How did so much salt get from the oceans and seas onto the land?

We think most of it has come in from wind blown accession from the oceans. Something like 20 to 200 kilograms per hectare per year. Because Australia wasn't swept clean by the ice sheets 10,000 years ago like in the northern hemisphere, we've had soils that have been accumulating salts for hundreds of thousands of years. If you do your sums you can soon account for a lot of the salt that's in the Australian landscape simply from wind blown accession from the oceans.

Dr David Chittleborough
Adelaide University

How much salt is in Australia's landscape?

Salt has been accumulating at a rate of about 20 kilograms per hectare for probably 30 to 100,000 years. In areas like the south west of Western Australia there is probably 5,000 to 10,000 tonnes of salt stored under every hectare.

Richard George
Agriculture WA

Is the salt in the ground the same as the salt I put on my fish and chips?

Yes. Principally its sodium chloride, something you put on your food every night or perhaps not if you are health conscious. It's principally sodium chloride, there are other ones but that's principally the one.

Dr David Chittleborough
Adelaide University

New Zealand has no problems with salinity because its rivers take the salt off the land and back out to sea. Why doesn't that happen here?

Australia is so different from any other land. Rivers normally build on high ground and run briskly down slopes and disappear into the sea. When rivers behave like that around the coastal parts of Australia any excess salts that get into river systems is carried back into the sea. However most of our major rivers rise on the western flanks of the Great Dividing Range and they don't run briskly down slopes and into the sea, they run into a very flat landscape. In the case of the Murray Darling it's our major river system and it travels mainly westward and then it has one very small exit to the sea. So you've got inward flowing rivers in a continent with a sunken centre. You end up with a very flat land, it gets flatter and flatter retaining its sediment and it becomes a land of flood plains and at the same time of course it is retaining its salt.

Mary White
Palaeobotanist

How did Australian plants deal with this salt prior to European colonisation?

Prior to clearing nearly all rainfall would have gone into the ground and been used by plants and trees. The roots of some trees go down 30 to 40 metres. They are very hungry for water so they don't let anything drain through the root chain. Around about a cup of water per square metre was all that ever made it through and that would have been on an occasional basis. The salt was still there but it was kept at a depth where it wasn't a great problem.

Richard George
Agriculture Western Australia.

Why has salinity become such a problem in Australia recently?

What we have done since European settlement is we've actually changed profoundly the water balance in the landscape. The vegetation, the woody trees and shrubs and perennial grasses had come to one way of living with the salt. What they have done is they have used all the water possible through evaporation or through runoff and so very little water in the native vegetation moved past the root zone. Now when we came along we tended to take out the deep-rooted trees and shrubs and perennial native grasses and now a great deal more water dribbles past the roots zones of our pastures and our annual crops.

To give you some indication of the size of that, in terms of numbers, before we interfered with the system the amount of water that dribbled beneath or leaked beneath the native root system was between half a millimetre and maybe five millimetres a year. Now, under our agricultural system, under our annual crops and annual pastures, that number can be as high as 50 or in some cases even as high as 150 millimetres, so we have seen a 10 fold change in the amount of water that is being pushed into the landscape. So if you can push water into the landscape in large rate compared to the small rate it can get out, it must fill up and bring the salt into our rivers and into the lower parts of the landscape as you see behind me here.

Dr John Williams
CSIRO Land & Water

When will Australia's hydrology again be balanced?

On a broad scale approach current estimates are maybe between 100 and 200 years. Obviously in certain catchments they may achieve that early on and some may take a lot longer but broad scale estimates are 100 to 200 years.

Hugh Middlemis
Institution of Engineers

When did science make the link between land clearing and dryland salinity?

The first evidence in Western Australia of salinisation as a consequence of land clearance goes back to the 1890s when railway engineers started to notice that their water supplies and dams they had developed for the rail had been salinising, and they began to link it causally to land clearance. The landmark scientific paper that established it beyond all reasonable doubt of that link between land clearing and salinisation was published in 1925 - so for 75 years we have known what causes salinity. Whether we have heeded that advice is another question.

Dr Tom Hatton
CSIRO Land & Water

What causes rivers to go salty?

The salt is getting into the water through two main mechanisms. It is coming from overland flow where we've got rain falling on salt affected land, and it's also coming into the rivers from groundwater - especially where the rivers are low. For instance, when the Darling is especially low, the groundwater starts to flow in and that puts salty water into the river.

Professor Peter Cullen
Co-operative Research Centre for Freshwater Ecology

Why does irrigation cause salinity?

When we decided to move to irrigation, not only did we take the deep-rooted trees and shrubs out we, also allowed more water to leak below the root zone. No matter how well and how skilfully we irrigate it's very hard to stop water moving past the root zone of our irrigated crops - whether they are fruit trees or rice paddies. Under irrigation we have increased it not 10 fold but sometimes 100 fold, and thus we have all the driving force for irrigated salinisation.

Dr John Williams
CSIRO Land & Water

How does salinisation affect fish, birds and other species that rely on wetlands?

