Cindy Mark
Jayne Matt
Comparison of Nitrate and
Phosphorus Levels in Retention and
Non-retention Ponds
BI 341
29 November 2001
Abstract
We tested whether phosphorus and nitrate levels are higher in retention ponds than in non-retention ponds. Retention ponds are designed to collect excess runoff that would otherwise tax the new or existing storm sewers. The ponds we tested showed a variety of nitrate levels, while only one pond had a discernible level of phosphorus. The retention ponds did not show higher levels of the nutrients.
Keywords: phosphorus, nitrate, retention pond, runoff, commercial fertilizers.
Water is an integral part of the environment of most organisms. It is constantly exchanged through hydrologic cycle. One aspect of this is water runoff. Developed subdivisions consisting of established lawns are routinely subject to commercial fertilizer applications by several residents. The homeowner, lawn maintenance service provider, or a contracted fertilizer application service can apply these fertilizer applications. Fertilizers are applied to increase the available nutrients for an aesthetically appealing lawn. Most fertilizers consist of nitrogen and phosphorus. Therefore, when it rains, the runoff could be contaminated with higher than expected levels of these nutrients.
Considered to be a postwar phenomenon in the United States, the total large-scale production of synthetic organic compounds has increased (Keith 1979). Nitrate and other nitrogen species, usually considered the end product from a sequence of biologically mediated reactions in which organic nitrogen and compounds are oxidized; occur in natural waters mainly from biological systems and other sources. Eventually becoming nitrate in the biological process of eutrophication, domestic and industrial wastewaters are excellent nitrogen sources (Faust and Aly 1981).
Because contents are influenced by commercial fertilizers and are quite variable, it is difficult to establish a precise range of concentrations for nitrate in unpolluted natural waters. Nitrates may be leached from soils into surface waters and ground water (Faust and Aly 1981).
An essential element in biological systems is the phosphates, or more commonly referred to as phosphorus. As far as the aspects of pollution are considered, phosphorus is similar to nitrogen. However, because there are naturally occurring mineral sources of phosphates, nitrogen is dissimilar to phosphates (Faust and Aly 1981).
There are several mineral sources for phosphates and these minerals may be found in marine sediments and igneous rocks. However, the insoluble nature of minerals in water may be responsible for controlling the phosphate content of natural waters. Due to the input from the many sources being quite variable in natural waters, it is difficult to establish a range of concentrations for phosphates. Decomposition of organic phosphorus compounds, commercial fertilizers, domestic and industrial wastewaters are known pollution sources in biological systems (Faust and Aly 1981).
The Environmental Protection Agency regulates storm water runoff under the Clean Water Act (Snoonian 2001). In short, the Clean Water Act has set standards and guidelines to improve the quality of the nations waters. In recent years, the Department of Natural Resources, City Planning Councils and County Planning Councils have requested that retention ponds be created in land designated for future development, whether the development be comprised of single family homes, duplexes, multi-family units, or for commercial or industrial use. Retention ponds can serve dual purposes. They can collect runoff from rainfall that would otherwise overtax the storm sewer systems and they can add to the aesthetic appeal of the development site. Due to this runoff, one could reasonably expect to find higher levels of nitrate and phosphorus resulting from fertilizer applications.
This study was performed to verify whether phosphorus and nitrate levels would be greater in retention ponds than in non-retention ponds. If the hypothesis were correct, then phosphorus and nitrate levels will be higher in retention ponds and lower in non-retention ponds. If phosphorus and nitrate levels were higher in non-retention ponds, the hypothesis would be falsified.
A LaMotte Model NPL Nitrate-N and Phosphate in Water Test Kit was used to determine the phosphorus and nitrate-N levels in retention and natural ponds. An Ever-Safe 033 340, 76 mm immersion thermometer was used to determine air and water temperature. Temperature readings were taken when the temperature had stabilized for at least a one-minute time interval. Sixteen ponds were selected within the southwest side of greater Milwaukee (Figure 1, p. 4, Appendix A p. 7 & Appendix B p.8). Subdivisions containing established lawns were the source of the eight retention ponds. Milwaukee County parks were the primary source of the eight non-retention ponds. Data collection commenced October 13 at 9:40 a.m. on an overcast day. It terminated the same day at 4:15 p.m. in heavy rain (Figure 1, p.4). The water samples collected were processed immediately to determine the levels of nitrate and phosphorus. Each water sample was collected, analyzed and recorded before collecting the next water sample. Test tubes and water sample collection bottles were cleaned with tap water after each use. Microsoft Excel was used for data analysis.
