Calculating Productivity
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The document presents a series of productivity calculation problems related to gross primary productivity (GPP), net primary productivity (NPP), and respiration (R) for various ecosystems, including forests, algae, and diatoms. It includes specific experimental scenarios and data, as well as practice questions that require interpreting the relationships between GPP, NPP, and R. The document also provides solutions and explanations to each problem to aid understanding of the concepts in environmental systems and societies.
Calculating Productivity
- 1. Calculating Productivity p. 1 IB Environmental Systems and Societies (SL) Calculate GPP, NPP, and R as required. These problems have been adapted from those originally published by Newport High School (www.newportapes.com). 1. If the GPP for a patch of forest is 10 kg C/ m2 -year, and the amount of carbon dioxide LEAVING the ecosystem (don’t ask how we measured this!) is 5 kg C/ m2 -year, what is the NPP? 2. In the patch of forest in problem #1, how much energy is available in the primary producer level for herbivore consumption? Assume 1 kg of carbon produces 10,000 kJ. 3. Imagine we run an experiment on the algae Cladophora glomerata . We place equal amounts of algae into a light bottle and a dark (covered) bottle. We measure the dissolved oxygen in both bottles and find it is at 10 mg/L. We let both bottles sit for a week. In one week, the light bottle has a dissolved oxygen value of 11 mg/L and the dark bottle has a value of 5 mg/L. CALCULATE the amount of respiration, the NPP and the GPP. (Hint: 1 mg of oxygen is equal to approximately 3 x 10-5 moles of oxygen) 4. Imagine we run an experiment on a marine diatom. We place equal amounts of the diatom species in light and dark bottles, and measure their starting dry weight (take another “equal amount”) and dry it out. We end up with the data table below. What is the NPP, GPP, and respiration of the species of diatom? Express your answer in grams per bottle. Bottle Beginning biomass Ending biomass Light 9 g/L 11 g/L Dark 9 g/L 8 g/L Productivity Practice Problems 1. Which will produce more apples, Orchard A with 1037 BTU/m2 /day of NPP, Orchard B with 773 BTU/m2 /day, or Orchard C with 2,000 J/m2 /day? (1BTU = approx. 1,000 J) 2. Which will give you more crops (by weight), a cornfield with a GPP of 5 kg/m2 /harvest or a wheat-field with a GPP of 10 kg/m2 /harvest? 3. Assuming GPP Forest A = GPP Forest B = GPP Forest C, which has the highest rate of respiration in it’s trees: Forest A, NPP = 1254 J/m2 /day; Forest B, NPP =2157 J/m2 /day; or Forest C, NPP = 779 J/m2 /day? 4. Which has a higher rate of respiration, Bog A with NPP = 300 g/m2 /day or Bog B with NPP = 100 g/m2 /day? 5. If a forest has a GPP of 200 J/m2 /day and 100 J/m2 /day worth of carbon dioxide flow out of that forest, what is the NPP? 6. If a dark bottle loses 1 g biomass/mL and a light bottle gains 5 g biomass/mL, what is the NPP? What is the GPP? 7. You start a light bottle/dark bottle measurement on algae Species X with 10 mg/L of oxygen in both bottles. You let the bottles sit for 1 week so that photosynthesis and respiration rates can be
- 2. Calculating Productivity p. 2 IB Environmental Systems and Societies (SL) calculated. At the end of 1 week, you have 7 mg/L of oxygen in your dark bottle and 10 mg/L oxygen in your light bottle. What is the NPP, GPP, and respiration? Express your answers in moles of oxygen per liter per week. Remember 1 mg of oxygen is equal to approximately 3 x 10-5 moles of oxygen. 8. Imagine we run an experiment on a simulated grassland ecosystem. We measure their starting weight (using an identical third sample, dried) and place equal amounts of a grass species in light and dark locations. After one week, we end up with the following data. Each sample is in a 10 cm2 container. What is the NPP, respiration, and GPP of the “grassland”? Express your answers in grams/cm2 /day (Hint: this requires some dimensional analysis from the units listed above). Week Dry Weight Start 10 grams One Week Later 17 grams (light bottle) One week Later 7.2 grams (dark bottle)
- 3. Calculating Productivity p. 3 IB Environmental Systems and Societies (SL) ANSWER KEY TO ALL PROBLEMS - DON’T LOOK AT THESE UNTIL YOU’VE DONE THE WORK! If the GPP for a patch of forest is 10 kg C/ m2-year, and the amount of carbon dioxide LEAVING the ecosystem (don’t ask how we measured this!) is 5 kg C/ m2-year, what is the NPP? NPP = GPP – Respiration GPP = 10 kg C/ m2 -year Respiration (CO2 leaving patch of forest) = 5 kg C/ m2 -year NPP = 10 kg C/ m2 -year – 5 kg C/ m2 -year = 5 kg C/ m2 -year In the patch of forest in problem #1, how much energy is available in the primary producer level for herbivore consumption? Assume 1 kg of carbon produces 10,000 kJ. 5 kg C/ m2-year * 10,000 kJ / kg C = 50,000 kJ/m2-year Imagine we run an experiment on the algae Cladophora glomerata. We place equal amounts of algae into a light bottle and a dark (covered) bottle. We measure the dissolved oxygen in both bottles and find it is at 10 mg/L. We let both bottles sit for a week. In one week, the light bottle has a dissolved oxygen