Nitrogen is an
element needed by all
plants and animals to build
protein. It is also important in
determining water quality.
As
aquatic plants and animals
die,
bacteria break down large
protein molecules into
ammonia, which is oxidized to form
nitrites and
nitrates. Like the problems with
phosphate,
eutrophication problems occur with the increase of nitrogen in the water. However, plants are not as sensitive to increase in ammonia and nitrate levels as they are with
phosphates.
Sewage is the main source of
nitrates added by
humans to rivers and can cause eutrophication.