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|Acid soils and algal blooms|
|While salinity gets most of the attention, acid sulfate soils exposed by cavalier development can have dangerous as well as damaging side effects. This major Canberra Times feature by Phil Dickie was one of the earliest and most comprehensive examinations of what are sometimes called “the nastiest soils in the world”. Originally published on 3 June 2000|
|No-one yet knows what caused toxic algae to suddenly spread over 38 square kilometres of Moreton Bay off Brisbane this year, but one prime suspect is the discharge from acid sulfate soils drained and dredged to provide prestige canal estates.|
The dyke building Dutch have known about the dangers of acid sulphate soils for more than four centuries. Much of the rest of the world is only now finding out about problems that are going to take much more than a few tons of seashells on the polders to fix.
In large areas of coastal Australia, acid sulfate soils disturbed for development or agriculture have for decades been leaking a cocktail of nasties into waterways which are now playing havoc with water supplies, building foundations, fish populations and the grand plans of governments and business.
Overseas, researchers associate acid sulfate soils with alarming effects on human health as well as agriculture and fisheries. In Bangladesh and West Bengal, 70 million people are being poisoned by vast quantities of arsenic being liberated from acid sulfate soils exposed to oxidation through the sinking of too many bores.
Elsewhere in Asia, where potential acid sulfate soils are believed common, villagers from Vietnam to Indonesia are suffering the stunted growth, poor health and mental impairment that comes from drinking waters contaminated with acid mobilised aluminium.
Australia’s first acid sulphate linked drinking water contamination scare occurred three years ago at Evans Head on the New South Wales north coast. Many residents turned to drinking bottled water and installing rainwater tanks after investigations into mysterious plumbing failures revealed heavy metal contamination of their water.
“I’ve never seen anything like it,” said local plumber Ron McLean after being called back to a house where pipes had failed. “I cut open the pipe and all this green gunk came out.” After his piping suppliers had exonerated themselves, he took his samples to Southern Cross University, in part to forestall any talk of him “using cheap Indonesian copper or something like that”.
The scientific investigation pointed the finger at bore water used to supplement water supplies in the rapidly growing coastal strip. Water going to Evans Head is not acidic but the acid sulfate soil from which it is partly drawn contributes hydrogen sulphide (or rotten egg) gas which produces sulphuric acid at joints or internal irregularities inside piping.
The investigation found that “Many of the tap water samples collected from houses in the Evans Head area had highly elevated lead and copper contents and in several samples the lead or copper concentration, or both, was well above the safety limits set for human consumption in Australia; water from these taps is unfit for human consumption.”
Local councils on the coastal strip have been dealing with the cost of acid sulfate soils for many years, mainly unknowingly, as they have been forced to replace infrastructure decades ahead of schedule. The specialist magazine Concrete Constructions reported on a highway bridge collapse in the Kakadu area of the Northern Territory, where concrete pylons with a design life of 200 years eroded away in 30. Concrete cancer isn’t a label much used in the technical press but it has been remarked on and wondered about by engineers for years.
Australian authorities have worked hard to remain so blissfully unaware of potential acid sulfate soil problems for so long. A Dutch soil scientist, working in West Australia in the 1920s, was the first to point out the presence of highly acid soils and caution authorities about their casual development. The warning was ignored and the reference forgotten until resurrected by Australian scientists a few years ago.
It was known, even then, that acid and metal leachates in old mine tailings were poisoning a number of Australian rivers, including the Molonglo, site of the soon to be built national capital of Canberra. The predominant response was to allow the mine sites to continue poisoning the rivers for decades more with action only being taken on some sites in relatively recent times.
But the real credit for “discovering” the coastal acid sulfate problem should probably go to CSIRO soil scientist Dr Pat Walker, who spent a mammoth 15 years trying to find reasons for declining pasture quality in the Kempsey area.of NSW. Starting in 1957, Walker examined the land during drought and flood, “seeing the country in all its moods, finding out what its processes were”.
Soil cores, up to 13 metres down, were hand-drilled using one inch water pipe, something Dr Walker described as “character building – we weren’t getting any hardship money back then”. In the Clybucca swamp, strongly acid water blistered his feet and attacked the metal of his spade, although he noted an unexpected benefit – “I didn’t get tinea for months”.
“In the end, the problem seemed to be in the floodplain, with the acidity and the salinity from all the sulfates” he said. “It seemed to me that these processes would be similar in most coastal flood plains on the east coast.”
In 1972, Walker noted in a journal article that between 400,000 and 600,000 hectares of coastal New South Wales could be affected and warned that “Artificial drainage undertaken without regard to details of stratigraphy could lead to severe acidity and salinity conditions which in backswamp soils could be ameliorated only over a long period”.
