AP BIO Lab 12 Dissolved Oxygen

OXYGEN AVAILABILITY Depends on: ~Temperature: Ability to hold oxygen decreases as water temp gets warmer ~ Photosynthetic Activity: In bright light, plants produce more oxygen ~ Decomposition Activity: As organic material decays, microbial processes consume oxygen ~ Mixing/turbulence: Wave action, water falls, and rapids all aerate water and increase oxygen concentration ~ Salinity: As water becomes more salty, it holds less oxygen

Temperature Warm water dissolves ~ MORE SOLIDS than cold ~ LESS GAS than cold – Reason why pop loses it’s fizz as it gets warm

PHOTOSYNTHESIS 6 CO H 2 O +Light energy C 6 H 12 O O 2 RESPIRATION C 6 H 12 O O 2 6CO H 2 O + energy → →

Waves, waterfalls, rapids all increase oxygen concentration

Amount of light drops off sharply with increasing depth Modeled by wrapping sample bottles in increasing layers of screen

PRIMARY PRODUCTIVITY = rate at which photosynthesizers produce organic compounds in ecosystem Can be measured by: ~ amount of CO 2 used ~ rate of sugar formation ~ rate of oxygen produced

GROSS PRODUCTIVITY = Total production of all organic compounds made by photosynthesis NET PRODUCTIVITY = Organic material that remains after cellular respiration uses some of these compounds for their energy needs

Net productivity = Gross productivity - respiraton Determined by measuring oxygen production in light Determined by measuring oxygen consumption in dark w/o Photosynthesis If measure these 2... We can calculate GROSS PRODUCTIVITY

PHOSPHATE TEST

NITRATE TEST

FIXATION OF VIALS

TITRATION Don’t fill or empty syringe past the number markings

Continue adding titrating solution until blue color changes to from purple to pale yellow/colorless. If color change does not occur when the ring on the plunger reaches the bottom of the scale, refill the titrator to the zero line and continue titrating. Keep track of volume used.

Maximum amount of oxygen can water hold = SATURATION What is the % saturation of a sample with 8 mg/L oxygen at 15° ? What is the % saturation of a sample with 8 mg/L oxygen at 5° ?

NITRATES

PHOSPHATES

WHY DO LAKES in SD TURN GREEN IN SUMMER? When an ecosystem receives a LARGE input of limiting nutrient (ie., fertilizer runoff) the population increases dramatically = ___________ REMEMBER YOUR OLD BIO ! ALGAL BLOOM

Nitrates & phosphates from fertilizer/manure get washed into the lake. Nutrients are no longer LIMITED. Cause algae to grow fast and cover the surface

Algae block out sunlight needed for photosynthesis by producers below. No photosynthesis → NO O 2 → organisms below start to die. Algae die too when they run out of food

Cellular respiration by decomposers as they break down dead organisms uses up more O 2

As O 2 in water is depleted, animals and plants die

Gulf of Mexico Dead Zone The DEADZONE forms each April, generally grows throughout the summer, reaching a peak in late July.

Gulf of Mexico Dead Zone At its peak, the nearly lifeless water can span 5,000 to 8,000-plus square miles, an area almost the size of New Jersey

NITRATES

PHOSPHATES