Question

Question 5: Write critical notes on the following: (a) Eutrophication (b) Biological magnification (c) Groundwater depletion and ways for its replenishment

Class 12 - Biology - Environmental Issues Page 286

Answer 1

Eutrophication : it is natural aging of a lake by nutrient enrichment of its water.In young lakes the water is cold and clear,supporting the little life but with due corse of time nutrient such as nitrogen and phosphorus get introduced in it which encourages the growth of aquatic organisms. over centuries lake grows shallower and warmer then marsh plants take a root in lake basin eventually it gets converted in land.

Biological magnification (BIOMagnification);
refers to increase in concentration of toxicant at successive tropic level.this happens due to a toxic substance gets accumulated by an organism cannot be metabolized or excreted and it is passed to next higher tropic level. this is known for mercury and DDT.

(c) Ground water depletion and ways for its replenishment:

The level of ground water has decreased in the recent years. The source of water supply is rapidly diminishing each year because of an increase in the population and water pollution. To meet the demand of water, water is withdrawn from water bodies such as ponds, rivers etc. As a result, the source of ground water is depleting. This is because the amount of groundwater being drawn for human use is more than the amount replaced by rainfall. Lack of vegetation cover also results in very small amounts of water seeping through the ground. An increase in water pollution is another factor that has reduced the availability of ground water.

Measures for replenishing ground water:-
1) preventing over exploitation of ground water table
2)optimizing water use and reducing water loss
3)Rain water harvesting
4)preventing deforestation and planting more and more trees.

Answer 2

Answer:

(a) Eutrophication –

It is referred to the natural ageing process of a lake as a result of nutrient enrichment caused by the overflow of nutrients such as fertilizers, animal wastes and sewage from land leading to an increased fertility of the lake. Consequently, there is a huge increase in the primary productivity of the ecosystem bringing about an increased growth of algae, hence in algal blooms. After sometime, the decomposition of these algae reduces oxygen supply, resulting in the death of aquatic animal life.

(b) Biological magnification

Pesticides are used on a large scale to protect crops from various diseases and pests. When these pesticides enter the soil, they are absorbed by plant parts with minerals and water from the soil. These chemicals can enter water sources as a result of rains, furthermore into the bodies of aquatic animals and plants, hence into the food chain. As these chemicals cannot be disintegrated, at each of the tropic levels, they keep getting accumulated, wherein most of the accumulation occurs at the top carnivore’s level. This is termed as biological magnification where there is increase in the concentration of harmful pollutants with each increasing tropic level.

For instance, high DDT concentration in a pond saw the producers (phytoplankton) to have a DDT concentration of 0.04 ppm. As these phytoplankton were consumed by zooplankton – the consumers, the concentration of DDT in the bodies of zooplankton was noted to be 0.23 ppm. When this in turn is consumed by small fish, more of DDT gets collected in their bodies. Consequently, the large fish (top carnivore) feeding on different small fish tend to have the maximum concentration of DDT.

(c) Groundwater depletion and ways for its replenishment

Since the past years, the level of ground water has decreased. Water supply from sources is declining rapidly with each passing year due to an increase in water pollution and population explosion. In order to meet the demand of water, water is being taken out from water bodies such as rivers, ponds etc. hence, the source of ground water is fast depleting as the quantity of groundwater that is withdrawn for human utilization is more than the quantity that is being replaced by rainfall. Small quantities of water penetrates through the ground due to lack of vegetation cover. Another factor that has caused a decline in the availability of ground water is an increase in water pollution.

Measures to replenish ground water are as follows:

Over-exploitation of ground water must be prevented

Water use must be optimized and water demand must be reduced

Promote and encourage rain water harvesting

Prevent deforestation

Promote afforestation, plant more trees