AP Lab #12
Dissolved Oxygen &
Aquatic Primary
Productivity part I
In an aquatic environment, O2 must be in a
solution in a free state before it is available for
use by heterotrophic organisms…
In an aquatic environment, O2 must be in a
solution in a free state before it is available for
use by heterotrophic organisms…
The concentration of O2, and its
distribution in an aquatic environment (the
pond, ocean etc.), are directly dependent
on factors that greatly affected by
biological processes!
In the atmosphere …
O2 is abundant
Terrestrial = 200 mL O2/ 1 L air
Aquatic
=
10 mL O2/ 1 L
water
In an aquatic
environment O2 is NOT
as abundant as in a
Terrestrial = 200 mL O2/ 1 L air
Aquatic
=
10 mL O2/ 1 L
water
O2 distribution in water
depends on: currents,
winds, tides etc. mixing it
up !
O2 diffuses 300,000 X’s
faster in air than water
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Terrestrial = 200 mL O2/ 1 L air
Aquatic
=
10 mL O2/ 1 L
water
O2 distribution in water
also depends on: pH,
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Terrestrial = 200 mL O2/ 1 L air
Aquatic
=
10 mL O2/ 1 L
water
O2 distribution in water
also depends on: salinity,
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decompressor
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Terrestrial = 200 mL O2/ 1 L air
Aquatic
=
10 mL O2/ 1 L
water
O2 distribution in water
also depends on:
elevation
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decompressor
are needed to see this picture.
Terrestrial = 200 mL O2/ 1 L air
Aquatic
=
10 mL O2/ 1 L
water
O2 distribution in water
also depends on:
temperature
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decompressor
are needed to see this picture.
HIGHER O2 (DO) “Help - I am
CONCENTRATION suffocating!!!”
(ppm) at:
neutral pH
low elevation
low salinity
low temperature
Terrestrial = 200 mL O2/ 1 L air
Aquatic
=
10 mL O2/ 1 L
water
O2 distribution in water
also depends on: partial
pressure of O2 in the air
above the water !
LESS O2 IN WATER
AT HIGHER
ELEVATIONS
THAN AT LOWER
ELEVATIONS
You could think
about the amount
of O2 in the air @
these locations…
Terrestrial = 200 mL O2/ 1 L air
Aquatic
=
10 mL O2/ 1 L
water
O2 distribution in water
also depends on: amount
(rate) of photosynthesis &
respiration
photosynthesis increases
the D.O. (ppm) !
respiration decreases the
D.O.(ppm) …
measuring D.O. is a
determiner as to whether
the biological activities
requiring O2 are occurring
(respiration)
Indicator of health of lake !
Which environment has the greater
concentration of dissolved oxygen:
Explain.
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a heavy algal mat?
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or a clear pond?
Clear water holds more dissolved oxygen
than water with a heavy algal mat.
Although photosynthesis in the algal mat
will produce a great deal of oxygen, the
decay of so much organic matter will
result in a net depletion of oxygen due to
DECOMPOSERS.
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??? SAY WHAT????
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DECOMPOSERS w/ be in a large amount
BECAUSE THE ALGAE WILL
EVENTUALLY DIE... The decomposers
w/ come on the scene and will USE THE
OXYGEN, thus decreasing the amount of
DO
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Just HOW
do you
measure
D.O.?
Just HOW
do you
measure
D.O.?
WINKLER METHOD
to
determine D.O.
1. Add alkaline iodide & manganous
sulfate to a water sample.
Manganous hydroxide will be produced.
This will be acidified, & will spontaneously
be converted to a manganese compound by
the O2 in the water sample
WINKLER METHOD
to
determine D.O.
2. Add alkaline potassium iodide azide
(KOH) to the water sample.
Iodine will be released -> H2O will turn
yellow
**The quantity of free iodine is
equivalent to the amount of D.O. in the
water.**
WINKLER METHOD
to
determine D.O.
3. A starch indicator is then added…
to determine amount of iodine
via. titration
H2O will turn purple
You remember, titration is adding a substance of known
concentration to a solution containing a substance of unknown
concentration… until a specific reactions completed and a color
change occurs.
WINKLER METHOD
to
determine D.O.
4. The amount of D.O. can then be
determined by titrating a portion of the
sample with sodium thiosulfate until a
colorless endpoint is reached.
