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Significant Ideas
• Ecosystems are linked together by energy and matter flow
• The Sun’s energy drives these flows and humans are impacting the flows of energy and matter both locally and globally
Knowledge & Understandings
• As solar radiation (insolation) enters the Earth’s atmosphere some energy becomes unavailable for ecosystems as the energy absorbed by inorganic matter or reflected back into the atmosphere.
• Pathways of radiation through the atmosphere involve the loss of radiation through reflection and absorption
• Pathways of energy through an ecosystem include:• Conversion of light to chemical energy
• Transfer of chemical energy from one trophic level to another with varying efficiencies
• Overall conversion of UB and visible light to heat energy by the ecosystem
• Re-radiation of heat energy to the atmosphere.
Knowledge & Understandings
• The conversion of energy into biomass for a given period of time is measured by productivity
• Net primary productivity (NPP) is calculated by subtracting respiratory losses (R) from gross primary productivity (GPP) NPP = GPP – R
• Gross secondary productivity (GSP) is the total energy/biomass assimulated by consumers and is calculated by subtracting the mass of fecal loss from the mass of food eaten. GSP = food eaten – fecal loss
• Net secondary productivity (NSP) is calculated by subtracting the respiratory losses (R) from GSP. NSP=GSP - R
Applications and Skills
• Analyze quantitative models of flows of energy and matter
• Construct quantitative models of flows of energy or matter for given data
• Analyze the efficiency of energy transfers through a system
• Calculate the values of both gross primary productivity (GPP) and net primary productivity (NPP) from given data
• Calculate the values of both gross secondary productivity (GSP) and net secondary productivity (NSP) from given data
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
What happens to solar radiation entering Earth’s system?
100%
entering
solar
radiation
49% absorbed
by ground
17% absorbed by
molecules & dust
3% absorbed by
clouds
Figure 10.1 Photoautotrophs
Only 0.06% of all solar radiation falling on
Earth is captured by photoautotrophs!
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
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
Producers
• Make their own food - photoautotrophs, chemoautotrophs
• Convert inorganic materials into organic compounds
• Transform energy into a form usable by living organisms
Photosynthesis
• Inputs – sunlight, carbon dioxide, water
• Outputs – sugars, oxygen
• Transformations – radiant energy into chemical energy, inorganic carbon into organic carbon
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
Primary Productivity
• The gain of energy or biomass by producers, per unit area per unit time.
• The conversion of solar energy into chemical energy.
• Depends on amount of sunlight (insolation) available, the efficiency of the producers to perform photosynthesis, and the availability of other factors needed for growth (nutrients).
Distribution of World Productivity
• Primary productivity is highest where conditions for growth is highest• High levels of insolation
• Good water supply
• Warm temperatures
• High nutrients
• Constant growing seasons
Secondary Productivity
• The biomass gained by consumers and decomposers through feeding and absorption
• Measured in mass or energy per unit area per unit time
• Depends on the amount of food available and the efficiency of the consumers for turning it into new biomass
Gross Productivity (GP)
• Total gain in energy or biomass produced per unit area per unit time
• 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
Net Productivity (NP)
• The gain in energy or biomass minus amount used by organism through respiration (R)
• Some of GP used to stay alive, grow and reproduce
• NP is what’s left
• Most NP• Estuaries, swamps, tropical rainforests
• Least NP• Open ocean, tundra, desert
• Open ocean has low NP but its large area gives it more NP total than anywhere else
Productivity & 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
GROSS PRIMARY PRODUCTIVITY (GPP)
• The rate at which producers use photosynthesis to make more biomass
• The mass of glucose created per unit area per unit time
NET PRIMARY PRODUCTIVITY (NPP)
• The rate at which energy for consumers is stored in new biomass per unit area per unit time after subtracting respiratory losses (R)
• This is the amount of energy/biomass available to the consumers at the next trophic level
• NPP = GPP - R
Productivity Calculations
• Total Primary Productivity = Gross Primary Production (GPP) Amount of light energy converted into chemical energy by photosynthesis per unit time• Joules / Meter2 / year
• Net Primary Productivity 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
Experiments to Calculate Productivity (Light/Dark Rxns)
• Use aquatic plants
• Measure both photosynthesis and respiration by looking at oxygen levels
• In water we must measure dissolved oxygen (DO) – indirect measure
• NPP can be estimated by measuring the increase in DO when in light
• GPP can be calculated by measuring the decrease in DO when put in the dark (only respiration (R) will occur)
• NPP = GPP – R so GPP = NPP + R
Experiments to Calculate Productivity (Light/Dark Rxns)
• 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 12 mg/L oxygen in your light bottle. What is the NPP, GPP, and respiration?
Experiments to Calculate Productivity (Light/Dark Rxns)
• 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 hour 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 12 mg/L oxygen in your light bottle. What is the NPP, GPP, and respiration?
• NPP = 12 mg/L – 10 mg/L = 2 mg O2 per liter per week
• Loss of dissolved O2 (R) = 10 mg/L – 7 mg/L = 3 mg/L/wk
• NPP = GPP – R so GPP = NPP + R
• GPP = 2 + 3 = 5 mg O2/L/wk
Problems
Dissolved Oxygen (mmol/L) in water samples
from Lake Ashby
Transparent Bottle Opaque Bottle
Initial, 6 a.m. 0.288 0.288
Final, 9 a.m. 0.292 0.282
Difference 0.004 0.006
1. Write the equation for and calculate the GPP
2. Write the equation for and calculate the NPP
3. Write the equation for and calculate the Respiration
GROSS SECONDARY PRODUCTIVITY(GSP)
• The total energy or biomass assimilated by consumers
• GSP = food eaten – fecal loss
NET SECONDARY PRODUCTIVITY(NSP)
• The gain by consumers in energy or biomass remaining per unit area per unit time after respiratory losses
• NSP = GSP - R
More Productivity Calculations
Producers:
• NPP = GPP – R
Consumers:
• GSP = Food eaten – fecal losses
• NSP = change in mass over time
• NSP = GSP – R
Measuring Secondary Productivity
• Gross Secondary Production• Measure the mass of food eaten by an organism
(best if controlled diet in lab)
• Measure mass of waste (excrement, shedding, etc.) produced
• GSP = food eaten – mass of feces
• Net Secondary Production• Measure organism’s starting mass and ending
mass for experiment duration
• NSP = Ending Mass – starting mass
Calculating GSP, NSP, and R
• NSP - gain in biomass of stick insect
• 9.2g – 8.9g = 0.3 g / 5 days = 0.06 g/day
• GSP = food eaten – fecal loss
• Food eaten 29.2g – 26.3g = 2.9g
• GSP = 2.9g – 0.5g = 2.4g/ 5 days = 0.48g/day
• NSP = GSP – R So R = GSP – NSP
• R = 0.48 g/day – 0.06 g/day = 0.42 g/day
Experiment was carried out over 5 days.
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