A salty problem that won't go away

Despite the knowledge gaps, we can be sure to see the West Australian pattern being repeated across the country with more than 2 million hectares of native vegetation at high risk of salt damage nationwide. The greatest challenge for natural resource managers and policy makers is to keep the total, complex picture in view and to work with scientists and the community to continue to reduce the areas of uncertainty.

It is clear that salinity is but one more way by which humanity is inadvertently unravelling the fragile web of life. At least until we know more, a precautionary approach is essential. This means preventative action in the first instance, coupled with the prudent setting of salt reduction targets.

Australia is a Naturally Salty Place

Beneath the surface, Australia is a naturally salty country. Over the ages, sediments and salts have accumulated between the soil and deeper rock layers, and also in groundwater and some wetlands. These widely distributed salt stores have their origins in the long, steady spray of seawater, in the rains and the erosion of rocks.

Additionally, the distinctive flatness of much of the landscape, together with relatively low rainfall and high evaporation rates, means that our waterways are slow to flush the country clean of salt.

Many native plants have adapted to the dryness and relative infertility of the place by means of deep, thick roots, and are thus very effective groundwater pumps. Left standing, they tend to strike a balance between rainwater leaching downwards through the soil and groundwater transpired back up into the air through their foliage.

Prior to the coming of European agriculture the salt tended to stay underground. We have stripped much of the land bare – as much as 95% in some cases – replacing the original vegetation cover with shallow-rooted annual crops and pastures, as well as roads and roofs.

Inadvertently, we have stopped a natural water-balancing service across vast areas of the country.

Depending on the climate, soil and lie of the land, much more rainwater (‘recharge’) now makes its way underground, below the root zone, raising the level of the groundwater, waterlogging the soil and bringing the ancient salt with it.

The salt typically discharges into the lower-lying parts of the landscape first, ie. rivers, wetlands, or a neighbour’s property down the way. Such discharge sites can be at quite some remove from the cleared recharge zone.

Astoundingly – given what we now know – native vegetation is still being destroyed, predominantly in Queensland and New South Wales. Ours is the sixth worst clearing nation on Earth and the highest in the ‘developed’ world! It is as though we have learned nothing.

Since salinity is far easier to prevent than to remedy once it has taken hold, it is imperative we conserve remnant bushland.

Unfortunately, land clearing controls alone cannot stop the steady advance of salinity across our catchments already set in train decades ago. Nor are ‘technofixes’ - such as clever engineering schemes – feasible solutions beyond the short-term protection of important environmental, cultural and economic assets.