Transcript Chapter 18

Chapter 18
Human Activities
& the Ecosystem
The effect of human activities on the
environment is proportional to the size of
the human population.
The size of the human population has been
rising exponentially because of the
intensive forms of food production and
the better medical care.
18.1 The Impact of Pre-industrial Man on
The Environment
18.1.1 Humans as Hunter
Pre-industrial man did not have a great
impact on his environment as a hunter.
The natural environment recovered quickly
with accidental burning of forests or created
grasslands.
18.1.2 Humans as Shepherd
Man domesticated animals such as sheep,
cattle, goats, etc.
Large herds would overgraze soil and led to
erosion, e.g. in the Mediterranean & Near
East, may have contributed to the
development of many of the deserts.
Grazing in
dsertified area
Effect of irrigation from the Nile
18.1.2 Humans as Shepherd
Man domesticated animals such as sheep,
cattle, goats, etc.
Large herds would overgraze soil and led to
erosion, e.g. in the Mediterranean & Near
East, may have contributed to the
development of many of the deserts.
Domestication also led to the extinction of
their wild ancestors.
18.1.3 Humans as Farmer
As the farmer, man settled down.
He built shelters for himself & his animals,
place to store his crops.
Man cleared forests for these purposes.
Soil fertility exhausted when he cultivated
the same crops of years on the same piece of
land.
18.2 Exploitation of Natural Resources
With the industrial revolution, machines enabled
more food production and a larger population with exponential rise, together with reasons like
better fertilizers, better crops and pesticides.
Man is dependent for his survival on the earth's
resources: renewable and non-renewable.
18.2.1 Renewable Resources
Renewable resources can be replaced. They
are things which grow, and are materials
based on plants and animals.
Sustainable yield: the amount that is
removed (yield) is equal, or less than, the
rate of production. Over-fishing: when
sustainable yields have exceeded the
reproductive rates of fish
Afforestation: artificial forests planted by man
Rows of larch (Pinus) planted on a hillside
Over-fishing: when sustainable yields have
exceeded the reproductive rates of fish
Thirty-tonne catch of fish by deep sea
trawler (拖拉船)
18.2.2 Non-renewable Resources
Non-renewable resources are not replaced as they
are used, examples: minerals (iron) and fuels (coal
& oil)
Metals can be recycled but impractical because:
1. Metals are easily oxidized, e.g. iron rust
2. Quantities of a metal within a material are too
little to recover it for recycle, e.g. tin layer over
most metal cans
3. Alloys are often difficult to separate; labour
costs of separation is too high
Fossil fuels are continually being formed, but too
slow when compared with its consumption.
Pollutants are produced by burning of fossil fuels.
Fuel from oil seed rape
Nuclear power is a potentially long-term
supplier of energy, but with inherent danger,
e.g. Chernobyl accident in Russia (1986)
Other sources of energy: wind, wave,
sunlight, biological fuels, etc.
Chernobyl nuclear reactor after
the explosion in April 1986
Examples of biological fuels:
1. Cellulose from photosynthesis
2. Gasohol programme in Brazil
3. Animal manure
4. Human sewage
5. Domestic & industrial wastes
18.3 Pollution
Pollution is the harmful effect of human
activities on the natural environment which
make air, water and land impure.
It may result from substances produced as
industrial, agricultural or domestic wastes.
It may also arise from some form of energy
such as heat and sound.
Substances that cause pollution are called
pollutants.
Natural pollutant: SO2 from volcanoes
Mt Semeru erupting in Indonesia
18.4 Air Pollution
- car exhausts, smokes from burning of fuels;
Pollutants: carbon monoxide, carbon dioxide,
oxides of nitrogen & sulphur and particles
such as carbon & dust
1. Carbon and Dust Particles/Smoke
- Carbon particles are produced from incomplete
burning of coal & oil, car exhausts
- Dust particles are produced at construction sites,
rock mines
- Both cause diseases of the respiratory tract
Smoke pollution
2. Sulphur Dioxide and Oxides of Nitrogen
- acidic gases which form strong acids which are
corrosive to stone buildings,
- harmful to crops & irritating to man
Indicator species/organisms
Indicator species/organisms:
The tolerance of lichen & moss species to
SO2 is very variable and is useful for
measuring SO2 pollution.
As one moves from the centre of a major
industrial city, the number of species of
lichen & moss increases.
In the centre only the most tolerant species
are found, whereas on the outskirts less
tolerant ones also occur.
3. Carbon dioxide
- 'Green house effect'
4. Carbon Monoxide
- comes from incomplete burning of oil & fuels;
- a highly toxic gas
5. Lead
- Lead compounds are added to petrol to improve its
combustion - 80% of lead in air
- Lead causes impaired mental development in
children
6. Formation of Smog
In 1952, four thousand
people in London died
from smog.
