Which measurement is most commonly used for assessing the condition of freshwater systems impacted by organic pollution?

Biochemical oxygen demand (BOD) is a critical measure for assessing the health of freshwater ecosystems, particularly in contexts affected by organic pollution. BOD quantifies the amount of oxygen that microorganisms will consume while decomposing organic matter in water over a specified period, typically five days. High BOD levels indicate a significant presence of organic materials, as well as possible waste issues that can lead to oxygen depletion in the water.

Oxygen is essential for aquatic life; therefore, an increase in BOD often correlates with a deterioration of water quality, suggesting that the system may be stressed due to excess organic matter. This is a common situation in freshwater systems receiving runoff that contains organic pollutants from agricultural sources, sewage, or industrial discharges.

In contrast, while total dissolved solids, pH levels, and nutrient levels can provide important insights into water quality, they are not as directly indicative of the effects of organic pollution. Total dissolved solids primarily indicate the concentration of all dissolved materials in the water, pH offers insights into acidity or alkalinity but not specifically organic pollution, and nutrient levels may indicate excess nutrients but do not directly measure the impact on biological oxygen demand. Therefore, BOD is the most relevant measurement for evaluating the condition of freshwater systems under the