Dissolved Oxygen and Dissolved Oxygen and Primary Productivity LabPrimary Productivity Lab

ObjectivesObjectives

• Biological importance of the carbon and oxygen Cycle in an ecosystem

• How primary productivity relates to the metabolism of organisms in an ecosystem.

• The physical and biological factors that affect the solubility of gases in aquatic ecosystems.

• The relationship between dissolved oxygen and the process of photosynthesis and respiration as they affect primary productivity.

Availability of Oxygen in Aquatic Availability of Oxygen in Aquatic EnvironmentsEnvironments

• Oxygen enters the water by diffusion.• Dissolved oxygen content is an indicator of

the health of an aquatic ecosystem.• Aquatic organisms can only access free

oxygen.• There is much less free oxygen in water

than air.• Oxygen diffuses much less efficiently in

water than in air.

Biotic Factors that Affect the Biotic Factors that Affect the Amount of Dissolved Oxygen.Amount of Dissolved Oxygen.

• Warmer temperatures encourage microbial growth that increases the demand for oxygen.

• Photosynthesis increases the amount of dissolved oxygen while cellular respiration decreases it.

• Sewage encourages microbial growth and decreases available oxygen.

Pollution Affects Availability of Pollution Affects Availability of Oxygen in an Aquatic EcosystemOxygen in an Aquatic Ecosystem

• Spills of herbicides and pesticides increases the numbers of decomposers that utilize oxygen.

• Fertilizers can cause algal blooms that use oxygen.– Produce oxygen at first but then die off and

decomposers proliferate.– Large fish kills cause massive decomposition

and oxygen starvation of the ecosystem.

Abiotic Factors that Affect Levels Abiotic Factors that Affect Levels Dissolved OxygenDissolved Oxygen

• Temperature– There is more dissolved oxygen in warm

water.

• Salinity– There less dissolved oxygen saline waters.

• pH – Lower pH less dissolved oxygen

Primary ProductivityPrimary Productivity

• Rate at which organic materials are stored in an ecosystem.– Only photosynthetic organisms can fix carbon and store organic

molecules.• Photosynthetic organisms fix CO2

• 6CO2 + 6H2O ---- C6H12o6 = 6O2

Primary productivity can be measured three ways:rate in which CO2 is usedmeasuring oxygen productionformation of organic compounds

Calculating Primary ProductivityCalculating Primary Productivity

• For every milliliter of O2 produced 0.536 is milligrams of CO2 has been assimilated.

• Light and dark bottle method is used to measure the amount of O2 produced.– Algal cultures are measured before and after

being incubated in light and darkness.– The difference in the measurements indicates

the amount of O2 being consumed by the respiring organisms in the culture since photosynthesis is not creating any more O2.

Gross Productivity, Net Productivity Gross Productivity, Net Productivity and Cellular respirationand Cellular respiration

• Gross Productivity – Difference in the final dissolved O2 concentration between the Iight bottle and the dark bottle– This is the total dissolved O2 productivity including

photosynthesis and cellular respiration occurring simultaneously.

• Net Productivity – Difference in dissolved O2 concentration between the initial and dark bottle.– This is the amount of dissolved O2 that is being

consumed by respiring organisms.

Calculating Dissolved OCalculating Dissolved O22

• ppm(parts per million)

• Mg O2 / L(milligrams of O2 per liter)

– ppmO2 = mg O2/L

– mg O2/L x 0.698 = mL O2/L

• From this you can calculate amount of carbon fixed/L– mL O2/L x 0.536 = mg carbon fixed/L