Physico-chemical indicators

There are a number of key indicators that can be monitored to measure the physico-chemical condition of waterways.  The indicators you choose to monitor will depend on what questions are being asked about the quality of water in a particular waterway.

Detailed information on each indicator, including why it is important, environmental factors that affect it, important details to consider when monitoring it, and monitoring methods are available from the Queensland community waterway monitoring manual, Chapter 5 (Physico-chemical monitoring methods).

Indicators

Dissolved oxygen — DO is a measure of the quantity of oxygen present in water. Oxygen is essential for almost all forms of life.

Electrical conductivity — Salty water conducts electricity more readily than purer water. Therefore, electrical conductivity is routinely used to measure salinity.

Flow — Stream velocity and discharge are among the most important of physical conditions. The amount of water and the rate at which it moves affects both ambient water quality and its downstream impacts.

Nitrogen — Nitrogen compounds can be found naturally in surface waters and in groundwater. High concentrations of nitrogen in water bodies are often the result of human activities. Nitrogen compounds commonly measured in waterways include nitrate, nitrite and ammonia.

Phosphorus — The phosphorus found in both surface water and groundwater is in a form called phosphate. It is naturally derived from the weathering of rocks and the decomposition of organic material, but it can also enter waterbodies as runoff or discharge. Soil and fertiliser particles can carry phosphorus and sewage is also rich in phosphorus.

pH — Refers to the acidity or alkalinity of the water which affects the survival of aquatic life. Pure water has a pH of 7, acidic solutions have lower pH values and alkaline solutions have higher values.

Turbidity (water clarity) — Refers to the opacity or muddiness caused by the amount of suspended particles (clay, silt, sand, algae and other substances). Turbidity affects how far light can penetrate into the water.  

Water temperature — The temperature of a waterbody directly affects many physical, biological and chemical characteristics. Warm waters are more susceptible to eutrophication (a build-up of nutrients and possible algal blooms) and oxygen is less soluble in warmer water which can affect aquatic life.

Last updated 19 February 2008