Tennessee Wastewater Operator Practice Exam

What is likely to cause the surface of a pond to change from sparkling green to dark pink during a local festival?

1. Decrease in sunlight

2. Increased BOD loading

3. Overgrowth of aquatic plants

4. Increase in algae activity

The correct answer is: Increased BOD loading

A change in the surface coloration of a pond from sparkling green to dark pink can be attributed to increased biochemical oxygen demand (BOD) loading. When BOD increases, typically this indicates a higher concentration of organic matter being introduced into the pond, often due to pollution or the discharge of waste materials. As organic matter decomposes, it often leads to increased microbial activity, which consumes oxygen in the water and can alter water chemistry significantly. Specifically, the decomposition process can result in the proliferation of certain bacteria that produce pigments or the occurrence of an algal bloom that may shift the color spectrum observed on the water's surface. In some cases, specific types of bacteria may produce reddish pigments as they metabolize organic substances, hence giving the water a dark pink appearance. This phenomenon is less likely to be attributed to decreased sunlight, overgrowth of aquatic plants, or general increases in algae activity alone, as these factors would not directly correlate with the production of a significant color change like the one described.