Tennessee Wastewater Operator Practice Exam

What does the observation of red clouds of tiny darting organisms at the edge of a pond in early morning suggest?

1. High nutrient levels

2. Low DO concentrations

3. Increased water temperatures

4. Presence of fish larvae

The correct answer is: Low DO concentrations

The observation of red clouds of tiny darting organisms at the edge of a pond in the early morning is indicative of a phenomenon commonly associated with high levels of nutrients in water bodies, particularly phosphorous and nitrogen. These nutrients stimulate the growth of microscopic organisms, including phytoplankton and zooplankton, which can result in the formation of visible blooms. While low dissolved oxygen (DO) concentrations can indeed occur as a result of excessive organic matter decomposition, leading to an increase in organisms that may utilize oxygen, it is not specifically characterized by the presence of darting organisms. In a scenario where nutrient levels are elevated, one would expect a dynamic and active environment, particularly in the morning when temperatures are cooler and oxygen levels may be higher due to photosynthesis, contributing to the observed behavior of these organisms. These darting organisms are often a sign of thriving aquatic life, which can also indicate shifts in the ecological balance of the pond, but they are not solely tied to low DO levels. Therefore, the presence of these organisms aligns more accurately with an environment rich in nutrients, which affects the overall health and composition of the aquatic ecosystem.