Dissolved Oxygen Lab 12 12 a 12 a
Dissolved Oxygen Lab 12
12 a § 12 a –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)
12 b 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
12 b. Primary Productivity – The rate at which organic materials are stored 6 CO 2 + 6 H 2 O → C 6 H 12 O 6 + 6 O 2 § Can determine by measuring oxygen. § 1 ml of O 2 =. 536 mg of C assimilated § To convert: ppm O 2 = mg O 2/L x 0. 698 = ml O 2/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 O 2 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 O 2 /L
Net Primary Productivity § § § Orgs make O 2 Orgs use O 2 How much is left over? I made 7 mg O 2/L today!!! Yeah, well I used up 4! DO= 9 Light- Initial 9 - 6 =3 mg O 2/L
Gross Primary Productivity § § Total O 2 made Net and the respiration (Light –initial) + (Initial – dark) This is Net + Resp (9 -6) + (6 -4) 3 + 2 = 5 mg O 2/ 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 O 2 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 10% 6. 55 2% 5. 6 Gross Carbon Fixed ml C/M 3 Net Carbon fixed ----- mg O 2/L x 0. 698 x=ml O 2/L x 0. 536 =mg C/L 1000 x mg C/L =mg C/M 3
% light DO mg/L Gross Net Initial 6. 30 --- Carbon fixed in mg. C/m 3 --- 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
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