1. 2.1 Energy Flow in Ecosystems
Biomass is the total mass of all living things in a given area.
Biomass is also sometimes used to the mass of organic materials used to produce biofuels such as biogas.
Biomass is generally measured in g/m2 or kg/m2
Within an organism’s niche, the organism interacts with the ecosystem by:
Obtaining food from the ecosystem
Contributing energy to the ecosystem
Plants are called “producers” because they produce
carbohydrates from carbon dioxide, water and the sun’s energy.
“Consumers” get their energy by feeding on producers or other consumers.
Decomposition is the break-down of wastes and dead organisms, by organisms called “decomposers”, through the process of biodegradation.
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2. Energy Flow and Energy Loss in Ecosystems: Food Chains
Scientists use different methods to represent energy moving through ecosystems.
Food chains
Food webs
Food pyramids
Food chains show the flow of
energy in an ecosystem
Each step is a trophic level
Feeding & niche relationship
Producers = 1st trophic level
Primary consumers = 2nd trophic level
Secondary consumers = 3rd trophic level
Tertiary consumers = 4th trophic level
Examples of terrestrial and aquatic food chains
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3. Energy Flow and Energy Loss in Ecosystems: Food Chains (continued)
Consumers in a food chain can be classified as:
Detrivores - consumers that obtain energy and nutrients from dead organisms and waste matter
Includes small insects, earthworms, bacteria and fungi
Detrivores feed at every trophic level
Detrivores have their own, separate food chains,
and are very numerous
Herbivores - primary consumers
herbivores eat plants (producers) only
Carnivores - secondary or tertiary consumers
Secondary consumers eat non-producers, such as herbivores
Tertiary consumers eat secondary consumers
Aka top consumers, top carnivores or top consumers
Omnivores - consumers that eat both plants and animals
Examples include humans and bears
This dung beetle is a detrivore.
See page 61
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4. Energy Flow and Energy Loss in Ecosystems: Food Webs
Most organisms are part of many food chains.
To represent interconnected food chains, scientists create a food web.
Food webs are models of the feeding relationship in an ecosystem.
Arrows in a food web represent the flow of energy and nutrients.
Following the arrows leads to the top carnivore(s).
This food web represents a terrestrial ecosystem that could be found in British Columbia.
See page 62
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5. Energy Flow and Energy Loss in Ecosystems: Food Pyramids
Food pyramids show the changes in available energy from one trophic level to another in a food chain.
Aka ecological pyramids
Energy enters at the first tropic level (producers), where there is a large amount of biomass, and therefore much energy
It takes large quantities of organisms in one tropic level to meet the energy needs of the next trophic level.
Each level loses large amounts of the energy
it gathers through basic processes of living.
80% - 90% of energy taken in by consumers
is used in chemical reactions in the body,
and is lost as heat energy.
There is very little energy if left over for
growth or increase in biomass.
See page 63
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6. Energy Flow and Energy Loss in Ecosystems: Food Pyramids (continued)
Food pyramids are also known as ecological pyramids.
Ecological pyramids may show biomass, population or energy numbers.
The amount of life an ecosystem can contain is based on the bottom level of the ecological pyramid, where producers capture energy from the sun.
Each level in the energy pyramid = a loss of 90% of total energy available
Lower trophic levels have much
larger populations than upper levels.
This shows the importance of
maintaining large, biodiverse
populations at the lowest levels
of the food pyramid.
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Take the Section 2.1 Quiz
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7. 2.2 Nutrient Cycles in Ecosystems
Nutrients are chemicals required for growth and other life processes.
Nutrients move through the biosphere in nutrient cycles, or exchanges.
Nutrients often accumulate in areas called stores.
Without interference, generally the amount of nutrients flowing into a store equals the amount of nutrients flowing out.
Human activities can upset the natural balance of nutrient cycles.
Land clearing, agriculture, urban expansion, mining, industry and motorized transportation can all increase the levels of nutrients more quickly than the stores can absorb them.
Excess nutrients in the biosphere can have unexpected consequences.
There are five chemical elements required for life.
Carbon, hydrogen, oxygen and nitrogen cycle between living things and the atmosphere.
Phosphorous cycles in from sedimentary rock.
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8. Nutrient Cycles: The Carbon Cycle
Carbon atoms are a fundamental unit in cells of all living things.
Carbon is also an essential part of chemical processes that sustain life.
Carbon can be stored in many different locations.
Short-term shortage is found in aquatic and terrestrial organisms,
and in CO2 in the atmosphere and top layers of the ocean.
Longer-term storage is found in middle and lower ocean layers as dissolved CO2, and in coal, oil and gas deposits in land and ocean sediments.
Sedimentation traps many long-term stores of carbon
Layers of soil and decomposing organic matter become buried
on land and under the oceans.
Slowly, under great pressure over many years, coal, oil and gas form.
Layers of shells also are deposited in sediments on the ocean floor, forming carbonate rocks like limestone over long periods of time.
Carbon stores are also known as carbon sinks
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9. Nutrient Cycles: The Carbon Cycle (continued)
Carbon is cycled through ecosystems in a variety of ways.
