a)
For the first part of the experiment, we
determined the amount of dissolved oxygen in two different water samples at
different temperatures. One was at 0° from Surprise Lake in Watchung and
the other was at 30° from Tommy’s Pond. We took the measurements of the number
of drops of sodium thiosulfate in each sample until the color changed from
purple to pale yellow or white. We also measured the pH of the samples before
we fixed them with the Winkler method. For the second part of the experiment we
determined the amount of dissolved oxygen in samples which received different
amount of sunlight after 24 hours. We also measured the amount of drops used
for the solution to change color. This experiment can help us determine the
importance of understanding ecosystem health and diversity because we see how
important environmental factors such as light affect organisms, which can in
turn affect many more individuals in a population.
b)
Our samples were taken from Tommy’s Pond in
Metuchen and Lake Surprise in Watchung. Tommy’s Pond, also known as Thomas
Pond, is a 0.4 acre pond. Grants from Green Acres and Middlesex County Urban
Forestry Advisory Committee, along with funding from the Borough Council and
landscape design support by Rutgers University faculty and students, have been
used to develop a long-term management plan for the park. The pond has been
made deeper, an aerator/fountain installed, and many plantings added. Several
community and civic groups, led by the Environmental Commission, have
participated in these efforts. Future plans include the installation of a
biofilter to continue to improve water quality and a connection from this
peaceful place to the Greenway. Lake Surprise is a 25-acre lake, at 1.0-mile
long and 100-feet wide, is in the midst of heavily populated towns. Located in
a ravine within the 2,000-acre Watchung Reservation, hemlock and pine are
interspersed with beech, maple, locust, and other hardwoods around the lake.
Lake depth averages four feet, with a number of spots on the southwest end
reaching eight feet. Painted and spotted turtles, butterflies, and birds are
its main wildlife. Miles of hiking trails take you up and down mountainous
terrain, where you’re likely to encounter deer, fox, and skunk.
c)
The objectives of the lab are to measure the
dissolved oxygen concentration, calculate gross productivity, net productivity,
and respiration rate, demonstrate the importance of carbon and oxygen cycles in
an ecosystem, identify physical and biological factors affecting solubility of
dissolved gases in aquatic ecosystems, measure primary productivity in an
aquatic ecosystem, and demonstrate the effect of light and nutrients.
d)
For part A of the experiment, our hypothesis was
that the colder sample would have more dissolved oxygen because as the
temperature of the water decreases, the ability for the water to hold oxygen
decreases. For part B of the experiment, we hypothesized that the bottle
receiving 100% light would have to most dissolved oxygen because the organisms
would have more light so they could photosynthesize.
e)
|
Percent Light
|
Dissolved Oxygen (mg/L)
|
Gross Productivity
|
Net Productivity
|
||||
|
Watchung Initial
|
10.47
6.3
|
|
|
||||
|
Watchung Dark
|
9.772
4.74
|
|
|
||||
|
Watchung 100%
|
9.074
8.98
|
-.684
4.24
|
-1.396
2.68
|
||||
|
Watchung 65%
|
6.282
6.98
|
-3.49
2.24
|
-4.188
.68
|
||||
|
Watchung 25%
|
5.584
5.49
|
-4.188
.75
|
-4.886
-.81
|
||||
|
Watchung 10%
|
5.584
4.98
|
-4.188
.24
|
-4.886
-.81
|
||||
|
Watchung 2%
|
8.376
4.24
|
-1.4
-.5
|
-2.094
-2.06
|
||||
|
Percent Light
|
Dissolved Oxygen (mg/L)
|
Gross Productivity
|
Net Productivity
|
||||
|
Tommy Pond Initial
|
6.3
|
|
|
||||
|
Tommy Pond Dark
|
4.4
|
|
|
||||
|
Tommy Pond 100%
|
6.98
|
2.58
|
.68
|
||||
|
Tommy Pond 65%
|
.35
|
6.63
|
-5.95
|
||||
|
Tommy Pond 25%
|
6.98
|
0
|
.68
|
||||
|
Tommy Pond 10%
|
|
|
|
||||
|
Tommy Pond 2%
|
2.5
|
4.48
|
-3.8
|
||||
|
Percent Light
|
Dissolved Oxygen (mg/L)
|
Gross Productivity
|
Net Productivity
|
|
Angela’s Creek Initial
|
3.5598
|
|
|
|
Angela’s Creek Dark
|
2.2336
|
|
|
|
Angela’s 100%
|
3.0014
|
.7678
|
-.5584
|
|
Angela’s 65%
|
3.5598
|
1.3262
|
0
|
|
Angela’s 25%
|
3.49
|
1.2564
|
-.0698
|
|
Angela’s 10%
|
3.49
|
1.2564
|
-.0698
|
|
Angela’s 2%
|
3.2108
|
.9772
|
-.349
|
Readings of Water Sample: 0° Lake Surprise
Dissolved oxygen: 6.481, pH: 6.6
Readings of Water Sample: 30° Tommy’s Pond
Dissolved Oxygen (with calculations):
29 drops, 1 mL =
28 drops
29/28 = 1.03571 mg O2 / L * .698 * 10= mL O2 /
L 1.03571 * .698 * 10 =
7.23
pH: 6.53
f)
We tested the samples of water at different
temperatures in part A to determine if cold water could hold more dissolved
oxygen than warm water. Our hypothesis was not supported by our data, but that
may be due to error in our process. For example, we forgot to put the cold
water on ice, while we performed the procedure for the experiment. There fore
