The influence of surface color on freshwater algae growth (Chlorophyta)
Sarah L. Weeks, 2122 N 120 W Apt. 295, Provo, Utah 84604 Email: weeksls@gmail.com
Abstract:
Experiments were conducted the Provo River of Provo, Utah. Algal growth was
observed under natural conditions in this river, with tiles light and dark in color. The
purpose was to test the hypothesis that darker colored surfaces will encourage more
growth of freshwater algae (Chlorophyta) than lighter colored surfaces will. To
demonstrate this, tiles were placed in the river and periodically removed, and the
percentage of the tile covered by algae was measured with a grid placed over each tile. The
algae was then scraped off and weighed on an electric scale. It was determined that darker
colored tiles did indeed grow algae better than lighter colored tiles, according the weight
and percentage of the tiles covered. It was noted that the places on each tile where algae
were most abundant did not follow a set pattern, but I offer no explanation.
Key words: Provo River, Chlorophyta, growth, surface color.
Introduction
According to The Physics and Chemistry of Color, when light is absorbed, it will be
released into the atmosphere as heat (Nassau 2001). Furthermore, objects with a darker
color will absorb more light (Overheim,Wagner, 1982). In studies involving algal growth
and temperature, it has been determined that the temperature of the water affects the
growth of algae. As the temperature of the water increases, the amount of algae that grows
also increases (Parker et. al 2007, Raven 1988, and Marshall 1965). During an algal
collection attempt, it was determined that ceramic tiles do not encourage the growth of
algae (Chaturvedi 2008).
While working in the Provo River, I noticed that algae grew on the rocks despite the
colder temperatures of the winter weather. I wondered if one were to build an outside
fishpond, what material color would best discourage the growth of algae, and thus reduce
the amount of time required to clean the pond. I hypothesized that darker colored tiles
would grow algae better than lighter colored tiles, and decided to test this hypothesis with
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non- ceramic tiles. This was done in accordance with the above noted source, so that more
algae would grow, and increase the possibility of being able to measure the weight of the
algae.
Methods and Materials
To discover the effect the color of the surface had on the growth freshwater algae
(Chlorophyta), I bought 12 tiles of tumbled marble, of approximately one square foot in
area (929.0333 cm^2) from the Lowe’s store in Orem, Utah. Half of the tiles were dark
brown in color, the other half were off-white in color. On the 19th of February I then took
these tiles and placed them in the Provo River. Three dark tiles and three light tiles were
placed in the middle of the river, about three meters from either shore, and under an
average 20 cm of water. They were placed about one meter apart from each other. Three
dark tiles and three light tiles were placed three meters away, downstream, spaced at
about 30 cm apart. They were under a bridge about one meter in width (see Figure 1).
I returned once each week for three weeks afterwards, at approximately 10:30 am,
and removed one dark tile and one light tile from each site. For each tile, I then recorded
the percentage of surface area covered by algae. I also removed the algae from the tile, and
weighed it to the nearest hundredth of a gram on an electric scale, obtained from the
Brigham Young University Biology Stock Room. An electronic thermometer, also obtained
from the Stock Room, was used to measure the temperature of the water to the nearest
tenth in degrees Celsius.
As another evaluation of the effect of surface color on the growth of freshwater
algae (Chlorophyta), I made a square wooden frame, and at appropriate intervals of every
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centimeter tied thread across its opening, which formed a grid. This grid was then placed
over the side, top and bottom of each tile, and the percentage of the surface area that was
completely covered by algae was recorded. Water depth was measured using a ruler that
measured in inches, and the measurements were later converted to centimeters.
Results
After one week, I returned on February 26th. The weather was sunny, and warm,
with the water temperature measuring approximately 4.1 degrees Celsius. I discovered
that not enough algae had grown to cover substantially any portion of the tiles placed
under the bridge, although on both tiles there were areas around small holes in the tiles
where algae appeared to be attempting to grow. The tiles removed from the middle of the
river showed some growth. I attempted to scrape the algae off of all tiles collected, but for
no tile was I able to gather an amount that was large enough for the electric scale to weigh.
(See Table 1 and 2)
On March 5th, 2010, I observed that the water level was about 10 cm lower than the
previous week’s depth. I observed that this was odd, because the weather that day had
been snowing most of the morning, and melting when it hit the ground. The water
temperature was 3.9 degrees Celsius. The darker tiles had grown more algae than the
lighter tiles, and from the dark tile from the middle of the river, it was possible to get a
reading for the weight of the algae. (See Table 1 and 2) However, the rest of the tiles did not
yield enough algae to register a weight on the scale.
On March 12, 2010 the water temperature was 5.3 degrees Celsius. For most of the
week the weather had been warmer than the previous two weeks. The darker tiles from
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both locations had more algae growing on them than their lighter colored counterparts. For
almost all tiles, except the light tile from under the bridge, enough algae had grown to be
scraped off and weighed. (See Tables 1 and 2)
Discussion
One of the most important factors to this experiment would be the amount of
sunlight available to the algae. It was noted that in comparison to the first two weeks, the
tiles of the third week appeared to have substantially more algae. This did not appear to be
the normal amount that would accumulate after one week according to the data I had
collected the previous two weeks; rather it seemed to be an effect of the unusually warm
weather of the week leading up to the recording. In the second week the results did not
follow an expected pattern, with the darker tile from under the bridge exhibiting a larger
percentage of algae than the darker tile from the middle of the river.
