Question

Choose the correct statement.

• A. Excessive nutrient inputs to lakes maintains the high dissolved oxygen of the lakes.
• B. Lakes with extensive algal blooms will have the good health of the lakes.
• C. Eutrophic lakes have high BOD.
• D. Oligotrophic lakes have high BOD compared to eutrophic lakes.

Hint:

- Oligotrophic: "Oligo" = few. Low nutrients, low algae, low BOD, high clarity, high oxygen. Good health. - Eutrophic: "Eu" = true/good (at growing things). High nutrients, high algae, high BOD, low clarity, low oxygen. Poor health.

Answer 1

The Correct Option is C

Step 1: Analysis of statement A.
Eutrophication from excess nutrients triggers algal blooms. These blooms, upon dying, are decomposed by bacteria, depleting dissolved oxygen and causing hypoxia or anoxia. The statement is therefore incorrect.

Step 2: Analysis of statement B.
Algal blooms are a key sign of eutrophication, indicating a lake's poor health, which frequently results in fish kills and biodiversity loss. Consequently, the statement is incorrect.

Step 3: Analysis of statement C.
Eutrophic lakes are nutrient-rich and highly productive, generating abundant organic matter (e.g., dead algae) that requires decomposition. This decomposition process consumes substantial oxygen, resulting in a high Biochemical Oxygen Demand (BOD). The statement is correct.

Step 4: Analysis of statement D.
Oligotrophic lakes are nutrient-poor and have low biological productivity. With little organic matter to decompose, they exhibit very low BOD. The statement incorrectly claims they have high BOD compared to eutrophic lakes. The statement is thus incorrect.