Comparison of Water Quality in Low Population
and High Population
Lakes of Waukesha County
Lofton, Tammi Nagel and Jean Strick
total nitrogen in ten pre-selected lakes of Waukesha County
to determine whether higher population densities in the communities
a lake would result in reduced water quality as characterized by
levels of nutrients (phosphorus and total nitrogen).
Of the five lakes designated as low population,
only one of the lakes exhibited detectable levels of total nitrogen
phosphates, compared to three of the five lakes designated as high
population. Despite a greater
proportional occurrence of total nitrogen and phosphate detections in
population lakes, the results of T-tests conducted for each group
P-values of greater than 0.05 for both phosphate and total nitrogen
0.466, respectively), indicating no statistically significant
water quality between the groups of lakes.
Additionally, phosphate and total nitrogen concentrations do not
correlate with total lake area or depth.
In an effort to further investigate the effect of human
water quality, future studies should be designed to consider land use
drainage basins up-gradient of lakes, and to take into account seasonal
water quality, population, total nitrogen,
Land use surrounding lakes can affect the
nutrients into the lake, and the resulting water quality.
In undisturbed settings, the banks of lakes
are typically densely vegetated. As a
result, the input of nutrients such as phosphorus and nitrogen are low
reduced levels of run-off from the land (Pitois et al, 2001). With an increase in both urban and rural
human populations, nutrients from sediment erosion, septic systems, and
fertilizers are exported to lakes from the surrounding watershed at a
can increase algal growth, resulting in eutrophication, or aging, of a
rates greater than would naturally occur in the absence of human
(Christopherson and Smith, 1995).
According to the Great Lakes Water Quality
Agreement, programs that are aimed towards controlling pollution to our
essential to preserve the
ecosystem (Gilbertson, 1999). It is the
role of the scientist to assist engineers in construction of waste
plants that minimize excessive introduction of nutrients into the Great
(Gilbertson, 1999). This same type of
preservation and restoration can be employed in smaller lakes
Wisconsin. The smaller county lakes are
also in danger of pollution from agricultural sources, insecticides,
industrial chemicals (Annin, 1999). It is
also the role of the scientist to educate the public about the effects
use on water quality (Christopherson and Smith, 1995).
Lakes with higher population densities may
have an increased use of fertilizers and pesticides to preserve lawns
resulting in overflow to the shoreline waters.
Our research team hypothesized that water quality, as determined
reduced phosphorus and total nitrogen, is higher in lakes with lower
densities when compared to lakes with larger populations.
hypothesis on October 8, 2003 and October 9, 2003.
Prior to water sample collection, ten lakes
in Waukesha County were selected for sampling and designated as either
high population. To determine a lake’s
designation, census information for the year 2000 was obtained from the
Wisconsin Department of Administration for Waukesha County (Demographic
Center, Wisconsin Department of Administration, 2003).
Next, the area of the towns, villages, and/or
cities surrounding each of the ten lakes was estimated using a grid
with a known area. The grid was placed
over a map depicting Waukesha County communities, and the area of each
community was estimated by addition of grid-squares covered by the
(Milwaukee Maps, Inc., 2003).
Population density for each lake was then calculated by dividing
total population of surrounding towns, villages, and/or cities, by the
estimated area of each respective community.
The resulting population density, measured in people per square
kilometer, was then used to designate each lake as either high or low
population. Lakes with surrounding
communities averaging population densities of greater than 250 people
square kilometer were designated as high population.
Lakes with surrounding communities averaging
population densities of less than or equal to 115 people per square
were designated as low population. Eagle
Spring Lake, Pine Lake, Beaver Lake, North Lake, and Okauchee Lake were
as low population lakes. Lower Phantom
Lake, Nagawicka Lake, Oconomowoc Lake, Lac La Belle, and Pewaukee Lake
designated at high population for the purpose of this study. Population data and population density
calculations are included as appendices to this report.
Average population densities calculated for
each lake are included in Table 1.
collected from each of the ten lakes and immediately analyzed in the
total nitrogen and phosphate (as orthophosphate). Water
samples were collected from an average
of 2-5 meters off the shoreline. Water
temperature was measured in conjunction with testing using a
thermometer. A LaMotte Nitrate-N and
Phosphate in Water
Test Kit was used to complete water quality analysis.
Prior to beginning each test, test tubes were
rinsed with a sample of the lake water about to be analyzed. The phosphate test was initiated first by
filling a test tube with approximately 10 milliliters (mL) of lake
water. 1.0 mL of reagent provided in the
added to the water sample and mixed. Approximately
0.1 grams (g) of phosphate reducing reagent were added to the sample,
mixed until the reagent was fully dissolved.