There was no difference in the phosphorus levels of the retention versus non-retention ponds (Figure 1, P=0.17 p.4). Of the sixteen ponds sampled, only one retention pond, site #16, had a discernible level of phosphorus. A difference was not evident in the nitrate levels of the ponds (Figure 1, P=0.31 p.4). Five non-retention ponds and five retention ponds had various levels of nitrogen. The most nitrate was identified at site #13, a retention pond. This pond was in a mature subdivision with sloped topography and buildings on all sides. A graph of the average nitrate and phosphorus levels show a trend towards more nitrates in the retention ponds (Figure 2, p.5). The graph also shows a trend towards more phosphorus, however this is based on data from one pond. The other fifteen ponds had no measurable levels of phosphorus.
|
Site |
Ret. |
Non-ret. |
Sample |
Time |
Air |
Water |
Weather |
Phos. |
N.-N |
Nitrate |
|
|
Pond |
Pond |
Location |
|
Temp.
(°C) |
Temp
(°C) |
|
(ppm) |
(ppm) |
(ppm) |
|
1 |
|
X |
West |
9:40 |
14.50 |
16.00 |
overcast |
0.00 |
0.00 |
0.00 |
|
2 |
|
X |
East |
10:15 |
15.00 |
13.00 |
overcast |
0.00 |
0.10 |
0.44 |
|
3 |
|
X |
Northwest |
10:40 |
14.00 |
14.00 |
overcast |
0.00 |
0.00 |
0.00 |
|
4 |
|
X |
East End |
11:45 |
14.90 |
13.80 |
light rain |
0.00 |
0.00 |
0.00 |
|
5 |
|
X |
Southwest |
12:00 |
14.00 |
14.00 |
heavy rain |
0.00 |
0.05 |
0.22 |
|
6 |
|
X |
West |
12:25 |
15.00 |
14.50 |
heavy rain |
0.00 |
0.05 |
0.22 |
|
7 |
|
X |
North |
12:40 |
14.20 |
14.00 |
heavy rain |
0.00 |
0.10 |
0.44 |
|
8 |
|
X |
South |
12:55 |
14.20 |
14.00 |
heavy rain |
0.00 |
0.05 |
0.22 |
|
9 |
X |
|
South |
1:40 |
14.20 |
15.00 |
light rain |
0.00 |
0.00 |
0.00 |
|
10 |
X |
|
North |
1:55 |
14.00 |
14.80 |
light rain |
0.00 |
0.05 |
0.22 |
|
11 |
X |
|
South |
2:30 |
15.00 |
14.80 |
light rain |
0.00 |
0.05 |
0.22 |
|
12 |
X |
|
West |
2:55 |
16.00 |
15.00 |
light rain |
0.00 |
0.15 |
0.66 |
|
13 |
X |
|
South |
3:10 |
15.00 |
15.50 |
heavy rain |
0.00 |
0.00 |
0.00 |
|
14 |
X |
|
North |
3:30 |
14.20 |
14.80 |
heavy rain |
0.00 |
0.00 |
0.00 |
|
15 |
X |
|
South |
4:00 |
15.00 |
15.20 |
heavy rain |
0.00 |
0.10 |
0.44 |
|
16 |
X |
|
North |
4:15 |
16.00 |
16.50 |
heavy rain |
0.05 |
0.10 |
0.44 |
T-test
P-Values
Phosphorus
P = 0.17
Nitrate P = 0.31
Figure 1. Experimental and Statistical Data
|
Pond Type |
Phosphorus |
Nitrate |
|
|
Average |
Average |
|
Non-retention |
0 |
0.1925 |
|
Retention |
0.00625 |
0.2475 |
Figure 2. Graph of Average Nitrate and Phosphorus Levels in Ponds
Phosphorus
and nitrate levels were not higher in retention ponds than in non-retention
ponds, therefore our hypothesis was not supported. One retention pond at site #16 had a small, but measurable amount
of phosphorus. A possible explanation
could be that there were four hours of rain prior to our test. In addition, the substantial runoff possibly
altered the water composition. The
increased water temperature also might have had an effect on the phosphorus and
nitrate levels. Although ten sites had
various nitrate levels, the retention pond at site #13 had the highest
level. This was the only pond
surrounded by buildings and a sloped topography. The sample was taken after three hours of rain. Our
study had several limitations of method.
We had no control over the season, weather, or accuracy of the
thermometer and LaMotte Test Kit. The
mean water temperature was 14.68°C, which is considerably less than the
recommended solution temperature of 23°C.
The location and type of ponds may have affected our results. The topography near the ponds was
significantly different. Some ponds
were located at rather flat areas while others had steeper grades surrounding
them. Southeast Wisconsin had
experienced a period of dry weather prior to the day of water sample
collection. It is possible that the
fertilizer nutrients had been absorbed by the soil before the day of
collection, or that the pond had been stagnant, allowing the nutrients to settle
to the bottom pond sediment. In
a recent study by the University of Wisconsin – Madison, the impact of
Milorganite’s use, a commercially produced organic fertilizer, was studied for
its possible contribution of nutrients in runoff. Milorganite’s typical analysis indicated the following levels for
the following nutrients: Nitrogen (N) 6.75%, Phosphorus (P) 2.65% and Potassium
(K) 0.46%. Homeowners and lawn
services in the Milwaukee area commonly use Milorganite. According to the research, the runoff water
amounts of Nitrogen and Phosphorus was related more to whether or not
fertilizer was applied than the type of fertilizer applied and strongly
reflected the fact that more Nitrogen and Phosphorus were detected in runoff
from the non-fertilized plots than from the fertilized plots (Kussow 1996). As
stated earlier, there is a level of difficulty in establishing a range of
concentrations for phosphates in natural waters due to a variable number of
input sources. Additionally, and for
the same reason, in unpolluted natural waters it is difficult to establish a
precise range of concentrations for nitrate.
