treatment Facility. CO₂ levels ranged from 55 ppm to 247 ppm. The relationship between CO₂ levels in urban and rural locations is statistically significant (p= 0.0047, Figure 1) with a positive correlation between CO₂ level and distance from downtown locations (R²=0.957511216, Figure 2). The R² value is significant because the closer the value is to 1.0, the more significant is it; as distance from the Port increased the level of CO₂ increased as well showing a positive correlation. To calculate the P-value we a calculated the average for each assay as well as a standard deviation for each and those values allowed us to conduct a statistical T-Test. In addition, we calculated the coefficient of determination which allowed us to obtain an R² value, both by using the 2007 version of Microsoft Excel©.

Figure 1: Comparison of average CO2 levels of urban (<5 km from downtown) and rural (>5 km from downtown) locations shows a significant difference (P-value=0.0047).

R²=0.957511216

Figure 2: Demonstrates positive correlation between the distance from the Milwaukee Port and increasing CO₂ levels (R²=0.957511216).

Figure 3: Comparison of average bromine levels in urban and rural locations is not statistically significant (P-value 0.046291).

Figure 4: Comparison of chlorine levels in urban and rural locations, not statistically significant (P-value 0.100932).

Figure 5: Comparison of average pH in urban and rural locations, not statistically significant (P-value 0.11584).

Figure 6: Comparison of average nitrate levels in urban and rural locations, not statistically significant (P-value 0.537191).

Discussion

We found that there was not a relationship between location (urban/rural) and chlorine, bromine, pH, and nitrate levels, however there was a relationship between location and CO₂ levels. These findings are not consistent with our hypothesis that CO₂ would be higher in urban areas and lower in rural areas, that pH would be lower in urban areas and higher in rural areas, and that there would be a difference in the amount of bromine and chlorine found in urban versus rural areas.

One important factor that likely contributed to the CO₂ being less in urban areas is the increased amount of algae and plant growth on concrete structures. This increased amount of algae would result in an increased amount of photosynthesis taking place in the presence of light. During photosynthesis, CO₂ is taken up by the plant and causes the overall pH to change, due to CO₂ being acidic (Gregory, 2006). We found that when the shoreline was sandy, there was less algae and plant growth. The shoreline can have a substantial effect because we know that different types of substrate affect the plant life that is able to grow and survive in a given location; as acidity and alkalinity play an important role in determining those factors. Within the rural locations where water samples were collected, we noticed that the more sandy the shoreline, the less algae and plant growth.

Another important factor that we thought might have had an impact on our data was the locations where water samples were taken from. Water treatment facilities could have produce a difference in our data, possibly due to the water treatment process. The South Milwaukee Water Waste Treatment Facility and The South Milwaukee Yacht Club were only separated by a delta; so the water from The South Milwaukee Yacht Club that was not from the South Milwaukee Water Waste Treatment Facility, were combined at the delta. The Treatment Facility could impact the water quality as this point because waste and chemicals are entering the lake and there is no barrier to prevent it. If we were to repeat this experiment again, we would test for the chemicals that are used in the treatment facilities. This would provide insight on whether they are entering the water supplies and if there are any potential implications of hazards to human health.

Literature Cited

Dorris, T., Wilhm, J. (2008). Biological Parameters for Water Quality Criteria. Bioscience. No. 6. Pp 477-481. Retrieved on September 19^th, 2010 from http://ebscohost.com.

Gregory, M. (2006). Photosynthesis in Elodea. Biology Web. Last updated April 18^th, 2006. Retrieved on October 10^th, 2010 from http://clintonic.suny.edu

Lee, F., Jones, A., Newbry, B. (2002). Water Quality Standards and Water Quality. Water Pollution Control Federation. Vol. 54. No. 7. Pp. 1131-1138. Retrieved on October 11^th, 2010 from http://jstor.org

Talling, J.F.. (1976). The Depletion of Carbon Dioxide from Lake Water by Phytoplankton. Journal of Ecology. Vol.64. No.1. Pp. 79-121. Retrieved on October 4^th, 2010 from JSTOR online database.

Wilson, E., Johnson, T., & Keith, D.. (2003). Regulating the Ultimate Sink: Managing the Risks of Geologic CO2 Storage. EPA National Risk Management Research Article. Retrieved October 4^th, 2010 from Elsevier online database.