Dissolved Oxygen and Primary Aquatic Productivity by xwm19580

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									               A Shady Situation:
An Examination Of The Effects Of Temperature And
    Light Concentration On Dissolved Oxygen




                           Sally Tyro
               Honors Freshmen Laboratory Science
            Wilson High School, Tacoma Public Schools
                            Period 1


                        February 18, 2010
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                       JUST COPYING THE TEXT.
            YOU NEED TO INSERT THE ACTUAL FORM!!!!

A Shady Situation: An Examination Of The Effects Of Temperature And Light
Concentration On Dissolved Oxygen
Sally Tyro
Wilson High School, Tacoma Public Schools, Tacoma, Washington



The purpose of this lab was to better understand the environmental affects on dissolved oxygen
content in an aquatic environment. Two different but related phenomena surrounding dissolved
oxygen in regular pond water were examined. First, the connection between temperature and
dissolved oxygen concentration was tested at 5° C and 21.5° C. Second, dissolved oxygen
concentration was used to determine net productivity in different light conditions (100%, 65%,
25%, 10%, 2%). Temperature was determined to have an inverse correlation to the solubility of
oxygen in water but directly correlated to percent concentration. As temperature rose the dissolved
oxygen levels decreased, 5° C water sample had 2.0 mg/l of dissolved oxygen and the 21.5° C
sample had 1.28 mg/l. The percent saturation showed that even though the 5° C sample, 16%,
contained more dissolved oxygen it was still less saturated than the 21.5° C sample, 19% saturated.
In limiting the amount of light, the natural oxygen balance between photosynthesis and respiration
was interrupted. The initial sample had 9.2ml O2/l while the net productivity in the 100% light
condition with -2.8ml O2/l, a difference of 12.0ml O2/l. In aquatic environments, an absence of
sufficient dissolved oxygen is an indicator of poor water quality. The data clearly shows that any
limit in amount of light causes a decrease in dissolved oxygen. This has direct implications on the
health of a pond. Trees provide shade for pond organisms, but blocking out too much light may be
detrimental to the water quality of a pond.
                                                                                                Tyro 3

                                         INTRODUCTION
Dissolved oxygen, DO, is a measure of the relative amount of oxygen dissolved in water. DO levels
are an extremely important factor in determining the quality of an aquatic environment as oxygen is
necessary for the metabolic processes of almost every organism on land and in the water. Since
terrestrial, or land, environments hold over 95% more oxygen than aquatic, or water, environments,
oxygen levels in aquatic environments fluctuate and are very vulnerable to even the slightest
environmental change. Oxygen is replenished from the atmosphere and through the process of
photosynthesis (Markfort and Hondzo 1766-1774).

There are several factors that affect the dissolved oxygen levels in aquatic environments.
Temperature is inversely proportional to the amount of dissolved oxygen in water. As temperature
rises, dissolved oxygen levels decrease. Wind allows oxygen to be mixed into the water at the
surface. Periods of windlessness, especially those at night when photosynthesis does not occur, can
lead to oxygen depletion in aquatic environments. Turbulence also increases the mixture of oxygen
and water at the surface. This turbulence is caused by obstacles, such as rocks, fallen logs, and
waterfalls and can cause extreme variations in oxygen levels throughout the course of a stream
(Markfort and Hondzo 1766-1774). Water environments may be classified by their trophic state, the
amount of nutrients in the water. There are two trophic classifications: oligotrophic and eutrophic.
Oligotrophic lakes are oxygen rich but generally nutrient poor. Their oxygen levels are constant.
Eutrophic lakes are nutrient rich and have variable levels of oxygen that constantly fluctuate from
high to low. Oligotrophic lakes are clearer and deeper than eutrophic lakes (Kevern, King, and
Ring).