The warning went largely unheeded. “I guess I was a voice in the void,” said Dr Walker. One far-sighted NSW agricultural officer tried to interest his department in developing a backswamp soil management program; the department and its farmer clientele however remained intent on drainage, clearing and cultivation and the officer, it is said, was rewarded for his heroism with the sack.
It took a massive fish kill on the Tweed River to finally highlight the problem A long drought followed by heavy rain in March 1987 effectively sterilised a 23 kilometre stretch of the river. Most assumed, as they had in the case of numerous smaller fish kills, that pesticide run off from cane farms was the culprit although a minority of dissenters, including the cane farmers, were pointing the finger at a local quarry.
It was Tweed Shire entymologist Clive Easton, out on mosquito patrol, who noted two peculiarities – what should have been turgid floodwater was unnaturally clear and that mosquito wrigglers were unaffected by whatever it was that had killed all other life.
“If it had been pesticide, the wrigglers would have been be the first to go,” he said. Acidity was first suggested by a fisheries scientist, who suggested a one off run off from “cat clays” in the hills.
Fish kills recurred following more heavy rains two months later. Finding a cause became a Tweed Shire priority and the order went out to measure water quality in every drain and tributary to the Tweed. Highly acid drainage from the cane fields was soon isolated as a major problem. Easton wrote up the episode, not in a scientific journal, but in Fishing World.
The article caused an uproar, “with people up and down the coast comparing what had happened on the Tweed with what had happened in their areas, as far away as central Queensland” he said.
It had taken the best part of two decades from Walker’s warning, but the genie was finally out of the bottle in NSW.. The fishing industry fell over itself commissioning research and Tweed and some other coastal councils led the way in persuading farmers and fisherfolk to stop hurling insults long enough to begin talking solutions with alarmed scientists and planners.
Queensland was to stay in denial phase for some time, however, even as scientists working in the north of the State were conducting ground breaking research into the geology and consequences of acid sulfate soil formation and disturbance.
East Trinity Inlet, an area of former mangrove swamp and low lying land within sight of the Cairns city centre, was intended to be developed as a residential and tourist facility area for about 20,000 people, starting in the mid-1990s.
Unlike many other much-hyped development proposals that sooner or later end up in the hands of a receiver, East Trinity was the proposal of a receiver wanting to turn a failed sugar cane growing enterprise into a real estate windfall.
Initially unnoticed in all the noise of conflict over the proposed development was a team of CSIRO scientists collecting soil and water samples in and around the site and carting them off to distant laboratories.
The reasons for the scientific interest went back about 10,000 years, to the end of the last ice age, when sea levels rose rapidly. Rivers backed up into their valleys – the new coast was one of immense estuaries and large coastal lakes, which filled with sediment to become our coastal flatlands and wide river basins. The chemical combination of iron (common in all sediments) and sulfates (common in seawater and vegetation) filled many of the brackish coastal lakes with large deposits rich in iron pyrites.
These soils were then overlaid with the river sediments that, for dairy farming or cane growing purposes, were often very good soils indeed. Not much attention was paid to the subsoils, variously known as cat clays, backswamp soils and even shark shit (when the manifestation is a grey clay)
Undisturbed and unexposed, such soils are not a problem. At East Trinity Inlet however, potential acid sulfate soils had been drained, cultivated and exposed to that highly reactive gas, oxygen, for more than 20 years.
“It is one of the worst sites I have seen, but it is not unusual,” said Dr Greg Bowman, then a senior CSIRO soils scientist. By comparing soil composition both inside and outside the drained area, Dr Bowman and his colleagues estimated that each year since being drained the site had leaked an average four million litres of concentrated sulphuric acid into Trinity Inlet.
But, although the acidity is alarming and makes for a good alarmist story, scientists caution about making it the only focus of tabloid analysis. Dr Bowman said the East Trinity discharges included 2500 tonnes of iron annually and around 700 times the concentrations of aluminium recommended in water quality guidelines for discharges into waterways. Iron and aluminium continue to produce acids, de-oxygenate water and contaminate sediments long after the first flush of sulphuric acid has dissipated.
Also mobilised are whatever toxic and heavy metals there happen to be hanging around in the soil profile. In the East Trinity case, about ¾ tonne of arsenic a year was flowing from the site each year towards the marine life of Trinity Inlet and the amateur fisherfolk of Cairns.
“In Trinity Inlet, we don’t know what the environmental effects of this run-off are,” said Dr Bowman. “We didn’t have the money to do that research.” But he dismissed out of hand the initial Queensland government response – long on politics and short on science – that the East Trinity concoction was being safely neutralised by seawater.
