Question

The residents of Nanganallur and Adambakkam wanted to revive an environment park on

AdambakkamEri. The lake needs to be desilted and deepened and a bund is to be formed for a walkers’

path. Moreover, steps are to be taken to prevent the discharge of sewage through storm water drains and

the dumping of garbage on the lake bunds. The environmentalists say that invasive species like water

hyacinth have clogged this water body. Also, the discharge of sewage into the lake has resulted in the

growth of unwanted plants. This is blocking the air-water interface, thereby reducing the dissolved oxygen

in the water and killing a lot of fish. The water bodies clogged by the invasive species also become a

breeding ground for mosquitoes. The State Government has been requested to expedite the works for this

at the earliest.

Question 26:

When an alien species (plant or animal) that does not belong to an ecosystem is introduced, it spreads and

competes with the native plants for space and nutrients and becomes problematic in the absence of

natural enemies. These intruders are called invasive alien species.

What are the ill effects of an invasive species like water hyacinth?

i. Blockage of sunlight from reaching native aquatic plants.

ii. Starving the water of carbon dioxide

iii. Domination and phasing out of fish and other native species.

iv. Change in the water quality with respect to the dissolved oxygen and the water pH due to release

of CO2 .

v. Starving the water of oxygen.

vi. Desilting of the water body

vii. An increase in algae blooms, mosquito infestation due to dense matting and decreased water flow.​

Answer 1

the answer is option b