Ecosystem Metabolism and Air-Water Fluxes of Greenhouse Gases in High Arctic Ponds
Ecosystem Metabolism 1: Primary Production
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Transcript of Ecosystem Metabolism 1: Primary Production
Ecosystem Metabolism 1:
Primary Production
• Population – distinct group of individuals of a species that live, interbreed, and interact in the same geographic area.
• Community – includes all of the populations of organisms that live and interact with one another in a given area at a given time.
• Ecosystem – consists of a self-sustaining, self-regulating community of organisms interacting with the physical (abiotic) environment within a defined geographical environment.
Levels of Integration:Landscapes
Ecosystems
Communities
Species
Populations
Individual Organisms
Organ Systems
Organs
Tissues
Cells
Subcellular Organelles
Molecules
Ecosystem Metabolism:
-requires constant energy input
Energy Flow in Ecosystems
Producers
Consumers
Decomposers
Two Laws of Thermodynamics
• First Law: Energy cannot be created or destroyed, but it can be changed from one form to another.
• Second Law: Energy cannot be changed from one form to another without loss of usable energy.
First law Second law
When energy transformations occur, energy is neither created nor destroyed (1st Law) but there is always loss of usable energy, usually as heat (2nd Law).
One Way Flow of Energy
Living Organisms Need Energy
• Autotrophs – gain energy from the sun and materials from non-living sources– Plants, algae, phytoplankton (primary producers)
• Heterotrophs – gain energy and materials from eating other living organisms– Herbivores eat plants (primary consumers)– Carnivores eat animals (secondary/tertiary consumers)– Omnivores eat both plants and animals
• Decomposers – gain energy and materials from organic material– Mushrooms, bacteria, some invertebrates
Photosynthesis:
CO2 (from
air)
H2O
O2 (to
air)
C6H12O6
Solar energy converted to chemical energy
CO2 converted to Carbohydrate
Solar energy + 6CO2 + 6H2O → C6H12O6 + 6O2
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Happy Rays of Sunshine
Overview of Cellular Respiration
• Cellular respiration is the step-wise release of energy from molecules (usually carbohydrates) used to synthesize ATP molecules.
• This is an aerobic process that requires oxygen (O2) and gives off carbon dioxide (CO2), and involves the complete breakdown of glucose to carbon dioxide and water:
C6H12O6 + 6O2 → 6CO2 + 6H2O + energy(in form of ATP)
• Primary production - the synthesis of organic matter by autotrophs– Always measured as a rate per unit of time
– Sugar cane farmers kg/ha/yr cane production
• To accumulate organic matter, photosynthesis must be greater than respiration
• Compensation point – when photosynthesis = respiration– No growth / no reproduction
Two Measures of Production
Gross Primary Production (GPP)
Energy (or carbon) fixed via photosynthesis per unit time
Net Primary Production (NPP)
Energy (or carbon) fixed in
photosynthesis – energy (or carbon) lost via respiration per unit time
=
=
NPP = GPP - RespirationYou need to know this
Primary Productivity
CO2
C6H12O6
Photosynthesis Respiration
Solar Energy
Heat Energy
Biomass (g/m2/yr)
O2
Available to Consumers
Chemical Energy (ATP)
NP
P
GP
P
Measuring Primary Production: Terrestrial
• Primary production measured as a rate per unit time
• Can measure CO2 uptake rate during the day = net production
• CO2 released at night = respiration
12H20 + 6CO2 + 2966kj (solar energy) C6H12O6 + 6O2 + 6H20
Energetic Equivalents
• Absorption of 6 moles of CO2 indicates that 2966kj of energy has been absorbed
• This gives us a relationship between carbon accumulated and energy gained
• We can determine the amount of carbon in a plant by measuring the amount of energy in that plant
Simple Method to Measure Primary Production: Harvest Method
B = biomass change in the community between time 1 (t1) and time 2 (t2)
• B1 = biomass at (t1)
• B2 = biomass at (t2)
B = B2 – B1
Harvest Method
