Solution:
Eutrophication is the natural ageing of a lake by nutrient enrichment of its water . Hence, Statement 1 is correct.
In a young lake, the water is cold and clear, supporting little life .
With time, streams draining into the lake introduce nutrients such as nitrogen and phosphorus , 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(bog), finally converting into the land.
Depending on the climate, the size of the lake , and other factors, the natural ageing of a lake may span thousands of years .
However, pollutants from man’s activities likeeffluents from the industries and homes can radically accelerate the ageing process . This phenomenon has been called Cultural or Accelerated Eutrophication.
During the past century, lakes in many parts of the earth have been severely eutrophied by sewage and agricultural and industrial wastes.
The prime contaminants are nitrates and phosphates, which act as plant nutrients. Hence statement 2 is correct.
They overstimulate the growth of algae, causing unsightly scum and unpleasant odours , and robbing the water of dissolved oxygen vital to other aquatic life .
At the same time, other pollutants flowing into a lake may poison whole populations of fish, whose decomposing remains further deplete the water’s dissolved oxygen content.
In such a fashion, a lake can literally choke to death
© examsiri.com