Effect of Phosphorus on Dissolved Oxygen Levels in the Jackson Park Pond and Lake Michigan

 

Sarah Jackson, Sara Klosiewski, & Sara Zavadsky

 

Abstract

            We tested whether the phosphate levels in Jackson Park Pond were higher than in Lake Michigan.  This would cause there to be lower levels of dissolved oxygen observed at Jackson Park Pond.  We found that the phosphate levels sampled from Jackson Park Pond (0.1 ppm) were significantly lower than at Lake Michigan (0.2 ppm; p= 6.73x10-6) and the levels of dissolved oxygen at Jackson Park Pond (12.02 mg/L) were statistically lower than at Lake Michigan (13.03 mg/L; p= 7.10x10-3).

Key words: dissolved oxygen, phosphate, lake, pond

 

Introduction

Levels of dissolved oxygen vary within bodies of water as a result of algae growth (Li et al., 2011).  Higher algae growth is due to a higher amount of phosphates present in the water.  The algae take in the phosphates for metabolic activity to occur, a process, which then lowers the dissolved oxygen in the water (Wang & Linker, 2009).  More decomposition occurs from the large amount of growth as the algae begin to die.  This decomposition takes in dissolved oxygen, thus lowering the total amount of dissolved oxygen in the body of water (MacPherson et al., 2007). 

We hypothesized that the levels of dissolved oxygen at Jackson Park Pond would be lower than at Lake Michigan due to higher phosphate levels at Jackson Park Pond.  We predicted that phosphate levels at Jackson Park Pond would be higher than phosphate levels at Lake Michigan.  This would cause the levels of dissolved oxygen at Jackson Park Pond to be lower than levels observed at Lake Michigan.

 

Materials and Methods

            Beginning on October 11, 2012, at approximately 0900 hours, water was sampled from two different bodies of water (pond and lake) located at the Jackson Park Pond and Lake Michigan (Milwaukee, Wisconsin).  At each location, ten different sites were chosen to collect the water samples and the mg/L of oxygen, temperature, and ppm of phosphorus were measured.  The first test site was chosen as a sample of convenience.  The first measurement was taken at N042⁰ 59.768' - W087⁰ 57.931' (iPhone application, OnWhat GPS) 1.0 m from the shore so that the probe (YSI Incorperade, 85 Oxygen Conductivity Salinity & Temperature, model# 85/25 FT, SN: 97H1423) was submerged 0.1 m under the surface.  The mg/L of oxygen and temperature (C⁰) were recorded.  A 10 ml sample of pond water was obtained in the same location in a test tube.  This sample was used to test the parts per million of phosphorus present in the pond with the LaMotte Nitrate-N Phosphorus Test Kit (model# NPL, code 3119).  Samples were tested according to the manual for the LaMotte Nitrate-N Phosphorus Test Kit.  The phosphate levels were recorded.  Each new test site was measured 30 m (Keson 50m, model# OTR50M) apart from the previous site before it along the perimeter of the pond, and the coordinates were recorded (Table 1).  The same procedure was used to obtain the mg/L of oxygen, temperature, and ppm of phosphorus in the pond at each of the nine remaining sites.

            At approximately 1030 hours, mg/L of oxygen, temperature, and ppm of phosphorus were measured at ten test sites along Lake Michigan near South Shore Park (Table 1).  Data was collected using the same procedure discussed previously.  Data were analyzed using a 1 tailed, type 3 independent T-test on Excel© for Windows 2011©. 

 

Table 1. A description of the locations (coordinates) used to obtain water samples from two different locations in Milwaukee, Wisconsin.

