Which statement about dissolved oxygen is true?

Which statement about dissolved oxygen is true?

• A. Dissolved oxygen is the amount of oxygen dissolved in water and is essential for aerobic life.
• B. Dissolved oxygen is the total amount of oxygen in the air.
• C. Dissolved oxygen measures only carbon dioxide levels.
• D. Dissolved oxygen is irrelevant to microbial activity.

Answer: (A)

Dissolved oxygen is the amount of oxygen gas that is dissolved in water, and it’s essential for aerobic life in aquatic environments. This measure is specific to water, not the total oxygen in the air, and it’s not about carbon dioxide levels. Microbial activity, especially the decomposition of organic matter, uses up dissolved oxygen, so DO levels reflect how much oxygen is available for aquatic organisms as microbes respire. In practice, DO is reported in mg/L or as a percent of saturation, and factors like warmer water, stagnation, or heavy organic pollution can lower it, stressing fish and other aerobic life.

Dissolved oxygen is the amount of oxygen gas that is dissolved in water, and it’s essential for aerobic life in aquatic environments. This measure is specific to water, not the total oxygen in the air, and it’s not about carbon dioxide levels. Microbial activity, especially the decomposition of organic matter, uses up dissolved oxygen, so DO levels reflect how much oxygen is available for aquatic organisms as microbes respire. In practice, DO is reported in mg/L or as a percent of saturation, and factors like warmer water, stagnation, or heavy organic pollution can lower it, stressing fish and other aerobic life.