How do human wastes affect biochemical oxygen demand (BOD)?

Human wastes significantly affect biochemical oxygen demand (BOD) by increasing it. BOD is a measure of the amount of dissolved oxygen that microorganisms will consume while decomposing organic matter in water. When human wastes, which are rich in organic matter such as proteins, carbohydrates, and fats, enter water bodies, they provide a substantial food source for bacteria and other decomposers.

As these microorganisms break down the organic material, they consume oxygen in the process. Consequently, higher concentrations of human waste lead to a greater demand for oxygen, resulting in an increase in BOD levels. This can have serious implications for aquatic ecosystems, as elevated BOD can deplete oxygen levels in the water, harming fish and other aquatic organisms that rely on dissolved oxygen for survival.

Therefore, the correct answer reflects the relationship between human waste and the increased demand for oxygen by microorganisms, demonstrating how human activities can impact water quality and aquatic health negatively.