What does biochemical oxygen demand (BOD) measure?

Biochemical oxygen demand (BOD) specifically measures the amount of dissolved oxygen that microorganisms will consume while decomposing organic matter in a water sample over a defined period, typically five days at a standard temperature. This metric is crucial for assessing the organic pollution level in a body of water, as it indicates how much oxygen is being depleted by biological activity. A high BOD value suggests that there is a significant amount of biodegradable material present, which could lead to oxygen depletion and adversely affect aquatic life. This makes BOD an essential parameter for environmental monitoring and wastewater treatment processes.

The other choices do not accurately represent what BOD measures. The amount of water in a sample is unrelated to biological activity, while temperature and nutrient levels, although important in aquatic ecosystems, are not directly related to the concept of BOD.