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Efficient Ecosystem Productivity Assessment

Understand photosynthesis and respiration, calculate primary and secondary productivity. Learn about energy transformation, gross and net productivity values, and the distribution of world productivity. Explore productivity calculations and measurements in ecosystems.

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Efficient Ecosystem Productivity Assessment

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  1. Ecosystem Productivity

  2. Assessment Statements • 2.5.2: Describe photosynthesis and respiration in terms of inputs, outputs and energy transformations. • 2.5.5: Define the terms gross productivity, net productivity, primary productivity, and secondary productivity • 2.5.6: Define the terms and calculate the values of gross primary productivity (GPP) and net primary productivity (NPP) from given data. • 2.5.7: Define the terms and calculate the values of gross secondary productivity (GSP) and net secondary productivity (NSP) from given data.

  3. Key terms • Gross productivity (GP) • Gross Primary Productivity (GPP) • Gross Secondary Productivity (GSP) • Net productivity • Net Primary Productivity (NPP) • Net Secondary Productivity (NSP) • Primary productivity • Secondary productivity

  4. Figure 10.1 Photoautotrophs

  5. Photosynthesis in Plants • Chloroplasts are the location of photosynthesis in plants • In all green parts of plants – leaves, stems,… • Green color from chlorophyll (photosynthetic pigment) • Found in cells of mesophyll – interior tissue of leaves • Gases exchanges through the stomata • Water enters through xylem of roots

  6. Figure 10.2 Focusing in on the location of photosynthesis in a plant

  7. Energy Processes • Photosynthesis (Green Plants) sunlight +water + carbon dioxide  oxygen + sugars • Respiration (All living things) oxygen + sugars  ATP +water + carbon dioxide • ATP is molecular energy storage

  8. Producers • Make their own food - photoautotrophs, chemoautotrophs • Convert inorganic materials into organic compounds • Transform energy into a form usable by living organisms

  9. Photosynthesis • Inputs – sunlight, carbon dioxide, water • Outputs – sugars, oxygen • Transformations – radiant energy into chemical energy, inorganic carbon into organic carbon

  10. Respiration • Inputs - sugars, oxygen • Outputs - ATP, carbon dioxide, water • Transformations – chemical energy in carbon compounds into chemical energy as ATP, organic carbon compounds into inorganic carbon compounds

  11. Definitions • gross productivity – total biomass produced • net productivity – total biomass produced minus amount used by organism • primary productivity – productivity at 1st trophic level • secondary productivity – productivity at higher trophic level • gross primary productivity – rate at which producers use photosynthesis to make more biomass • net primary productivity – rate at which energy for use by consumers is stored in new biomass

  12. Distribution of World Productivity

  13. Gross Productivity • Varies across the surface of the earth • Generally greatest productivity • In shallow waters near continents • Along coral reefs – abundant light, heat, nutrients • Where upwelling currents bring nitrogen & phosphorous to the surface • Generally lowest • In deserts & arid regions with lack of water but high temperatures • Open ocean lacking nutrients and sun only near the surface

  14. Ocean Area vs Productivity

  15. Effects of Depth

  16. Net Productivity • Some of GPP used to stay alive, grow and reproduce • NPP is what’s left • Most NPP • Estuaries, swamps, tropical rainforests • Least NPP • Open ocean, tundra, desert • Open ocean has low NPP but its large area gives it more NPP total than anywhere else

  17. Agricultural Land • Highly modified, maintained ecosystems • Goal is increasing NPP and biomass of crop plants • Add in water (irrigation), nutrients (fertilizer) • Nitrogen and phosphorous are most often limiting to crop growth • Despite modification NPP in agricultural land is less than many other ecosystems

  18. Productivity Calculations • Total Primary Production = Gross Primary Production (GPP)  Amount of light energy converted into chemical energy by photosynthesis per unit time • Joules / Meter2 / year • Net Primary Production  GPP – R, or GPP – some energy used for cell respiration in the primary producers (R = respiratory loss) • Represents the energy storage available for the whole community of consumers • Standing crop = Total living material at a trophic level

  19. More Productivity Calculations Producers: • NPP = GPP – R Consumers: • GSP = Food eaten – fecal losses • NSP = change in mass over time • NSP = GSP – R

  20. Measuring Primary Production • Measure aspects of photosynthesis • In closed container measure O2 production, CO2 uptake over time • Must measure starting amount in environment then amount added by producers • Use dissolved oxygen probe or carbon dioxide sensor • Measure indirectly as biomass of plant material produced over time (only accurate over long timer periods)  this gives NPP

  21. Light and Dark Bottle Method – for Aquatic Primary Production • Changes in dissolved oxygen used to measure GPP and NPP • Measures respiration and photosynthesis • Measure oxygen change in light and opaque bottles • Incubation period should range from 30 minutes to 24 hours • Use B.O.D. bottles

  22. Light and Dark Bottle Method – for Aquatic Primary Production • Take two sets of samples measure the initial oxygen content in each (I) • Light (L) and Dark (D) bottles are incubated in sunlight for desired time period • NPP = L – I • GPP = L – D • R = D – I

  23. Sample Data

  24. Method evaluation • Tough in unproductive waters or for short incubation times • Accuracy in these cases can be increased by using radioactive isotopes C14 of carbon • Radioactivity measured with scintillation counter

  25. Can use satellite imaging: Nutrient rich waters of the North Atlantic

  26. Measuring Secondary Productivity • Gross Secondary Production • Measure the mass of food intake (I) by an organism (best if controlled diet in lab) • Measure mass of waste (W) (excrement, shedding, etc.) produced • GSP = I – W • Net Secondary Production • Measure organism’s starting mass (S) and ending mass (E) for experiment duration • NSP = E-S

  27. Method evaluation • GSP method difficult in natural conditions • Even in lab hard to get exact masses for waste • NSP method hard to document mass change in organism unless it is over a long time period

  28. What types of things effect productivity? • What can we measure for an experiment? • Effects of light exposure – strength, time, color, … • Effects of temperature • Differences between types of plants • Differences between types of producers • Effects of nutrient additions • Effects of salinity

  29. Other parameters to change • Terrestrial vs. aquatic • Oxygen, carbon dioxide • Biomass • B.O.D. bottles

  30. GPP estimates

  31. Problems Dissolved Oxygen (mmol/L) in water samples from Lake Ashby 1. Write the equation for and calculate the GPP • Write the equation for and calculate the NPP 3. Write the equation for and calculate the Respiration

  32. Problems • The GPP of the producers in the area, large rainforest trees, is 0.0050 g/cm2/day and 25% of this productivity is consumed in respiration. Calculate the NPP.

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