Lime, acid and salt: a fishy mix

Sally-Anne Penny and colleagne liming a dam. Aquaculture gaining popularity as a diversified

Lime is being used successfully to increase the pH of saline groundwater, according to Merredin Soil Acidity Development Officer Sally-Anne Penny.

At a Mukinbudin dam, groundwater has seeped in to a depth of 1 metre, and the water quality in the dam is around one-third the salinity of seawater, with very low pH, Ms Penny said.

She is working with Peter Lacey from the Outback Ocean Project to calculate the amount of lime required to increase the pH of the dam water in a farm aquaculture project.

Limesand with an approximate neutralising value of 93 per cent and a particle-size fineness of 100 per cent was applied at the rate of 4 t/ha of dam surface.

The aim was to increase the pH of the water to between 6 and 8, to provide a suitable environment for rainbow trout.

Ms Penny said that two weeks after the addition of lime, the water pH had increased to 7. "As well as increasing pH, lime has the added benefit of increasing the ability of the dam water to buffer any further changes in pH, making a more stable environment for the rainbow trout," she confirmed.

"Rapid changes in pH are stressful to fish, so stabilising the pH at the critical level is the key to healthy growth."

Once the pH was steady at 7, the dam was seeded with local zooplankton, weed and micro-organisms. Sheep manure was also added as a nutrient source. The organisms and nutrients assist in establishing an ecosystem suitable for trout growth. The dam was populated with one-year-old rainbow trout fingerlings weighing about 50 grams each.

Contact: Ms Sally-Anne Penny 08 9081 3104