Water Quality Parameters

1
Water Quality Parameters
Dissolved Oxygen
2
Introduction

• Ponds and aquatic systems containing free oxygen
  molecules are aerobic those without are
  anaerobic.
• Anaerobic aquatic systems will not support higher
  life forms such as fish and bacteria. They are
  characterized by the presence of noxious
  chemicals such as hydrogen sulfide, which can
  cause odors.
• Anaerobic conditions are normally found in bottom
  sediments and dirty filters

3
When does Dissolved Oxygen become a problem?

• At 20 C (room temperature) the maximum amount of
  oxygen that can be dissolved is 9 ppm.
• If the water temperature is less than 20 C, it
  may have more oxygen dissolved in it.
• A dissolved oxygen level of 9-10 ppm is
  considered very good.
• At levels of 4 ppm or less, some fish groups
  (example- bass and trout) will begin to decline.
• Sludge worms and leeches are able to survive in
  water with low dissolved oxygen levels.

4
Sources of the Dissolved Oxygen

• Air consists of 21 percent oxygen and
  approximately 75 percent nitrogen by volume.
  Oxygen dissolves poorly in water and can only
  exist there at a low concentration.
• The level of oxygen in the water moves naturally
  during the day and night and also from season to
  season. This is because plants use
  photosynthesis, or make oxygen from sunlight,
  during the day and respire or use oxygen during
  the night.
• Low dissolved oxygen levels may occur during
  warm, stagnant conditions that prevent mixing.

5
The Impact Dissolved Oxygen has on the organism
in the water

• Total dissolved gas amounts in water should not
  be above 110 percent. Amounts above this level
  can be harmful to aquatic life.
• Fish in waters containing excessive dissolved
  gases may suffer from "gas bubble disease"
  however, this is a very rare occurrence. The
  bubbles or emboli block the flow of blood through
  blood vessels causing death.
• External bubbles (emphysema) can also occur and
  be seen on fins, on skin and on other tissue.
  Aquatic invertebrates are also affected by gas
  bubble disease but at levels higher than those
  lethal to fish.