aquatic ecosystems in lakes, rivers, and coastal estuaries
have probably suffered the most so far. They are the ultimate receptacles
of much of the nutrient overload, which tends to accumulate in runoff
or to be delivered directly in the form of raw or treated sewage.
(Sewage is very high in nitrogen from protein in the human diet.)
In these aquatic systems, excess nitrogen can often stimulate the growth of algae
and other plants. When this extra plant matter dies and decays,
it can rob the water of its dissolved oxygen, suffocating many aquatic
organisms.