Tennessee Wastewater Operator Practice Exam

Under what conditions would the DO concentration be highest in a facultative pond?

1. The water is warm and sunlight is scarce

2. The water is cold and sunlight is plentiful

3. The water is stagnant and dark

4. The water is warm and oxygen is limited

The correct answer is: The water is cold and sunlight is plentiful

The scenario where the dissolved oxygen (DO) concentration is highest in a facultative pond occurs when the water is cold and sunlight is plentiful. This is because cold water has a greater capacity to hold dissolved oxygen compared to warm water. In addition, abundant sunlight promotes photosynthesis by aquatic plants and algae. During photosynthesis, these organisms take in carbon dioxide and release oxygen, leading to an increase in the dissolved oxygen levels in the water. In this context, plentiful sunlight helps sustain high levels of oxygen production through photosynthesis, while cooler temperatures enhance the solubility of oxygen in the water, making it more available for aquatic life. The other conditions listed would not support high levels of dissolved oxygen in the same way; warm water reduces oxygen solubility, stagnant conditions would limit oxygen replenishment from the atmosphere, and dark conditions would halt photosynthesis entirely, leading to lower oxygen levels.