IB Environmental systems and societies 4.4B Water Quality Notes

Water quality is measured by direct chemical and physical tests plus indirect indicators like BOD

1. Water quality refers to the chemical, physical, and biological characteristics of water that determine its suitability for supporting life and human use.
2. Monitoring these parameters helps identify pollution sources, track ecosystem health, and guide restoration.

Direct chemical and physical tests each reveal a different pollution signal

1. Dissolved oxygen (DO)
   1. Oxygen dissolved in water is essential for aquatic life, and low DO signals organic pollution, eutrophication, or thermal pollution.
   2. It is measured with oxygen probes or the Winkler titration method.
   3. About 75% saturation indicates healthy water, while below 10% indicates severe pollution.
2. pH
   1. pH indicates the acidity or alkalinity of water, with normal freshwater ranging from about 6 to 8.
   2. Deviations suggest acid rain, industrial effluent, or alkaline runoff.
   3. It is measured with pH probes, meters, or litmus paper.
3. Temperature
   1. Temperature affects dissolved oxygen, metabolic rates, and species distribution.
   2. Warmer water holds less dissolved oxygen, so thermal pollution from power plants lowers oxygen solubility.
4. Turbidity
   1. Turbidity measures the clarity of water, reduced by sediment, organic matter, and algae, which lowers sunlight penetration for photosynthesis.
   2. It is measured with a Secchi disc or turbidity tube, where Secchi visibility below 0.5 m indicates heavy sediment or an algal bloom.
5. Nutrients (nitrates and phosphates)
   1. High concentrations come from agricultural runoff or sewage and drive eutrophication, causing algal blooms and oxygen depletion.