Scientists have made an international call to change water quality standards, with the aim of protecting biodiversity from salt pollution of freshwater.
- Water quality standards currently measure total salinity
- This fails to assess toxicity to aquatic organisms
- An international team is calling for change
- Salinity remains a threat to Australia
Human activities like agriculture and mining can result in rivers and lakes becoming polluted by salt.
While most countries limit the amount of salt in drinking and irrigation water, they do not normally consider the effect of salinity on aquatic organisms.
Australia is one of the few countries that have water quality standards designed to protect aquatic life, but even then there is a problem, said an international team writing today in the journal Science.
Current standards to measure salinity do not adequately assess the toxicity of saline water to aquatic organisms, the researchers said.
The team have proposed a new method of measuring salinity that will provide a more accurate assessment of the impact on aquatic life.
Measuring the saltiness of water isn't enough
The current method to assess salinity measures the electrical conductivity (EC) of the water sample, which provides a measurement of the total salinity.
But water samples with the same total salinity measurement can contain vastly different compositions of chemical ions — the positively or negatively charged atoms that form when salt is dissolved in water — and these can have markedly different effects on freshwater fauna.
These different ions can include sodium, chloride, magnesium, potassium and bicarbonate ions.
"Not accounting for the different proportions of ions can mean that we don't protect biodiversity," said the co-author of the new study, Dr Ben Kefford, a freshwater ecologist and ecotoxicologist at the University of Canberra.
Aquatic organisms are affected by the specific ratio of ions in saline water.
"It's the ratios of ions that is important, as well as their absolute quantities," said Dr Kefford.
"The ratios alter their toxicity."
Setting new standards will make it easier to assess impacts
Dr Kefford is helping develop "ion-specific standards".
These would be very location specific, as aquatic organisms in different locations respond differently to ions depending on the environment they have evolved in.
Australia is on a bit of salinity holiday ... But right now I am not prepared to bet the future.
And, he said, it is possible standards might be set higher for relatively pristine systems.
But given the enormity of the salinity problem, society as a whole must be involved in determining at what level the standards should be set, the researchers said.
"Standards could be in terms of the percentage of species protected, and then it becomes a societal issue in terms of what level of species should be protected," Dr Kefford said.
Such an approach would make it easier for society to weigh up the benefits and costs of standards, and come to an agreement on their introduction.
"You can set these great standards but if they are not accepted they won't be enforced and if they are enforced people will find a way around the letter of the law," Dr Kefford said.
Salinity in still an issue in Australia
Former head of the Murray Darling Basin Commission, Dr Don Blackmore, said the drying climate had reduced the problem of salinity in Australia, meaning the problem is not expected to be as extensive as was predicted in the 1990s.
However he said continued attention to the problem, and ion-specific standards, was as important as ever, as there were still billions of tonnes of salt that is "not going anywhere".
"Even in a drying climate, salinity could get worse if there is a wet cycle," Dr Blackmore said.
And reduction of groundwater flow caused by drought can also concentrate salinity in some circumstances, he said.
"Australia is on a bit of salinity holiday," he said.
"But right now I am not prepared to bet the future."