Previous Year Question
“If rainforests and tropical forests are the lungs of the Earth, then surely wetlands function as its kidneys.” Which one of the following functions of wetlands best reflects the above statement?
The water cycle in wetlands involves surface runoff, subsoil percolation and evaporation.
Algae form the nutrient base upon which fish, crustaceans, molluscs, birds, reptiles and mammals thrive.
Wetlands play a vital role in maintaining sedimentation balance and soil stabilization.
Aquatic plants absorb heavy metals and excess nutrients.
Correct Answer: D
Detailed Solution
Just as kidneys filter wastes and harmful substances from blood and maintain the body’s chemical balance, wetlands act as natural water-treatment systems by removing pollutants and excess nutrients from the water flowing through them.
Aquatic plants can absorb or accumulate excess nutrients such as nitrogen and phosphorus and certain heavy metals through their roots and other tissues. This plant-based removal of contaminants is broadly associated with phytoremediation.
Plants are not the only components involved. Wetland soils, sediments and microorganisms also adsorb, immobilize or transform pollutants. Heavy metals are generally not destroyed; instead, they may become accumulated and immobilized in plant tissues or sediments.
Removal of excess nitrogen and phosphorus is important because their enrichment can cause eutrophication, excessive algal growth and depletion of dissolved oxygen in water.
Option (a) represents wetland hydrology, option (b) represents the food web and biological productivity, while option (c) represents sediment control and soil stabilisation. These are important wetland functions but do not directly represent the kidney-like function of filtration and purification.