Comparing pH Levels of an Urban Watershed to Agricultural/Rural Watershed in

Southeastern Wisconsin

 

Lorraine Brito

 Jodi Uszler

 

Abstract

                We tested pH levels of the Milwaukee River and the Rock River to determine whether the urban Milwaukee River watershed would be more acidic than the mixed agricultural/rural Rock River watershed.  We measured pH of the water in ten locations along the Milwaukee River in Estabrook Park and ten locations along the Rock River located in Jefferson County on Highway B.  From the measurements, we found that neither sites measured an acidic pH level, however the urban watershed did have lower pH readings compared to the mixed agricultural/rural watershed (p=0.01).

Keywords: ph, acidic, basic, watershed, pollutants

Introduction

                As areas become urbanized, their surfaces are typically covered by pavement and roads which leads to more storm water runoff versus groundwater absorption (Zhang et al. 2012). Materials such as gasoline, motor oils, lawn fertilizers, pesticides and heavy metals including nickel, copper, zinc, cadmium and lead can be washed directly into surrounding watersheds rather than being reduced by minerals and nutrients found in soils (Jang, Seo & Bishop, 2005).  The toxicity of urban watersheds has been a well-studied topic as the mentioned pollutants are known to have a direct affect on the surrounding ecosystem.   Some of the effects of pollutants entering urban water systems include changes in dissolved oxygen levels, species intolerance to pH changes, and bacterial contamination.  However, it is the runoff from low pH rainwater that seems to have the most impact on the pH of urban waters and urbanized areas tend to produce more acidic rain than rural areas. When atmospheric sulfuric acid combines with water in the air and precipitation occurs, the new acid compound can fall directly into our waterways (Strassler, Pritts, & Strellec, 1999).   To contrast, runoff from agricultural land to watersheds can contaminate water sources by other methods.  Heavy use of chemical pesticides and fertilizers can have a negative effect on aquatic life as infiltration alters the biochemistry of the watersheds (Schriever & Liess, 2007).  We hypothesized that the majority urban land cover Milwaukee River watershed would measure more acidic pH values compared to the mixed agricultural/rural Rock River watershed. 

Methods

On September 29, 2012 at 0945, we conducted our research at two Wisconsin rivers: Rock River and Milwaukee River.  Measurements for the Rock River were taken at Rock River Park along county highway B in Jefferson County, WI.  Measurements for the Milwaukee River were taken at Estabrook Park located at 4400 N. Estabrook Dr. Milwaukee, WI 53211. Using a pH monitor (Pasco-Xplorer GLX model #: PS2002) from the Alverno College laboratory located at 3400 S. 43rd St., we obtained pH samples at 10 different spots located along the Rock River. We placed the pH probe halfway into the water for about 20 seconds and removed it. We recorded the pH level displayed on the pH monitor. We used a tape measure (Workforce ™ 5/8 x 12 ft. [1.59 cm x 3.66 m]) to calculate the distances of approximately 2 meters between each test spot.  We also used a compass (Commander Compass Lite for iPhone Applications) to obtain the locations of the test spots. We followed the same testing procedure and used the same tools at Milwaukee River to obtain pH levels of the water. All data were analyzed using Excel© for Windows 2010. A type two, one-tailed T-test was used.

Results

The Rock River results provided a neutral and slightly alkaline pH (Mean=8.90, S.D. =0.09) than Milwaukee River’s pH (Mean=8.34, S.D. =0.72) which is more neutral.  The calculated p-value (p=.01) reveals that there was statistical significance. (Fig. 1).

Figure 1. Mean (+/- S.D.) pH levels of 10 locations along the Rock River compared to pH of 10 locations along the Milwaukee River.

Discussion

Although our results show statistical significance (p=0.01), our hypothesis was not supported.  Results did not provide acidic readings for the Milwaukee River as hypothesized, potentially due to the location where readings were taken.  The Milwaukee River running through Estabrook Park is surrounded by soil and plant life where pollutants can be reduced before entering the water.  Soil, specifically containing calcium carbonate, can reduce sulfuric acid, neutralizing the acid precipitation. (Geary & Driscoll, 1996).  Results may have differed if measurements were taken in a setting with less surrounding soils and closer to central downtown.  In addition, some measurements were taken in relatively close proximity to each other due to inability to reach further distances.  City regulations on filtering processes may also regulate the amount of pollutants reaching the river.  Regulations or filtering process may also be in effect in the agricultural location of the Rock River.  User error may have had an effect on the pH readings as neither researcher had any background using the specific equipment prior to the date of readings.  If additional research were to be followed, we would attempt to take pH readings for the Milwaukee River in an area where urban runoff could potentially be directly flowing into the water before being reduced by surrounding soil. 

References

Geary, R. J., Driscoll, C. T. (1996). Forest soil solutions: Acid/base chemistry and response to calcite treatment. Biogeochemistry, 32(3), 195-220. Retrieved from http://0-www.jstor.org.topcat.switchinc.org/stable/1469262

Jang A., Seo, Y. (2005). The removal of heavy metals in urban runoff by sorption on mulch. Environmental Pollution, 133(1), 117-127. Retrieved from: http://0-dx.doi.org.topcat.switchinc.org/10.1016/j.envpol.2004.05.020

Schriever C. A., Liess, M. (2007). Mapping ecological risk of agricultural pesticide runoff. Science of the Total Environment, 384(1-3), 264-279. Retrieved from http://0-dx.doi.org.topcat.switchinc.org/10.1016/j.scitotenv.2007.06.019

Strassler, E., Pritts, J. & Strellec, K. (1999). Preliminary data summary of urban storm water

best management practices. www.epa.gov. Retrieved November 1, 2012 from http://water.epa.gov/scitech/wastetech/guide/stormwater/upload/2006_10_31_guide_stormwater_usw_a.pdf

Zhang, B., Xie, G., Zhang, C. & Zhang, J. (2012). The economic benefits of rainwater-runoff reduction by urban green spaces: A case study in Beijing, China. Journal of Environmental Management, 100(15), 65-71. Retrieved from http://0-dx.doi.org.topcat.switchinc.org/10.1016/j.jenvman.2012.01.015