Observe the data given in the following table.ClassesArea in 1967(Km2)

1.	Observe the data given in the following table.ClassesArea in 1967(Km2)Area in 2004 (Km2)Lake – water spread area70.7062.65Lake with sparse weed047.45Lake with dense weed015.20Lake-liable to flood in rainy season100.970Aquaculture ponds099.74Rice fields8.4016.62Enchrochment0.311.37Total180.38180.38i) In which year lake-water spread area is more? Why?ii) How do you think weeds are more in the lake?iii) What are the reasons for decrease in lake area?iv) How do the above reasons lead to pollution?iv) How do the above reasons lead to pollution?vi) What could be the reasons for the migration of birds to this lake?
Answer» i) In the year 1967. Because lake was not brought under cultivation. ii) Excessive nutrient addition, especially from anthropogenic sources, led to explosive weed growth. Ex: Eichornia, pistia. iii) 1. In 1996, almost entire lake was brought under cultivation. 2. Industries came along in ever growing intensity in the catchment area of the lake. iv) 1. Consequently, the drains and rivulets carry substantial quantity of various types of pollutants into the lake. 2. The major sources of pollution are agricultural runoff containing residues of several agrochemicals, fertilizers, fish tank discharges, industrial effluents containing chemical residues. v) 1. The water of the lake turned alkaline in nature, turbid, nutrient rich, low in dissolved oxygen and high in biochemical oxygen demand. 2. Water borne diseases like diarrhoea, typhoid, amoebiasis and others are said to be common among the local inhabitants who are unaware of the state of pollution in the lake water. 3. Vector borne diseases were also increased. vi) To avoid extreme cold weather conditions in Northern Asia and Eastern Europe birds migrate to Kolleru lake.

Observe the data given in the following table.ClassesArea in 1967(Km2)Area in 2004 (Km2)Lake – water spread area70.7062.65Lake with sparse weed047.45Lake with dense weed015.20Lake-liable to flood in rainy season100.970Aquaculture ponds099.74Rice fields8.4016.62Enchrochment0.311.37Total180.38180.38i) In which year lake-water spread area is more? Why?ii) How do you think weeds are more in the lake?iii) What are the reasons for decrease in lake area?iv) How do the above reasons lead to pollution?iv) How do the above reasons lead to pollution?vi) What could be the reasons for the migration of birds to this lake?

Answer»

i) In the year 1967. Because lake was not brought under cultivation.

ii) Excessive nutrient addition, especially from anthropogenic sources, led to explosive weed growth. Ex: Eichornia, pistia.

iii)

1. In 1996, almost entire lake was brought under cultivation.

2. Industries came along in ever growing intensity in the catchment area of the lake.

iv)

1. Consequently, the drains and rivulets carry substantial quantity of various types of pollutants into the lake.

2. The major sources of pollution are agricultural runoff containing residues of several agrochemicals, fertilizers, fish tank discharges, industrial effluents containing chemical residues.

1. The water of the lake turned alkaline in nature, turbid, nutrient rich, low in dissolved oxygen and high in biochemical oxygen demand.

2. Water borne diseases like diarrhoea, typhoid, amoebiasis and others are said to be common among the local inhabitants who are unaware of the state of pollution in the lake water.

3. Vector borne diseases were also increased.

vi) To avoid extreme cold weather conditions in Northern Asia and Eastern Europe birds migrate to Kolleru lake.

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