According to my results, the overall pattern was that darker colored tiles
encouraged the growth of freshwater algae better, which did not vary between the two
locations. This confirmed my hypothesis that darker colored tiles would grow more algae
than lighter colored tiles. I noticed that where the algae chose to grow on each tile did not
follow any set pattern, growing better on the top of one tile, but not as well on the top on
another tile.
When comparing the lighter tiles of the same week, two things were noted. From the
tile under the bridge the top had grown more algae than the bottom. Yet as for the tile from
the middle of the river, the bottom portion of the tile had grown more algae. The reason for
this is unknown, but in the future it would be helpful to understand if the tile facing the
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surface and the sun is warmer than the surface facing the bottom of the river, and if the
flow of the water affects the temperature of any particular spot. It would also be a good
idea to know if a few centimeters of depth difference in a river could affect the
temperature.
It would further narrow the experiment to make the placement of each tile as
similar as possible to each of the other tiles, for example, placing the tiles of both locations
the same distance apart. Another variable to be considered is how depth of water might
affect how much sunlight is received, and how that would affect the growth of algae. Thus
when repeating this experiment, it would be beneficial to place all tiles at the exact same
depth.
According to a study which included the effect of water speed on algal growth, the
speed of water affects the amount of algae that grows. Slower moving waters grew more
algae than faster moving waters (Poff et. al 1990). Reattempting this experiment in slower
waters may produce more algae to weigh.
Performing this experiment in warmer weather may provide a clearer picture of the
abiotic factors that affect the growth of the algae. I hypothesize that the warmer weather of
the last week of the experiment may have been the cause of the greater algal growth for
that week. However, in weather that was continually warm it may become apparent that
algae will be slow to begin growing, but after an initial period, the algae may grow at a
faster rate than before.
By knowing that darker colored surfaces encourage the growth of freshwater algae
(Chlorophyta), when building aquariums, and outdoor marine parks, the amount of algae
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that grows could be reduced, and tanks would not need cleaning as often. This would save
time and money for the owners.
Literature Cited
Chaturvedi S. 2008 Algal biofouling on ceramic surface. Journal of Phytological Research.
21(2) p. 325-326
Marshall, Harold, G., 1965 The Annual distribution and stratification of phytoplankton at
aurora lake, portage county, Ohio. The Ohio Journal of Science 65(4): 190-202
Nassau K. 2001. The Physics and Chemistry of Color. New York (NY) John Wiley and Sons
Inc. p. 26-27
Overheim, R., Daniel, Wagner, David, L. 1982. Light and Color. New York. John Wiley and
Sons Inc. p. 40-41
Parker, F., Davidson, M., Freeman, K., Hair, S., & Daume, S. 2007. Investigation of optimal
temperature and light conditions for three benthic diatoms and their suitability to
commercial scale nursery culture of abalone (Haliotis Laevigata). Journal of Shellfish
Research, 26(3): 751-762
Poff, N., LeRoy, Voelz, Neal, J., Ward, J.,V., and Lee, R., E., 1990 Algal Colonization under Four
Experimentally-Controlled Current Regimes in High Mountain Stream. Journal of the
North American Benthological Society, 9(4): 303-318
Raven, John, A. , Geider, Richard, J. 1988. Temperature and Algal Growth. New Phytologist,
110 (4): 441-461
Appendix
Table 1:
Dark
Light
Week 1
0.0 grams
0.0 grams
Week 2
0.1 grams
0.0 grams
Week 3
.2 grams
.1 grams
The Weight of the Algae from the tiles removed from the middle of the river for each week.
Bolded data represents enough algae to be scraped off, but not enough to register a reading
from the scale. The weight represents algae removed from all sides of the tile.
Table 2
Week 1
Week 2
Dark
Light
0.0 grams
0.0 grams
0.0 grams
0.0 grams
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Week 3
0.1 grams
0.0 grams
Weight of Algae from the tiles removed from under the bridge for each week. Bolded data
represents enough algae to be scraped off, but not enough to register a reading from the
scale. The weight represents algae removed from all sides of the tile.
Table 3
Dark,
bottom
Week 1
Week 2
Week 3
Dark,
Top
Light
Bottom
Light
Top
0.13%
0.06%
0.06%
0.00%
0.56%
0.25%
0.00%
0.00%
0.06%
0.50%
0.00%
3.13%
Percentage of surface area covered for the tiles removed from the middle of the river, for
each week. A bolded 0% shows that there were signs of algal growth, but not enough to
measure.
Dark,
bottom
Week 1
Week 2
Week 3
0.00%
0.06%
0.00%
Dark,
Top
0.00%
100%
0.31%
Light
Bottom
0.00%
0.00%
0.00%
Light
Top
0.00%
0.75%
0.00%
Table 4: Percentage of surface area covered for the tiles removed from under the bridge
for each week. A bolded 0% shows that there were signs of algal growth, but not enough to
measure.
Figure 1:
A photograph of the bridge that half of the tiles were placed under. The bridge in the
foreground is the one used, not the one in the background.