Dissolved Oxygen
Lab 12
12a
 12a –Measure dissolved oxygen content
as a function of temperature.
 Use water at 0-5, 20, 30 degrees
 Using the nomogram to measure %
saturation. (p 139 in lab manual)
12b How does the amount of
light affect productivity?
Model depth in a lake with screens
100%- 0 screens
65% - 1 screen
25% - 3 screens
10% - 5 screens
2% - 8 screens
12b. Primary Productivity –
The rate at which organic materials are stored
6CO2 + 6H2O → C6H12O6 + 6O2
 Can determine by measuring oxygen.
 1 ml of O2 = .536 mg of C assimilated
 To convert: ppm O2 = mg O2/L
mg O2/L x 0.698 = ml O2/L
ml O2/L x 0.536 = mg carbon fixed/L
12 B





Fill 7 water sampling bottles
I= Initial
D= Dark
100%, 65%, 25%, 10%, 2% with screens
0
1
3
5
8
Initial
 The DO value when you begin
your test.
DO = 6
Dark
 Respiration Only
 How much O2 you started with
– how much is used up (say in
24 hours).
 Initial -Dark
How much do you think
we have left?
DO= 4
6-4=2 mg O2 /L
Net Primary Productivity
 Orgs make O2
 Orgs use O2
 How much is left over?
I made 7 mg O2/L
today!!!
Light- Initial
9 - 6 =3 mg O2/L
DO= 9
Gross Primary
Productivity




Total O2 made
Net and the respiration
(Light –initial) + (Initial – dark)
This is
Net + Resp
(9-6) + (6-4)
3 + 2 = 5 mg O2/ L
Or…Light-Dark
9-4=5
DO
Light
Net
Initial
Gross
Resp
Dark
Time



L-I = Net Productivity (In the light bottles, photosynthesis and respiration
are occurring. How much change from the starting point-initial? )
I-D = Respiration (The difference between the O2 in the bottle you started
with-Initial- and the bottle in the dark.)
L-D = Gross Productivity ( The difference between the light bottle and the
dark bottle represents the total, or gross, productivity.)
% light DO
mg/L
Gross
Net
Initial
6.30
---
---
Dark
4.10
---
---
100%
7.95
L-D
L-I
65%
7.85
25%
7.30
Gross
Carbon
Fixed
ml C/M3
Net
Carbon
fixed
-----
mg O2/L x 0.698 x=ml O2/L
ml O2/L x 0.536 =mg C/L
10%
6.55
2%
5.6
1000 x mg C/L =mg C/M3
% light
DO
mg/L
Gross
Net
Initial
6.30
---
---
Carbon
fixed in
mgC/m3
---
Dark
4.10
---
---
---
100%
7.95
3.85
1.65
1440
65%
7.85
3.75
1.55
1402
25%
7.30
3.20
1.00
1197
10%
6.55
2.45
0.25
938
2%
5.6
1.50
-0.70
561