Smog in Rio de Janeiro
7. Ozone depletion and the greenhouse effect
- by chlorofluorocarbons as propellants in
aerosol sprays, in refrigerators and in plastic
foams
- cause 'green house effect' by CFC's; skin
cancer by extra UV radiation in the southern
continents
18.5 Water Pollution
18.5.1 Sewage and its disposal
Sewage has two main origins: from industry and home
Domestic effluent is 95-99% water, the remainder is
organic and acts as food for saprophytic organisms
especially bacteria.
When oxygen is available, aerobic saprophytes
decompose organic matter - putrefaction and uses up
oxygen in water.
This creates a biochemical oxygen demand (BOD).
Biochemical Oxygen Demand (BOD):
- a measure of eutrophication (rich in nutrients)
- BOD measures the rate of oxygen depletion
by organisms.
- It is assumed this primarily reflects microorganism activity in decomposing organic
matter present in waters.
- Standard measure: the weight of oxygen in
milligrams consumed from a decimetre
cuboid of sample when stored in darkness for
5 days at 20oC.
Clean water: BOD of 3 mg dm-3,
Polluted water: 10,
Sewage: 250 - 350
- High BOD means very little dissolved
oxygen in water for living organisms.
Outlet pipe discharging sewage
on to a beach
Fig. 18.2 Physical and
chemical changes in a
river due to sewage
effluent
PHYSICAL CHANGES
- BOD increases greatly
because sewage contains
many saprophytes (aerobic)
which decompose organic
matter & use up oxygen
- BOD decreases to normal
slowly when saprophytes
are diluted downstream
PHYSICAL CHANGES
- O2 decreases sharply at
outfall because
of
consumption by sewage
saprophytes
-
O2
concentration
increases again because
saprophytes are diluted
downstream
and
consumes less O2
CHEMICAL CHANGES
- NH4+
ions
increase
abruptly because they are
present in sewage.
Its concentration continues to
increase due to bacteria
breakdown of organic
matter in sewage.
NH4+concentration decreases
due to conversion to NO3-,
decrease of saprophytes
downstream and dilution
effect downstream.
CHEMICAL CHANGES
NO3concentration
decreases because of
their consumption by
sewage saprophytes
Its concentration increases
when NH4- ions are
converted to NO3Its concentration decreases
downstream because of
algal consumption &
dilution effect
Fig. 18.3 Changes in the
flora and fauna of a river
due to sewage effluent
CHANGES IN FLORA
Bacteria:
Initial increase due to
sewage which contains
saprophytic bacteria &
then slight increase because
of aeration on entry when
provides O2 for growth.
Decrease later due to the
decrease of their food
(organic
substances)
which
are
being
consumed & diluted
downstream.
Algae:
Decrease - suspended
solids in sewage block
off light intensity for
photosynthesis of the
algae / oxygen decrease
Increase - due to increase
of nitrates from sewage
as a result of bacterial &
fungal
decaying
activities
Decrease - conc of NO3decreases due to dilution
of stream water &
consumption by algae
CHANGES IN FAUNA
Tubifex:
Increase
- haemoglobin
for
efficient absorption of
O2
at
low
O2
environment
- organic
matter
in
sewage is a food source
- remove of clean water
animals which predate
on Tubifex
Decrease further
downstream due to less
sewage and more
predators
Chironomus:
Decreases initially because
of too low oxygen
concentration.
Population increases when
oxygen level is tolerable.
Asellus:
Decreases initially because
oxygen level is not high
enough.
Population increases when
oxygen level is again
tolerable.
Clean water fauna:
- Abrupt decrease due to
rapid decrease of oxygen
in water which causes
suffocation of these
animals
Continual
decrease
because of NH4+ which
is toxic OR
some are algal grazers
which deprive of food
(algae)
- Increase again when
oxygen level increases
to suitable level
- Chemicals are released into water from
dyeing & bleaching industries, tanneries, etc
- Chemicals: dyes, detergents, cyanides, lead
& mercury compounds, DDT, etc
In order to remove organic material but also
potentially dangerous pathogenic organisms,
sewage treatment plants are introduced in
Hong Kong:
Sewage treatment works
- primary sedimentation
Sewage Treatment Plant:
(a) Sedimentation - sewage stands in large
settling tanks to form a sludge
(b) Decomposition - fluid pumped into
oxidation pond;
putrefying bacteria & fungi break down
organic molecules into inorganic compound
(c) Fermentation - solid sludge is passed into
the digester to produce methane gas (fuel) by
anaerobic respiration of bacteria - remaining
solid is dried and used as fertiliser.