Which statement about dissolved oxygen in streams is correct and how temperature affects DO?

Which statement about dissolved oxygen in streams is correct and how temperature affects DO?

• A. DO indicates habitat health; warmer water holds less oxygen
• B. DO indicates mineral content; warmer water holds more oxygen
• C. DO has no relation to temperature
• D. DO measures salinity

Answer: (A)

Dissolved oxygen shows how much oxygen gas is actually dissolved in the water, and it’s crucial for fish and other aquatic life. Because streams need adequate oxygen to support organisms, DO levels serve as a good indicator of habitat health—the higher the DO, the more favorable the environment for aquatic life; low DO often means stress, pollution, or high microbial demand. Temperature matters because the amount of oxygen that can stay dissolved in water decreases as temperature rises. Cold water can hold more oxygen, while warm water holds less. That’s why the idea that warmer water holds less oxygen is the correct part of the statement, and why DO is linked to temperature. The other ideas don’t fit: DO isn’t a measure of mineral content or salinity, and it does vary with temperature rather than being unrelated.

Dissolved oxygen shows how much oxygen gas is actually dissolved in the water, and it’s crucial for fish and other aquatic life. Because streams need adequate oxygen to support organisms, DO levels serve as a good indicator of habitat health—the higher the DO, the more favorable the environment for aquatic life; low DO often means stress, pollution, or high microbial demand.

Temperature matters because the amount of oxygen that can stay dissolved in water decreases as temperature rises. Cold water can hold more oxygen, while warm water holds less. That’s why the idea that warmer water holds less oxygen is the correct part of the statement, and why DO is linked to temperature.

The other ideas don’t fit: DO isn’t a measure of mineral content or salinity, and it does vary with temperature rather than being unrelated.