The water sample was then set aside for five minutes, in
test kit instructions, during which time a second water sample was
total nitrogen analysis. The total
nitrogen test was initiated by first filling a test tube with
mL of lake water. The 2.5 mL sample was
diluted to 5.0 mL with acid reagent, and allowed to equilibrate for two
minutes. Following the two minute
equilibration period, approximately 0.1 g of reducing reagent was
the water sample was inverted at a rate of approximately 40 times per
for a total of one minute. The water
sample was then set-aside for ten minutes, in accordance with test kit
instructions. Following recommended
equilibration times, the phosphate and total nitrogen samples were read
LaMotte Axial Reader, and the results were noted. Total
nitrogen and phosphate readings were
recorded in parts per million (ppm).
measurements with a Secchi disc were originally proposed for inclusion
study, but were deemed inappropriate because sufficient lake depths
accessible by the research team. General
clarity and water color observations are included on Table 1. Table 1 also includes the results of total
nitrogen, phosphate, and temperature measurements obtained for each
lake. In addition to measured parameters,
of each lake and maximum depth, as obtained from the Wisconsin
Natural Resources (WDNR, 2003), are also tabulated.
General information pertaining to vegetation
and bank types noted surrounding each lake is also included in Table 1.
Table 1. – Population Densities, Lake Area,
Water Quality Parameters, and Visual Observations of Ten Waukesha
and phosphate concentrations were compiled into an ExcelÓ spreadsheet for graphing
and statistical analysis. A T-test was
completed to evaluate whether there was a statistically significant
between total nitrogen and phosphate in low population Waukesha County
when compared to lakes designated as high population.
evaluate whether total lake area (square kilometers) and maximum depth
affect nutrient concentrations, area and depth were correlated
with phosphate and total nitrogen concentrations.
nitrogen and/or phosphate were detected in three of the five high
lakes, compared to only one of the five low population lakes, P-values
generated for each set of data (0.098 and 0.466, for phosphate and
nitrogen, respectively) indicated no significant difference in water
between the groups of lakes. The average
amount of phosphates in low population lakes
(Fig. 1) was lower than the average amount of phosphates in high
Fig 1. – Comparison of Average Phosphate
in Five Low Population Lakes and Five High Population Lakes of Waukesha
amount of total nitrogen was higher in the low population lakes (Fig
to a single detection of total nitrogen (1ppm) in one of the five low
lakes (North Lake).
Fig 2. – Comparison of Average Total Nitrogen
Concentrations in Five Low Population Lakes and Five High Population
and phosphate concentrations were correlated, a correlation coefficient
–0.33 was calculated, indicating a very weak negative correlation
area and phosphate concentrations.
Likewise, a correlation coefficient of –0.32 was calculated when
area and total nitrogen concentrations were correlated, also indicating
weak negative correlation. Very weak
correlation coefficients of –0.15 and 0.13 were calculated when maximum
depth was correlated with phosphate and total nitrogen concentrations,
respectively. Based on calculated
correlation coefficients, phosphate and total nitrogen concentrations
correlate with lake area or depth.
water at one
of the low population lakes, Pine Lake, was observed to have a green
tint. Water in the remaining four low
lakes was clear and colorless. The water
at four of the five high population lakes was observed to have a green
tint. The water in high population
Oconomowoc Lake was clear and colorless.
Water color observations were not statistically analyzed.
results of our research, there was no statistically significant
water quality between the groups of lakes included in this study;
among the lakes designated as low population, only one of the five
Lake) had detectable levels of total nitrogen and phosphate. North Lake was sampled at a location near a
stream that entered on the northernmost tip of the lake.
It is possible that the stream was a source
of nutrients entering the lake near the sample location.
Similarly to lakes, water quality in streams
and rivers can deteriorate due to land practices along their banks
1997). Land use in the drainage basin
contributing to the stream entering North Lake was not taken into
prior to this study. Further
investigation of land-use in the greater drainage basin of North Lake
identify processes that contribute to addition of nutrients, such as a
concentration of agricultural activities.
Research has shown that agricultural activities, including
of cropland, have the potential to add nutrients to the local watershed
et al, 2001).
designated as high population lakes, only two of the five lakes had
total nitrogen and phosphates that were both below detection (Lac La
Pewaukee Lake). The waters of Lac La
Belle and Pewaukee Lake were green in color due to a noted growth of
algae. Nitrogen and phosphorus are
“limiting” nutrients for algal growth (Pitois et al, 2001). Addition of these of nutrients to the
watershed, as would be expected in highly populated areas, can
algal growth (Pitois et al, 2001). It is
possible that nitrogen and phosphorus were previously present in the
Lac La Belle and Pewaukee Lake, but that they had been utilized during
summer months for production of algae and were therefore no longer
detectable levels in the lake water.
Future studies of lake water quality should take into account
seasonal fluctuations in nutrient levels.
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