Tennessee Wastewater Operator Practice Exam

When is the dissolved oxygen concentration highest in an un aerated facultative pond?

1. On a bright sunny day

2. During heavy rain

3. At night

4. When it is cold

The correct answer is: On a bright sunny day

The highest concentration of dissolved oxygen in an un-aerated facultative pond occurs on a bright sunny day due to the process of photosynthesis. During daylight hours, aquatic plants and algae utilize sunlight to convert carbon dioxide and water into glucose and oxygen. This process significantly boosts the dissolved oxygen level in the water as these organisms release oxygen as a byproduct of photosynthesis. In contrast, during periods of heavy rain, the increased turbidity and mixing of the water can lead to a reduction in sunlight penetration, which can limit photosynthesis and thus lower dissolved oxygen levels. At night, photosynthesis ceases, and although respiration continues, oxygen is consumed by organisms, leading to lower levels of dissolved oxygen. Finally, cooler temperatures may correlate with lower biological activity, which can also impact the rates of photosynthesis and respiration, respectively. Therefore, the conditions that maximize photosynthetic activity—characterized by bright sunlight—lead to the highest concentration of dissolved oxygen in an un-aerated facultative pond.