1. GLOBE Trainer Certification Program Adapted from 1 DISSOLVED OXYGEN

2. GLOBE Trainer Certification Program Adapted from 2 Dissolved Oxygen Dissolved Oxygen (DO) refers to microscopic bubbles of oxygen gas that occur between water molecules. DO does NOT refer the oxygen portion of a water molecule (H 2 O)

3. Why Measure Dissolved Oxygen? 3

4. GLOBE Trainer Certification Program Adapted from 4 Scientists want data to… Determine the mixing of air and water at the water’s surface Determine what animals can live in the water What are we looking for…?

5. GLOBE Trainer Certification Program Adapted from 5 Dissolved Oxygen oxygen accounts for one of every five molecules in the air but only five of every one million molecules in water DO is measured as parts per million (ppm) or mg/L (by mass)

6. GLOBE Trainer Certification Program Adapted from 6 Oxygen enters water … by diffusion from the atmosphere by aeration of water as it tumbles and falls downstream (rapids, falls, etc.) as a by-product of photosynthesis ( by aquatic plants and algae)

7. GLOBE Trainer Certification Program Adapted from 7 O 2 depleted from water by… respiration decomposition other environmental conditions

8. GLOBE Trainer Certification Program Adapted from 8 Dissolved Oxygen Levels DO is highest in fast-moving waters that churn and fall thus creating plenty of air bubbles In slow, stagnant waters, oxygen enters only the top layer leaving the deeper water DO deficient

9. GLOBE Trainer Certification Program Adapted from 9 Dissolved Oxygen Levels Colder waters can hold more dissolved oxygen than warmer waters Therefore, seasonal changes and thermal pollution have a direct impact of DO levels

10. GLOBE Trainer Certification Program Adapted from 10 Dissolved Oxygen Levels Sunlight and warmer weather bring increased activity in plant and animal life. Depending on the balance of these factors, DO concentration may increase or decrease.

11. GLOBE Trainer Certification Program Adapted from As photosynthesis increases, oxygen levels increase: CO 2 + H 2 O Biomass + O 2 As respiration increases due to organic materials or decay, oxygen levels decrease: Biomass + O 2 CO 2 + H 2 O 11

12. GLOBE Trainer Certification Program Adapted from DO increases as … plant growth increases photosynthesis rates increase temperature decreases flow rate increases Fluctuations in Dissolved Oxygen DO 12

13. GLOBE Trainer Certification Program Adapted from DO decreases as … temperature increases elevation increases total dissolved substances increases (ex., salts) flow rate decreases decomposition increases DO Fluctuations in Dissolved Oxygen 13

14. GLOBE Trainer Certification Program Adapted from 14 Dissolved Oxygen Levels 4 – 5 ppm is the minimum that will support a large and diverse fish population DO levels below 3ppm are too stressful for even the hardiest fish Affects on Fish Populations

15. GLOBE Trainer Certification Program Adapted from 15 High DO makes drinking water taste better High DO also speeds up corrosion in water pipes * Therefore, industries use water with the least possible amount of DO Affects on Water Supplies Dissolved Oxygen Levels

16. GLOBE Trainer Certification Program Adapted from 16 Measuring Dissolved Oxygen Influencing parameters that must be considered when measuring DO: WATER TEMPERATURE SALINITY

17. GLOBE Trainer Certification Program Adapted from 17 Measuring Dissolved Oxygen Because the amount of DO in a water sample can change rapidly immediately the sample should be tested immediately on site FIXED if this is not feasible, the sample must be FIXED at the site and tested within 2 hours.

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19. GLOBE Trainer Certification Program Adapted from 1. Sample Preservation 2. Sample Testing Dissolved Oxygen test kits TWO involve TWO overall parts: 19

20. GLOBE Trainer Certification Program Adapted from 20  Rinse sampling bottle 3 times with sample water.  Submerge bottle in water and allow to fill completely.  While bottle is submerged, replace cap  If there are air bubbles in the bottle, empty and repeat  Preserve sample immediately. Taking a Sample

21. GLOBE Trainer Certification Program Adapted from This should be done in the field.  Preservation : 1. Add a chemical that precipitates in the presence of dissolved oxygen 2. Add a chemical that causes the solids to dissolve and produce a colored solution. Sample Preservation 21

22. GLOBE Trainer Certification Program Adapted from This can be done in the lab.  Titration of preserved sample.  Repeat the test 3 times.  Take the average to see if all values are within the precision of the kit. (Discard outliers) Sample Testing 22

23. GLOBE Trainer Certification Program Adapted from So what is actually happening … chemically speaking? 23

24. GLOBE Trainer Certification Program Adapted from MnSO 4 + 2KOH  Mn(OH) 2 + K 2 SO 4 Manganous + Potassium Sulfate Hydroxide Hydroxide Sulfate Chemical Reactions Preserving DO (Done in the field) Adding Manganous Sulfate Solution and Alkaline Potassium Iodide Azide Solution creates a white precipitate, or floc*. 24

