Basic Wastewater Operator Practice Exam

What effect does ice and snow cover have on BOD levels?

1. It causes BOD to slowly increase

2. It causes BOD to slowly decrease

3. It causes BOD to rapidly increase

4. It has no effect on BOD

The correct answer is: It causes BOD to slowly increase

Ice and snow cover can lead to a slowly increasing biochemical oxygen demand (BOD) due to several factors associated with the environmental conditions created underneath and around the ice. When ice and snow cover water bodies, it restricts the exchange of gases between the water and the atmosphere, limiting the diffusion of oxygen into the water. As organic materials decompose under these conditions, they consume oxygen, which subsequently leads to an increase in BOD levels. The accumulation of organic matter during thawing or from runoff can also contribute to this increase, as the microbial activity that occurs when temperatures rise tends to elevate BOD levels further once the ice begins to melt. The other choices would not accurately reflect the dynamics occurring under ice and snow cover. A rapid increase, for instance, may occur under certain conditions, but the presence of ice generally results in slower processes until the ice melts and biological activity resumes more robustly. Therefore, the impact of ice and snow cover is characterized by a gradual increase in BOD levels rather than an immediate or stable response.