Leached from soils into ground water and surface waters, mineral
contents are quite variable and are influenced by the use of commercial
fertilizers (Faust and Aly 1981). Some
of these variables suggest further studies.
Perhaps an analysis of the ponds’ sediment would have provided
statistically significant results.
Would nutrient levels be greater during the summer months of lawn
fertilization and pesticide application?
Are nutrient levels greater in ponds when it is raining than when it has
been dry? Does topography and/or
erosion affect nutrient levels in ponds?
Our results demonstrate a possibility of increased nitrate levels in
retention ponds but expanded nutrient studies should be done for confirmation. Literature Cited Faust, S. D.
and Aly, O. M. 1981. Chemistry of Natural Waters. Ann Arbor Science Publishers, Inc., Ann Arbor. 21 p. Keith, L.H.
1979. Identification & Analysis of Organic Pollutants in Water. Ann Arbor
Science Publishers, Inc., Ann Arbor. 51 p. Kussow, W. R. (1996)
Runoff and Leaching Losses of Nutrients from Kentucky Bluegrass Turf. Available: http://www.milorganite.com/research/re_runoff.html
Accessed: 2001, October 28. Snoonian, D.
2001. Drain It Right: Wetlands for
Managing Runoff, Architectural Record, August, 2001. Appendix A Location and
Description of Ponds (see Appendix B for location maps) 1. Jackson Park Medium
pond, several geese and ducks in the water and at sore, fowl waste on the
ground, green slime on the water’s surface and bottom, leaves and feathers in
the water, trees at the pond edge, sloped topography at the south, green water. 2. Arlington Cemetery Small
pond, several ducks in the water, large trees at the pond edge, brown pond
bottom, clear water consisting of a tan hue. 3. Wilson Park Large
pond, no fowl at the sample location, leaves and feathers at the visible pond
bottom, trees at the pond edge, clear water to a depth of several inches. 4. Grobschmidt Park Large
pond in a natural setting, no fowl visible, wetlands, cattails, natural foliage
and trees at the edge, trees in the pond, bottom visible, clear water. 5. Scout Lake Park Large
pond, shallow, several ducks at the southwest side, wetlands, lily pads in the
water, natural foliage and trees at the edge, mucky bottom, clear water. 6. Whitnall Park Medium
pond, no fowl visible, willows at the edge, leaves on the surface, mucky
bottom, reasonably clear water. 7. Boerner Botanical Gardens
South Pond Small
pond, shallow, ducks in the pond, a few trees and grass at the edge, mucky
bottom, tan water. 8. Boerner Botanical Gardens
North Pond Small
pond, ducks in the pond, trees and vegetation at the edge, feathers on the
surface and bottom, tan water. 9. Hillview Estates Subdivision Small
pond, new subdivision with buildings on two sides, undeveloped on two sides,
fowl waste on the grass, grass at the pond edge, substantial muddy inflow,
slimy bottom with grass and decaying grass, clear water. 10. Mission Ridge Subdivision Small
pond, mature subdivision with buildings on three sides, road on one side, fowl
waste on the grass, grass at the edge, slimy bottom and water with green plant
material, green water. 11. Whitestone Village
Subdivision Small
pond, mature subdivision with buildings on two sides, road on two sides, a few
ducks in the pond, fowl waste on the grass, trees and grass at the stone edge,
slimy bottom with green plant material, clear water. 12. Kelly Pointe Subdivision
West Pond Two
small, connected ponds, mature subdivision with buildings on three sides, road
on one side, no fowl visible, grass edge, construction debris at the bottom,
clear water. 13. Kelly Pointe Subdivision
East Pond Medium
pond, mature subdivision with buildings on all sides, no fowl visible, floating
plant material, grass, trees, and reeds at the edge, mucky bottom, sloped
topography around the pond, tan cloudy water. 14. Somerset Gardens
Subdivision Small
pond, mature subdivision (established for nearly ten years) with buildings on
two sides, freeway with steep slope on two sides, now fowl waste visible,
natural vegetation with a few trees at the edge, mucky bottom, relatively clear
water. Muskrat and Blue Heron were
sited in the pond. 15. Fountain Square Subdivision Medium
pond, mature subdivision with buildings on three sides, natural vegetation on
one side, no fowl visible, substantial clear inflow, 10 feet of muck without
water at the edge, relatively clear water. 16. Tiffany Square Subdivision Small
pond, mature subdivision with buildings on two sides, road on two sides, no
fowl visible, substantial clear inflow, grass and trees at the edge, relatively
clear water. Appendix B Location
maps of pond sites. Discussion