25. GLOBE Trainer Certification Program Adapted from When the precipitate forms, manganous hydroxide is immediately oxidized to a brown-colored manganic hydroxide. For every 1 molecule of oxygen, 4 manganous hydroxide molecules are converted to manganic hydroxide. 4Mn(OH) 2 + O 2 + 2H 2 O  4Mn(OH) 3 Manganous + Oxygen + Water Manganic Hydroxide Hydroxide Chemical Reactions Preserving DO (Done in the field) 25

26. GLOBE Trainer Certification Program Adapted from Adding Sulfuric Acid at this point converts the manganic hydroxide to manganic sulfate. The sample is considered “fixed” and the possibility of additional oxygen entering the sample is reduced. 2Mn(OH) 3 + 3H 2 SO 4  Mn 2 (SO 4 ) 3 + 6H 2 O Manganic + Sulfuric Manganic + Water Hydroxide AcidSulfate Chemical Reactions Preserving DO (Done in the field) 26

27. GLOBE Trainer Certification Program Adapted from The formation of manganic sulfate oxidizes the iodine (from potassium iodide in step 1) releasing free iodine in the water. As a result. the water will turn yellowish- brown. Mn 2 (SO 4 ) 3 + 2KI  2MnSO 4 + K 2 SO 4 + I 2 Manganic + Potassium  Manganous + Potassium + Iodine Sulfate Iodide Sulfate Sulfate Chemical Reactions Preserving DO (Done in the field) 27

28. GLOBE Trainer Certification Program Adapted from The reaction of sodium thiosulfate with the free iodine causes the sample to change from yellow-brown* to colorless 2Na 2 S 2 O 3 + I 2  Na 2 S 4 O 6 + 2NaI Sodium + Iodine  Sodium + Sodium Thiosulfate Tetrathionate Iodide Chemical Reactions Titration: Testing the Sample (can be done in lab) *As the solution turns pale yellow, add a starch indicator to enhance the visual of the color change 28

29. GLOBE Trainer Certification Program Adapted from Check technique and quality of kit chemicals every 6 months.  Rinse the 250 mL bottle twice with distilled water.  Measure 100 mL of distilled water with a graduated cylinder and pour this water into the 250 mL bottle. Quality Control 29

30. GLOBE Trainer Certification Program Adapted from  Put the lid on tightly and shake vigorously for 5 minutes. The water will be saturated with dissolved oxygen.  Uncap the bottle and take the temperature of the water. Be sure the tip of the thermometer does not touch the bottom or sides of the bottle. (Record the temperature on the Hydrology Investigation Quality Control Procedure Data Sheet.) Quality Control 30

31. GLOBE Trainer Certification Program Adapted from  To determine the dissolved oxygen value use a dissolved oxygen test kit that meets the specifications in the Toolkit of the GLOBE Teacher's Guide. Follow the instructions carefully.  On the Hydrology Investigation Quality Control Procedure Data Sheet, record the value as mg/L DO for the saturated distilled water. Quality Control 31

32. GLOBE Trainer Certification Program Adapted from  The DO of the shaken distilled water must be within 1.0 mg/L of the expected value for a distilled water sample saturated with oxygen. Quality Control 32

33. GLOBE Trainer Certification Program Adapted from To find the expected DO value for a saturated distilled water sample: Quality Control Step 1: Using Table HY-DO-1 find the solubility of oxygen (mg/L) that corresponds to the temperature of your sample. –Example: A temperature of 22 C has a corresponding DO solubility of 8.7 mg/L. 33

34. GLOBE Trainer Certification Program Adapted from Step 2: Using Table HY-DO-2 find the value that corresponds to your elevation. Example: An altitude of 1,544 meters has a corresponding saturation calibration value of 0.83. Quality Control 34

35. GLOBE Trainer Certification Program Adapted from Step 3: Multiply the solubility of oxygen found in Step 1 by the calibration value found in Step 2. Example: At an altitude of 1,544 meters and a temperature of 22 C: 8.7 mg/L x 0.83 = 7.25 mg/L. Step 4: Compare this value to the measured DO value of the shaken distilled water. Quality Control 35

36. GLOBE Trainer Certification Program Adapted from For Help AMSTI-GLOBE The GLOBE Program www.amsti.org/globe www.globe.gov Lynn VaughanJerry CobbsAMSTI-GLOBE Resource SpecialistTechnology Specialist lynn@amsti.org jerry@amsti.org Robin Nelson AMSTI-GLOBE Administrator robin@amsti.org 36