question_answer 5)

Write critical notes on the following: (a) Eutrophication. (b) Biological magnification. (c) Ground water depletion and ways for its replenishment  

Answer:

                (a) Eutrophication: Eutrophication is the phenomenon of nutrient enrichment of a water body that initially supports a dense growth of plant and animal life. It is caused by run-off from fertilized fields, sub-urban lawns, feed lots and detergent rich sewage. Organic loading or occurrence of excess organic matter occurs inside water. The rapid growth of water plants especially the algae, is called bloom. Algal blooms cut off light from submerged plants causing their death. This decreases dissolved oxygen replenishment inside water. Blue green algae present in the bloom also release toxins. Both toxicity and decreased oxygen level kill aquatic animals.                 (b) Biological magnification: Industrial wastes released into water contain toxic substances, such as arsenic, cadmium, lead, zinc, copper, mercury, and cyanides, besides some salts, acids and alkalies. All these materials can prove harmful for our health. They may reach human body directly with contaminated food or indirectly by way of plants and other animals. Concentration of the toxic materials increases at each trophic level of a food chain. This is called biological magnification. River water may have a very low concentration of DDT, but the carnivorous fish in that river may contain high concentration of DDT and become unfit for eating by man. Mercury discharged into rivers and lakes is changed by bacteria to the neurotoxic form called methylmercury. The latter is highly poisonous and may be directly absorbed by fish.                 Biomagnification of non-biodegradable pesticide through a food chain can be represented as follows:                 (c) Ground water depletion and ways for its replenishment:  Ground-water depletion is defined as long-term water-level decline caused by sustained ground-water pumping. The volume of ground water in storage is decreasing in many areas of the world in response to pumping. Some of the negative effects of ground-water depletion include increased pumping costs, deterioration of water quality, reduction of water in streams and lakes etc.                 Some ways for water replenishment are:                 (i) Reduction in consumption: Sprinkler and subsurface irrigation techniques reduce the amount of water used in irrigation.                 (ii) Rain water harvesting: Rain water collected over roots is allowed to pass into ground through deep water pipes.