1. 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 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
See page 78

2. Nitrogen Fixation occurs in 3 different ways.
Nitrogen fixation is the conversion of N2 gas into compounds containing nitrate (NO3–) and ammonium (NH4+).
Both nitrate (NO3) and ammonium (NH4) compounds are usable by plants.
Nitrogen fixation occurs in one of three ways.
Atmosphere
Soil
Water
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3. Nitrogen fixation occurs in the Atmosphere.
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 provides only a small amount of nitrogen fixation.

4. Nitrogen fixation occurs in the Soil.
In the soil – nitrogen-fixing bacteria like Rhizobium convert N2 gas into ammonium ions in a mutualistic association with legumious plants.
These bacteria grow on the root nodules of a plant and fix nitrogen which they share with the plant.
In exchange the plants provide the bacteria with a source of carbon (sugars) for growth.
Nitrogen-fixing Rhizobium bacteria
colonized on the root hairs of
clover plants.
Nodules containing Rhizobium
bacteria on the plant roots

5. Nitrogen fixation occurs in Water.
In the water – some cyanobacteria convert N2 into ammonium (NH4) during the process of photosynthesis.

6. Nitrification and Nitrogen Uptake
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
through the process of
uptake.
These nitrogen compounds
compose plant proteins.
Herbivores then eat plants
and use nitrogen for DNA
and protein synthesis. .
Nitrification
See page 80

8. Human activities and the nitrogen cycle
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).

9. 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 called algae blooms.
Algae blooms use up all CO2 and O2 and block sunlight, killing many aquatic organisms.
Algae blooms can also produce neurotoxins that poison animals.

10. When the nitrogen cycle is not in harmony…
Some algal blooms produce biotoxins that are harmful to birds, fish,
and other animals. This Canada goose swims among a floating layer of
heavy, but probably harmless, algal growth.
Acid rain damaged these trees
Alberta's lakes turned into tepid baths in July, warming up
to 25 C, as much as 7 C higher than normal and an optimum
temperature for maximum growth of blue-green algae

11. The Nitrogen Cycle
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 undergo hundreds of years of weathering.
See page 81

13. Nutrient Cycles: The Phosphorous Cycle
Phosphorus is essential for life processes in plants and animals.
Phosphorus is a part of the molecule that carries energy in living cells.
Phosphorus promotes root growth, stem strength, and seed production.
In animals, phosphorous and calcium are important for strong bones.
Phosphorus 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, including wind, water and freezing, releases phosphates.
Phosphates are then absorbed by plants, which are then eaten by animals.
Weathering does not occur until there is geologic uplift,
exposing the rock to chemical and physical weathering.
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14. Nutrient Cycles: The Phosphorous Cycle (continued)
Humans add excess phosphorus to the environment through mining for fertilizer components.
Extra phosphorus, often along with potassium, then enters the ecosystems faster than methods can replenish the natural stores.
Humans can also reduce phosphorus supplies.
Slash-and-burning of forests removes phosphorus from trees, and it then is deposited as ash in waterways.
See page 85
The Phosphorus Cycle

15. How Changes in Nutrient Cycles Affect Biodiversity
Any significant changes to any of these nutrients
(C, H, O, N, or P) can greatly affect biodiversity.
Carbon cycle changes contribute to climate change and global warming.
Slight temperature fluctuations and changes in
water levels can drastically change ecosystems.
Changes influence other organism in the
food webs.
Increased levels of nitrogen can allow certain plant
species to outcompete other species, decreasing
resources for every species in the food webs.
Decreased levels of phosphorus can inhibit the
growth of algae that are very important
producers in many food chains.
Salmon are sensitive to temperature changes.
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