Tennessee Wastewater Operator Practice Exam

What causes ponds to change color from green to brown as days become shorter?

1. Increased algae blooms

2. Diatoms capturing light over more of the spectrum

3. Reduced water levels

4. Decreased nutrient availability

The correct answer is: Diatoms capturing light over more of the spectrum

The transition of ponds from green to brown as days become shorter can be correctly attributed to diatoms capturing light over a broader spectrum. During the longer days of summer, conditions are often favorable for the growth of green algae, which thrive in sunlight and produce a green color in the water due to the chlorophyll they contain. As daylight decreases in fall and winter, these algae may decline due to reduced photosynthetic activity. Diatoms, a type of algae that are typically brown due to their silica-based cell walls and the presence of accessory pigments, can become more prevalent under lower light conditions. They have the ability to utilize different wavelengths of light for photosynthesis, which allows them to thrive when green algae are less competitive. This shift in dominant species can change the water's color from green to brown as the diatom population increases. Other options don't accurately explain this phenomenon. For instance, increased algae blooms would usually maintain or deepen green coloration of the water. Reduced water levels might concentrate nutrients but doesn't directly lead to color changes at the same level of detail. Decreased nutrient availability can limit growth but would not specifically explain the transition from green to brown in this context. Thus, the presence and activity of diatoms in shifting light conditions is the key aspect