1. The Nitrogen Cycle

2. Learning Targets Explain the importance of nitrogen to living things
Trace the movement of nitrogen through the nitrogen cycle including:
Sources of nitrogen
Processes and organisms that convert nitrogen
Spheres involved
Form used by plants
Explain how humans impact the nitrogen cycle and the how excess nitrogen affects human health and the environment

3. Importance of Nitrogen (N)
N is an essential plant nutrient (N, P, K)
All living things need nitrogen for amino acids, proteins and nucleic acids (DNA and RNA)
Concentrations of N are important indicators of water quality.
Excess N also affects air quality and human health

5. Forms of Nitrogen Nitrogen exists in all four spheres:
The atmosphere is 78% N2 gas
Nitrogen exists in several forms, organic and inorganic
Organic means it is part of living organisms or the biosphere
Examples - amino acids, proteins, DNA and RNA all contain Nitrogen
Inorganic forms in soil (geosphere) and water (hydrosphere) include
Nitrate (NO3), nitrite (NO2), and ammonium (NH4+)

6. Plants can’t use N2
Plants cannot absorb the Nitrogen gas from the atmosphere
It must be fixed in the soil or water for them
Meaning changed to a useable form
Plants use ammonium or nitrate nitrogen

7. Nitrogen Fixation
Lightning makes nitrate and rain carries it into the soil Bacteria – living in root nodules of legumes (soybeans, clover) convert N2 to ammonia Humans manufacture fertilizers and burn fossil fuels Cyanobacteria (blue-green algae) fix nitrogen in water

8. Decomposers produce ammonia
Ammonium ion is in waste products from animals (sewage) and produced from bacterial decomposition of dead plants and animals

9. Denitrification by anaerobic bacteria (without oxygen)
Converts ammonia to nitrite and nitrate and N
Gases are released into the air

10. Human impact
Over last 100 years we’ve more than doubled the amount of N entering the cycle
60% of N entering the cycle comes from commercial inorganic fertilizers
Burning fossil fuels adds nitrates to the air which forms nitric acid in our atmosphere and contributes to acid deposition and global warming
Nitrous oxide, N20 from anaerobic bacteria working on livestock waste and fertilizer contributes to global warming and ozone loss.
Discharge of municipal sewage also add N to lakes
Excess nitrates enters ground water and can harm young children and pregnant mothers (blue-baby syndrome)

11. Cultural Eutrophication:
Excess nutrients (nitrogen and/or phosphorus) stimulate
plant growth (algal bloom)
When these plants die, decomposers use up the available oxygen during decomposition

13. This can lead to Dead Zones

14. Learning Target Check
Explain the importance of nitrogen to living things
Trace the movement of nitrogen through the nitrogen cycle including:
What are the sources of nitrogen?
What are processes and organisms that fix nitrogen in soil/water?
What are the processes and organisms that release nitrogen to the atmosphere?
What spheres contain nitrogen, and in what form?
What form of nitrogen is used by plants?
How do humans impact the nitrogen cycle and the how excess nitrogen affects human health, water quality/aquatic ecosystems, and air quality?