THE EFFECT OF VARYING ROAD SALTS ON THE OXYGEN PRODUCTION OF
ALGAE.
By:
Honors Biology
Mrs. Rosperich
2/15/2010
2
TABLE OF CONTENTS
Statement of the Problem ............................................................................................................ 3
Hypothesis ................................................................................................................................... 4
Literature review ......................................................................................................................... 5
Materials……………………………………………………………………………………….10
Procedures……………………………………………………………………………………..11
Results ....................................................................................................................................... 13
Conclusions ............................................................................................................................... 16
References……………………………………………………………………………………..20
3
STATEMENT OF THE PROBLEM
How do sodium chloride, calcium chloride, and magnesium chloride road salts affect the
oxygen production of freshwater algae?
4
HYPOTHESIS
If different types of road salt, such as sodium chloride (NaCl), calcium chloride (CaCl2),
and magnesium chloride (MgCl2) enter freshwater environments that contain algae, then the
oxygen production of algae exposed to magnesium chloride will decrease the least
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LITERATURE REVIEW
In order to combat the harsh winters that are bestowed on the U.S annually, cities use
more than 18 million tons of road salt each year (Morton, 2010). Although the road salt is
beneficial to the safety of humans, it also has a major adverse effect on many freshwater
ecosystems. The salt reaches rivers and streams through snow runoff, and once in the water
quickly increases the salinity. This increase can cause major environmental issues, as most
freshwater species cannot live in a saltwater environment. One of the most crucial organisms
living in freshwater habitats are algae, aquatic plants that conduct photosynthesis. According to
Roach (2004), more than half of the world’s oxygen is produced by freshwater and saltwater
algae. Without this vital source, Earth would not be able to maintain the amount of life that lives
on it today. Because of freshwater algae’s’ importance, it is vital that their environment is stable
and healthy. If different types of road salt, such as sodium chloride (NaCl), calcium chloride
(CaCl2), and magnesium chloride (MgCl2) enter freshwater environments that contain algae, then
the oxygen production of algae may be severely reduced.
By definition, the term “road salts” usually refers to the three common chloride
salts used to treat roads: sodium chloride (NaCl), calcium chloride (CaCl2), and
magnesium chloride (MgCl2) along with an anti-clumping agent, ferrocyanide salt
(Hounsell, Mercer, & Lintner, 2006). Road salts work by lowering the freezing point of
water. When snow or ice accumulates, it forms a bond with the surface of a roadway or
sidewalk. Road salts dissolve in the available water in snow or ice to form brine. This
brine then breaks the bond of ice or snow to the surface of the roadway by lowering the
freezing temperature (Hounsell et all. 2006). Because of road salt’s efficiency and
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reliability, it is used commonly and generously throughout the U.S and other countries.
However, all of the salt cannot always be picked up and this leads to many environmental
problems.
Each of the common chemical road salts: sodium, magnesium, and calcium chlorides
found in the U.S, have certain characteristics and benefits that define it. According to Kylar
(2003), sodium chloride is an effective deicer for areas that receive road traffic. It draws heat
from the environment rather than releasing it and it loses most of its deicing effectiveness when
temperatures are below 25 degrees F. Heat generated by the friction of moving traffic on busy
roadways assists rock salt's effectiveness. Calcium chloride often outperforms other deicing
products especially at lower temperatures. It produces an exothermic reaction, giving off heat as
it melts. Calcium chloride also has a greater capacity to attract and retain moisture directly from
its surroundings, which enables it to dissolve faster and start the melting process (Kylar, 2003).
Magnesium chloride is very similar to calcium chloride but it is considered less corrosive, safer
for use on concrete and less damaging to plants (Kylar, 2003). It has been noted, however, that
high concentrations of MgCl2 ions in the soil with plants may be toxic or change water
relationships such that plants cannot easily accumulate water and nutrients (Goodrich and Jacobi,
2008).
After the road salt is used to de-ice roads, it causes many ecological problems throughout
the region. Instead of disappearing, the road salt washes into lakes, streams, groundwater, and
the public water supply through snow runoff. Once there, the road salt remains there,
contaminates the water, and greatly increases the salinity. According to Homstad (2010),
researchers at the University of Minnesota recently found that, in Minneapolis, 70 percent of the
salt applied to roads stays within the region's watershed, and the rest of the salt drains into the
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Mississippi River. Once the road salt reaches a lake or other freshwater source, it begins to
contaminate and kill the organisms that live in that environment. It has been shown that
continuous levels of chloride concentration as low as 230 mg/L (equivalent to roughly 1
teaspoon of salt in 5 gallons of water) have been shown to be harmful to aquatic life (Homstad,
2010).
