Question

What is the reason for a region of a lake turned into a dead zone?

• A. All of the above
• B. Acid rain
• C. Eutrophication
• D. Washed off fertilizers in the lake

Answer 1

Answer: (A)

Dead zone refers to the hypoxic zones that is low oxygen containing zones in oceans and large lakes. It is caused because of the washed away nutrients from the lake and introduction of pollutants from the soil or man made nutrients into these lakes.

Eutrophication occurs when excessive fertilizers from the soil run into the rivers and lakes which encourages the growth of algae and other aquatic plants in the lakes. Due to this overcrowding, there is a competition for sunlight space and oxygen, turning the lakes into dead zone, having low oxygen content.

Acid rain is caused when waste gases from industries including carbon dioxide, nitrogen dioxide and sulphur dioxide mix with atmospheric water to form acids. These acids combine with rainfall and fall on lakes and forests making them polluted. The reactions can be written as-

$S{O}_2+O_2$$\to$$S{O}_3$

$S{O}_3+H_{2}O$$\to$$H_{2}S{O}_4$ (Sulpuric acid)

$N_2+O_2$$\to$$NO$

$NO+O_2$$\to$$N{O}_2$

$N{O}_2+H_{2}O$$\to$$HN{O}_3+NO$ (Nitric acid)

All these acids added to rainfall, fall on the lakes, polluting them and turning them into dead zones.

Similarly washed off fertilizers from the land flow into the lakes. Growth of aquatic plants and algae occur there. Thus a competition for sunlight and oxygen happens, which further turns the lakes into dead zones.

Thus, option D is the correct answer.