the water may not have been as cold as it should have been. For part B, our hypothesis was correct,
although our numbers were slightly larger than the expected outcome, which we
acquired from the Ward’s lab. For part A, our results mean that we may have
made an error in counting the number of drops it took to change the color of
the sample from purple to colorless. In part B, our results mean that the
amount of dissolved oxygen in the water depends on the amount of light the
water receives because photosynthesis that takes place in phototrophic
organisms in the water depends on light. The results for dissolved oxygen in
Angela’s creek were much lower than the results of dissolved oxygen in Lake
Surprise. This could mean that Angela’s creek was in a much more shady area
than Lake Surprise.
g)
Comparison or the Winkler and Vernier method:
Both the Winkler and the Vernier method are
used to calculate the amount of dissolved oxygen in a water sample. The Winkler
method however uses chemicals to determine the dissolved oxygen content. The
procedure to do this involves the addition of alkaline iodide and manganous
sulfate to a water sample, which produces man-alkaline hydroxide. Then after a teacher
adds acid to the sample, the
man-alkaline hydroxide is converted to a manganese compound by the oxygen in
the water sample. The compound reacts with the iodide to release iodine, which
gives the water a dark yellow coloring. The amount of free iodine present is equivalent
to the amount of oxygen in the water. The amount of iodine can be measured by
titration with sodium thiosulfate . The experimenter stops adding drops of
sodium thiosulfate when the sample loses its coloring. This method has a precision
range of .1 to .6, however there is a wide range for human error present. On
the other hand the Vernier method uses a probe first cleaned with distilled
water before use, which is then attached to the Vernier device which will tell
you the amount of dissolved oxygen in the sample after the probe is inserted
into the water sample.
h) In conclusion, our hypothesis for part A was
not supported but our hypothesis for part B was supported. From part A, we
learned that different lakes at different temperatures may have a similar pH,
but they have different amounts of dissolved oxygen. From part B, we learned
that the amount of light allowed in a sample of water affects the amount of
dissolved oxygen in the sample. Some sources of error could be that we could
have incorrectly counted the number of drops it took to change the sample from
purple to colorless, we measured the amount of sodium thiosulfate in drops and
not milliliters so we had to do a rough conversion, and we may have moved the
samples around too much, and the turbidity of the water could have added extra
oxygen from the inside of the sample container. Our data could be used by water
treatment facilities, land developers, or the government to determine whether
or not a human community could be sustained nearby without harming the
ecosystem. For example, if the sewage ran into the water source, it could kill
all the organisms or promote the growth of bacteria that could make the
ecosystem unbalanced.
i.)
Organizations like The borough of Metuchen environmental
commission distributed a flyer on earth day focusing on non point source pollution to homeowner living near Thomas
pond. They knew that the pond was being polluted by utilizing data similar to
the data that was collected during the lab that pertains to the health of the
lake. The Metuchen high school environmental
club participated in taking water samples from Tommy’s pond that would then go
one to be tested so that updated information on the health of the pond could be
recorded.
j.) A conservation/ action plan that could be instated would be that if
residents living near or around lake surprise or Tommy’s lake where to received
an informational package in the mail that would stress their importance and
impact on the health of these two ponds, and would also include recommendations
of different house hold products such as dishwashing liquid that they can use that
are low in phosphate levels and eco friendly. These products would decrease the
harm being imposed on the lake by these household products. A conservation/ action plan that could also be
set into place for lake surprise, would be if the horse stables that was on the
reservation where made to store their manure pile (which is high in phosphate
levels) somewhere in which it would be impossible for it become polluted runoff
that would enter the lake. This would help conserve the lake because high
phosphate levels in a lake, promote algae blooms, which in turn depletes the
oxygen levels in the lake when the algae is growing, and when it dies and is
eaten by anaerobic bacteria.
K.)Citations:
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