Class 12th Biology 2012 Set2 Delhi Board Paper Solution

Presence of large amounts of nutrrients in waters also causes execessive growth of planktonic algae called an algal bloom which imparrts a distinct colour to the wate rbodies. Algal blooms causes deterioration of the water quality and fish mortality.Eutrophication is the natural aging of a lake by nutrient enrichment of its water.

Streams draining into the lake increases nutrients such as nitrogen and phosphorous which encourage the growth of aquatic organisms. As the lake’s fertility increases,plant and animal life burgeons, and organic remains begin to be deposited on the lake bottom. Over the centuries as silt and organic debris pile up, the lake grows shallower and warmer, with warm-water organisms supplanting those that thrive in a cold environment marsh plants take root in the shallows and begin to fill in the original lake basin. Eventually, the lake gives way to large masses of floating plants, finally converting into land.

 

Eichhornia crassipes water hyacinth can grow in entrophic lake.