2.3 Flows of Energy & Matter -Productivity

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

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

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

Ecological Efficiency

Ecological Efficiency

Ecological Efficiency

Pearson Environmental Systems and Societies 2015

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

Ocean Area vs Productivity

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

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