Page 5 - LN-CH-16

(a) Biological magnification can be defined as the increase in concentration of toxicants at
successive trophic levels.
• Mercury and DDT are well known for biological magnification.
• Toxic materials cannot be metabolised or excreted. Therefore, they get accumulated in an
organism and pass on to higher trophic levels.
• DDT accumulates in birds and disturbs calcium metabolism, which results in thinning of
egg shell. This results in decline of bird population.
(b) Eutrophication can be defined as the natural ageing of a lake by nutrient enrichment of
its water.
Process of Eutrophication
• Water in young lake is cold and clear to support life.
• Gradually with time, it gets enriched with nutrients as nitrogen and phosphorus by streams
draining in it.
• Due to this, aquatic life (plants and animals) flourish in lake.