• Whole plant, aerial production, or root production
• Two possible losses must be recognizedL = biomass losses by death of plants or plant parts
G = biomass losses to consumer organisms
• With those values:
NPP = B + L + G
Harvest Method Energy Determination
• NPP can be converted to energy by measuring the caloric equivalent of the material in a bomb calorimeter
Mean of 57 plant species
cal/g dry wt J/g dry wt
Leaves 4,229 17,694
Roots 4,720 19,748
Seeds 5,065 21,192Golly 1961
Aquatic Primary Production
• The most important primary producers in aquatic systems are phytoplankton– Single cell plants suspended in the water
column
• Estimate primary production by measuring gas-exchange using light bottle dark bottle– Light bottle determines oxygen produced by
photosynthesis – Dark bottle measures oxygen consumed by
respiration
Phytoplankton:
Light – Dark BottleMeasure initial oxygen concentration in both bottles
Place bottles in water for a specific period during the day
Measure final oxygen concentration in both bottles
LBI = initial O2 in the light bottle DBI = initial O2 in the dark bottle
LBF = final O2 in the light bottle DBF = final O2 in the dark bottle
GPP = LBF – DBF (Total oxygen produced)
NPP = LBF – LBI (Oxygen increase)
Respiration = DBI – DBF (Oxygen decrease)
GPP = LBF – DBF (Total oxygen produced)
NPP = LBF – LBI (Oxygen increase)
Respiration = DBI – DBF (Oxygen decrease)
LBI = 5.3 DBI = 5.3 LBF = 6.8 DBF = 4.2; 1 hr
GPP = LBF – DBF = 6.8 – 4.2 = 2.6 mg/L/hr
NPP = LBF – LBI = 6.8 – 5.3 = 1.5 mg/L/hr
Respiration = DBI – DBF = 5.3 – 4.2 = 1.1 mg/L/hr
NPP = GPP – Respiration = 2.6 – 1.1 = 1.5 mg/L/hr
What Does Production Actually Mean??
• More carbon fixed from the atmosphere = more food available
• The greater the productivity, the greater the biomass of heterotrophs that can be supported
How to Estimate Carbon Produced
• 1 mg/L O2 = 0.375 mg Carbon
• GPP = 2.6 mg O2/L/hr * 0.375 = 0.975 mg C/L/hr
• NPP = 1.5 mg O2/L/hr * 0.375 = 0.563 mg C/L/hr
• For this example, 0.563 mg of carbon per liter of water per hour are added as biomass to the system
Estimated NPPVegetation Type Annual net primary production
Ocean 48.5 46% of total production
Land
Tropical rainforests 17.8
Broadleaf deciduous forests 1.5
Broadleaf and needleleaf forests 3.1
Needleleaf evergreen forests 3.1
Needleleaf deciduous forests 1.4
Savannas 16.8
Perrenial grasslands 2.4
Broadleaf shrubs 1.0
Tundra 0.8
Desert 0.5
Cultivated areas 8.0
Total for land vegetation 56.4 54% of total production
Total for globe 104.9
Units = petagrams of carbon; 1 petagram = 1015 grams = 109 metric tons
Worldwide Production
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Ocean Productivity
• On a per square meter basis the oceans are about as productive as the arctic tundra– Sometimes called a biological desert
• However, because the ocean’s make up 71% of the Earth’s surface, they account for 46% of total productivity
Photosynthetic Efficiency
• Percentage of received solar energy a plant uses:
Energy fixed by primary production*
Energy input per unit area per unit time
Efficiency of GPP = X 100
*Calculate number of carbon atoms from plant weight. Can then calculate the amount of energy required to build the plant.
Efficiency of Lake Mendota, Wisconsin
20,991 kJ/m2/yr gross primary production
4,973,604 kJ incident sunlight
Efficiency of GPP = X 100 = 0.42%
Vegetation Type GPP Efficiency*
Forests 2.0 – 3.5%
Herbaceous Communities 1.0 – 2.0%
Crops < 1.5%
Phytoplankton Communities Usually < 0.5%
*NPP is even less efficient. Overall, terrestrial plants usually convert approximately 1% of incoming solar energy to NPP during the growing season.
• Depth of light penetration determines the photic zone:
Where:
l = amount of solar radiation (joules per m2 per unit of time)
t = depth
k = extinction coefficient
• Typically, more than half of the solar radiation is absorbed in the first meter of water:
Limiting Factors – Aquatic Communities
dldt = kl
Attenuation of Solar Radiation
Pure water
Oceanic seawater
Coastal seawater ~k=0.3
Mississippi River?
