Quality of a River - Water Quality
Dissolved oxygen (pg 1 of
Each natural stream has its characteristic
regime of dissolved oxygen, related largely to
temperature and the breakdown of organic material
in the water.
In aquatic systems, oxygen is typically referred
to as "dissolved oxygen" or O2, to
distinguish it from "O" or oxygen in the
H2O molecule. O2 is the
available form of oxygen for aquatic organisms.
Just as water can hold a certain amount of
dissolved sugar in suspension (its saturation
point), water can also hold a given amount of
dissolved oxygen. Unlike sugar, however, the
saturation point of dissolved oxygen decreases as
Water temperature strongly influences the amount
of dissolved oxygen in a stream because (1) the
ability of water to hold dissolved oxygen decreases
as temperature increases, and (2) warm temperatures
increase the oxidation rates that remove dissolved
oxygen from solution. For those reasons, warm
streams often have much lower concentrations of
dissolved oxygen than cold streams.