There are three main gases dissolved in aquatic environments: nitrogen, oxygen, and carbon dioxide
(KY Water Watch). Most gases obey Henry’s law, which says that at a constant temperature, the
amount of gas absorbed by a given volume of liquid is proportional to the pressure in the
atmosphere that the gas exerts.
                                             c = K ×p
                                 in which…
                                 c = Concentration of the gas that is absorbed
                                 K = Solubility factor
                                 p = Partial pressure of the gas
Altitude may affect the p value of the equation. Higher altitudes decrease the solubility of gases in
water. Temperature also has an affect, as temperature rises, solubility decreases. Salinity, the
occurrence of various minerals in solution, also lowers the solubility of gases in water (Sanders).

Oxygen isn’t the only important consideration in looking at an aquatic environment; it acts in
conjunction with other factors. Photosynthesis, the process plants use to convert light energy into
chemical energy, releases oxygen as a byproduct and, therefore, contributes to the amount of
dissolved oxygen as well as the amount of chemical energy available in an aquatic environment.
The equation for photosynthesis is as follows:
                             12H2O + 6CO2 → C6H12O6 + 6O2 + 6H2O
In the presence of light energy water and carbon dioxide react within the chloroplast, an organelle in
a plant cell, to form a simple sugar, chemical energy, releasing oxygen gas and water as by-products
(Carter, Photosynthesis).
                                                                                                  Tyro 4

The flow of energy through a community begins with photosynthesis, the chemical energy
“creators”. This energy can be tracked from sun to plant. The sun’s energy used in photosynthesis is
called gross primary production. The energy accumulated by plants is called primary production
and is the first and most basic form of chemical energy storage. The energy remaining after plant
respiration and stored as organic matter in the plant is called the net primary production, or growth
of the plant (Carter, Photosynthesis).

Ponds do not only contain plant material but also animal. From the microscopic to the macroscopic,
organisms inhabit every facet of the pond ecosystem. One drop of pond water likely contains
multiple microscopic plants and animals, referred to as plankton. As if in an opposite reaction to
photosynthesis, plants in the dark and animals in both light and dark go through the process of
cellular respirations. Cellular respiration, the process of making useable cellular energy from food,
involves multiple steps. It starts with the process of glycolysis, the splitting of sugar, a 6-carbon
molecule, into two pyruvic acids, each is a 3-carbon molecule. Then the pyruvic acid reacts with
oxygen to further produce useable energy with carbon dioxide as a by-product (Carter, Cellular
Respiration and Fermentation).

This lab will look at two different but related phenomena surrounding dissolved oxygen. First, the
connection between temperature and dissolved oxygen concentration was examined. Second,
dissolved oxygen concentration and gross and net productivity of plants was measured in different
light conditions (100%, 65%, 25%, 10%, 2%). The purpose of this lab was to better understand the
environmental affects on dissolved oxygen content in an aquatic environment.


                                     TESTABLE QUESTION
How does temperature affect the dissolved oxygen in pond water? Further, how does the amount of
light affect the dissolved oxygen and aquatic productivity in pond water?


                                            VARIABLES
MV: temperature and amount of light
RV: dissolved oxygen and aquatic productivity measure through dissolved oxygen
CVs: containers, amount & type of organic material, amount of water, location of water sample


                                            HYPOTHESIS
It was hypothesized that if dissolved oxygen is measured over increasing temperatures and primary
aquatic productivity is measured over differing intensities of light, then the amount of dissolved
oxygen will increase as the temperatures increases and the amount of primary aquatic productivity
will increase as the amount of light increases. The temperature/dissolved oxygen relationship is
because increases in temperature generally speed up chemical reactions, so photosynthesis will
occur faster, creating more oxygen in the water. The light/aquatic productivity relationship will
occur because cellular respiration is not affected by light and will therefore be constant over all light
conditions but an increase in light will provide more energy for photosynthesis, creating more
photosynthesis and thus more by-product, oxygen.


