LECTURE 23 ICA 6 HUMAN USE OF SUN’S ENERGY
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Relevant ecological topics:
Sun: origin of (almost) all energy that humans use
Ecosystem = energy-transforming machine
Photosynthesis: sun energy transferred to chemical bond energy
Respiration: release (and transfer) of chemical bond energy; generation of heat
Aerobic
Anaerobic: less release as heat
PAST: storage of chemical bond energy
Scenario: Accumulation of chemical bond energy from past photosynthesis
Production > consumption
Death, then decomposer food chain
Bury by sediments – decomposition slowed and incomplete
Biomass accumulates
Organic matter transformed to ‘fossil’ fuels
(Chemical) Fossil Fuels = Geologic Compost
Formation
Carboniferous = Devonian, Mississippian, Pennsylvanian 3-400,000,000 yrs ago!
Ocean
Algae (diatoms)
Sedimentation; decomposition by bacteria/protists
Pressure/heat
(Crude) oil + natural gas
Land
Woody plants in swamps
Biogas via anaerobic respiration by bacteria
Incomplete decomposition
Peat (a fuel)
Sedimentation
Weight squeezed out water
Pressure + heat transformed
wood fragments  thermogenic natural gas
leaves and wood  oil + coal
Trapped by overlying sediments
Retrieval by drilling/strip mining
Chemical transformation of organic matter
Lipids, proteins, carbos, lignin, cellulose in biomass
Kerogens (mix of complex heavy hydrocarbons)
Heat
Lighter hydrocarbons by breaking bonds of kerogens
PRESENT: break fossilized chemical bonds
Use of fossil fuels: heat (oil, coal, gas); machines (oil; gas); electricity (oil, coal)
Which fuels used for which use?
Relation of oil + gasoline:gas is one of many products derived from distillation of oil
Relation to electricity: use coal, oil  steam, wind  turn turbines wrapped in
copper and with magnets  strip electrons from copper  flow of electrons
Sources: relative cleanliness: amount of CO2 produced:
gas generates 45% less than coal; gas generates 30% less than oil
amount of SO4 generation: high if coal has high S content
Speed of Depletion of Non-renewable Energy (stored 3-400,000 million years ago
+ used up in about 300 years!
Discovery time: coal: 1700s = Industrial Revolution; oil (and gasoline) in 1859
in Titusville, Pa. Electricity (late 1800s) - Edison
Projected depletion: oil peak is now (or past in many oil-producing countries)
Oil will be gone this century
Alternative fuels (that relate to sun’s energy)
Solar  heat and electricity
Wind  electricity
Biofuels (see PPT)
Seed  ethanol
Vegetable oil (from seed)  biodiesel
Crop residues +
Non-crop cellulose  ethanol
Production methods
II. HUMAN USE OF ENERGY AS FOOD
Relevant ecological concepts:
population size + need (vs. ‘demand’ for animal food)
productivity of plants and animals
trophic level of consumption
ecological efficiency (‘10%)
land use (landscape and conservation ecology)
Improvements in past 50 years: Green Revolution
Genetics
Remove limiting factors of water and nutrients
Challenges now and in future
Less water for irrigation
Increasing temperatures  drought
Loss of land to nonfarm uses
Increased fuel costs
Increased costs to produce fertilizers
Fewer new technologies on horizon
Approaches to Feeding 7 Billion Well!!
1. Improve land (plant) productivity
A. increase multi-cropping
B. improve water-use efficiency
plant less water-demanding crops
C. move down food chain so less water used to produce animal feed
D. raise the cost of water
E. put local people in charge to manage resources
2. Produce animal protein more efficiently
A. 38% of grain is used as animal feed in world
B. variation in animal efficiency in conversion of grain to protein
beef – lowest; aquaculture of herbivorous fish highest
C. variation among countries in type of meat consumed
China consumes most – and loves pork; 2nd in world = chickens; fish on rise
D. Most soybeans used as grain for animal food; has improved efficiency greatly
3. New animal protein production systems
A. Milk in India: feed animals with roughage (corn stalks; straw; grass)
B. Use crop residues (straw and corn stalks) as feed for cattle
C. China: aquaculture - 4 fish feeding at different trophic levels
4. Move down food chain
A. How many people can the earth support? Depends at what trophic level
1. US consumes 800 kg grain/ person/yr – at this level support 2.5 billion
2. Italy
400
5
3. India
200
(almost all directly to humans
10
B. Of our 800 kg grain, 100 kg is eaten as grain directly; 700 goes to feed animals
C. Complete this table to understand the concept of eating lower on the food chain:
DIET of
2000 calories
Calorie Source
# Calories
Consumed
Ecologically
Equivalent
Calories*
1. 100% Plant
0% Animal
2. 90% Plant
10% Animal
3. 70% Plant
30% Animal
Plant
Animal
Plant
Animal
Plant
Animal
2000
XXXX
1800
200
1400
600
2000
XXXX
1800
2000
1400
6000
Total
Ecologically
Equivalent
Calories
2000
XXXX
XXXX
3800
XXXX
7400
4. 50% Plant
Plant
1000
50% Animal Animal
1000
5. 0% Plant
Plant
XXXX
100% Animal Animal
2000
* Assume 10% Ecological Efficiency
1000
10000
XXXX
20000
XXXX
11000
XXXX
20000
5. Cultural evolution of diet
carbos + protein
amino acid complementarity;
can get all required AAs from vegetables if combine plants with different AAs.
e.g. Latin America: beans + rice (corn)
Asia: soybeans + rice
Middle East: chickpeas + wheat/millet
Note: all three based on a legume with much protein (N)
6. Government policies about food under dedate:
Controversy: Biofuels: corn as food vs. biofuel
Controversy: Farm bill with subsidies for corn, soybeans, etc.
7. The Hungry Planet (Peter Menzel and Faith D’Aluisio)
$ spent on food (ranges from $1 to $500 /week
calories in diet (ranges from 2114 (Darfur) to USA 3774 (28% from animal products)
sugar used (ranges from almost none to USA 158 pounds/year)
obesity levels (ranges from 1% (China/Japan) to 27% (USA))
meat consumption (ranges from 7 in Bhutan to 275 pounds/year in USA
8. My daily required calories…
based on height, bone mass index, weight, level of activity, age