The Trees Couldn’t Survive Australia’s Salt Flats. The Fish Could.

Part 1

In 1989, Australia set itself a deadline that sounded less like an environmental program than a wager against the land.

One billion trees.

Ten years.

The purpose was not beautification, timber, or even conventional reforestation. The trees were supposed to hold back an enemy most people could not see.

Salt.

It was already costing Australian farmers more than half a billion dollars every year, but the real damage was happening quietly underground. Across enormous stretches of agricultural country, groundwater was rising through ancient deposits of salt and carrying that salt toward the surface. Productive soil was turning white. Crops weakened. Pastures disappeared. Roads cracked. Wetlands deteriorated.

The government responded on a scale appropriate to the threat. Heavy machinery cut planting rows through hardened ground. Eucalyptus, acacia, and native shrubs went into degraded country by the millions.

Then by the tens of millions.

Then by the hundreds of millions.

Australia reached the billion-tree target ahead of schedule.

In some places, it worked.

The young shelter belts drew water from the soil. Water tables dropped three to six feet. Roots held vulnerable topsoil together. Wind erosion declined. Protected patches developed better microclimates, and pasture grasses began creeping back into places where farmers had watched them disappear.

For a while, the enormous gamble seemed justified.

Then came the worst of the salt country.

There, in some of the most badly affected areas, more than eighty percent of the eucalyptus and acacia seedlings died during their first season.

The trees had been planted to defeat the salt.

The salt killed the trees.

To understand why, it was necessary to look much farther back than 1989—farther back than Australian agriculture, farther back than European settlement, and even farther back than the landscapes people recognized as modern Australia.

Millions of years earlier, shallow inland seas had covered large areas of the continent. When those seas disappeared over geological time, they left salt behind, buried beneath sediment, clay, and rock.

That ancient inheritance was only part of the problem.

Ocean winds carried salty particles inland and deposited them over the continent. Large river systems drained toward the interior rather than efficiently carrying their dissolved minerals out to sea. Australia’s dry climate then completed the process: evaporation removed water but left minerals behind.

Year after year, century after century, millennium after millennium, salt accumulated.

Billions of tons of it lay beneath the land.

Yet for a very long time, the landscape had its own defense.

Mallee eucalypts and other deep-rooted native vegetation sent roots astonishing distances underground—sometimes sixty-five to one hundred feet. Those roots acted as biological pumps. Rain fell, entered the soil, and was taken up by vegetation before too much of it could penetrate deeper underground. The trees released much of that water back into the atmosphere through their leaves.

The system was not designed by anyone.

It simply worked.

As long as the deep-rooted vegetation remained, the groundwater stayed low enough that much of the buried salt remained buried.

Then the trees disappeared.

European settlement brought an agricultural transformation to enormous areas of the continent. Government-backed programs encouraged the clearing of native woodland for wheat and other agricultural production. Roughly forty-four million acres of native woodland were removed.

Deep-rooted perennial vegetation was replaced by shallow-rooted crops.

To a farmer standing on the surface, the change was obvious: woodland had become agricultural land.

Underground, another transformation had begun.

Rain that once encountered thirsty tree roots could now move deeper into the soil. The shallow crops used only part of it. More water entered the groundwater system.

The water table began rising.

In some places, it climbed more than three feet in a year.

Eventually, it reached the old salt deposits.

Fresh groundwater dissolved the minerals and became brine. Then the rising water carried that salt upward, closer and closer to the roots of crops, grasses, and young trees.

The result looked almost impossible.

Plants could stand in visibly wet ground and still die of thirst.

The explanation was chemistry.

Ordinarily, plant roots absorb water from the soil through differences in water potential across their cell membranes. But when the soil contains sufficiently concentrated salt, that relationship changes. The saline ground can effectively draw water away from plant tissues rather than allowing the roots to take it up.

The field can look wet.

The roots can be surrounded by moisture.

And the plant can still dehydrate.

By the time the scale of the problem was understood, vast areas of productive land had been damaged. Around fourteen million acres had become barren, salt-crusted country.

The destruction did not stop at farm fences.