Photosynthesis: energy from the sun allows CO2 and H2O to react
CO2 + H2O + sunlight  C6H12O6 + O2
Carbon in the atmosphere is transformed by plants into carbohydrates.
Photosynthesis also occurs in cyanobacteria and algae in oceans.
Cellular respiration: carbohydrates release energy in consumers
C6H12O6 + O2  CO2 + H2O + energy
The energy released is used for growth, repair and other life processes.
Decomposition: decomposers break down large quantities of cellulose
Cellulose is a carbohydrate most other organisms cannot break down
Ocean Processes: CO2 dissolves in cold, northern waters and sinks
Ocean currents flow to the tropics, the water rises and releases CO2
This process is called ocean mixing.
Eruptions and fires - volcanic eruptions can release CO2
Forest fires also release CO2
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10. Nutrient Cycles: The Carbon Cycle (continued)
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11. Nutrient Cycles: The Carbon Cycle (continued)
Many human activities can influence the carbon cycle
Since the start of the Industrial Revolution (160 years ago), CO2 levels have increased by 30% from the increased burning of fossil fuels.
The increase in CO2 levels in the previous years was 1% - 3%
Carbon is being removed from long-term storage more quickly than it naturally would as we mine coal and drill for oil and gas.
CO2 is also a greenhouse gas, which traps heat in the atmosphere.
Clearing land for agriculture and urban development reduces plants that can absorb and convert CO2.
Farmed land does not remove as much CO2 as natural vegetation does.
See page 77
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12. Nutrient Cycles: The Nitrogen Cycle
Nitrogen is very important in the structure of DNA and proteins.
In animals, proteins are vital for muscle function.
In plants, nitrogen is important for growth.
The largest store of nitrogen is in the atmosphere in the
form N2.
Approximately 78% of the Earth’s atmosphere is N2 gas.
Nitrogen is also stored in oceans, and as organic matter in soil.
Smaller nitrogen stores are found in terrestrial ecosystems and
waterways.
Nitrogen is cycled through processes involving plants
Nitrogen fixation
Nitrification
Uptake
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13. Nutrient Cycles: The Nitrogen Cycle (continued)
Nitrogen fixation is the conversion of N2 gas into compounds containing nitrate (NO3–) and ammonium (NH4+)
Both nitrate and ammonium compounds are usable by plants.
Nitrogen fixation occurs in one of three ways
In the atmosphere - lightning provides the energy for N2 gas to react with O2 gas to form nitrate and ammonium ions.
Compounds formed by these ions then enter the soil via precipitation
This only provides a small amount of nitrogen fixation.
In the soil - nitrogen-fixing bacteria like Rhizobium in the soil convert N2 gas into ammonium ions
These bacteria grow on the root nodules of legumes like peas.
The plants provide sugars, while bacteria provide nitrogen ions.
In the water - some species of cyanobacteria also convert N2 into ammonium during the process of photosynthesis.
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14. Nutrient Cycles: The Nitrogen Cycle (continued)
Nitrification occurs when certain soil bacteria convert ammonium.
Ammonium is converted into nitrates (NO3–) by nitrifying bacteria.
Ammonium is converted to nitrite (NO2–), which is then converted to nitrate.
Nitrates enter plant roots via uptake
These nitrogen compounds compose plant proteins.
Herbivores then eat plants, and use nitrogen for DNA and protein synthesis.
Nitrogen is returned to the
atmosphere via denitrification.
Nitrates are converted back to N2
by denitrifying bacteria.
N2 is also returned to the
atmosphere through volcanic eruptions.
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15. Nutrient Cycles: The Nitrogen Cycle (continued)
Excess nitrogen dissolves in water, enters the waterways, and washes into lakes and oceans.
The nitrogen compounds eventually become trapped in sedimentary rocks, and will not be released again until the rocks weather.
See page 81
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16. Nutrient Cycles: The Nitrogen Cycle (continued)
Human activities can also affect the nitrogen cycle.
Due to human activities, the amount of nitrogen
in the ecosystem has doubled in the last 50 years.
Burning fossil fuels and treating sewage releases
nitrogen oxide (NO) and nitrogen dioxide (NO2).
Burning also releases nitrogen compounds that increase acid precipitation in the form of nitric acid (HNO3).
Agricultural practices often use large amounts of nitrogen-containing fertilizers.
Excess nitrogen is washed away, or leaches, into the waterways.
This promotes huge growth in aquatic algae = eutrophication
These algal blooms use up all CO2 and O2
and block sunlight, killing many aquatic organisms.
The algal blooms can also produce neurotoxins that
poison animals.
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17. Nutrient Cycles: The Phosphorous Cycle
Phosphorous is essential for life processes in plants and animals.
Phosphorous is a part of the molecule that carries energy in living cells.
Phosphorous promotes root growth, stem strength and seed production.
In animals, phosphorous and calcium are important for strong bones.
Phosphorous is not stored in the atmosphere.
Instead, it is trapped in phosphates (PO43–, HPO42–, H2PO4–) found in rocks and in the sediments on the ocean floor.
