What substance presence in water usually indicates fresh pollution?

Ammonia is a key indicator of fresh pollution in water bodies. It is a compound that can originate from various sources, including agricultural runoff, sewage discharge, and industrial effluents. When ammonia is present in high concentrations, it typically signifies that there has been recent contamination from organic matter or nutrient loading, as this compound is primarily derived from the breakdown of nitrogenous organic materials.

The presence of ammonia in water can be particularly harmful to aquatic life, as it is toxic in certain concentrations. Therefore, monitoring ammonia levels is crucial in assessing water quality and environmental health. In contrast, other substances like nitrogen in forms other than ammonia, phosphorous, and chlorine may not specifically indicate fresh pollution in the same way ammonia does. For instance, nitrogen can be present naturally in various forms in water, phosphorus is associated with nutrient loading but not strictly indicative of recent pollution, and chlorine is often used as a disinfectant rather than a pollutant. Hence, the presence of ammonia stands out as a strong marker of immediate pollution concerns in freshwater systems.