What depletes oxygen in receiving water when organic wastes are discharged?

Bacteria are responsible for depleting oxygen in receiving waters when organic wastes are discharged. This occurs because bacteria break down organic matter through a process called decomposition. During this process, bacteria consume oxygen from the water to facilitate their metabolic activities. As organic wastes, such as food scraps or sewage, enter a water body, the increase in bacterial activity leads to a higher demand for oxygen, potentially depleting the dissolved oxygen levels that are critical for the survival of aquatic life.

In contrast, algae produce oxygen during the day through photosynthesis, which helps to increase oxygen levels in the water rather than deplete them. Pathogens, while harmful to human health and can cause disease, do not significantly contribute to the depletion of oxygen in the same manner as bacteria. Limestone rocks have no direct impact on oxygen levels in the water related to organic waste decomposition; instead, they can influence pH levels and overall chemistry of the water. Thus, the role of bacteria in breaking down organic material clearly indicates why they are the primary factor in depleting oxygen in receiving waters due to the discharge of organic wastes.