Dissolved oxygen and aquatic
primary productivity
Overview
 Measure and analyze the dissolved oxygen (DO)
concentration in water samples at varying
temperatures.
 Measure and analyze the primary productivity of
natural waters or lab cultures using screens to simulate
attenuation of light with increasing depth.
Objectives
 Before doing this lab you should understand
 Biological importance of carbon and oxygen cycling in ecosystems
 How primary productivity relates to the metabolism of organisms in an
ecosystem.
 The physical and biological factors that affect the solubility of gases in
aquatic ecosystems, and
 The relationship between dissolved oxygen and the processes of
photosynthesis and respiration and how these affect primary productivity.
 After doing this lab you should be able to
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Measure primary productivity based on changes in dissolved oxygen
in a controlled experiment.
Investigate the affects of changing light intensity on primary
productivity in a controlled experiment.
Dissolved Oxygen
 Oxygen must be in solution in a free state to be available for
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use by organisms.
Its conc. and dist. depends directly on chemical and
physical factors, and are greatly affected by biological
processes
Concentration of Oxygen in aquatic environments is a very
important aspect of water quality
Air 200 ppm (200 ml per L air) = 20%
Water 5- 10 ppm (ml per L water) = 0.5- 1%
Salinity, pH, temperature all affect D.O.
Measuring D.O.
 Three common methods
 Azide- Winkler titration
method
 Computer probe
 Field test kit (usually a
variation of the AzideWinkler method)
Figure 1: Niskin Bottle Mr. Fazio used to collect Water samples
from Dana Point, CA
Azide-Winkler Titration Method
 Fill a special bottle called a BOD with
water sample (no bubbles)
 Then you fix the sample with
Manganese Sulfate, Alkali- iodide azide,
and concentrated sulfuric acid (this can
be stored for a brief period of time)
 Titrate with sodium thiosulfate to a pale
yellow color, then add indicator starch,
finish titrating with sodium thiosulfate
until clear.
 Read the amount of thiosulfate titrated
this gives you D.O. in ppm
Oxygen saturation
Productivity
 Primary productivity of an ecosystem is defined as the
rate at which organic materials are stored.
 The rate of carbon dioxide utilization, the rate of the
formation of organic compounds, or the rate of
oxygen production over time provides a basis for
measuring primary productivity
 Light and dark bottle method:
 difference in D.O. in initial and dark incubated bottle
indicates respiration is occurring.
 The difference in initial and light incubated bottle
measures net productivity.