Dissolved oxygen

Dissolved Oxygen (DO) is important to the health of aquatic ecosystems. All aquatic animals need oxygen to survive. Natural waters with consistently high dissolved oxygen levels are most likely healthy and stable environments, and are capable of supporting a diversity of aquatic organisms. Natural and human induced changes to the aquatic environment can affect the availability of dissolved oxygen.

Dissolved Oxygen % Saturation is an important measurement of water quality. Cold water can hold more dissolved oxygen than warm water. For example, water at 28*C will be 100% saturated with 8 ppm dissolved oxygen. However, water at 8*C can hold up to 12 ppm of oxygen before it is 100% saturated. High levels of bacteria from sewage pollution or large amounts of rotting plants can cause the % saturation to decrease. This can cause large fluctuations in dissolved oxygen levels throughout the day, which can affect the ability of plants and animals to thrive.

Dissolved oxygen procedure

  • Record the temperature of the water sample (see page 30).

  • Submerge the small tube (0125) into the water sample. Carefully remove the tube from the water sample, keeping the tube full to the top.

  • Drop two Dissolved Oxygen TesTabs' (3976) into the tube. Water will overflow when tablets are added.

  • Screw the cap on the tube. More water will overflow as the cap is tightened. Make sure no air bubbles are present in the sample.

  • Mix by inverting the tube over and over until the tablets have disintegrated. This will take about 4 minutes.

  • Wait 5 more minutes for the color to develop.

  • Compare the color of the sample to the Dissolved Oxygen color chart. Record the result as ppm Dissolved Oxygen.

    Locate the temperature of the water sample on the % Saturation chart. Locate the Dissolved Oxygen result of the water sample at the top of the chart. The % Saturation of the water sample is where the temperature row and the Dissolved Oxygen column intersect. For example: if the water sample temperature is 16*C and the Dissolved Oxygen result is 4 ppm, then the % Saturation is 41.

    % Saturation

      0 ppm 4 Pom 8 ppm
    2 0 29 58
    4 0 31 61
    6 0 32 64
    8 0 34 68
    10 0 35 71
    12 0 37 74
    14 0 39 78
    16 0 41 81
    18 0 42 84
    20 0 44 88
    22 0 46 92
    24 0 48 95
    26 0 49 99
    28 0 51 102
    30 0 53 106

    * Calculations based on the solubility of oxygen in waterat sea level from Standard Methods for the Examination of Water & Wastewater, 18th Edition.