Salt affected more than twelve thousand miles of roads, corroding metal and damaging pavement. More than a thousand miles of rail infrastructure deteriorated. Hundreds of rural towns faced drinking-water problems. Wetlands of national significance lost ecological function.

In the Murray-Darling Basin, the consequences were measured in hundreds of millions of dollars a year through agricultural losses and damage to infrastructure.

Salinity was not simply a farmer looking across a field where wheat would no longer grow.

It was a regional problem spreading beneath farms, towns, roads, rivers, and wetlands.

And Australia’s first great answer was to put the trees back.

The logic seemed impeccable.

Trees had once controlled the water table. Clearing them had helped the water table rise. Therefore, restoring trees should push it down again.

Hence the billion-tree effort.

And in less severely affected places, that reasoning had merit. Trees did stabilize soil and use groundwater. Shelter belts did help. Vegetation did return.

But the places most desperate for rescue presented a brutal contradiction.

They needed deep-rooted vegetation most.

They were also too salty for young deep-rooted vegetation to become established.

Seedlings could not instantly produce roots sixty or one hundred feet deep. First they had to survive near the surface.

And near the surface was exactly where the salt was waiting.

The revegetation effort therefore encountered a limit that money and planting numbers could not simply overwhelm. You could put more seedlings into the ground, but if the chemistry around their roots prevented them from taking up enough water, planting another million did not change the chemistry.

The worst land remained the worst land.

The salt had created a trap.

To repair the landscape, Australia needed vegetation.

To grow the vegetation, Australia needed to reduce the salt.

To reduce the salt naturally, Australia needed the vegetation.

The large-scale approach eventually gave way to Landcare and more targeted, locally informed strategies. But in the most damaged areas, another question remained.

If the salt could not simply be planted away, what could be done with it?

At Wakool in southwestern New South Wales, engineers attacked the problem from beneath.

Drilling crews sank hundreds of wells into the saline aquifer. Fifty-four submersible pumps were installed. Instead of waiting for trees to intercept groundwater, the system physically pulled the saline water out.

At its peak, more than nine million gallons of brine could be pumped every day.

The water had to go somewhere.

Large synthetic-lined evaporation ponds appeared inland, holding water that nobody wanted in the soil. A similar operation functioned in South Australia.

The objective was straightforward.

Pump saline groundwater.

Lower the water table.

Protect the surrounding land.

Then someone examined the water itself.

That was when the story changed.

Mineral analyses showed something remarkable about the underground brine. In important respects, its chemistry resembled seawater.

Here was water being treated as an agricultural waste product—water extracted from beneath damaged inland farms precisely because it was too salty for conventional agriculture.

But if the water behaved like seawater, perhaps asking what crops could tolerate it was the wrong question.

Perhaps the better question was what normally lived in saltwater.

The answer was sitting hundreds of miles away on Australia’s coastline.

Barramundi.

Tiger prawns.

Brine shrimp.

Marine life.

The idea sounded almost perverse. Australia had spent years trying to save inland country from salt, and now scientists and engineers were considering deliberately putting marine animals into ponds filled with that same saltwater.

It was not the kind of solution anyone would have proposed when the billion-tree target was announced.

Yet the trees had revealed the central lesson.

The salt could not be ordered away.

Chemistry did not care how ambitious the program was.

So the next experiment would begin with the chemistry exactly as it existed.

They would bring the ocean species inland.

The first problem was getting them there alive.

Specialized tanker trucks were equipped with liquid oxygen systems, ammonia filtration, and refrigeration. The water had to be held near seventy-two degrees Fahrenheit while the trucks crossed country where outside temperatures could reach 113 degrees.

The journey could take twenty hours.

A cooling failure was not an inconvenience. A severe temperature shift could kill an entire shipment.

The animals survived the road.

They reached the inland ponds.

After all the machinery, all the planning, all the distance, and all the effort, the experiment had finally reached the moment that mattered.

The fish entered the brine.

Then they began to die.

Within days.

The water looked right.

The overall salinity seemed right.

The fish had survived the desert crossing.

Yet something inside those ponds was killing them.

Once again, Australia had reached the same infuriating point it had reached with the trees.

The broad idea appeared sensible.

The living organism entered the salt-affected environment.

And the chemistry won.

