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: Analyze statement A.
Excessive nutrient inputs (eutrophication) cause massive algal blooms. When these algae die, they are decomposed by bacteria, a process that consumes large amounts of dissolved oxygen, leading to hypoxia or anoxia (low or no oxygen). Thus, the statement is incorrect.

Step 2: Analyze statement B.
Extensive algal blooms are a primary symptom of eutrophication, which is a state of poor ecological health for a lake, often leading to fish kills and loss of biodiversity. Thus, the statement is incorrect.

Step 3: Analyze statement C.
Eutrophic lakes are rich in nutrients and have high biological productivity. This leads to a large amount of organic matter (dead algae, etc.) that needs to be decomposed. This decomposition requires a lot of oxygen, meaning the lake has a high Biochemical Oxygen Demand (BOD). This statement is correct.

Step 4: Analyze statement D.
Oligotrophic lakes are nutrient-poor and have low biological productivity. There is little organic matter to decompose, so they have a very low BOD. The statement claims they have high BOD compared to eutrophic lakes, which is the exact opposite of the truth. Thus, the statement is incorrect.