Define pollution. With reference to water pollution, explain biochemical oxygen demand, algal bloom, biomagnification and eutrophication.

Explanation

Pollution is defined as an undesirable change in physical, chemical or biological characteristics of air, land, water or soil.
Water pollution is defined as any undesirable change in physical, chemical and biological properties of water that may affect the human beings and domestic species.
BOD (biochemical oxygen demand)
The amount of oxygen required for microbial breakdown of biodegradable organic matter is called BOD.
It is higher in polluted water and lesser in drinking water.
Algal bloom
Domestic sewage contains nutrients like nitrogen and phosphorus which the excessive growth of planktonic (free-floating) algae called algal bloom. Algal bloom causes mortality and deterioration of water quality.
Biomagnification
Biomagnification is defined as increase in concentration of toxicants at sucessive trophic levels. Toxic substances cannot be metabolised or excreted, therefore they get accumulated in an organism and passed on to higher tropic levels.
Eutrophication
It is defined as the natural aging of a lake by biological enrichment of its water, water in a young lake is cold and clear to support life, with time, it is enriched with nutrients which encourages growth of aquatic life, plants and animals life. Organic remains at the bottom makes water warm, eventually floating water develop in the lake, finally converting into land.