1. Productivity Review and Calculations

2. Recap of Definitions! Key term Definition Productivity
The total gain in energy of the producers.
Primary Productivity
The total gain in energy/biomass per unit area per unit time.
Secondary Productivity
Production per unit area per unit time
Gross Productivity (GP)
The gain in energy/biomass per unit area per unit time remaining after allowing for respiration losses which is passed onto the herbivores.
Gross Primary Productivity (GPP)
The rate at which energy/biomass is formed through photosynthesis
Net Productivity (NP)
The gain in energy/biomass per unit time remaining after allowing for respiration (R) loses.
Net Primary Productivity (NPP)
The rate at which primary material is synthesised into animal tissue per unit area in a given time.

3. Important Calculations
How do we calculate GPP?
GPP = NPP + R
How do we calculate NPP?
NPP = GPP – R
How do we calculate GSP:
GSP = food eaten – faecal losses
Or… NSP + R
How do we calculate NSP
NSP = GSP – R

4. Calculating Productivity Values
Some easy ones to start you off!
What is the % energy from sunlight that is fixed as GPP if the total energy from the sun in 3 x 106 and the gross primary productivity = 2.8 x 104?
What is the GPP of an ecosystem if the NPP is 1660 kJm-2yr-1 and the energy lost during respiration is 573 kJm-2yr-1 ?
What is the NPP if the GPP is 2700 kJm-2yr-1 and the energy used in respiration is 1850 kJm-2yr-1?

5. Calculating Productivity Values
Now for some slightly harder ones!

6. Photosynthetic Efficiency = Net production ÷ Light Energy Absorbed
Energy Flow Diagrams
Energy flow diagrams illustrate energy flow through communities and include values for respiratory losses and energy flow through the decomposers
Information from energy flow diagrams can be used to calculate ecological efficiencies
Ecological Efficiency is the net production of new biomass at each trophic level as a percentage of the total energy flowing through that trophic level
Therefore, for photoautotrophs, photosynthetic efficiency is determined as:
Photosynthetic Efficiency =
Net production ÷ Light Energy Absorbed

7. Use information from the energy flow diagram to:
Explain the meaning of the term Gross Primary Production
Explain the meaning of the term Net Primary Production
Calculate the Photosynthetic Efficiency of the phytoplankton

8. Gross Primary Production is the total energy fixed
by photoautotrophs during photosynthesis
Photosynthetic Efficiency =
3.7 x 104
x 100
172 x 104
= 2.15%
Net Primary Production is the energy stored as biomass (gross production – energy lost as heat
in respiration)

10. NPP =
800 kJ m-2year-1
Photosynthetic
efficiency = 1.3%
GPP =
24 x106 kJ m-2year-1
NPP =
69.7 x 103 kJ m-2year-1
NPP =
200 kJ m-2year-1
114 x 103 kJ m-2year-1