Weathering releases these phosphates from rocks.
Chemical weathering, via acid precipitation or lichens, releases phosphates.
Physical weathering, where wind, water and freezing release the phosphates.
Phosphates are then absorbed by plants, which are then eaten by animals.
Weathering doesn’t occur until there is geologic uplift,
exposing the rock to chemical and physical weathering.
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18. Nutrient Cycles: The Phosphorous Cycle (continued)
Humans add excess phosphorous to the environment through mining for fertilizer components.
Extra phosphorous, often long with potassium, then enters the ecosystems faster than methods can replenish the natural stores.
Humans can also reduce phosphorous supplies.
Slash-and-burning of forests removes phosphorous from trees, and it then is deposited as ash in waterways.
See page 85
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19. How Changes in Nutrient Cycles Affect Biodiversity
Any significant changes to any of these nutrients
(C, H, O, N or P) can greatly impact biodiversity.
Carbon cycle changes are add to climate change and global warming.
Slight temperature fluctuations and changes in
water levels can drastically change ecosystems.
Changes influence every other organism in those
food webs.
Increased levels of nitrogen can allow certain plant
species to out-compete other species, decreasing
resources for every species in those food webs.
Decreased levels of phosphorous can inhibit the
growth of algal species which re very important
producers in many food chains.
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Take the Section 2.2 Quiz
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20. 2.3 Effect of Bioaccumulation on Ecosystems
Amphibians (like frogs) live on both land and in the water.
They are also sensitive to chemicals changes in the environment.
They are therefore valuable indicators of environmental health.
Since the 1980s, much of the world’s amphibian species have suffered declines in population.
There has also been alarming increases in amphibian birth deformities in that time.
Many theories attempt to explain these changes, including drought, increased UV rays, pollution, habitat loss, parasites and diseases.
Amphibians, like this frog, have exhibited drastic changes since the 1980s.
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21. Bioaccumulation refers to an organism slowly building
up the amount of chemicals in their bodies.
Many harmful chemicals cannot be decomposed naturally.
These chemicals can be eaten or absorbed, and sometimes
cannot be removed from the body of the organism effectively.
If a keystone species suffers a chemical bioaccumulation,
it can affect every other organism in its far reaching niches.
A keystone species is a vital part of an ecosystem.
Biomagnification refers to the animals at the top of the food pyramid receiving huge doses of accumulated chemicals.
At each level of the food pyramid, chemicals that do not get broken down build up in organisms.
When the consumer in the next trophic level eats organisms with a chemical accumulation, they receive a huge dose of the chemical(s).
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22. Bioaccumulation (continued)
An example of bioaccumulation in BC is the effect of PCBs on the Orca.
PCBs are a chemical that were used for many industrial and electrical applications in the mid 20th century.
PCBs were banned in 1977 because of fears of their environmental impact.
PCBs bioaccumulate, and
also have a long-half life
(they break down very slowly).
PCBs will affect the
reproductive cycles of Orcas
until at least 2030.
See page 95
The bioaccumulation of PCBs begins with the absorption of the chemicals by microscopic plants and algae.
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23. Bioaccumulation (continued)
Chemicals like PCBs and DDT are called
persistent organic pollutants (POPs)
POPs contain carbon, like all organic compounds, and remain in water and soil for many years.
Many POPs are insecticides, used to control pest populations.
DDT was introduced in 1941 to control mosquito populations, and is still used in some places in the world.
Like PCBs, DDT also bioaccumulates
and has a long half life.
At even low levels (5 ppm), DDT in
animals can cause nervous, immune
and reproductive system disorders.
ppm = parts per million
Spraying DDT, 1958
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24. Bioaccumulation (continued)
Heavy metals also bioaccumulate.
Lead, mercury and cadmium of the most polluting heavy metals.
Lead is found naturally at low levels, but levels have increased.
Lead is not considered safe at any level.
Many electronics contain lead, and must
be recycled carefully.
Lead can cause anemia, nervous and
reproductive system damage.
Cadmium is also found in low levels naturally.
Cadmium is used in the manufacture of plastics
and nickel-cadmium batteries.
It is toxic to earthworms, and causes many health problems in fish.
In humans, the main source of cadmium exposure is cigarette smoke.
Cadmium causes lung diseases, cancer,
nervous and immune system damage.
See page 97
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25. Bioaccumulation (continued)
Mercury also is found naturally.
Much more has entered ecosystems through the burning of fossil fuels, waste incineration, mining and the manufacture of items like batteries.
Coal burning adds 40% of of the mercury released into the atmosphere.
Mercury bioaccumulates in the brain, heart and kidneys of many animals.
Fish bioaccumulate mercury compounds, adding risk for any organisms eating fish.
Reducing the effects of chemical pollution
By trapping chemicals in the soil, they cannot enter the food chains as easily.
Bioremediation is also used, as micro-organisms or plants are used to help clean up, and are then removed from the ecosystem.
The oil industry will often use bacteria to “eat” oil spills.
Certain natural species are also excellent at bioremediation.
See pages
Take the Section 2.3 Quiz
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