5.4 Eutrophication pp. 230 – 237
IMPACT
Eutrophication – due to increase of N or P in water causes increase of nutrients
in water especially for plants. This causes too much plant growth ( POSITIVE
FEED BACK) than normal causing algae blooms ( large masses of plant and
alga growth). Although plants will produce O2 during the day via photosynthesis
plants also “ RESPIRE” – absorb O2 at night via photorespiration. This will
decrease overall DO. Too much plant growth on surface of lakes etc. will also
block sunlight getting to bottom of lakes reducing photosynthesis.
Eutrophication = HIGH BOD ( biochemical oxygen demand) = ORGANIC
POLLUTION
New word : anoxia = oxygen starvation in water
Other changes as a result of eutrophication:
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Turbidity – murkiness and reduces light reaching submerged plants
Sediment deposition
Net primary productivity increases – increased plant and algal blooms
Diversity of primary producers changes and finally decreases. In the end
cyanobacteria take over.
Fish diversity decreases. Perch and pike take over.
Loss of Nitrogen fertilizer from farms by leaching causes loss of money to
farmers
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IB Qs
See IB Q 16 for 25 and 26
25. Outline one method of direct measurement that would indicate that a lake
is becoming eutrophic.
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measure nitrate/phosphate/turbidity levels repeatedly over a period of time
measure turbidity by lowering a secchi disc into the water
nitrate levels increase as input of nutrients increases/phosphate
levels increase as input of nutrients increases/
turbidity increases as algae populations increase
measure amount of dissolved oxygen/BOD or similar;
26. Outline one method of indirect measurement using a biotic index, that would
indicate that a lake is becoming eutrophic.
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measure the abundance and diversity of species upstream/downstream
the abundance of low oxygen tolerant species (e.g. carp fish , Tubifex worms)
would increase
the abundance of high oxygen tolerant species (e.g. trout fish , may flies) would
decrease
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MANAGEMENT STRATEGIES read pp. 235 – 237 and answer
questions
27. What are the there main ways of dealing with eutrophication?
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changing human activities that produce pollution by using alternative
types of fertilizers
regulating and reducing pollutants – sewage treatment plants that
reduce nitrates
clean up restoration of lake by pumping mud out
28. Changing human activities. Know these :
29. Regulating and reducing pollutants.
a) What does “ divert sewage effluent” mean?
To divert sewage from body of water
b) List 3 domestic campaigns used in Australia.
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30. Clean up strategies. List the main clean up methods.
31. Prevention of eutrophication at the source. List basic ideas.
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IB Qs
32. Describe and evaluate management strategies to restore (i.e clean up) a
eutrophic lake.
Describe:
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add aerators to the lake (to maintain survival of species)
remove aquatic plants during their growing period
dredge the mud from the bottom of the lake to remove nutrients
introduce species of fish which consume algae;
Evaluate:
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aerators are expensive to operate
aerators do not reduce the pollution problem, so must be
used continuously;
aquatic plants which have been removed from the lake transfer
the nutrient overload to another ecosystem;
mud pumped from the lake transfers nutrient overload to
another ecosystem;
33. Development of a tourist resort near a lake is proposed. Outline strategies
for determining the environmental impact of the development on the
lake (i.e. question is asking you to check direct and indirect methods to
test for eutrophication see IBQ 16, 25 and 26)
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Environmental Impact Assessment/EIA/baseline study must
occur before any development begins
select biological (species diversity) biotic index to test abundance of
species in relation to pollution. Tubifex worms, may flies, carp fish (
low DO) and trout fish ( high DO). Compare DO and BOD.
Select chemical (nutrient status) indicators to test : nitrates,
phosphates.
monitoring of the environment must continue at regular intervals
during and after development
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