Australia: The Land Where Time Began

A biography of the Australian continent 

The Effects of GAB Water on Soils

In Earth Alive, Mary White reports a case study of the sinking of a bore on a property in southwest Queensland in 1921 and the subsequent changes to the soils affected by the bore water that flowed down 70 miles of drains. Very large quantities of water soaked into the mulga loamy red earths and sandy loams. Melons and pumpkins were planted in the soaks along the drain and for the first few of years the vines grew prolifically, producing large pumpkins and melons. After a short time the soil was hardened, and the strongly acid soils were highly deficient in nitrogen and phosphorous.

Water birds brought the eggs of fish and yabbies in mud on their feet. The yabbies created havoc, their holes increasing seepage from the drains and riddled the ground around culverts and divisor plates. The drains flowed over much shorter distances and the ground around the drains became boggy. Feral pigs were also attracted. They ate yabbies but caused major problems with their digging, further increasing the water loss. Eventually the banks of the drains became so hard that the problems with digging animals were greatly reduced. Garden beds that were watered with the bore water became too hard to grow anything without the addition of large amounts of manure.

It has been estimated that the loss of water from the Great Artesian Basin since the first bores were sunk in the 1880s, more than 95 % of the water has been lost to seepage and evaporation. So much water has been taken out of the GAB that many bores have stopped flowing, the water needing to be pumped. Another effect has been the degradation of the land around the water sources as a result of not only stock but also feral and native animals overgrazing the area.

According to a report by scientists from the Department of Natural Resources in Charleville, extraction of artesian water has led to a reduction in the artesian pressure, its use on the surface has altered the hydrology of the surface, degraded land resources, and influenced social and economic development. Over the last 10-30 years there have been changes to areas around bore drains. The deleterious changes include scalded soil, soil erosion, reduced cover, increases of woody weeds, increased salinity and increased tree mortality. The seepage and wall breaches of the bore drains caused the same type of problems large-scale irrigation causes on a massive scale.

Some preliminary findings of a study of changes in soil chemistry are

  • The chemical characteristics of the soils most commonly in south-west Queensland
  • The artesian water is alkaline, mostly sodium bicarbonate, with some chloride and sulphate, accounting for the pH, electrical conductivity, chloride and exchangeable sodium
  • Exchangeable sodium percentage (ESP) is greatly increased, which affects the soil clay particles, causing them to swell and disperse, which changes the soil structure significantly
  • Sodicity leads to physical deterioration, hardsetting and increased erosion. The result is reduce plant growth.

 

Sources & Further reading

  1. Mary E. White, Earth Alive, From Microbes to a Living Planet, Rosenberg Publishing Pty. Ltd., 2003
  2. Mary E. White, Running Down, Water in a Changing Land, Kangaroo Press, 2000

 

 
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                                                                                           Author: M.H.Monroe  Email: admin@austhrutime.com     Sources & Further reading