As the scientists began to generate findings that threatened high profile developments, there was a concerted effort to bury the findings and wind back the research. Dr Stephen Rogers, of CSIRO Land and Water, told a Senate committee in 1996 that acid sulfate soil research was considered to be of fairly low priority.
Significantly, however, he added: “That is not because it is not a significant issue and potentially a significant problem in coastal development, but because it is very difficult or was historically very difficult for us to receive any funding to do the research work.”
Then north Queensland fishing activist Mr Vern Veitch propelled acid sulfate soils back on to the national agenda by tabling three dead fish – a bream, a mullet and a javelin all suffering from red spot disease - before some surprised Senators by way of “a brief opening statement”.
The Senate inquiry was part of the long running stoush over the Port Hinchinbrook development being promoted by Keith Williams. Veitch however blamed clearing and draining of low lying land for sugar cane as the main culprit in polluting Hinchinbrook Channel, saying there was a need to stop the Great Barrier Reef area being used as “a big, blue wheelie bin”.
The sugar industry reacted in outrage, later telling the committee that Veitch had exaggerated the area affected by acid sulfate soils about 40 fold, that the water quality of the area’s major rivers was “under more scrutiny than Monica Lewinsky’s dress” and that it was drawing a very long scientific bow to associate red spot disease in Hinchinbrook channel fish with the activities of Herbert River cane growers.
“We have a site at the southern end of the Hinchinbrook Channel showing production of very large quantities of acid,” Dr Bowman told the Senate committee. “It is being produced by lowering of the water table due to drainage for sugar cane production and it is also producing iron, aluminium and other metals that are going straight into Hinchinbrook Channel.”
Research and government attention to the acid sulfate problem benefitted considerably from the often highly unscientific antics of witnesses to the Senate committee hearings on Port Hinchinbrook..
The CSIRO rearranged its research priorities, finding the money from somewhere to go back to East Trinity and sending out a flurry of news releases highlighting acid sulfate mine tailings as an “ecological time bomb” and claiming that coastal development worth $10 billion was at risk from acid sulfate soils.
A much needed impetus was given to the drafting of a national strategy for the management of acid sulfate soils. And in Queensland, a scientific team within the Department of Natural Resources continued with a highly regarded project to map the extent of at risk soils in the State.
However, the conflict between science and development continues, with the Queensland Acid Sulfate Soil Investigation Team (QASSIT) being pushed back into the background after a report warned that the State may have some legal liability for acid sulfate induced problems in structures erected at the Port Hinchinbrook development. The Department of State Development put the boffins back in their box with a study from private consultants which came up with contrary findings, a maneuver which has outraged the national soil science community.
Experience in the United States shows that litigation over developments in acid sulfate soil areas is a real risk and one case, involving corrosion to bulk fuel tanks, has already been settled out of court in Australia.
The lyngbya outbreak in Moreton Bay will put the spotlight on councils which have yet to formulate a policy on development in acid sulfate soil areas.
For the canal estate, the question will be whether such developments remain economic when the cost of treatment is factored in. In NSW, the Road and Traffic Authority works on a multiplier of about 300 percent when calculating road base costs in acid sulfate soil areas.
|Acid Sulfate Soils Around Australia|
|New South Wales has the unfortunate combination of the largest proportion of potential acid sulfate soils and the most development pressure threatening to expose them. Queensland government and environment officials once believed no such soils existed north of the New South Wales border but are now engaged in a 30 year project to map extensive deposits around virtually the entire coastline.|
Victorian officials believed that state’s somewhat different coastal history had spared them any undue anxiety over acid sulfate soils. Now it appears that some of the most extravagant edifices of the reign of former Premier Kennett are built on acid sulfate soil foundations. Vast heaps of minimally or untreated spoil from assorted casinos and toll roads now cover paddocks near that most favored site of toxic waste repository proposals, Werribee.
Debate goes on as to whether the spoil itself merits the label of hazardous waste, and on who may be responsible for paying for treatment. Out at Werribee however the soil has fortuitously ended up on top of one of relatively rare areas of soils with some capacity to neutralise acid run-off.
Western Australia, where a soil scientist made a fleeting reference to possible problems with soil acidity back in the 1920s, has problems with acid sulfate sands rather than the clays better known elsewhere. The areas at risk are not huge, but their placement may be unfortunate. Margaret River winemakers are currently contesting a major sandmining proposal which, some claim, could contaminate the groundwater helping to produce some of Australia’s best vintages.
Large areas of potential acid sulfate soils also exist across north Australia, although they have long been periodically exposed in the big wet, big dry cycle and life in the rivers has learned to live with the odd acid flush. Development pressure is also relatively low for most of the area, although a CSIRO publication in the early 1990s noted particularly high concentrations of acid sulfate soils around the Jabiluka uranium deposit which “would pose immense engineering problems” on any mine.