Colac Otway Shire Council - Descriptions - Parameters Tested
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   Page Last Updated:
 Thursday, 3 May 2007
 Home>Lake Colac>Water quality and testing>Lake Colac Catchment Monitoring Program - 2007/08>Descriptions - Parameters Tested  
Descriptions - Parameters Tested  Printer Friendly

Turbidity refers to how clear the water is:
The greater the amount of total suspended solids (TSS) in the water, the murkier it appears and the higher the measured turbidity. The major source of turbidity in the open water zone of most lakes is typically phytoplankton which are microscopic floating plants, mainly algae, that live suspended in bodies of water and that drift about because they cannot move by themselves.

Particulates may also be clays and silts from shoreline erosion. This is often what causes the "foam" which can appear on Lake Colac on a windy day.

Electrical Conductivity (Salinity)
EC is controlled by:

Geology - The rock composition determines the chemistry of the watershed soil and ultimately the lake.

The size of the lake basin relative to the area of the lake - A bigger watershed to lake surface area means relatively more water draining into the lake because of a bigger catchment area and more contact with soil before reaching the lake.

Other sources of ions - eg. wastewater, urban run off from roads, soil and pesticides

Evaporation of water from the surface of a lake concentrates the dissolved solids in the remaining water - and so it has a higher EC.

pH is a measure of acidity (or alkalinity). Pure water has a pH of 7; acidic solutions have lower pH values and alkaline solutions have higher values. Values of pH range from 0 (highly acidic) to 14 (highly alkaline). Where water has no net alkalinity or acidity it is said to be neutral and has a pH of 7. pH can be a little misleading unless you remember that one pH unit represents a ten-fold change.
So if the pH of a water sample falls from pH 7 to pH 6, that is equivalent to a 10-fold increase in acidity.

All animals and plants are adapted to specific pH ranges, generally between 6.5 and 8.0. If the pH of a waterway or waterbody is outside the normal range for an organism it can cause stress or even death to that organism.
Changes of more than 0.5 pH units from the natural seasonal maximum or minimum in fresh water should be investigated.

Dissolved Oxygen
Dissolved oxygen analysis measures the amount of gaseous oxygen (O2) dissolved in an aqueous solution. Oxygen gets into water by diffusion from the surrounding air, by aeration (rapid movement), and as a waste product of photosynthesis. Total dissolved gas concentrations in water should not exceed 110 percent. Concentrations above this level can be harmful to aquatic life. Adequate dissolved oxygen is necessary for good water quality. Oxygen is a necessary element to all forms of life. Natural stream purification processes require adequate oxygen levels in order to provide for aerobic life forms. As dissolved oxygen levels in water drop below 5.0 mg/l, aquatic life is put under stress. The lower the concentration, the greater the stress.

Phosphorus is an important nutrient for plant and animal growth. Excess phosphorus is a concern because it can stimulate the growth of algae. High phosphorus levels consistently recorded at a certain stormwater drain could, for example, indicate an ongoing pollution source eg. detergent being allowed to go to stormwater.


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