Plants and vegetation are greatly affected by the road salt that is put on roads. Road salts
reach plants through runoff, and then they are quickly absorbed into the soil. According to
Wegner and Yaggi (2001), road salts that are added into soil cause elevated sodium and chloride
levels that create osmotic imbalances in plants, which lowers water absorption and reduces root
growth. Road salts also disrupt the uptake of plant nutrients and hinder long-term growth, which
may cause a lower concentration of the plant in an area. This information can possibly be applied
to algae, as it is a marine plant-like organism, and would experience many of the same problems
faced by terrestrial plants. However, algae are also very different from land plants in a variety of
ways, as algae live in a completely dissimilar environment.
One of the most important of all living plants is the aquatic phytoplankton or algae. Algae
is usually unicellular protists (single-celled aquatic plants) that grow abundantly and are the basis
of the marine food chain. One of the most abundant is the diatom, a one-celled protist with a
delicate, thin shell made of silica (Spaulding & Namowitz, 2003). While diatoms are essentially
cool water inhabitants, their counterparts in tropical waters are called dinoflagellates. Equipped
with whip-like projections, they propel themselves about in a jerky motion, while also (like
diatoms) having the ability to photosynthesize, (Stout, 2001). Another important group of algae
are the coccolithophorids, unicellular little plants with calcite shells (Phillips, 2005).
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Algae are extremely important to the environment in numerous ways. Most of the food
chains in the ocean begin with algae, which are eaten by tiny zooplankton. These tiny
zooplankton in turn are eaten by larger animals living under the water, including sharks and blue
whales, and so on, (Kaya, 2004). Without algae, many ecosystems would not be able to function
properly. Algae are not only significant for their food-chain value, but also for their rare ability
as marine organisms to photosynthesize. Algae photosynthesize by absorbing energy from the
sun, carbon dioxide from various mammals/the atmosphere, and nutrients from the water through
their cell walls. These items are then converted into oxygen (which is released into the water)
and glucose (Roach, 2010). Through this process, Earth receives more than half of the oxygen in
the atmosphere from algae.
In order to survive, algae depend upon sunlight, water, and nutrients. Physical or
chemical change in any of these three ingredients over time for a given region will affect the
algae/algae concentrations there. It has been proven that populations of this marine plant will be
greatly affected (mainly by increasing or decreasing rapidly) in response to changes in its
environment. Based on this fact, scientists can be alerted that there may be environmental change
going on in a certain area, (Herring, 2003). It can be inferred from this information, that the
introduction of road salts into a freshwater environment that contain algae will have an effect on
the concentration of the algae due to a change in the chemical properties of the water that the
algae is living in. There is also a change in the nutrients that the algae are getting, as road salt
may contaminate these nutrients, which would directly cause adverse effects on the algae.
The experiment that will be conducted will test how sodium chloride (NaCl), calcium
chloride (CaCl2), and magnesium chloride (MgCl2) road salts, which are used throughout the
U.S., affect freshwater algae and their oxygen production. This is scientifically important as
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increasing amounts of road salt continue to be drained into freshwater sources, where vital algae
populations live, each year. If action is not taken to help stop road salt from being introduced to
freshwater supplies, algae may consequently be affected adversely. If the road salts reduce
freshwater algae’s’ oxygen production ability, these organism may not be able to
photosynthesize properly, which would lead to a decrease in oxygen in the atmosphere, this in
turn could cause catastrophic results. This experiment is different than experiments done in the
past mainly because in this one, sodium, magnesium, and calcium chlorides all will be tested on
algae rather than only one type of road salt. This will clearly illustrate which types of road salt
are the most harmful and which are the least harmful, something that hasn’t been done before
and could be used for numerous applications. The independent variable in this experiment are the
different types of road salt, including salts that use sodium chloride (NaCl), calcium chloride
(CaCl2), and magnesium chloride (MgCl2) in order to deice roads. The dependent variable will
be the amount of oxygen released by the algae. The control in this experiment will be freshwater
algae that are placed in tap water without any road salts added to the water. The amount of
oxygen produced/released by this algae group will be used to compare against the algae that are
in water with different road salts. The amount of oxygen produced will be measured through a
dissolved oxygen test kit, which will accurately measure the results of the experiment. The main
constants would be the amount of light each plant receives, the length of time that all algaes be
with or without road salts, the amount of algae per container, the amount of road salt for each
algae group, and the amount of water each algae group is in.
