Quality of a River - Water Quality
Dissolved oxygen (pg 2 of
Riffles and other turbulence help to saturate
water with dissolved oxygen. Photosynthesis from
aquatic plants also oxygenates water.
Other processes remove oxygen from the water.
Rising temperature is one. Respiration of fish,
insects, zooplankton, algae, and other plants and
animals is another. Chemical reactions is a third
Decomposition also removes oxygen from water. A
stream carrying a large quantity of nonliving
organic matter, such as a decaying algae bloom or a
load of only partially treated sewage, is said to
have a high biochemical oxygen demand.
Biochemical oxygen demand (BOD) represents the
amount of dissolved oxygen consumed by bacteria and
other microorganisms as they decompose the organic
matter in the water.