Measuring primary productivity and dissolved
oxygen in a water sample using the Winkler Method
Racia McLean
26 May 2011
Room 219
I.
Objectives: The purpose of the dissolved oxygen was to investigate the relationship and
effect of temperature on the concentration of dissolved oxygen and determine the
amount of oxygen dissolved in water. The purpose of the aquatic primary
productivity lab was to use the DO (dissolved oxygen) to determine the primary
productivity of an aquatic system in light and dark model pond ecosystems and to
factor in that the light measures net primary productivity, while the sample in the dark
measures the loss due to respiration. With this in mind, this will reveal what is going
on in those specific ecosystems and whether it can support a large biomass or not.
II. Procedure: A, and B
Activity A: Get all required materials out. Label three BOD bottles: 4°C, 20°C, and 30°C.
Fill one BOD bottle with water of their matching temperature. You have a choice
between submerging the bottle in the sample and allowing it to fill, or using a 60 mL
syringe with a piece of tubing attached. In either case, do not trap air or disturb the bottle
when you cap it. Using the Winkler Method of oxygen fixation and titration, you will
determine the dissolved oxygen of the sample. To conduct oxygen fixation, uncap the
BOD bottle and add 8 drops of manganous sulfate solution to the bottle. After, add 8
drops of alkaline potassium iodide azide to the bottle and cap it. Mix well and a
precipitate will form. Place the bottle down and allow the precipitate to settle to the
shoulder of the bottle. Use a 1-g spoon to add 1 gram of sulfamic acid powder and cap
the bottle afterward. Mix the bottle until reagent (the substance) and precipitate dissolve.
After oxygen fixation, titration will be conducted. Uncap a BOD bottle and use its
content to fill the titration sampling vial to the 20 mL line. Then fill the titration syringe
to the top of the scale with sodium thiosulfate. Add one drop of sodium thiosulfate at a
Racia McLean
26 May 2011
Room 219
time and swirl in between each drop. Make sure to occasionally stop adding drops to
shake it up. Keep adding drops until the sample becomes faint yellow. Remove the
titration syringe and cap, and add 8 drops of starch indicator solution. Place the cap back
on and swirl the sample until it is blue. Use the sodium thiosulfate in the previous syringe
and add one drop at a time to the sample until the blue color disappears. Record how
much of each solution you have used. (Note: Each 0.1 mL of sodium thiosulfate = 1ppm
DO)
Activity B: To determine the initial DO, fill a BOD bottle with water from the Chlorella
culture (model pond) and cap the bottle. Refer back to Activity A to conduct the two
steps in the Winkler Method Protocol. Once you have concluded with that, fill two BOD
bottles with water from the model pond and cap them. This will be used to prepare the
100% light and dark bottle. Wrap one bottle (dark bottle), in aluminum foil and leave the
other bottle in the light. Label the bottles with your group names and the appropriate
treatment. Lay the bottles on their sides under a grow light, and leave them overnight.
Next prepare four additional BOD bottles and fill them with model pond water. Cover
each one with one or more screens based on the chart. Secure the screens with rubber
bands. Label the bottles with the appropriate percent light/treatment. Lay the bottles on
their side under grow light, seam side down and leave them overnight. (Note: Light bottle
prepared in step 2 = 100% light in chart). This should be done in one day. On day two,
determine the dissolved oxygen (DO) of each of the sample bottle by following the steps
outlined in Activity A for the Winkler Method Protocol (oxygen fixation and titration).
Record your data in Table 2.
Racia McLean
26 May 2011
Room 219
III. Background: Dissolved oxygen (DO) is a measure of the amount of oxygen in water that
is available for aquatic organisms. Dissolved oxygen is important for the chemical
processes that happen in the water, and not only that, but it is the indicator of the
health of an aquatic ecosystem. The level of dissolved oxygen essentially determines
what organisms will be present in that body of water, which won’t and which will
migrate into that area. With a stable, high DO organisms are able to conduct these
processes; therefore the aquatic ecosystem is able to support a larger amount of
organisms and their needs. With a low DO, that usually indicates pollution, humancaused changes, or natural processes. Some factors affecting dissolved oxygen
addition of organic waste (sewage, animal manure, etc), and addition of nutrients
from fertilizers and runoff. These organic materials are decomposed by
microorganisms, but in doing so they use up the oxygen in that ecosystem. Some
natural factors that affect dissolved oxygen is the rate at which the water flows. For
example, if the water is very unsettled, it may hold too much oxygen which will cause
stress to the aquatic organisms. Also, the type and number of organisms in the body
of water affect the amount of DO because of night time oxygen use by plants or the
decay process that consumes oxygen.
