Lab 12 Dissolved Oxygen

Dissolved oxygen indicates water quality  Air contains 95% more oxygen than water  Water’s ability to hold dissolved oxygen decreases as water temperature increases

Life in water depends on dissolved Oxygen

Sewage depletes oxygen  Decomposition of the organic material uses up the oxygen

Eutrophication  Algae on surface, block light to lower plants

Colder water holds more DO

More dissolved oxygen on surface

Seasonal change in DO  Temperature

Wind  Wind stirs water, mixes Oxygen  Calm nights can deplete O2  No wind = fish die

Turbulence  Streams with turbulence increase oxygen  trout

Trophic state  The amount of nutrients (calcium and nitrogen) determines how much life can be sustained which affects amount of DO in water

Primary production of plants  Total photosynthesis production of free energy minus energy used for growth or maintenance  Or the energy stored as organic matter

Primary production measured by oxygen  2 bottles with phytoplankton  Dark bottle – control respiration only  Light bottle – photosynthesis and respiration

Initial bottle, - start with algae  Respiration = initial bottle – dark bottle  Net primary production = light bottle – initial bottle  Gross production = (light bottle – initial bottle) + (initial bottle – dark bottle) OR OR Gross prod. = Net production –respiration OR Gross production = light bottle – dark bottle

Conversion of oxygen data to Carbon  Limnologists (study lakes) – express primary production in terms of carbon  1 mol oxygen = 1 mole CO2

Oxygen cycle  Oxygen for photosynthesis is used in cell respiration and incorporated into CO2

Photosynthesis

Dissolved gasses in water  Oxygen  Nitrogen  Carbon dioxide

Altitude  Altitude increases  DO decreases

Temperature  Temperature increases decrease DO

Fish need dissolved Oxygen to survive

Measuring dissolved oxygen  Winkler method of titration 1) Add alkaline iodide and manganous sulfide to water sample produces SOLID manganous hydroxide. 2) O 2 turns this to manganic hydroxide 3) Add Sulfamic acid 4) This releases causes iodide  iodine water turns dark yellow 5) Amount of iodine is measured by titration purple to pale yellow

SUMMARY 1- Take water sample 2- Add MnSO 4 + KI reacts with O 2 (Solid) reacts with O 2 (Solid) 3- Add acid, iodine released turns yellow 4- Add starch indicator turns purple 5 - Titrate until turns Light yellow Light yellow

titration  Drop and swirl, drop and swirl  Watch carefully

Part B. Primary Productivity Use 7 bottles marked 1 – initial 2 – Dark 3 – 100% 4 – 65% 5 – 25% 6 – 10% 7 – 2%

Fill bottle with water sample (algae culture)  Submerge bottle in water/algae culture  Tap to remove air bubbblees  Cap under water

Wrap each bottle with appropriate material 1 – initial 2 – Dark Foil 3 – 100% 0 screens 4 – 65%1 screen 5 – 25%3 screens 6 – 10%5 screens 7 – 2%8 screens

Place bottles in uniform light over night

FIX all bottles  Do steps 3 – 7  Add manganeous sulfate  Add Alkaline iodide  Cap and mix  Add 1 scoop acid

Then Titrate again  Just like part A

Part C Simulation  Use values given to analyze