Calculating Productivity

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

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)

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

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

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

Calculating Productivity

Recommended

Recommended

More Related Content

What's hot

What's hot (20)

Similar to Calculating Productivity

Similar to Calculating Productivity (20)

More from Brad Kremer

More from Brad Kremer (20)

Recently uploaded

Recently uploaded (20)

Calculating Productivity