Lecture 22: Primary Production

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Lecture 22 Primary Production

• EEES 3050

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Ecosystem processes

• Thus far this semester our focus has been on
• Populations
• Communities
• Both of these are composed of individuals.
• Ecosystem ecology is concerned about the flow of
  energy and materials (carbon, nutrients)
• Going beyond the individual

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Ecosystem terminology

• Autotrophs
• Energy from sun and nutrients from nonliving
  sources
• Heterotrophs
• Eat autotrophs.
• Ecosystems link abiotic and biotic in common
  currency.

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Ecosystem terminology

• Biomass
• Weight of biological material or standing crop.
• Most common variables of study are
• Energy
• Carbon
• More and more important due to issues of climate
  change and carbon

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Energy

• From sun photosynthesis.
• 12H20 6CO2 solar energy
  C6H12O6 6O2 6H2O
• C6H12O6 IS ?
• Carbohydrate (sugar)
• Respiration
• C6H12O6 6O2 12H20 6CO2 energy

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Energy

• If photosynthesis equals respiration, what
  happens?
• Nothing grows
• Gross primary production
• Energy fixed per unit time.
• Net primary production
• Energy fixed in photosynthesis energy lost via
  respiration per unit time.

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Energy

• How to measure NPP in nature?
• 1) Measure the changes in CO2 and O2 in the air
  around a plant.
• When?
• During day photosynthesis and respiration are
  happening simultaneously.
• CO2 being removed from air, and O2 being released
• At night, only respiration.
• Only 02 being released

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Energy

• 2) Radioactive isotope
• Introduce 14C labeled CO2
• After time harvest plant and measure uptake of
  14C
• 3) Harvest method.
• Directly measure the amount of biomass at two
  times.
• Plus biomass losses by death or production and
  losses by consumption.
• NPP Change in Biomass losses (death and
  consumption)

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NPP for the Globe
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Annual Net Primary Production (grams of carbon
per m2 per year).
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Energy efficiency

• Whenever you measure a rate you can think about
  efficiency.
• How efficient are communities at producing, i.e.
  how well do they convert energy?
• To calculate
• Efficiency of GPP GPP/energy of sun
• Example
• Aquatic community in Lake Mendota
• 0.42
• Forests
• 2-3.5

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What controls NPP?

• Light the ultimate limiting factor
• Nutrients
• Nitrogen
• Phosphorous
• micro-nutirients
• Temperature
• Look at this in aquatic and terrestrial
  communities.

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Limiting factors in aquatic communities

• Light?
• Light only penetrates water so far.
• Water attenuates or absorbs solar radiation.
• Dependent on water clarity and content

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Clear Water
Seawater
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• Light attenuation in different types of lakes.
• Light attenuation a decrease in the energy of
  light due to absorption and scattering in the
  water column
• Three lake types
• Eutrophic.
• High nutrients, very productive lakes
• Mesotrophic
• Medium level of nutrients
• Oligotrophic
• Few nutrients.

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Light penetration and lake type.

• Observation
• Water clarity affects light attenuation in lakes.
• Hypotheses
• _________ lakes have the highest light
  attenuation. (photosynthesis only occurs at
  shallow depths.)
• _________ lakes have the lowest light
  attenuation.
• Test
• Look at rates of photosynthesis in 3 lakes.

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Results.
Eutrophic
Mesotrophic
Oligotrophic
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Results

• Did you notice the changes in scale on the
  y-axis?
• Eutrophic lake at 60 grams carbon/m2/day
• Mesotrophic 2 grams carbon/m2/day
• Oligotrophic 0.2 grams carbon/m2/day
• Is light the limiting factor?
• If so, what should be the pattern in the oceans?
• More production near equator?

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• Is the highest production in oceans at the
  equator?
• No!
• Along coasts and mid-latitiudes
• Oceans limited by nutrients.
• Nitrogen and phosphorus.
• Iron?

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Vertical distribution of different parameters in
North Pacific
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Nutrient limitations off of Long Island

• Observation
• Duck farms along the bays of Long Island added
  nutrients (N and P). Caused high algal growth.
• Which was limiting?
• Experiment
• Control
• Ammonium enriched
• Phosphate enriched.

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NPP limitations

• Oceans not limited by light
• What about freshwater?
• Light
• Nutrients
• Example of phosphorus.

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Whole-lake experiment

• Arthur Hesler Univ. of Notre Dame
• Experiment
• Divided a lake in 1951

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Whole Lake Experiments
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Whole-lake experiment

• Arthur Hesler Univ. of Notre Dame
• Experiment
• Divided a lake in 1951
• Added lime to one lake
• Results
• Raised pH from 5.9 to 7.3
• Humic colloids precipitated
• Increasing light penetration
• Rate of zooplankton production more than doubled.
• What was the true mechanism for these changes?

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Whole lake experiment

• Experimental Lakes region of Ontario
• By David Schindler early 70s
• In Lake 226
• Split in half with a curtain
• Hypothesis
• Primary production controlled by phosphorus,
  nitrogen or carbon.
• Phosphorus is the limiting factor
• Methods
• Half 1 N, C and P
• Half 2 N, C

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Lake Erie

• What limits NPP in Lake Erie?
• Historical (and recurrent) problems with algal
  blooms.
• Associated with phosphorus.
• Phosphorus story.

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History of Dead Zones in Lake Erie
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History of Dead Zones in Lake Erie

• In the 60s and 70s Dead zones were common in
  the central basin of Lake Erie
• A driver for Clear Water Act
• Limited the input of phosphorus.
• Farms
• Phosphate free detergents.
• What is current status?

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Station Locations
Courtesy of Pete Richards of Heidelberg College.
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DRP Load (metric tons/day)
Sandusky
Courtesy of Pete Richards of Heidelberg College.
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Where is the new phosphorus coming from?

• Weather?
• Population growth and exurbanization?
• No-till concentrates nutrients at surface?
• Concentrated animal agriculture?
• Winter spreading of manures?
• Global climate change?

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NPP Limitation

• In terrestrial systems?
• Temperature
• Light
• Moisture
• Nutrients

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NDVI in January
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NDVI in July
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Nutrient Limitations?

• What limits production in subartic salt-marshs?
• Hypothesis
• Arctic only limited by light and temp, not
  nutrients.
• Methods
• 4 treatments Control, P only, N only, N P

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Results
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Results

• Salt-marshes were nutrient limited.
• Primarily N limited
• With N, became P limited.

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NPP and Diversity

• What is the relationship between production and
  diversity?
• Low production ?
• High production ?

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NPP and Diversity
This pattern has been observed in many plant and
animal communities.
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Happy ThanksgivingGo and be eutrophic.