-Turbulence
Lake Classification Based on Production
• Eutrophic – high production but little light penetration
• Oligotrophic – low production but high light penetration
Rate of Photosynthesis Measured as grams of carbon fixed per m2
Note the scale
Eutrophic
Intermediate
Oligotrophic
Marine Communities
North Pacific Gyre
Euphotic Zone – the surface down to 1% light level
Nutrient Limited?
Why are the Ocean’s so Unproductive?
P – High; N – Low
Nitrogen, not phosphorous, is limiting
Surprising because of the ability of cyanobacteria to fix atmospheric nitrogen?
What else?
• Top down control – Predation (by herbivores) is actually limiting the phytoplankton population– Nutrients phytoplankton zooplankton fish– Herbivory limits phytoplankton
• Bottom up control – Some other nutrient than nitrogen or phosphorous may be limiting– Nutrients phytoplankton zooplankton fish– Nutrients limit phytoplankton
Sargasso Sea
• Found not to be N or P limited, but Iron limited
Nutrients added to experimental culture
Relative uptake of 14C by cultures
None (control) 1.00
N + P only 1.10
N + P + metals (excluding iron) 1.08
N + P + metals (including iron) 12.90
N + P + iron 12.00
Why Iron
• Cyanobacteria fix atmospheric nitrogen to a form available to phytoplankton
• Iron is necessary for this process:
Iron cyanobacteria N fixation phytoplankton
Nutrient Addition:303 studies combined
Silica important when community dominated by diatoms
Freshwater Production Limits
• Solar radiation usually limits primary production in a given freshwater lake on a day to day basis– Temperature is highly correlated to solar radiation, so it
is hard to tease out specific temperature effects
• Plants require nitrogen, calcium, phosphorous, potassium, sulfur, chlorine, sodium, magnesium, iron, manganese, copper, iodine, cobalt, zinc, boron, vanadium, and molybdenum– Any one of these could be limiting in a freshwater lake,
but is usually nitrogen and/or phosphorous– Ocean water usually has a constant amount of these
nutrients
Eutrophication
• Eutrophication – increase in phytoplankton density due to anthropogenic increases in nutrients– Usually shift from a diatom or green algae
dominated community to a blue-green algae dominated community
– To control eutrophication, you must control nutrient source
• Sewerage or runoff
Blue-green Algae Negative
• Can become very abundant when nutrients are abundant and form a floating ‘scum’– Zooplankton do not graze as heavily on blue-
green algae– Can fix their own N when it is limiting
• Low nutrient food item for zooplankton
Limited by Phosphorous
Phosphorous is limiting in this system, not nitrogen
More Phosphorous
Chlorophyll a increases as phosphorous increases
Nitrogen-to-phosphorous ratio can regulate the phytoplankton community; nitrogen limited
Aquatic Summary
• Phytoplankton dominates primary production
• Ocean primary production is nitrogen limited– Indirectly iron limited– Overall, ocean productivity is low
• Freshwater lake primary production is phosphorous limited– But can be limited by other nutrients– FW lake productivity can vary from highly
oligotrophic to highly eutrophic
Terrestrial Limits to Primary Production
• Solar Radiation– Equator to poles
• Temperature– Tropical mountains
• Rainfall
• Nutrients– Nitrogen, phosphorous
Using satellite imagery to estimate global primary production
(a) June 1988 – August 1998
Latitude & Solar Radiation
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Evapotranspiration
• Evapotranspiration – the amount of water pumped into the atmosphere by evaporation from the ground and via transpiration from vegetation– A measure of solar radiation, temperature and
rainfall
Can be used to predict above ground NPP
Vegetation Type
• Leaf – area index – The greater the surface area the greater amount of photosynthesis– Conifers (pine trees) have a
higher leaf-area index than deciduous trees (oak trees)
– Conifers keep their leaves much longer, thus they have a longer growing season
Warm Temperate Zone
Cool Temperate Zone
Leaf Area Duration
Leaf-area index times length of growing season (determined by temperature) in months. Accurately predicts GPP.
Another value used to describe temperature over time is degree day: the sum of daily average temperatures for a specific period.
Needle - leaves
Broadleaves
Nutrients Are Often Limiting
Like in aquatic systems, N and P can be limiting.
Competition can limit primary production
Year # species
1856 49
1862 28
1872 16
1903 10
1919 8
1949 3
Species diversity can affect primary production
Primary production can affect species diversity