ASSESSING THE ACIDITY OF WATER DRAINING INTO RIVERS AND ESTUARIES

ASSESSING THE ACIDITY OF WATER DRAINING INTO RIVERS AND ESTUARIES

Introduction
Effect of Acidity
Visual signs
Testing pH

It is very likely that water in a drain or river is acidic, or at risk of becoming acidic, if you see any of the following signs:

Crystal-clear water - This often indicates that the pH is in the range 3 to 4. Although visually appealing, crystal clear water may indicate that the water contains high concentrations of aluminium, which is very toxic to fish.
Yellow-brown, turbid water - This is due to large amounts of iron that are leached by acidic water. The more intense the colour and turbidity, the greater the risk that acid will eventually leach into a river or estuary. The iron is dissolved when the pH is less than 4.
Iron flocs (particles) - Particles of iron minerals can occur in water below pH 4. They are usually coloured red-brown or brown-yellow. The particles may sit on the bottom as a sludge, or may float as a film on the water and look like an oil slick (you can tell that they are not an oil slick by poking the film with a stick - an iron film will break up into a number of "rafts" whereas an oil slick will not break up). Iron flocs generally form below a pH of 4.
Milky blue-green water - In coastal areas, this is caused by aluminium mineral flocs. The pH of water with this appearance is typically 4 to 5.
Scalds - These are bare patches in areas with swampy vegetation where the soil is particularly acidic. There may be dead trees and salt crusts.