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Answer» (a) Primary succession on rocks - Lichens are the pioneer species on a bare area.
- The lichen secretes some acids to dissolve rock and help in weathering and soil formation.
- Later, some small bryophytes invade and hold the small amount of soil.
- The bryophytes are succeeded by herbs, shrubs and ultimately big trees.
- At last, a stable climax forest is formed.
- The xerophytic habitat gets converted into a mesophytic one.
(b) Algal bloom - Domestic sewage contains nutrients like nitrogen and phosphorus which favour the excessive growth of planktonic (free-floating) algae called an algal bloom.
- Algal bloom causes fish mortality and deterioration of water quality.
- Excessive growth of water hyacinth (Eichhornia crassipes), the world’s most problematic aquatic weed, also called “Terror of Bengal”, grows abundantly in eutrophic water bodies and imbalances water ecosystem.
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