Tennessee Wastewater Operator Practice Exam

What is the likely cause if a facultative pond turns dark purple?

1. A bloom of green algae

2. Anaerobic conditions have caused a bloom of purple sulfur bacteria

3. Excessive BOD loading

4. High levels of ammonia

The correct answer is: Anaerobic conditions have caused a bloom of purple sulfur bacteria

A facultative pond turning dark purple typically indicates the presence of purple sulfur bacteria, which thrive under anaerobic conditions. These bacteria are part of a specialized group that can perform photosynthesis using light energy to convert sulfide into elemental sulfur in environments where oxygen is limited. When organic matter decomposes in a facultative pond, it can lead to anaerobic conditions, especially if there is an overload of organic material, such as in cases of high Biological Oxygen Demand (BOD). This depletion of oxygen creates an environment conducive to the growth of purple sulfur bacteria, which can cause the water to take on a dark purple hue. While other conditions mentioned might affect the overall health and composition of a facultative pond, the dark purple coloration specifically points to the bloom of purple sulfur bacteria due to reduced oxygen levels, making this the most accurate explanation for such a phenomenon. These bacteria are usually an indicator of specific environmental conditions that necessitate further assessment and potential intervention to restore balance in the pond's ecosystem.