Site

Jackson Park Pond

Lake Michigan

1

N042° 59.768' - W087° 57.931'

N042° 59.205' - W087° 52.138'

2

N042° 59.758' - W087° 57.922'

N042° 59.196' - W087° 52.113'

3

N042° 59.747' - W087° 57.905'

N042° 59.185' - W087° 52.099'

4

N042° 59.735' - W087° 57.886'

N042° 59.179' - W087° 52.086'

5

N042° 59.722' - W087° 57.867'

N042° 59.173' - W087° 52.060'

6

N042° 59.732' - W087° 57.848'

N042° 59.166' - W087° 52.042'

7

N042° 59.725' - W087° 57.827'

N042° 59.158' - W087° 52.029'

8

N042° 59.716' - W087° 57.801'

N042° 59.145' - W087° 52.010'

9

N042° 59.713' - W087° 57.778’

N042° 59.140' - W087° 52.003’

10

N042° 59.716' - W087° 57.756’

N042° 59.126' - W087° 52.978'

 

Results

            There was a significant difference in the ppm of O2 (mg/L) sampled from Jackson Park Pond compared to Lake Michigan (Fig 1. p= 6.73x10-6).  The levels of dissolved oxygen were lower in Jackson Park Pond than in Lake Michigan.  There was also a significant difference in phosphate levels sampled from Jackson Park Pond compared to Lake Michigan (Fig 2. p= 7.10x10-3).  The levels of phosphates were lower in Jackson Park Pond than in Lake Michigan.

 

Figure 1. Mean (+/- S.D.)  O2 (mg/L) of water based on location.

 

Figure 2. Mean (+/- S.D.) Phosphates (ppm) of water based on location. Standard deviation for Lake Michigan was 0. 

 

 

Discussion

Our data refuted our hypothesis that the phosphate levels would be higher and the dissolved oxygen would be lower at Jackson Park Pond than in Lake Michigan.  In our study, our data were not similar to the findings of Li et al. (2011), MacPherson et al. (2007), and Wang & Linker (2009), who all found that higher amounts of phosphate led to a lower amount of dissolved oxygen. Our findings may have differed because we only obtained 10 samples from two areas, whereas the experiments in the articles obtained more samples and not from the same bodies of water as in our experiment.

There were several limitations to our experiment that may have caused error in our findings.  The data from Jackson Park Pond was collected one and a half hours earlier than the data from Lake Michigan due to instrument availability.  This could have caused a higher surface water temperature at Lake Michigan, which may have influenced the dissolved oxygen.

Another limitation was in the method used to sample the water around the pond.  At Lake Michigan we were able to sample every 30 meters because the coastline was straight.  However, at Jackson Park Pond we could not be certain that we sampled every 30 meters because the perimeter was curved.  The samples were also not a consistent one-meter distance away from the shore because the depth of the water limited the distance into the water we could walk to sample the water.

The Lake Michigan site was behind a break wall, which reduces the amount of flow/exchange in and out to the entire lake.  This limitation could have affected the true representation of Lake Michigan’s DO concentration because the water was not flowing as much.

If this experiment were performed again, we would analyze whether or not the water temperature was a significant factor affecting the dissolved oxygen levels.  We recorded the water surface temperature while sampling our water but we did not analyze the data for this report.  Temperature can increase or decrease dissolved oxygen, so our results could have been influenced by water temperature along with the other factors previously mentioned.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

Literature Cited

Li, X., Yu, Z., Song, X., Cao, X., & Yuan, Y. 2011. The seasonal characteristics of dissolved oxygen distribution and hypoxia in the Changjiang Estuary. Journal of Coastal Research, 27: 52-62. Retrieved September 18, 2012, from EBSCOhost database

MacPherson, T. A., Cahoon, L. B., & Mallin, M. A. 2007. Water column oxygen demand and sediment oxygen flux: Patterns of oxygen depletion in tidal creeks. Hydrobiologia, 586: 235–248. Retrieved October 15, 2012, from EBSCOhost database

Wang, P. & Linker, L. C. 2009. Assessment of nitrogen and phosphorus control

trade-offs using a water quality model with a response surface method. Journal of Water Resources Planning and Management, 135(3): 171-177. Retrieved October 15, 2012, from EBSCOhost database