                                            MATERIALS
                                                                                                 Tyro 5

Measurement of Dissolved Oxygen: sample bottle of water from a natural source, a BOD bottle,
thermometer, mangonous sulfate, alkaline iodide, thiosulfate, a 2-mL pipette, sulfuric acid, a 20-mL
sample cup, a white piece of paper, starch solution, and a nomograph.

Measurement of Primary Productivity: sample bottle of water from a natural source, 7 BOD
bottles, aluminum foil, 17 cloth screens, rubber bands, a light, thermometer, concavity slides, light
microscope, mangonous sulfate, alkaline iodide, thiosulfate, a 2-mL pipette, sulfuric acid, a 20-mL
sample cup, a white piece of paper, starch solution, and a nomograph

Productivity Simulation: pencil, paper, calculator, and graph paper.


                                               SAFETY
Chemical hazard: goggles, lab apron,


                                             PROCEDURES
1. Fill a six sample bottles (three trials for each test) was filled from a natural source making sure
   there were no air bubbles.
2. Take one sample bottle and leave the sample bottle in the refrigerator until it reached 5°C.
3. Make a wet mount to observe under a light source, to identify the different organisms present.
   Identify and list the organisms present.

Measurement of Dissolved Oxygen
1. Fill a BOD bottle with the sample water until it contains no air bubbles.
2. Add eight drops of mangonous sulfate to the bottle.
3. Add eight drops of alkaline iodide, forming the precipitate manganous hydroxide.
4. Invert the bottle several times and then allow the precipitate to settle until it is below the
    shoulders of the bottle.
5. While the solution was settling, fill a 2mL pipette with thiosulfate.
6. Add a scoop of sulfuric acid to the bottle and invert until all of the precipitate dissolved. (Detect
    a yellowish color to the sample).
7. Pour 20mL of the sample into the sample cup.
8. Place the cup on a white sheet of paper so that the color changes could be observed.
9. Add 8 drops of starch solution to the sample. (It will turn purple.)
10. Titrated the sample with the thiosulfate. Add one drop of the titrant at a time until the color
    changes to a pale yellow color. Count and record the number of drops added.
11. Use a nomograph to determine the percent saturation of dissolved oxygen in the sample. Record
    the answer.
12. Repeat process two more times.

Measurement of Primary Productivity
1. Fill seven BOD bottles completely with the sample with no air bubbles.
           a. Label the first bottle #1-Initial.
           b. Label the second bottle #2-Dark, which serves as the dark bottle.
           c. Label the other five bottles each according to the light intensity: #3-100%, #4-65%,
               #5-25%, #6-10%, and #7-2%.
                                                                                              Tyro 6

2. Wrap bottle #2 completely in aluminum foil so that it received no light. Hold the screens in
   place with rubber bands.
3. Fix bottle #1 by following the Winkler method.
          a. Add eight drops of mangonous sulfate to the bottle.
          b. Add eight drops of alkaline iodide to form the precipitate manganous hydroxide.
          c. Invert the bottle several times and allow the precipitate to settle below the shoulders
               of the bottle.
          d. Add a scoop of sulfuric acid and invert the bottle until all of the precipitate
               dissolved. The sample will turn a shade of yellow.
          e. Leave the sample at room temperature until the other samples will be processed.
4. Wrap the other five bottles in screens to produce the desired light intensity.
          a. Bottle #3 - no screens, bottle #4 - 1 screen, bottle #5 - 3 screens, bottle #6 - 5
               screens, and bottle #7 - 8 screens.
5. Place bottles #2-7 under a light source and leave overnight.
6. The next day, fix bottles #2-7 following the same method used on Bottle #1 (see Measurement
   of Primary Productivity procedure 3a-e).
7. Determine the dissolved oxygen levels in each of the seven bottles in the same manner as
   described in Measurement of Dissolved Oxygen procedures 7-11.
8. Repeat process two more times.

Productivity Simulation
1. The respiration data from Measurement of Primary Productivity was converted to carbon
   productivity.


