Which of these statements is true ?

Options

A. Eutrophication is always the result of anthrognic action .
B. A water body severely polluted with organic matter will have a low biological oxygen demand
C. In the town of Arcata, California biologists developed a series of ten connected marshes over sixty hectares of marshland
D. Recycling is the only solution for the treatment of electronic waste.

Answer

To solve the question "Which of these statements is true?", we will analyze each statement one by one.

### Step-by-Step Solution:

1. **Statement 1: Eutrophication is always the result of anthropogenic action.**
- **Analysis:** Eutrophication is the process where water bodies become enriched with nutrients (mainly nitrates and phosphates), leading to excessive growth of algae. While human activities (anthropogenic actions) can contribute to eutrophication through pollution, it can also occur naturally over time. Therefore, this statement is **false**.

2. **Statement 2: A water body severely polluted with organic matter will have a low oxygen demand.**
- **Analysis:** Biological Oxygen Demand (BOD) measures the amount of oxygen required to decompose organic matter. If a water body is heavily polluted with organic matter, the BOD will be high, indicating a high oxygen demand. Thus, this statement is **false**.

3. **Statement 3: In the town of Arcata, California, biologists developed a series of 10 marshes over 60 hectares of marshland.**
- **Analysis:** The correct information states that biologists developed a series of **6 connected marshes** over 60 hectares of marshland for integrated wastewater treatment. Therefore, this statement is **false**.

4. **Statement 4: Recycling is the only solution for the treatment of electronic waste.**
- **Analysis:** While recycling is a significant and environmentally friendly method for managing electronic waste (e-waste), it is not the only solution. Other methods include repair, refurbishment, and safe disposal. However, the statement emphasizes recycling as a key solution, which can be interpreted as true in the context of promoting environmental sustainability. Therefore, this statement is **true**.

### Conclusion:
The correct statement is **Statement 4: Recycling is the only solution for the treatment of electronic waste.**

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