Murphy, Sheila. "BASIN: General Information on Dissolved Oxygen." Boulder
Community Network - Serving Boulder County since 1994. Web. 01 June 2011.
<http://bcn.boulder.co.us/basin/data/NEW/info/DO.html>.
"Dissolved Oxygen." Changing Hudson Project. Cary Institute of Ecosystem Studies.
Web. 1 June 2011.
<http://docs.google.com/viewer?a=v&q=cache:qFe0DonSpkcJ:www.ecostudies.org/chp/
Module1/1C1_dissolved_oxygen_reading.pdf+factors+that+affect+the+amount+of+disso
lved+oxygen+in+water&hl=en&gl=us&pid=bl&srcid=ADGEESieAHsr7qp3KRBEKlhV
BJydOjPa1dgUq6fiyGUOUblY8VreOF_ZuL1bhiDWG8A6pDApz43PYOTeSt3Req6rM
Racia McLean
26 May 2011
Room 219
0RdTj9MAAshiaIBFMvLKZMOCt2DgHkaIOdST7cyJpolitzOD-g0&sig=AHIEtbTLivRH2BvwcfjqeurIH0I_mjzxw>.
IV. Data Table(s):
Table 1: Temperature and Dissolved Oxygen
Temperature
5°
20°
30°
Group DO
2.5 ppm
5.2 ppm
3.0 ppm
Class Average
6.5 mg/L
5.6 mg/L
4.8 mg/L
Group %
Saturation
51%
62%
60%
Class Average
% Saturation
51%
62%
60%
Table 2: Group Productivity Data
Bottle
DO
Net Productivity
Baseline (Initial)
7.40
Dark
4.90
Light (0 screens)
10.90
3.50
1 screen
10.60
3.20
3 screens
8.95
1.55
5 screens
7.80
0.40
8 screens
5.10
-2.30
R = 2.50 mg/L (*Loss of oxygen due to respiration)
Racia McLean
26 May 2011
Room 219
Gross Productivity
6.00
5.70
4.05
2.40
0.20
V. Results:
Activity A:
Activity B:
Racia McLean
26 May 2011
Room 219
VI. Discussion/Analysis
Activity A:
1. a. The independent variable is temperature.
b. The dependent variable is dissolved oxygen.
2. As temperature increases, DO decreases. DO is inversely related to temperature.
3. Refer back to results
4. a. The independent variable is temperature (or mg/L).
b. The dependent variable is percent saturation.
5. As temperature increases, percent saturation increases.
6. As was stated in #2, when temperature increases, dissolved oxygen decreases, so the total
amount of DO that can be retained by the water will also decrease. With this in mind, percent
saturation of DO will still increase as temperature increases even if the amount of DO
remains constant or decreases.
Activity B:
1. 2.50 mg/L
2. Refer back to data tables (R=7.40-4.90)
3. Refer back to data tables
4. –
5. a. The independent variable is number of screens (light intensity)
b. The dependent variables are net productivity and gross productivity.
6. –
7. Well, the productivity is probably greater at the Toolik Field Station in Alaska than at La
Selva Biological Station in Costa Rica which would mean that the freshwater pools can
Racia McLean
26 May 2011
Room 219
support a greater number of consumers. Also, it could be because of the differences in
light in this month being that their on opposite sides of the pole.
8. In Case A, the dissolved oxygen in the water decreases with increased temperature, and
as the heat wave continues, water temperature in the small pond rose. The water would
then reach a point where it could not hold enough oxygen for the size and required
oxygen for the fish population. As oxygen levels continue to drop, the fish die off,
because they cannot conduct their chemical processes or live without oxygen. In Case B,
the heavy rain would produce runoff from the pastureland, which is one of the factors that
contribute to lower dissolved oxygen levels. The runoff carried ammonium nitrate
solution, which stimulated a lot of algae growth because all plants need nitrogen as one
nutrient. At night the increased population of algae uses up the oxygen in the aquatic
ecosystem, dropping the dissolved oxygen levels further. Due to the fact that there was an
increase in algae growth, the fish were deprived of their ideal DO levels, to be traded off
to the plants which, during the night were used by the algae. Based on this fact, the fish
would also die and the algae would as well because the nitrogen would be used up and
the population wouldn’t be able to be maintained.
Racia McLean
26 May 2011
Room 219