But this time, the scientists did not have a billion seedlings spread across a continent.

They had fish dying in controlled ponds.

And that meant they could ask a much more precise question.

Not whether the water was salty.

But exactly what was in the salt.

Part 2

A team led by Dr. Jeff Allan at the New South Wales Department of Primary Industries began breaking down the brine mineral by mineral.

The distinction mattered.

Calling something “saltwater” made it sound simple. Natural seawater, however, was not merely fresh water with sodium chloride stirred into it. It was a complex mineral environment. Marine animals had evolved within particular chemical balances, and matching the overall salinity did not necessarily reproduce those balances.

The inland brine had passed the obvious test.

It was salty enough.

But the fish were demonstrating that the obvious test was insufficient.

The investigators found a critical deficiency.

Potassium.

For barramundi trying to live in the inland brine, that missing mineral was not a minor nutritional inconvenience. Potassium was essential to the mechanisms that allowed their cells to regulate the movement of water and salts.

Without enough of it in the surrounding environment, the fish began drawing on their own reserves.

Muscle tissue deteriorated.

The animals had made a twenty-hour journey across punishing desert heat only to enter ponds where an invisible imbalance was destroying them from within.

There was a bitter symmetry to it.

The seedlings had died in wet soil because salt interfered with their ability to manage water.

Now fish were dying in water because the wrong balance of minerals interfered with their ability to manage salt and water.

The entire Australian salinity crisis seemed determined to teach the same lesson repeatedly: appearances were not chemistry.

Then came the solution.

Potassium chloride.

Ordinary industrial fertilizer could supply the mineral that the brine lacked.

Engineers added it in large quantities and adjusted the water until its mineral profile more closely resembled the environment the fish required.

The result transformed the experiment.

Barramundi survived.

Then they did more than survive.

They grew.

Under the stable inland conditions described by the project, they could reach market size in around eight months rather than the roughly fourteen months associated with conventional ocean farming. Reported growth rates ran thirty to forty percent above conventional coastal operations.

The desert ponds offered something the coast could not easily provide: isolation.

Hundreds of miles of dry Australian interior separated the fish from many marine pathogens and parasites. Temperatures could be controlled. The water chemistry could be adjusted. Instead of accepting whatever conditions the ocean delivered, operators could manipulate the environment.

For the first time, the very remoteness that had made the experiment look absurd became an advantage.

Then the tiger prawns exposed another weakness.

The prawns would molt as they grew, shedding their old shells and producing new ones. During that vulnerable period, the new shell needed to harden.

In the inland brine, it did not harden properly.

The problem was magnesium.

Without sufficient magnesium, newly molted prawns remained dangerously soft. In crowded aquaculture conditions, vulnerability quickly became mortality. Other prawns attacked them.

Cannibalism devastated batches.

Again, the project came down to a missing mineral.

Again, the water was adjusted.

Magnesium salts were added.

The shell-hardening problem was corrected, and the prawns began growing successfully. Reported growth could reach roughly twice the rate of ocean counterparts under the project conditions.

The pattern was becoming clear.

The inland brine was not natural seawater.

It did not need to be discarded for that reason.

It needed to be understood.

Potassium for the fish.

Magnesium for the prawns.

Precise intervention instead of a broad assumption.

That principle extended to another creature: artemia, the tiny brine shrimp famous for tolerating water too saline for most aquatic animals.

Artemia offered more than another commercial species.

They could consume organic material and convert it into protein-rich biomass, which could in turn serve as live feed.

A rudimentary biological cycle began to emerge.

Brine pumped from beneath salt-damaged farmland could support aquaculture. Aquaculture produced organic waste. Brine shrimp could use some of that waste.

But fish and prawns still produced enormous quantities of nutrient-rich water.

The next problem was what to do with it.

Sending it back onto ordinary fields would merely return saline water to land already suffering from salinity.

The answer was not ordinary crops.

It was plants that had spent their evolutionary history learning to tolerate salt.

Salicornia—often called sea asparagus—could grow in saline conditions that would destroy wheat or many pasture plants. Its roots could absorb nutrients such as nitrogen and phosphorus from aquaculture water.

That made the plant both crop and filter.

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