AP Lab #12 Dissolved Oxygen & Aquatic Primary Productivity part I

AP Lab #12 Dissolved Oxygen & Aquatic Primary Productivity part I

In an aquatic environment, O2must be in a solution in a free state before it is available for use by heterotrophic organisms…

In an aquatic environment, O2 must be in a solution in a free state before it is available for use by heterotrophic organisms… The concentration of O2, and its distribution in an aquatic environment (the pond, ocean etc.), are directly dependent on factors that greatly affected by biological processes! In the atmosphere … O2 is abundant

Terrestrial = 200 mL O2/ 1 L air Aquatic = 10 mL O2/ 1 L water WHY??? In an aquatic environment O2 is NOT as abundant as in a terrestrial…

Terrestrial = 200 mL O2/ 1 L air Aquatic = 10 mL O2/ 1 L water O2distribution in water depends on: currents, winds, tides etc. mixing it up ! O2 diffuses 300,000 X’s fasterinair than water

Terrestrial = 200 mL O2/ 1 L air Aquatic = 10 mL O2/ 1 L water O2 distribution in water also depends on: pH,

Terrestrial = 200 mL O2/ 1 L air Aquatic = 10 mL O2/ 1 L water O2 distribution in water also depends on: salinity,

Terrestrial = 200 mL O2/ 1 L air Aquatic = 10 mL O2/ 1 L water O2 distribution in water also depends on: elevation

Terrestrial = 200 mL O2/ 1 L air Aquatic = 10 mL O2/ 1 L water O2 distribution in water also depends on: temperature

HIGHER O2 (DO) CONCENTRATION (ppm) at: “Help - I am suffocating!!!” neutral pH low elevation low salinity low temperature

Terrestrial = 200 mL O2/ 1 L air Aquatic = 10 mL O2/ 1 L water O2 distribution in water also depends on: partial pressure of O2 in the air above the water !

LESS O2 IN WATER AT HIGHER ELEVATIONS THAN AT LOWER ELEVATIONS

You could think about the amount of O2 in the air @ these locations…

Terrestrial = 200 mL O2/ 1 L air Aquatic = 10 mL O2/ 1 L water O2 distribution in water also depends on: amount (rate) of photosynthesis & respiration

photosynthesis increases the D.O. (ppm) ! respiration decreases the D.O.(ppm) …

measuring D.O. is a determiner as to whether the biological activities requiring O2 are occurring (respiration) Indicator of health of lake !

Which environment has the greater concentration of dissolved oxygen: Explain. or a clear pond? a heavy algal mat?

Clear water holds more dissolved oxygen than water with a heavy algal mat. Although photosynthesis in the algal mat will produce a great deal of oxygen, the decay of so much organic matter will result in a net depletion of oxygen due to DECOMPOSERS.

??? SAY WHAT????

DECOMPOSERS w/ be in a large amount BECAUSE THE ALGAE WILL EVENTUALLY DIE... The decomposers w/ come on the scene and will USE THE OXYGEN, thus decreasing the amount of DO

Just HOW do you measure D.O.? Winkler method

Just HOW do you measure D.O.? via. titration

WINKLER METHOD to determine D.O. 1. Add alkaline iodide & manganous sulfateto a water sample. Manganous hydroxide will be produced. This will be acidified, & will spontaneously be converted to a manganese compound by the O2 in the water sample

WINKLER METHOD to determine D.O. 2. Add alkaline potassium iodide azide (KOH)to the water sample. Iodine will be released -> H2O will turn yellow **The quantity of free iodine is equivalent to the amount of D.O. in the water.**

WINKLER METHOD to determine D.O. 3. A starch indicator is then added… to determine amount of iodine via. titration H2O will turn purple You remember, titration is adding a substance of known concentration to a solution containing a substance of unknown concentration… until a specific reactions completed and a color change occurs.

WINKLER METHOD to determine D.O. 4. The amount of D.O. can then be determined by titrating aportion of the sample with sodium thiosulfate until a colorless endpoint is reached.

AP Lab #12 Dissolved Oxygen & Aquatic Primary Productivity part I

MEASURING D.O. In order to measure how much oxygen water can hold (the saturation) you will also need to be able to read a nomograph:

the percent oxygen saturation for a water sample at 10oC that has 7mg O2/L is 45% saturation nomograph

the percent oxygen saturation for a water sample at 25oC that has 7mg O2/L is 65% saturation nomograph

Day 1 temp. effect 4 degrees C 25 degrees C 30 degrees C Goggles and gloves MUST be worn

AP Lab #12 Dissolved Oxygen & Aquatic Primary Productivity Day 2

Day 2 we will compare D.O. values in water samples exposed to differing amounts of light

Primary Productivity the rate @ which biomass is produced & stored (by autotrophs) via. photosynthesis in an ecosystem

Primary Productivity amount of organic compound formed from photosynthesis amount of organic compound used by respiration - Aquatic P.P.

Primary Productivity amount of organic compound formed from photosynthesis - amount of organic compound used by respiration Net Primary Production

Primary Productivity can be measured by: *rate of CO2 utilization *rate of sugar formation (glucose produced) *rate of O2 production in the light

Primary Productivity can be measured by: can calculate the amount of carbon that has been “bound” in organic compounds over a time via. RATE OF O2 PRODUCTION

You will monitor the effect of varying light levels on D.O. in an algae-rich water culture

Just HOW do you measure primary productivity? Light-Dark bottle O2 method

Light-Dark bottleO2method to determine primary productivity 1. Measure D.O. concentration in an initial sample CONTROL TO COMPARE 2. Measure D.O. concentration in a dark sample JUST CELL RESPIRATION 3. Measure D.O. concentration in a light sample PHOTOSYNTHESIS & CELL RESPIRATION

Light-Dark bottleO2method to determine primary productivity RESPIRATION -> initial sample - dark sample GROSSPRIMARYPRODUCTION -> light sample+ amount used in dark sample NETPRIMARYPRODUCTION -> light sample- dark sample

Day 2 primary productivity

Day 2 primary productivity 3. Each bottle will have the % light it will receive..

Day 2 primary productivity

AP Lab #12 Dissolved Oxygen & Aquatic Primary Productivity part I