AP Lab #12
Dissolved Oxygen &
Aquatic Primary
Productivity part I
MEASURING D.O.
In order to measure how much oxygen
water can hold (the saturation) you will
also need to be able to read a nomograph:
the percent oxygen
saturation for a
water sample at
10oC that has 7mg
O2/L is 45%
saturation
nomograph
the percent oxygen
saturation for a
water sample at
25oC that has 7mg
O2/L is 65%
saturation
nomograph
Goggles and gloves
MUST be worn
AP Lab #12 Dissolved
Oxygen & Aquatic
Primary Productivity
Day 2
Day 2 we will compare D.O.
values in water samples
exposed to differing amounts
of light
Primary Productivity
the rate @ which biomass is
produced & stored (by autotrophs)
via. photosynthesis in an
ecosystem
Primary Productivity
-
amount of organic
compound formed from
photosynthesis
amount
of organic
compound used by
respiration
Aquatic P.P.
Primary Productivity
amount of organic compound
formed from photosynthesis
-
amount of organic compound
used by respiration
Net Primary Production
Primary Productivity
can be measured by:
*rate of CO2 utilization
*rate of sugar formation
(glucose produced)
*rate of O2 production
in the light
Primary Productivity
can be measured by:
can calculate the amount
of carbon that has been
“bound” in organic
compounds over a time
via. RATE OF O2
You will monitor
the effect of
varying light
levels on D.O.
in an algae-rich
water culture
Just HOW
do you
measure
primary
Light-Dark bottle O2method
to determine primary productivity
1. Measure D.O. concentration in an
initial sample CONTROL TO
COMPARE
2. Measure D.O. concentration in a
dark sample JUST CELL
RESPIRATION
3. Measure D.O. concentration in a
light sample PHOTOSYNTHESIS &
CELL RESPIRATION
Light-Dark bottle O2method
to determine primary productivity
RESPIRATION ->
initial sample - dark sample
GROSS PRIMARY PRODUCTION ->
light sample + amount used in dark
sample
NET PRIMARY PRODUCTION ->
light sample - dark sample
3. Each bottle will
have the % light it
will receive..
3. Each bottle will
have the % light it
will receive..
3. Each bottle will
have the % light it
will receive..
L - I = Net Productivity
I - D = Respiration
L - D = Gross Productivity
L
note: dark is a negative number
Net
Productivity
I
Respiration
I = Initial Bottle
L = Light Bottle
D = Dark Bottle
0
D
24
net productivity + respiration
= gross productivity
(light - initial) + (initial - dark) = gross productivity
(light)
+
(- dark) = gross productivity
light
-
dark = gross productivity
this number will
be negative
this number will
be negative
How do lakes age?
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OLIGOTROPHIC
OLIGOTROPHIC
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• Very little nutrients
(nitrogen &
phosphorus
• Deep
• Clear
• Very little algae
• Colder
• Highly oxygenated
A oligotrophic lake
Oligotrophic lakes are very low in
nutrients, so few algae grow and
the water is very clear.
Oligotrophic lakes are biologically
less productive lakes (they have the
lowest level of biological
productivity), and support very few
plants and fish.
MESOTROPHIC
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• Medium amount of
nutrients (nitrogen &
phosphorus)
• Clear
• Algal blooms in late
summer on top~ D.O.
higher on top
• Warm on top /Colder
on bottom
• Higher decomposition
rate on bottom~ D.O.
lower on bottom
EUTROPHIC
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• High amount of
nutrients (nitrogen
& phosphorus)
• Shallow/ Murkey
• Algal blooms b/c of
nutrients / high fish
• Higher
decomposition rate
on bottom~ D.O.
lower all over
EUTROPHICATION
a natural process that occurs in an
aging lake or pond as that body of water
gradually builds up its concentration of
plant nutrients.
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EUTROPHICATION
Cultural or artificial eutrophication
occurs when human activity introduces
increased amounts of these nutrients,
which speed up plant growth and
eventually choke the lake of all of its
animal life.
A eutrophic lake
A eutrophic lake is shallow
with high nutrient content.
•The phytoplankton are very productive and
the waters are often murky.
•Ecologist use the term to describe relatively
productive habitats and communities having
good nutrient supply and to separate them
from unproductive oligotrophic ones,
characterized by a nutrient deficiency.
A eutrophic lake
A oligotrophic lake
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SPRING TURNOVER