                                        RESULTS
Table 1. Average dissolved oxygen concentration at different temperatures.
    Temperature in        Dissolved Oxygen
                                                    % Dissolved Oxygen
       Celsius                  (mg/l)
          5C                     2.00                      16%
        21.5C                    1.28                      19%

As Table 1 and Figure 1 show, as temperature goes up the solubility of oxygen in water goes down.
Temperature and dissolved oxygen are inversely proportional.
                                                                                              Tyro 7



                          Figure 1. Dissolved Oxygen content at
                                 different temperatures.

                         2.5
                                            2
   Amount of Dissolved




                          2
     Oxygen (mg/l)




                         1.5                                                 1.28

                          1

                         0.5

                          0
                                        5C
                                         1                                21.5C
                                                                            2
                                                Temperature in Celsius

                                                            Series1
Table 2. Average dissolved oxygen as a measure of gross and net productivity in different
amounts of light.
                                dissolved            gross
                                                                 net productivity
   percent light               oxygen (ml         productivity
                                                                    (ml O2/l)
                                  O2/l)            (ml O2/l)
          Initial                 9.2                 na               na
           dark                   4.6                 na               na
          100%                    6.4                1.8              -2.8
           65%                    3.8                -0.8             -5.4
           25%                    4.5                -0.1             -4.7
           10%                    3.7                -0.9             -5.5
            2%                     4                 -0.6             -5.2

The amount of respiration in all of the experimental bottles exceeded the amount of photosynthesis
that occurred, resulting in a negative productivity. The initial sample had 9.2ml O2/l while the net
productivity in the 100% light condition with -2.8ml O2/l, a difference of 12.0ml O2/l. 100% light
had a net productivity of -2.8ml O2/l while the 2% light condition had a net productivity of -5.2ml
O2/l, a difference of 2.4ml O2/l. Each experimental condition had a negative productivity, but the
results showed no discernable pattern. The net productivity at 2% light was -5.2ml O2/l, at 25%
light was -4.7ml O2/l, at 65% light was -5.4ml O2/l.
                                                                                                    Tyro 8


                                        Figure 2. Using dissolved oxygen to determine the
                                           net productivity in different amounts of light.


                                   0
                                            1           2           3            4            5
                                          100%        65%         25%           10%          2%
                                   -1
    Gross Productivity (mg C/m3)




                                   -2


                                   -3     -2.8

                                   -4
     Net




                                   -5                             -4.7
                                                                                             -5.2
                                                      -5.4                      -5.5
                                   -6
                                                             Percent of Light




                                           DISCUSSION
The purpose of this lab was to better understand the environmental affects on dissolved oxygen
content in an aquatic environment. Two different but related phenomena surrounding dissolved
oxygen in regular pond water were examined. First, the connection between temperature and
dissolved oxygen concentration was tested at 5° C and 21.5° C. Second, dissolved oxygen
concentration was used to determine gross and net productivity of plants in different light
conditions (100%, 65%, 25%, 10%, 2%).

Temperature was determined to have an inverse correlation to the solubility of oxygen in water but
directly correlated to percent concentration. As temperature rose the dissolved oxygen levels
decreased, as can be seen by comparing the 5° C water sample with 2.0 mg/l of dissolved oxygen
and the 21.5° C sample with 1.28 mg/l. The percent saturation showed that even though the 5° C
sample, 16%, contained more dissolved oxygen it was still less saturated than the 21.5° C sample,
19% saturated.

