Quality of a River - Water Quality
Contaminants (pg 1 of
Streams carry a staggering array of harmful
artificial contaminants. These pollutants come from
point sources, such as industrial plants or
sewage treatment plants, and nonpoint
sources, such as runoff from cities or farmland
or from atmospheric deposition.
Organic pollutants include animal wastes,
such as manure or feedlot runoff, and human wastes,
such as untreated or partially treated sewage.
Ammonia, a byproduct of these wastes and a major
effluent from sewage treatment plants, is toxic at
relatively low concentrations. Also, the presence
of human waste (measured as fecal coliform) causes
concern for disease pathogens. But the primary
effect of organic pollutants on stream ecology is
the consumption of dissolved oxygen from water as
they degrade (see Dissolved
oxygen and Nutrients).
A variety of substances can act as contaminants
in streams. Two important groups are toxins and