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MATERIALS
 2 40 watt grow lights
 40 ml of algae
 60 Hefty Crystal Clear cups (15 for each type of algae with road salt and control), each
holds 250 ml
 6 liters of water
 22.68 kg of SafeStep magnesium chloride
 9.07 kg of Prestone Heat calcium chloride pellets
 22.68 kg of Halite Salt Crystals sodium chloride
 1 Pipette
 Mini Lab Oxygen Test Kit for Freshwater and Saltwater (dissolved oxygen test kit)
 Timer
 50-ml graduated cylinder
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PROCEDURES
1. Place the 2 40 watt grow lights in a uniform environment where they emanate equal light
(such as one large table, bench, etc)
2. Add 15 drops of algae culture using the pipette into all the cups
3. Fill the 60 cups with 50 ml of water each using the graduated cylinder, ensuring that the
water covers the algae
4. Add/mix 4 grams of road salt into 45 of the cups, with 15 cups containing magnesium
chloride, 15 cups with calcium chloride, 15 with sodium chloride, and the other 15 cups
represents the control (has algae without any road salts)
5. Place two groups of algae under each grow light.
6. Ensure that each light is only on for 10 hours a day (turn off the lights after 14 hours
every day, or set a timer)
7. Measure the oxygen released by each algae group over a period of three days using a
dissolved oxygen test kit, measuring the amount of oxygen produced at the end of the
third day
1. To use a dissolved oxygen test kit first take a sample of the water
in a half liter water bottle (after three days)
2. Add one type of chemical (sodium thiosulfate) to the sample
3. Then add a second type of chemical (manganous sulfate) to sample
4. Place stopper on the water bottle immediately
5. Shake rapidly to mix water and chemicals
6. A cloudy mixture called floc will form.
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7. If oxygen is present, the floc will be orange
8. Compare and record the amount of oxygen produced by each algae group against the
control using the data from the dissolved oxygen test kit
9. Because the data is quantitative in this experiment use multiple t-tests to analyze data
10. Repeat steps 1-9 more times for best results
Note: the constants are the type and size of the cup/container, amount of road salt for each cup,
amount of potting soil, amount of algae, type of algae, and the amount of time each algae group
is exposed to the light and salt.
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RESULTS
The purpose of this study was to demonstrate the effects of road salt on algae’s oxygen
production. The independent variables in this experiment were the road salts used which
included magnesium chloride (MgCl2), sodium chloride (NaCl), and calcium chloride (CaCl2).
The dependent variable was the oxygen production of the algae, measured by using a dissolved
oxygen test kit. The control group used to compare the road salt groups was algae placed in tap
water without road salt. Quantitative (ratio) data was measured in this experiment through a
dissolved oxygen parts per million (ppm) scale.
As seen in Table 1, the mean of the control’s oxygen production was 5.6 ppm. The
means of the magnesium and sodium chloride groups’ oxygen productions were 4.5 and 5.9
ppm, respectively. In addition, the mean of the calcium chloride group’s oxygen production was
6 ppm. As shown in Figure 1, the mean oxygen production of the calcium chloride group was the
greatest while the mean oxygen production of magnesium chloride was the least. Many t-tests
were conducted to test for statistically significant data in this experiment. t-tests were used to
compare the groups with road salts’ oxygen production to the control’s oxygen production and to
each other to find if road salt significantly affected algae oxygen production.
The null hypothesis stated that if different types of road salt, such as sodium chloride
(NaCl), calcium chloride (CaCl2), and magnesium chloride (MgCl2) enter freshwater
environments that contain algae, then the oxygen production of algae will not be affected. This
hypothesis was rejected as the magnesium chloride group’s oxygen production was statistically
different from the control with a p value of p = .0000027 (p < .005). However, as shown in Table
1, there was no statistically significant difference between the sodium chloride group’s oxygen
production and the control with a p value of 0.19 (p >.005). In addition, there were no
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statistically significant differences between the calcium chloride group’s oxygen production and
the control as there was a p value of 0.10 (p >.005).
