Eutrophication & Thermal Wastewaters MCQ - Practice Questions with Answers

• Eutrophication is the natural aging of a lake by biological enrichment of its water. 
• 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 land. 
• Depending on climate, size of the lake and other factors, the natural aging of a lake may span thousands of years. 
• However, pollutants from man’s activities like effluents from the industries and homes can radically accelerate the aging 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. 
• They overstimulate the growth of algae, causing unsightly scum and unpleasant odors, 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 fashion, a lake can literally choke to death.
• The plants of water hyacinth (Eichhornia crassipes) which were introduced into India for their lovely flowers have caused havoc by their excessive growth by causing blocks in our waterways. 
• They grow faster than our ability to remove them. These are the world’s most problematic aquatic weeds, also called ‘Terror of Bengal’. 
• They grow abundantly in eutrophic water bodies, and lead to an imbalance in the ecosystem dynamics of the water body.

Thermal Wastewaters:

• Heated (thermal) wastewaters flowing out of electricity-generating units, e.g.thermal power plants, constitute another important category of pollutants. 
• Thermal wastewater eliminates or reduces the number of organisms sensitive to high temperature, and may enhance the growth of plants and fish in extremely cold areas but, only after causing damage to the indigenous flora and fauna.