Which pattern in a diel oxygen curve indicates a healthy, well-functioning lake compared to a stressed one?

Which pattern in a diel oxygen curve indicates a healthy, well-functioning lake compared to a stressed one?

• A. Daytime supersaturation and nighttime minima above critical thresholds indicate a healthy system.
• B. Daytime DO is consistently low, indicating health.
• C. Nighttime DO spikes indicate health.
• D. Diurnal DO fluctuations are not informative.

Answer: (A)

During a diel cycle, sunlight fuels photosynthesis, which adds oxygen to the water and can push DO above what the atmosphere can hold (supersaturation) in the day. In a healthy, well-functioning lake, this daytime gain is paired with nighttime minima that stay above the level needed by aquatic life. So the pattern where daytime DO reaches supersaturation and the lowest DO at night remains above the critical threshold is a sign of robust oxygen dynamics, good production, and sufficient mixing, all indicating a healthy system. If daytime DO stays low, that points to limited photosynthesis or high respiration and stress. Nighttime DO spikes are not typical of a healthy lake, since DO usually falls when photosynthesis ceases. And diurnal fluctuations are informative about how production and respiration balance over the day, so treating them as uninformative would miss important health signals.

During a diel cycle, sunlight fuels photosynthesis, which adds oxygen to the water and can push DO above what the atmosphere can hold (supersaturation) in the day. In a healthy, well-functioning lake, this daytime gain is paired with nighttime minima that stay above the level needed by aquatic life. So the pattern where daytime DO reaches supersaturation and the lowest DO at night remains above the critical threshold is a sign of robust oxygen dynamics, good production, and sufficient mixing, all indicating a healthy system.

If daytime DO stays low, that points to limited photosynthesis or high respiration and stress. Nighttime DO spikes are not typical of a healthy lake, since DO usually falls when photosynthesis ceases. And diurnal fluctuations are informative about how production and respiration balance over the day, so treating them as uninformative would miss important health signals.