The alternate hypothesis stated that if different types of road salt, such as sodium chloride
(NaCl), calcium chloride (CaCl2), and magnesium chloride (MgCl2) enter freshwater
environments that contain algae, then the oxygen production of algae exposed to magnesium
chloride will decrease the least. This hypothesis was not supported by the data and must be
rejected. According to Table 1, the mean oxygen production of the magnesium chloride group
was 4.5 ppm. In Figure 1, this is clearly shown as the lowest value and mean out of all of the
road salts. In addition, as seen in Table 1, the magnesium chloride group’s oxygen production
was statistically different from the control with a p value of.0000027. This statistically
significant data does not mean that the alternate hypothesis is supported, but rather that it is not
supported. This data and p value shows that magnesium chloride significantly decreased the
oxygen production of algae, instead of making the algae decrease the least. Therefore the
hypothesis is not supported by the data and is rejected.
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TABLE 1: THE EFFECT OF ROAD SALTS ON ALGAE OXYGEN PRODUCTION (ppm)
Control Group
Amount of Oxygen
produced (ppm)
Sodium Chloride
Group
Amount of Oxygen
produced (ppm)
Calcium Chloride
Group
Amount of Oxygen
produced (ppm)
Magnesium
Chloride Group
Amount of
Oxygen produced
(ppm)
Mean
5.6 ppm
5.9 ppm
6 ppm
4.5 ppm
Variance
0.26
0.64
0.57
0.41
Standard Deviation
0.51
0.80
0.76
0.64
Number
15
15
15
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Results of t-test
Sodium Chloride
vs. Calcium
Chloride
p = 0.82
Sodium Chloride
vs. Magnesium
Chloride
p = 0.0000014
Sodium Chloride
vs. Control
p = 0.19
Calcium Chloride
vs. Control
p =0.10
Calcium Chloride
vs. Magnesium
Chloride
p = 0.00000041
Magnesium
Chloride vs.
Control
p = .0000027
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CONCLUSIONS
The purpose of this study was to demonstrate the effects of various road salts on algae’s
oxygen production. The alternate hypothesis stated that if different types of road salt, such as
sodium chloride (NaCl), calcium chloride (CaCl2), and magnesium chloride (MgCl2) enter
freshwater environments that contain algae, then the oxygen production of algae exposed to
magnesium chloride would decrease the least. This hypothesis was not supported by the
data/findings and must be rejected. According to Table 1, the mean oxygen production of the
magnesium chloride group was 4.5 ppm. In Figure 1, this is clearly shown as the lowest value
and mean out of all of the road salts. In addition, as seen in Table 1, a t-test found that the
magnesium chloride group’s oxygen production was statistically different from the control group
with a p value of 0.0000027. However, this statistically significant data does not mean that the
alternate hypothesis is supported, but rather that it is not supported. This data and p value shows
that magnesium chloride significantly decreased the oxygen production of algae the most,
instead of making the algae’s oxygen production decrease the least. Therefore the hypothesis is
not supported by the data and is rejected. The other road salts had no significant effect on algae
oxygen production as shown in Table 1 as there was no statistically significant difference
between the sodium chloride group’s oxygen production and the control with a p value of 0.19 (P
>.005). Also, there were no statistically significant differences between the calcium chloride
group’s oxygen production and the control as there was a p value of 0.10 (p >.005). To
summarize this, based on numerous t-tests, only magnesium chloride greatly affected oxygen
production of algae, all of the other road salts had no significant impact on the oxygen
production.
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The magnesium chloride may have decreased the oxygen production the most for several
reasons. One main reason is that the magnesium chloride may have deeply affected the way the
algae functions. It has been found that high concentrations of MgCl2 ions in plants may be toxic
or change water relationships such that the plant cannot easily accumulate water and nutrients
(Goodrich and Jacobi, 2008). This could have happened to the algae as it may have absorbed the
magnesium chloride which may have led to the algae not being able to take in nutrients and
water, effectively crippling the algae and consequently its oxygen production. This decrease may
also have occurred as it has been proven that road salts, such as magnesium chloride, that are
added to plants can create osmotic imbalances in plants, which lowers water absorption, disrupts
uptake of nutrients, and reduces root growth in addition to hindering long-term growth (Wegner
& Yaggi, 2001). The algae in the magnesium chloride group may have experienced this, and
would not have had the ability to take in the proper nutrients to function and survive, leading to a
decrease in production of oxygen as reflected in the experiment.
