Dissolved Oxygen

0 Dissolved Oxygen Lab 12

12a 0 • 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? 0 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 stored6CO2 + 6H2O → C6H12O6 + 6O2 0 • 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 0 • Fill 7 water sampling bottles • I= Initial • D= Dark • 100%, 65%, 25%, 10%, 2% with screens • 0 1 3 5 8

Initial 0 • The DO value when you begin your test. DO = 6

Dark 0 • 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 0 • Orgs make O2 • Orgs use O2 • How much is left over? Light- Initial I made 7 mg O2/L today!!! 9 - 6 =3 mg O2/L Yeah, well I used up 4! DO= 9

Gross Primary Productivity 0 • 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

Light Net Initial Gross Resp Dark 0 DO • 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.) Time

0 mg O2/L x 0.698 x=ml O2/L ml O2/L x 0.536 =mg C/L 1000 x mg C/L =mg C/M3

Dissolved Oxygen