Human activities like agriculture, industry, and fishing can negatively impact ecosystems. Deforestation causes soil erosion, flooding, desertification, and climate change by removing trees that stabilize soil and regulate water cycles. Over-fishing depletes fish populations and destroys habitats by using unsustainable and destructive practices like trawling and dredging that indiscriminately catch other species and damage seabeds. Conservation efforts are needed to protect natural resources and environmental balance.

1. Our Impact on the
Ecosystem
Chapter 22
Content
• Effects of Man on the Ecosystem
• Conservation (Environmental
Biotechnology)

2. Ecosystem

3. Balance in the ecosystem

4. How do we affect the ecosystem?
 Natural resources are resources supplied by
nature that are used by humans
 Air, water, soil, wildlife and forests are
renewable resources (i.e. they can be replaced
in the ecosystem by natural cycles as long as
humans do not overuse them)
 On the other hand, fossil fuels take millions of
years to form naturally
 They cannot be replaced once they are
used, hence they are called non-renewable
natural resources

5. How do we affect the ecosystem?
Human activity
Agriculture Industry
Uses natural resources
leading to
1. Deforestation
2. Over-fishing
3. Pollution

6. 1) Deforestation

7. Deforestation
Definition:
The removal of forests by cutting and burning
to provide land for agricultural
purposes, residential or industrial building
sites, roads, etc., or by harvesting the trees for
building materials or fuel.

8. Deforestation

9. Reasons for deforestation
1. Urban development
2. Cultivation
3. Grazing
4. Timber
5. Fibres

10. Damaging effects of deforestation
i) Soil erosion
ii) Flooding
iii) Desertification
iv) Climate changes

11. i) Soil erosion

12. Soil erosion

13. Importance of plants
 Leaf canopy → protects soil from impact of rain
 Roots → hold soil + water (water released
gradually to soil below and nearby streams and
lakes)

14. Removal of plants
 Soil exposure to direct force of the rain
 Without a shelter belt, water runoff become
intense
 Topsoil (fertile layer) washed away (esp. on
slopes)
 Severe in tropical areas (due to high rainfall)

15. Sheet erosion
 The removal of a fairly uniform layer of soil from
the land surface by raindrop splash and/or
runoff.

16. Gully erosion
 Removal of layers of soil due to heavy
rainfall, thus creating small channels which
eventually widen and deepen as more soil
is removed, forming gullies

17. Gully erosion

18. ii) Flooding

19. Why do floods occur?
 With trees removed, rainwater is not retained
and released slowly
 Blockage of water flow in rivers/streams due
to silting (eroded soil)
 Water levels rise rapidly and flows inland
Silting

20. iii) Desertification

21. Desertification
Definition:
Destruction of land leading to desert-like conditions
What leads to desertification?
1) Hardening of soil (due to water evaporation caused
by the heating of soil by the sun)
→ Plant life not supported
→ Animal life is not supported
→ Land becomes barren
→ habitats are lost and many
species of organisms become extinct
2) Overgrazing by animals
- because plants cannot regenerate fast enough

22. Result of desertification
 Loss of habitats
 Extinction of species of organisms
 Loss of potential medicinal resources
which may be useful in treating diseases
 Upsetting O2 and CO2 balances

23. iv) Climate changes

24. How does deforestation result in
climatic changes?
→ with forests, rainwater is retained and absorbed by
roots of trees
→ water lost during transpiration
→ relative humidity of air around forests high
→ water vapour condenses + precipitates as rain
→ However when trees are cleared the area becomes
dry & warm
→ annual rainfall decreases

25. What have we learnt so far?
 Deforestation
- definition
- reasons for deforestation
- damaging effects of deforestation
(i) soil erosion
(ii) flooding
(iii) desertification
(iv) climatic changes

26. 2) Over-fishing

27. How do uncontrolled fishing
practices harm the ecosystem?
i) Humans catch fish for food. As the human
populations increases, so does the demand
for fish. Some species of fish have been
caught in such large numbers that their
populations have decreased drastically
(over-fished)
ii) Indiscriminate fishing (i.e. do not distinguish
between the targeted catch and immature
organisms or unwanted species e.g. gigantic
drift nets trap almost everything in their path.
Marine life e.g. sharks, turtles, dolphins are
unintentionally caught. Though dumped back
into the sea, they often die

28. How do uncontrolled fishing
practices harm the ecosystem?
iii) Some methods of fishing destroy the seabed and marine
habitat
- shrimp/prawn trawlers drag large fishing nets along
the bottom of the sea. Many unwanted species are
trapped in the process
- scallop dredges scrape the seabed, destroying coral
reefs and organisms that live on the seabed
- In cyanide fishing, cyanide (a poison) is squirted in
the water around coral reefs. The cyanide stuns reef
fish and makes them unable to swim properly.
Fishermen then capture the fish for sale as pets.
Explosives (e.g. dynamite) are also used to stun and
catch reef fish. Both cyanide and explosives kill corals
and many other reef organisms

29. Destructive fishing methods
1. Trawling
2. Dredging
Dredging
Trawling