In the portion of the experiment looking at the affect of amount of light on net productivity, the
natural oxygen balance between photosynthesis and respiration was interrupted by limiting the
amount of light in the environment with the screens. The amount of respiration in all of the
experimental bottles exceeded the amount of photosynthesis that occurred, resulting in a negative
productivity. The initial sample had 9.2ml O2/l while the net productivity in the 100% light
condition with -2.8ml O2/l, a difference of 12.0ml O2/l. The data clearly shows that any limit in
                                                                                               Tyro 9

amount of light causes a decrease in dissolved oxygen. 100% light had a net productivity of -2.8ml
O2/l while the 2% light condition had a net productivity of -5.2ml O2/l, a difference of 2.4ml O2/l.
This is caused because photosynthesis cannot occur without sufficient light. The results were not
consistent though. Each experimental condition had a negative productivity, but the results were
inconclusive as there was no discernable pattern. The net productivity at 2% light was -5.2ml O2/l,
at 25% light was -4.7ml O2/l, at 65% light was -5.4ml O2/l. The most plausible explanation for these
results may be due to difference in the amount and types of organisms present in the sample, more
plankton means more respiration.

The most significant error occurred in maintaining the temperature of the sample. The temperature
likely deviated from the normal pond temperature before the actual temperature intervention
occurred. This could be better controlled in the future by running the test immediately after
collection or using a programmable thermostat regulated cooler. Another error could have been
caused by the difficulty of collecting a pure sample without introducing any oxygen to it.
A third error exists in the lack of controlling the amount of plankton in each environment. Since the
plankton, both plant and animal, utilize cellular respiration, lack of control in this area create
unreliable data for the second part of the experiment. This could be controlled in the future by using
organism free water and introducing a specific number and kind of plankton. In future
experimentation, multiple ponds should be sampled. Samples from each pond should be taken
during different season, recording the temperature of each, to determine if seasonal temperatures
cause differences in dissolved oxygen content. Also, the amount of naturally occurring light should
be determined for each pond. Comparing the dissolved oxygen in ponds with different levels of
light might further explain if net productivity differences do exist.


                                         CONCLUSION
In aquatic environments oxygen production and oxygen usage must be balanced to prevent de-
oxygenated environments. An absence of sufficient dissolved oxygen in a pond is an indicator of
poor water quality. The data clearly shows that any limit in temperature or amount of light causes a
decrease in dissolved oxygen. This has direct implications on the health of a pond. Though trees
provide shade for pond organisms, blocking out too much light may be detrimental to the water
quality of a pond.
                                                                                          Tyro 10

                                           WORK CITED
Carter, J. Stein. "Photosynthesis." Biology 104. 02 Nov 2004. Clermont College Biology, Web. 10
        Feb 2010. <http://biology.clc.uc.edu/Courses/Bio104/photosyn.htm>.

Carter, J. Stein. " Cellular Respiration and Fermentation." Biology 104. 02 Nov 2004. Clermont
        College Biology, Web. 10 Feb 2010. <
        http://biology.clc.uc.edu/Courses/Bio104/cellresp.htm>.

Kevern, Niles R., Darrell L. King, and Robert Ring. "Lake Classification System – Part 1."
      Michigan Riparian Feb. 1996. Web. 10 Feb 2010. <http://www.mlswa.org/lkclassif1.htm>.

KY Water Watch. "Dissolved Oxygen." Water Quality. 23 Nov 2005. KY Water Watch, Web. 10
     Feb 2010. <http://www.state.ky.us/nrepc/water/wcpdo.htm>.

Markfort, Corey J., and Miki Hondzo. "Dissolved Oxygen Measurements in Aquatic Environments:
      The Effects of Changing Temperature and Pressure on Three Sensor Technologies." Journal
      Environmental Quality 38. (2009): 1766-1774 . Web. 10 Feb 2010.
      <http://jeq.scijournals.org/cgi/content/abstract/38/4/1766>.

Sander, Rolf. "Henry's Law Constants (Solubilities)." Rolf Sanders. 29 Sept 2009. Max-Planck
       Institute for Chemistry, Web. 10 Feb 2010. <http://www.mpch-
       mainz.mpg.de/~sander/res/henry.html>.




***This lab report example was modified from a lab available at
http://www.biologyjunction.com/ap_sample_lab_12_dissolved_oxyge.htm on February 10, 2010.

								
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