Download Dissolved Oxygen (DO)

Dissolved Oxygen (DO)
• Dissolved Oxygen is the amount of
gaseous oxygen (O2) dissolved in the
water.
• Oxygen enters the water by
(1)direct absorption from the
atmosphere, by rapid movement, and/or
(2) as a by-product of plant
photosynthesis.
Photosynthesis
Dissolved oxygen and Water quality
Water quality
Good
Slightly polluted
Moderately
polluted
Heavily polluted
Severely polluted
Dissolved oxygen
(mg/L)
> 8.0
6.5-8.0
4.5-6.5
4.0-4.5
< 4.0
Dissolved oxygen
• Fish need at least 5-6 mg/L DO to
grow and thrive. They stop feeding if
the level drops to around 3-4 mg/L and
die if DO falls to 1 mg/L.
• The solubility of oxygen in water
decreases as water temperature increases.
• Oxygen becomes dissolved in surface
waters by diffusion from the atmosphere
and from aquatic-plant photosynthesis.
Dissolved oxygen
• Although water plants produce
oxygen during the day, they
consume oxygen at night as an
energy source (respiration).
• When water plants die and decay,
dead plant matter serves as an
energy source for microbes, which
consume additional oxygen.
DO meter to measure the amount of
Dissolved Oxygen (mg/L) contained
in water
DO SAG CURVE