Which of the following pairs of elements is most important in the process of…

CONCEPT

Eutrophication is the enrichment of a water body with growth-supporting nutrients, followed by excessive algal or aquatic-plant production.

Nitrogen supports amino acids and proteins, whereas phosphorus is central to nucleic acids and cellular energy-transfer compounds; either nutrient can limit primary production in aquatic ecosystems.

APPLICATION

When nitrogen- and phosphorus-bearing runoff, sewage, or fertilizer enters a lake, the added nutrient supply removes a growth limitation. Algal biomass can then rise rapidly; its decay increases microbial oxygen demand and may deplete dissolved oxygen.

CONTRAST

• Calcium and magnesium mainly influence water hardness and mineral or ionic balance.

• Nitrogen and phosphorus are macronutrients whose increased supply directly supports the formation of new aquatic biomass.

• Nickel and cobalt are required only as trace components of selected enzymes and vitamin-related processes.

• Iron and copper are trace micronutrients used in electron-transfer and enzyme systems, and excess concentrations may be toxic.

CROSS-CHECK

The usual control measures target nitrogen and phosphorus inputs from wastewater and agricultural runoff. Reducing those inputs limits the nutrient supply that drives blooms, which confirms the nutrient pair.

RESULT

Therefore, the most important pair among the offered choices is nitrogen-phosphorus.