The sodium and calcium chloride was shown to have had little to no effect on oxygen
production of algae. As seen in Table 1, the mean oxygen productions of sodium chloride and
calcium chloride were 5.9 and 6 ppm, respectively. Both of these values were only slightly
greater than the control of 5.6 ppm.
Uncertainty is clearly present in this experiment and its results. One source of uncertainty
was the measurement of algae. Algae was measured through a pipette, however exact and equal
measurements/volumes of algae could not be done through the pipette, leading to some cups
containing slightly more or slightly less algae than others. This could be solved by using a
graduated cylinder to measure precise and extremely exact amounts of algae into every
container, which would make all containers have the same amount of algae. Uncertainty was also
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seen in the measurement of road salt. Road salt was measured through a teaspoon, but
differences in physical structures of road salt (pellet vs. small grains) lead to slightly different
quantities of each road salt used in each group. This could be solved by using road salts that all
have similar physical structures. There appears to be no systematic errors in the
execution/performance of this experiment. Most directions were followed exactly and accurately.
Also, there appears to be no random errors as no mistakes were made while performing this
experiment. In addition, there appears to be no limitations in the instrumentation and methods
used in this experiment.
The results of this experiment can be generalized for all freshwater species of algae as
these types of algae share many common chemical characteristics, which also means that they
will react in similar ways if exposed to road salts.
If this experiment were to be replicated, a few improvements could be made. The
measurement of algae could be more precise using a graduated cylinder or other specific
measurement tool. The road salts could be measured more exactly and equally though the use of
a scale or graduated cylinder. An increase in the number of days of testing would also give better
and more accurate results, as the long term effects and mortality of the algae could also be noted
over a longer period of time.
The results of this experiment could benefit society greatly. The results of this experiment
reveal the fact that magnesium chloride, which is somewhat used in this area, is considered
harmful to algae oxygen production. Because of this, it may be helpful to establish laws that
restrict the use of magnesium chloride in areas where algae is present or nearby. There is a
discrepancy however, on the true effects/strength of magnesium chloride as recent studies have
found conflicting results about how harmful the effects of magnesium chloride are. Therefore
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more studies should be conducted before creating a definitive answer on the true effects of
magnesium chloride on vegetation and algae.
This experiment and the results helped raise questions for future research. These include
how do various amounts of road salt affect algae oxygen production? How do road salts affect
saltwater algae’s oxygen production? How does sodium chloride affect different types of algae’s
oxygen production? How does calcium chloride affect different types of algae’s oxygen
production? How do different road salts affect the mortality rate of freshwater fish?
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REFERENCES
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http://www.ext.colostate.edu/pubs/garden/07425.html
Herring, D. (2003). What are Algae? NASA Earth Observatory, Retrieved from
http://earthobservatory.nasa.gov/Features/Algae/algae1 on June 12, 2010
Homstad, M. (2010). Hold the salt. Minnesota Conservation Volunteer, 9 (5), 46-47.
Hounsell, J, Mercer, K, & Lintner, A. (2006). A low-salt diet for Ontario's roads and rivers. 2-6.
Kaya, Z. (2004). The bottom of the food chain plankton. Fountain Magazine, 15(4), 16-18.
Kylar-Kievet, D. (2003). Deicing strategies for safeguarding both guest and the environment.
Green Resources for the Green Hotel, Retrieved from
http://www.vtgreenhotels.org/articles/deice.htm on October 2, 2010
Morton, M.C. (2009). Clearing roadways: a little salt goes a long way. Earth Magazine.
Retrieved from http://www.earthmagazine.org/earth/article/2b1-7d9-b-11 on November
29, 2010.
Phillips, J. (2005). Plankton power: foundation of marine life. Florida Sportsman, 6 (5), 34-37.
Roach, J. (2004). Source of half earth's oxygen gets little credit. National Geographic, 345 (1),
45-46.
Spaulding, N.E, & Namowitz, S.N. (2003). Earth science. Evanston, Illinois: McDougal Littell.
Stout, P. (2007). Algae: plants of the sea. Rhode Island Sea Grant, 57, 637-638.
Wegner, W, & Yaggi, M. (2001). Environmental impacts of road salt and alternatives in the new
york city watershed. Stormwater, 2 (4), 20-23.