Sources of pollution that lead to a decrease in dissolved oxygen levels in water are primarily organic pollutants and excess nutrients that fuel oxygen-consuming processes.
A significant source mentioned in available information is the accidental release of untreated sewage into a watercourse. This type of pollution introduces large amounts of organic matter and bacteria into the water body.
How Sewage Reduces Dissolved Oxygen
When untreated sewage enters a water source, it acts as a readily available food source for naturally occurring bacteria in the water. Here's the process:
- Bacterial Growth: The bacteria consume the organic material in the sewage, leading to a rapid increase in their population.
- Respiration: These bacteria, during their metabolic processes (including decomposition of the sewage), respire. This respiration uses up the oxygen dissolved in the water.
- Oxygen Depletion: As the bacterial population booms and respiration increases, they consume dissolved oxygen faster than it can be replenished from the atmosphere or aquatic plants (through photosynthesis). This leads to a drop in dissolved oxygen levels.
This decrease in dissolved oxygen is detrimental to other aquatic life, such as fish, insects, and other organisms, many of which require sufficient oxygen to survive. Low dissolved oxygen levels can stress or even kill these organisms, disrupting the entire aquatic ecosystem.
Other Common Sources (Not detailed in the provided reference but generally known)
While the provided reference focuses on sewage, other common sources that reduce dissolved oxygen include:
- Agricultural Runoff: Carries excess nutrients like nitrogen and phosphorus from fertilizers into water bodies. These nutrients can cause algal blooms. When algae die, bacteria decompose them, consuming large amounts of oxygen.
- Industrial Wastewater: Can contain organic pollutants and chemicals that are decomposed by bacteria, or can be hot water discharges that reduce oxygen solubility.
- Urban Runoff: Carries various pollutants, including organic matter and nutrients, from streets and paved areas into waterways.
Understanding these sources is crucial for protecting aquatic ecosystems and managing water quality. Preventing pollutants from entering water bodies through improved wastewater treatment, agricultural best practices, and managing stormwater runoff are key solutions.
