Soil salinity in Australia This audiovisual uses historical and scientific evidence to show why Australia is so salty. Windows Media Player required Play it here: Broadband | Modem

Here is an extract from the script:

Salt. White death. All over Australia it's rising out of the ground and destroying our farms, homes and towns. To understand why we have this problem we need to go way, way back in Australia's history.

360 million years ago. Australia was once part of a huge supercontinent called Gondwana. It was joined to Antarctica, India, Africa and South America. Since then, a lot has happened to the land that became Australia...

300 million years ago. During a severe ice age part of it was covered by an ice sheet. As the ice moved across the land it ground up rock to make new soil. It was the last time new soil was made that way in this continent.

160 million years ago
Later...India broke away...

Flood plains 160 million years ago. The climate was much wetter than today and parts of Australia sank under the weight of river sediments

118 million years ago Still later, when the sea level rose, a lot of the land went under water.

84 million years. Then the east coast tilted up when it broke from the New Zealand sub continent.

84 million years. And at the same time...parts sank...

60 million. And continued to sink...

45 million years. When Australia finally broke free of Antarctica large areas were still sinking.

One of those areas forms the Murray Darling River basin which is the site of our biggest river system and major farming lands.

Today, the sinking continues and Australia is shaped like a giant shallow saucer. If you look at a cross section from east to west, you can see that Lake Eyre, near the centre, is well below sea level. This means that rain falling on much of the country drains inwards.

For millions of years clouds have dumped salt on the earth in rain. Because of the shape of the country, the salt hasn't been able to get back to the sea. It's had nowhere to go but into the ground. The water that took it there forms a layer of salty underground water. The top of that layer is called the water table.

Australia's native vegetation has evolved in harmony with the water cycle. Many trees and grasses are deep rooted, so they can take up most of the rain that falls on the ground. Because they grow all year, there's no time that water isn't soaked up. Not much water gets through to the ground water below so the water table stays at pretty much the same level.

We've disrupted the water cycle in two ways: by clearing vegetation and by pouring more water on the land when we irrigate for farming.

When European farmers cleared the land they planted shallow-rooted crops that grew for only part of the year, taking up a mere fraction of the water falling as rain. The excess water moved down to the subsoil. Eventually the water table rose, bringing salt to the surface.

This salt kills most plants and makes it impossible to grow crops. Without plant roots to hold the soil in place, the soil washes or blows away. Terrible erosion results.

One of the ways to reverse the problem is to plant deep-rooted trees, grasses or crops that can suck up the water out of the ground. This will lower the water table and allow the salt to go back down into the ground, below the root zone. Water can also be removed by pumping it out but that's very costly.

Irrigation presents another problem. Many of our crops are grown using water that's poured onto the land. Water seeps from irrigation channels and from over-watered crops into the water table. It's important to add just enough water to the soil to grow the plants because any extra water causes the water table to rise.

Every year Australia loses large areas of farming lands to salt. If we don't turn this situation around quickly we'll have difficulty feeding ourselves. We need to change our landuse patterns, and start gaining income from the native plants that grow so well in our landscape.

It's not only plants that are affected by salt. Homes across Australia are crumbling as salt eats away at the foundations and walls. Houses built to last 25 years are surviving only 2 years.

By growing native trees and shrubs around homes and reducing the size of the lawn, the need to water the garden can be reduced. This stops water seeping into the water table.

Playing fields, footpaths, swimming pools and the whole infrastructure of towns and cities is damaged by salt.

Roads, too, crumble when attacked by salt. Roads need four times the amount of maintainance where water tables are high.

We're all in this together. Australia was made rich from the agricultural exports of the last two centuries. The wealth in the towns and cities flowed from government initiatives to clear and use the land. History has caused the problem we face. The future is up to us.