The Effect that Phosphorus Usage has on Different Areas of the Milwaukee River


Wendy Gadouas

Sara Lieske



            We tested whether or not the Milwaukee River’s agricultural areas had higher phosphorus concentrations in the water than that of the urban areas that surround the river. We did so by collecting water samples from the river in various areas around metro Milwaukee, Cedarburg, and Mequon, Thiensville, and Grafton, Wisconsin. Through our testing, we found that phosphorus use in the form of fertilizer for agricultural practices does not cause an increase in the phosphate levels in the river as compared to urban areas of runoff (P= 0.005). In fact, the concentrations of phosphorus in the water samples were higher in the urban areas than that of rural areas.

Keywords: phosphorus, agricultural areas, urban areas





            Phosphorus is a macronutrient essential for life (EPA 2010). It is also used in a variety of household goods such as detergents, pesticides, and fertilizers.  Agricultural practices rely heavily on the use of fertilizers to produce a larger crop each year (Withers & Jarvie 2008). An assessment performed recently found that about 40 to 60 % of crop yields are directly related to the application of fertilizers (Stewart et al. 2005). The fertilizer plays a vital role in replacing the phosphorus in the soil that has previously been removed by the crops. However, an overload of phosphorus in water bodies is detrimental to aquatic systems, because it promotes the growth of undesirable species such as algae (EPA 2010). The transfer of phosphorus occurs from the terrestrial areas to the surrounding area’s body of water occurs during runoff after it rains (Dixon & Turner 2002). We hypothesized that phosphate levels in the water amongst agricultural areas will be higher in concentration than in urban areas along the Milwaukee River.


Materials and Methods

Beginning on November 1, 2011 we began collecting samples from 8 sites around the Southeastern portion of Wisconsin which were split between farmland areas and city areas.  The agricultural sample sites included: River Barn Park 9808 N Cedarburg Road 44W, Mequon, WI , Cedar Creek Winery 6340 Bridge Road  Cedarburg, WI 53012 , Thiensville Village Park , 250 Elm Street  Thiensville WI 53092, and  Lime Kiln Park 860 Badger Circle Grafton, WI 53024 While the city sites included :downtown North Avenue: 1438 East North Avenue Milwaukee, WI 53211, 3565 North Morris Boulevard, Milwaukee, WI, 162 East Lincoln Avenue, Milwaukee, WI, and 1st St & W Lincoln Ave Milwaukee, WI 53207. We repeated these collection processes 3 times for each site, giving us 24 samples total; 12 for urban areas of the river and 12 for agricultural areas. The dates of sample collection were October 30, 2011, November 1, 2011, and November 7, 2011 between the hours of 15:00 and 17:00.

            Once the samples were collected we tested temperature and phosphate levels. We took the temperature of the water samples right before the test for phosphorus concentrations because the phosphate kit states that the samples should be around 23ºC for optimum results. We did this by using YSI Inc. thermometer model # 85/25 FT and recording the data in our laboratory notebooks prior to testing. The phosphate concentrations were found using a Phosphate Test Kit model NPL, LaMotte ®. To conduct the test, three test tubes were filled with 10 ml of one sample, two being untreated samples, and the third was treated with 1 ml of phosphate acid reagent (V-6282-H), next a pre-measured amount of phosphate reducing reagent (V-6283-C) was added to the treated test tube. After thoroughly mixing the test tube, a five minute waiting period was required before reading the results. The three test tubes were placed in the Axial reader viewing system and the comparator (code 2071) facilitates the decision as to which color was a best fit match to the treated test tube. Each color in the comparator corresponded to a concentration of phosphate. We repeated these steps for each sample collected and recorded the data in our notebooks. We then placed our data into Excel for Windows© and performed a T-test in Excel to obtain a P-value for the data in order to disprove or support out hypothesis; the T-test was type 1 and 2 tailed.



            Our testing results concluded there was a significant difference in the phosphorus levels in the agricultural areas as compared to the urban areas of the Milwaukee River (Fig. 1, P=0.005). However the urban areas proved to be higher in phosphorus concentrations than the agricultural areas did.  The concentration of phosphorus in areas along the river that are used for farming on average (mean) is 0.38 ppm of phosphates with the standard error of 0.4 ppm. The areas in the surrounded by cites along the river had a mean phosphate concentration of 0.53 ppm with a standard error of 0.3 ppm.

Figure 1. Mean of agricultural areas (S.E +/-0.4) compared to mean of urban areas (S.E +/-0.3)


            These findings did not support the hypothesis that phosphate concentrations would be higher in agricultural areas than in urban areas along the Milwaukee River due to the heavy use of fertilizer in modern farming practices. However to support this data, more testing should be done in order to provide a more clear outcome. Agricultural practices rely heavily on the use of fertilizers that contain phosphorus to produce a larger crop each year (Stewart et al. 2005) with that said, if we were to perform the test again, we should change the experimental design. We should have considered the time of year as a variable because fertilizer is typically applied in spring and summer months during peak farming seasons. The rain that accompanies these times of the year would also affect the runoff rates into the surrounding bodies of water which would change the data results.


Literature Cited

EPA. (2010). Watershed Protection: Clean Lakes Study: Phosphorus Inactivation and Wetland Manipulation Improve Kezar Lake, NH. Retrieved on September 21, 2011 from

 Stewart, W.M.; Dibb, D.W.; Johnston, A.E.; Smyth, T.J. (2005). The Contribution of Commercial Fertilizer Nutrients to Food Production. Agronomy Journal 97: 1–6. doi:10.2134/agronj2005.0001

Withers, P. J. A., & Jarvie, H. P. (2008). Delivery and cycling of phosphorus in rivers: A review. Science of theTotal Environment, 400(1-3), 379-395.