Which of the following statements about eutrophication is/are correct? 1. Eutrophication takes place in young lakes when the water is cold and clear. 2. Eutrophication is caused by nutrient enrichment in water bodies. Select the answer using the code given below.
- A.1 only
- B.2 only
- C.Both 1 and 2
- D.Neither 1 nor 2
Correct answer
Explanation
The correct answer is B, 2 only. Eutrophication is the enrichment of a water body with nutrients, so statement 2 is correct, while statement 1 describes the opposite condition.
When nitrates and phosphates from fertiliser run-off, sewage and detergents enter a lake, algae and other plants grow very fast. This algal bloom blocks sunlight, and when the plants die, bacteria decompose them and use up the dissolved oxygen. Fish and other animals then die, and the lake slowly fills with organic matter. Natural ageing of lakes follows the same path over thousands of years; human activity speeds it up, which is called cultural or accelerated eutrophication.
Statement 1 is wrong because a young lake with cold, clear water and few nutrients is oligotrophic, the state before eutrophication sets in. So A (1 only), C (both) and D (neither) are all incorrect.
Exam tip: young, clear, nutrient-poor lake = oligotrophic; old, green, nutrient-rich lake = eutrophic.
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