What is a common indicator of nutrient pollution in surface water?

Elevated levels of nitrogen and phosphorus are commonly recognized as indicators of nutrient pollution in surface water. These nutrients, when present in excess due to agricultural runoff, wastewater discharge, or stormwater, can lead to algal blooms. These blooms not only deplete oxygen levels in the water as they decay but can also produce toxins harmful to aquatic life and humans. Monitoring nitrogen and phosphorus levels in water bodies is essential to assess the health of the ecosystem and to implement management strategies effectively.

While dissolved oxygen levels provide insight into the water's health, high levels typically indicate good water quality and are not direct indicators of nutrient pollution. Low water temperatures may suggest conditions that are less likely to support algal blooms, and the absence of aquatic life can indicate severe pollution or habitat degradation, but it does not specifically point to nutrient pollution. Therefore, elevated levels of nitrogen and phosphorus directly relate to the causes and effects of nutrient pollution in surface waters.