value of 11 mg/L and the dark bottle has a value of 5 mg/L. CALCULATE the amount of respiration, the NPP and the GPP. Challenge/extension: calculate NPP, GPP, and R in moles carbon per liter. (Hint: 1 mg of oxygen is equal to approximately 3 x 10-5 moles of oxygen). We know: Starting with the dark bottle: Start=10mgO2/L After1week=5mgO2/L During the week, 5 mg O2/ L was consumed by RESPIRATION. This is... 5 mg O2/L-wk*(3x10-5 moles of oxygen/mg O2)*(1 mol C/1 mol O2) = 15x10-5 moles of C/L-wk Then we work with the light bottle: Start = 10 mg O2/L After 1 week = 11 mg O2/L Light Bottle has process of photosynthesis AND respiration Dark Bottle has only process of respiration. So we can say: Light bottle measures NPP of algae (NPP = GPP – Rplants = Photosynthesis – Respiration of Plants) Dark Bottle measures respiration. During the week, 1 mg O2/L was PRODUCED—both photosynthesis and respiration were going on, so this must be the NPP. This is... 1mgO2/L-wk*(3x10-5 moles of oxygen/mg O2)*(1 mol C/1 mol O2)=3x10-5 moles of C / L-wk To calculate GPP: NPP = GPP – Rplants NPP + Rplants = GPP
- 4. Calculating Productivity p. 4 IB Environmental Systems and Societies (SL) 3x10-5 moles of C/L-wk+15x10-5 molesofC/L-wk = 18x10-5 molesofC/L-wk 4. Imagine we run an experiment on a marine diatom. We place equal amounts of the diatom species in light and dark bottles, and measure their starting dry weight (take another “equal amount”) and dry it out. We end up with this data. What is the NPP, GPP, and respiration of the species of diatom? Express your answer in grams per bottle. SEE GENERAL STATEMENT OF LOGIC IN SOLUTION TO PART 3 Starting with the dark bottle: Start = 9 grams biomass After 1 week = 8 grams biomass During the week, 1 gram of biomass was consumed by RESPIRATION. This is: 1 g / bottle-wk Then we work with the light bottle: Start = 9 grams biomass After 1 week = 11 grams biomass During the week, 2 grams of biomass were PRODUCED as NPP. This is: 2 g/ bottle-wk To calculate GPP: NPP = GPP – Rplants NPP + Rplants = GPP 2 g/bottle-wk + 1 g/bottle-wk = 3 g/bottle-wk Productivity Practice Problems Which will produce more apples,Orchard A with 1037 BTU/m2 /day of NPP, Orchard B with 773 BTU/m2 /day, or Orchard C with 2,000 J/m2 /day? NPP really is equal to the amount of apples—remember we can define it as the amount of biomass/energy available for herbivores to consume. (For the nitpickers, you do need to assume that each orchard has similar species with similar amounts of flowers and then apples...but work towards making—and allowing yourself—to make and state simplifying assumptions to help you solve problems). So, which has the greatest NPP? Remember that 1,000 J is about 1 BTU, so 2,000 J is about 2 BTU’s. That means ORCHARD A is the most productive. Which will give you more crops (by weight), a cornfield with a GPP of 5kg/m2 /harvest or a wheat-field with a GPP of 10 kg/m2 /harvest? You should not be able to answer this. GPP doesn’t tell you anything about production available for herbivores. You need to calculate in energy lost to respiration before you can answer this question. Assuming GPP Forest A = GPP Forest B = GPP Forest C, which has the highest rate of respiration in its trees: Forest A, NPP = 1254 J/m2 /day; Forest B, NPP =2157 J/m2 /day; or Forest C, NPP = 779 J/m2 /day? If GPP is equal, then we can manipulate the NPP equation and solve. NPP = GPP – respiration of plants; Respiration of Plants = GPP – NPP This means that the smallest NPP corresponds to the largest respiration. That is FOREST C
- 5. Calculating Productivity p. 5 IB Environmental Systems and Societies (SL) Which has a higher rate of respiration, Bog A with NPP = 300g/m2 /day or Bog B with NPP = 100 g/m2 /day? You should not be able to answer this. Without knowing GPP, you cannot talk about respiration. NPP = GPP – Rplants If a forest has a GPP of 200J/m2 /day and 100J/m2 /day worth of carbon dioxide flow out of that forest, what is the NPP? Simple formula plug in: NPP = GPP – Rplants Rplants = 100 J/m2 /day worth of carbon dioxide (refer to equation) GPP = 200 J/m2 /day NPP = 200 J/m2 /day – 100 J/m2 /day = 100 J/m2 /day = NPP If a dark bottle loses 1 g biomass/mL and a light bottle gains 5 g biomass/mL, what is the NPP? What is the GPP? You start a light bottle/dark bottle measurement on algae Species X with 10 mg/L of oxygen in both bottles. You let the bottles sit for 1 week so that photosynthesis and respiration rates can be calculated. At the end of 1 week, you have 7 mg/L of oxygen in your dark bottle and 10 mg/L oxygen in your light bottle. What is the NPP, GPP, and respiration? Express your answers in moles of carbon per liter per week. Remember 1 mg of oxygen is equal to approximately 3 x 10-5 moles of oxygen. 1) Species X has consumed 3 mg O2/L/week by respiration in the dark bottle. This is equivalent to: 3mgO2/L/week*(3x10-5 moles of oxygen/mg O2)*(1 mol C/1 mol O2) = 9 moles C / L-week = RESPIRATION 2) Species X has not produced any net productivity in the light bottle. NPP = 0 mg O2 / L/ week = 0 moles C/ L-week = NPP 3) To calculate GPP, we again manipulate to find GPP = NPP + Rplants GPP = 0 moles C/ L-week + 9 moles C/L-week = 9 moles C / L-week = GPP