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Does the presence of nitrates affect water quality?

Unlike temperature and dissolved oxygen, the presence of nitrates usually does not have a direct effect on aquatic insects or fish.  However, excess levels of nitrates in water can create conditions that make it difficult for aquatic insects or fish to survive.  

Algae and other plants use nitrates as a source of food.  If algae have an unlimited source of nitrates, their growth is unchecked. So, why is that a problem?

Which river is most likely affected by high levels of nitrates?

Comparison of rivers

The river on the right is as green as pea soup, a result of high concentrations of algae.  Click here to see other examples of how nitrate levels affect algae growth in lakes.

Large amounts of algae can cause extreme fluctuations in dissolved oxygen.  Photosynthesis by algae and other plants can generate oxygen during the day. However, at night, dissolved oxygen may decrease to very low levels as a result of large numbers of oxygen consuming bacteria feeding on dead or decaying algae and other plants.

Can the presence of nitrates affect human health?

People who use wells as a source of drinking water need to monitor the level of nitrates in their well water.  If you drink water that is high in nitrates, it can interfere with the ability of your red blood cells to transport oxygen.  Infants who drink water high in nitrates may turn "bluish" and appear to have difficulty in breathing since their bodies are not receiving enough oxygen.

Just like dissolved oxygen, temperature, and pH, the amount of nitrates in water is determined by both natural processes and human intervention.  A body of water may be naturally high in nitrates or have elevated nitrate levels as a result of careless human activities.

In this unit, you will be introduced to the concept of nitrates and how nitrates can influence the aquatic environment.  The relationship between nitrate and dissolved oxygen levels will be introduced.  This unit will also discuss how nitrate levels are influenced by nature as well as man-made processes.

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