The document discusses the nitrogen cycle and how excess nitrogen from fertilizers can cause eutrophication in bodies of water. It describes how nitrogen is used by plants and animals and returns to the soil through decomposition. The use of chemical fertilizers since World War 1 has increased nitrogen in agricultural soils. Excess fertilizer can run off into water systems, providing too many nutrients and causing algal blooms that reduce oxygen and kill fish. The sources of excess nutrients that can cause eutrophication include agricultural runoff, sewage treatment plants, industrial plants, and sewage discharges.

1. Topic 5: Pollution Management
5.4: Eutrophication
The Nitrogen Cycle
and Eutrophication

2. Topic 5: Pollution Management
5.4: Eutrophication
• All living organisms use nitrogen to
make molecules such as protein and
DNA.
• Nitrogen is the most abundant gas in
the atmosphere (about 80%).
• Atmospheric nitrogen can not be used
by most plants and animals, though
some specialised micro-organisms can
fix atmospheric nitrogen.

3. Topic 5: Pollution Management
5.4: Eutrophication
• Plants get Nitrogen compounds from
the soil
• Animals get nitrogen compounds by
eating plants

4. Topic 5: Pollution Management
5.4: Eutrophication
• When animals excrete or
defecate they return nitrogen
compounds to the ground
• When animals and plants die
they rot and return nitrogen to
the soil
• Dead Organic Matter (DOM)

5. Topic 5: Pollution Management
5.4: Eutrophication
• Farmers since prehistoric times have added manure to fields

6. Topic 5: Pollution Management
5.4: Eutrophication
• Traditional Human Nitrogen gas in the atmosphere
N2 Atmospheric fixation
during lightning
activities have formed storms
part of the Nitrogen
Cycle
Plant and Animal Biomass Nitrates taken up
containing nitrogen by plants
Dead Organic Nitrogen
Excretion
Matter DOM Fixing
bacteria
Denitrifying
bacteria
Decomposition
Ammonia
NH3
Nitrite Nitrate
NO2 NO3
Nitrifying Nitrifying
bacteria bacteria Nitrogen Cycle

7. Topic 5: Pollution Management
5.4: Eutrophication
• Since the First World
War, traditional methods Chemical inorganic
fertilisers;
Organic fertilisers;
animal manure,
Dead Organic
Matter (DOM);
of maintaining soil fertility provide controlled
amounts of mineral
urine and compost natural remains of
dead plants and
have been augmented by nutrients animals
the use of chemical
fertilisers
• Millions of tons of
nitrogen based chemical
fertilisers have been
added to agricultural land
Available mineral nutrients in the soil

8. Topic 5: Pollution Management
5.4: Eutrophication
• Fertiliser in solution if used
in excess can enter water
systems
• This can lead to the
problem of Eutrophication

9. Topic 5: Pollution Management
5.4: Eutrophication
N-P-K
Increased growth of
Fish begin to die algae shading out other
as oxygen levels fall plants
Excess use of Chemical
Fertilisers leads to run of and
ground water contamination
The inorganic salts dissolved ground water
eventually enter lakes, ponds and rivers
Increased nutrients
absorbed by algae Inreased decomposition of
dead algae uses up
oxygen in the water

10. Topic 5: Pollution Management
5.4: Eutrophication
• Increasing nutrient loads can lead to Positive Feedback
Increased
Nutrient
Inputs
Increased Fewer
Primary Consumers
Productivity (Invertebrates and Fish)
Increased
Decomposition Increased
Oxygen
Consumption
(BOD)

11. Topic 5: Pollution Management
5.4: Eutrophication
Similar pathways exist for both
eutrophication caused by Phosphates and
Carbon

12. Topic 5: Pollution Management
5.4: Eutrophication
Sources of Eutrophication
Source Type of problem
Point Sources
Power plants Combustion of fossil fuels emit nitrogen products into the atmosphere,
which are carried down by rainfall and other processes, causing
eutrophication in water bodies
Sewage Treatment Treatment process releases oxides of N and P in effluents, which drain
Plants into water bodies
Industrial Plants Industrial processes release N and P products in effluents, which drain
into water bodies
Non-Point Sources
Agriculture Farming practices, including use of fertilisers rich in N and P, deposit
increased amounts of these nutrients in the soil.
Run-off from these farms cause eutrophication in water bodies
Sewage Direct discharge of sewage from domestic sources, not connected to
treatment plants, will eventually make its way into water bodies