Too much salt in our rivers is just like another pollutant such as oil or pesticides. As we increase that level of pollution in our rivers the species retreat more and more into smaller areas and refuges away from salinity. A good example is the Macquarie Marshes - a wonderful wetland where the salinity level predicted to hit the marshes in 30 years is 1500 EC units, which is the level at which we are set to lose whole plant communities. Fish species are in real trouble, and invertebrates are well and truly disappeared in many of the river systems.

Dr Stuart Blanch
Australian Conservation Foundation

What does salinity do to agricultural crops?

What we are doing essentially is making the plant suffer a drought. The salt has an osmotic effect. By osmotic, I mean it dries out the water in terms of the plant's ability to extract it. Now the plant essentially suffers a drought under salting. Also the excess amount of sodium causes an imbalance in the other nutrients in the plant needs such that the plant suffers nutrient deficiency as well.

John Williams
CSIRO Land & Water

Why have engineers installed pumping sites in the Murray Darling Basin and how do they help control salinity?

Engineering solutions really have brought us the space for the last decade otherwise the River Murray would be in a very parlous state. To put it in context we need to look at it like this. Along the river Murray I have 80 kilometres of bore field, that's 80 kilometres of the river with bores along pumping 1100 tones of salt away from the river every day 365 days a year. That costs us as a community two million dollars a year in power. Now if we were to switch those pumps off the River Murray would be unusable for two, three or four months each year. That's reality and that intervention has already occurred and without it we wouldn't have the luxury to have a look at land based solutions.

Don Blackmore
Chief Executive, Murray-Darling Basin Commission

How much does Adelaide and other South Australian cities rely on the Murray River for water?

The River Murray is really a vital water resource for South Australia. Adelaide, for example, in an average rainfall year it gets about 40% of its water resources from the River Murray, but in drought years it can be as high as 90% - and there are many other towns in South Australia that rely 100% on water from the River Murray for its water supply.

Professor Don Bursill
Co-operative Research Centre for Water Quality and Treatment

What are some signs of urban salinity?

The sort of tell-tale signs are dampness under houses, vegetation dying, roads breaking up, salt in table drains and in the gutters of roads. What tends to happen with older houses is a combination of the damp course failing and the groundwater table rising to near the surface. A brick is like a sponge and it will draw the water up and in some places where the damp course is maybe 60, 70 years old the water will rise up to two metres up the wall. If that wall is exposed to sunlight on a regular basis then salt crystals will form and that will start to fret away the surface of the brick. Over a period of time with that continuous wetting up and drying by the sun the structure of the bricks disintegrates completely and you'll end up with holes in the bricks you can put your fist through. It also impacts on the render inside the house and we start to see render falling off inside the houses, which can be up to a metre inside the house you will get render falling off.

Bryan Short,
Wagga Wagga City Council

What causes urban salinity?

We have salts in our soil, and when urban development goes ahead and we increase the amount of water going into our soils we mobilize salt as you do in a ground water situation. The salts will affect buildings, roads and parkland areas. What we tend to do in urban development is use a lot more water. We water our gardens and our lawns, we build concrete structures and the roofs get a lot more run off them, so there's more water from that source. We also have pipes under our houses that sometimes are leaking, and that adds more water to the system as well.

Rebecca Nicolson
Salinity Officer Western Sydney

What should I look for at my house?

The first signs would be the white effervescence on the concrete paths, lawns or brickwork. If you see a white salt, touch it with your finger and see if it tastes like salt. If it is then you should get a civil engineer around to look at what they can do to rectify that problem whether it is local drainage or it is an urban salinity problem. If your dampcourse has broken down then a civil engineer can give correct advice on how to correct the damage caused by the rising damp.

Greg Bugden
NSW Land & Water Conservation

Why does salinity affect roads?

With bitumen it doesn't matter if the water is salty or fresh - if you have water ponded under bitumen it will break it up. That's why you have potholes in roads for example. So it's almost like infrastructure cancer due to too much water and salt being in close proximity to construction materials.

Hugh Middlemis
Institution of Engineers

Has salinity occurred in other countries?

There's significant evidence to suggest that there has been some salinisation or at least changes in climate that have affected irrigation in the Middle East going back 6,000 years. The plains of Canada are very similar to Australia in that there is very low topography and they have about two and a half million hectares that are affected by salinity. Other areas include India, central Asia and California.

Dr Warren Wood
Oxford School of Geography & the Environment.

How will Australia be affected by salinity?

I guess it's really hard to exaggerate the problems we face. I am not one to say the sky is falling in but this is one environmental problem, which would have to be one of the most serious environmental problems anywhere in the world. We are looking at losing 8 million hectares of land. We have already lost 44 species. We could lose 450 species off planet Earth forever. We are looking at disastrous consequences to infrastructure like roads and to hundreds of towns and even flooding of coastal cities, so it's a major environmental problem.

Dr Syd Shea
University of Notre Dame Australia