does oxygen get in the water?
Basically, oxygen gets into water by three
different ways. It is by these means that most lakes,
rivers, streams, and oceans
receive the oxygen necessary to support aquatic life.
Diffusion from surrounding
air. If you remember the definition of diffusion,
it is the movement of a substance from an area of higher concentration to
an area of lower concentration. In this case of oxygen, if
the air in the atmosphere has a higher concentration of oxygen than water
- oxygen diffuses or is "pushed" from the air into the water.
The speed of this movement of oxygen is related to the difference in
the concentration of oxygen in the air and in the water and the atmospheric pressure. To see a current measure of atmospheric
pressure, click here.
Atmospheric or barometric pressure is measured in units of
"inches of mercury" and on a normal day, at sea level, the
pressure is 29.92 inches of mercury.
This relatively calm water in the lake
(shown above) is an example of
a body of water that receives its oxygen by natural diffusion.
Aeration of water.
A river that flows rapidly will have a turbulent
surface, with much more surface area for oxygen to diffuse across
than a flat, slow moving river. Thus the atmospheric pressure
can drive more oxygen into the water. Also, the turbulence created
by churning waters causes air to hit the water at a high pressure,
allowing more oxygen to become dissolved.
This white water creek is an example of how turbulence
creates more surface area, allowing more oxygen to diffuse into
Waste products of plants.
Rooted aquatic plants and algae "breathe" in the same way that trees
and other land dwelling plants do. They use carbon dioxide as fuel and
generate oxygen as a waste product. This oxygen is immediately
dissolved into the water. There is only one problem with this
source of aquatic oxygen: the process is reversed at night!
In darkness, plants will consume oxygen as fuel. Thus,
a body of water with a high plant density will have high dissolved
oxygen levels during the day and low levels of dissolved oxygen at night.
Aquatic vegetation can supply dissolved
oxygen provided that there is sunlight. When there is no light
for photosynthesis, plants consume some of the oxygen, leaving less
oxygen for the fish.
the amount of dissolved oxygen (DO) differ for every body of water?
Absolutely! The conditions
stated above have a large impact on the amount of dissolved oxygen.
Barometric pressure will influence how much dissolved oxygen will
the water. Thus, altitude of the body of water and prevailing weather conditions
can be factors that affect the amount of dissolved oxygen in
Do you remember the pictures on the introduction
page to this unit?
A bayou swamp will usually have much less dissolved oxygen than a white
water river. The water in the bayou is calm and, therefore,
has less surface area for oxygen diffusion.
The presence of algae and rooted aquatic plants will
the amount of dissolved oxygen in water.
There are also other factors that can affect the amount of
oxygen dissolved in water. Some of these factors are
associated with the impact of humans on the environment.
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