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Quality of a River - Water Quality
Nutrients: Phosphorus and nitrogen (pg 1 of 2)

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Nutrients, principally nitrogen and phosphorus, are other important components of water chemistry.

Phosphorus occurs naturally in rocks and minerals, finding its way to streams primarily through runoff in its oxidized form, phosphate. Unlike nitrogen, which can be liberated to the atmosphere (through denitrification), phosphorus remains in the stream system, cycling through plants, animals, and water throughout the river's course.

Nitrogen is one of the most common elements on earth, making up three-fourths of our atmosphere. But it is not this gaseous form that is important to stream life. Gaseous nitrogen must be "fixed" and then nitrified, primarily by soil-dwelling bacteria, to form compounds (primarily nitrate). These compounds dissolve in stream water and are taken up as nutrients by aquatic plants and by animals for the synthesis of protein.

High levels of phosphorus and nitrogen can cause an explosion of algae and other plant growth in streams. The decomposition of this growth can rob a stream of dissolved oxygen. In freshwater systems, phosphorus is generally the limiting factor or determinant of the level of plant growth. In marine environments, nitrogen is frequently the limiting nutrient.

Common sources of abnormally high levels of these nutrients are runoff of fertilizer from lawns and farmland; runoff from feedlots; manure spills; and effluent from sewage treatment plants and poorly functioning septic systems.

The breakdown of nitrogen in the form of ammonia into nitrates consumes oxygen and may reduce dissolved oxygen to lethal levels.

(Engstrom and Almendinger, 2000); (James et al., 2000).


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