Quality of a River - Water Quality
Nutrients: Phosphorus and
nitrogen (pg 1 of 2)
Nutrients, principally nitrogen and phosphorus,
are other important components of water
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
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
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.
and Almendinger, 2000); (James
et al., 2000).