Typical dissolved oxygen (DO) in river water In a healthy, well-aerated river reach, the dissolved oxygen concentration is commonly around how many parts per million (ppm)?

Introduction / Context:
Dissolved oxygen (DO) is a core indicator of aquatic ecosystem health. Adequate DO supports fish respiration, aerobic biodegradation, and overall riverine biodiversity.

Given Data / Assumptions:

• We consider typical temperate conditions with moderate temperature.
• Values are in ppm, interchangeable with mg/L for dilute aqueous solutions.
• Water is not supersaturated and is free from extreme organic loading.

Concept / Approach:
Oxygen solubility in water at ambient conditions is on the order of single-digit mg/L. Natural rivers often have DO around 5 to 9 mg/L depending on temperature, turbulence, and biological activity. Values in the hundreds of ppm are physically unrealistic for oxygen solubility at normal pressure.

Step-by-Step Solution:

Verification / Alternative check:
Field measurements and standards (often DO > 5 mg/L for aquatic life) align with this range; environmental guidelines use similar thresholds.

Why Other Options Are Wrong:

Common Pitfalls:
Confusing DO with BOD or COD values that may be larger, and misinterpreting ppm scales across different pollutants.

Final Answer:
5