Subterranean water: how much do we need?

How much water does the environment need?

Ecological researchers often need to move from project to project, because you can only work on what you have funding for. For my PhD I worked on the free-flowing streams and rivers along the east coast of Australia describing new species of aquatic beetles. Then I moved to Western Australia, and my focus changed to describing the invertebrate foodwebs of the wetlands of Perth and the WA wheatbelt. Then I was lucky enough to do a trip to Central Australia that took me to Watarrka National Park to look at some of its springs – and it turned out they contained some of the aquatic insects that I’d studied for my PhD, that we thought only occurred in the cool, fast-flowing waters of the Great Divide. That got me very interested in Central Australia’s relictual springs and waterholes, and their role as aquatic refugia.

I’m now working in the Northern Territory, studying floodplain wetlands, rivers and springs but I’ve kept my Central Australian work going because I’m a huge believer in the value of long-term data sets. Australia has such extreme climatic variability that unless we’re tracking what’s going on over time, we can’t really understand things. Studying animals for a year or two doesn’t tell us nearly enough if we’re going to conserve and protect and manage them.

Person standing in the desert using a fishing pole to dangle into bore hole
Stef Oberprieler bore fishing.

A lot of my work has been driven by environmental disasters. These include a mass die-off of migratory waders in a Ramsar wetland near Perth; the wetlands on the Swan Coastal Plain that became eutrophic because of nutrient run-off; and WA wheatbelt wetlands that became very salty because of land clearing. The reason we started looking at the groundwater here in the NT was to do the baseline surveys needed before the onshore gas industry (fracking) starts to produce gas from the Beetaloo Basin.

There’s a lot of emphasis on groundwater now. We’re realising that in a country like ours the likelihood of extreme events under climate change is very high. And those extreme events include very long droughts. In any of the arid and semi-arid regions of Australia, which is pretty much everywhere except the coast, groundwater is what keeps us going.

Unless we’re tracking what’s going on over time, we can’t really understand things.

Groundwater is used for drinking water, remote towns use it for their water supplies, pastoralists rely on it for their cattle. The entire inland of eastern Australia couldn’t have been developed without the presence of the water of the Great Artesian Basin – a vast underground system.

Two people standing at a festival with a sign saying 'save our stygofauna'
Jenny Davis and Erica Garcia at the SeaBreeze Festival.

The Beetaloo region encompasses karst limestone – it’s full of underground caverns and potentially underground rivers. Hydrogeologists describe it as the “Swiss cheese” of limestone. I’d love to have a better way of visualising what’s going on under there – it’s actually very difficult to map it. The “next big thing” could be the equivalent of ground-penetrating radar that would give us subterranean images so we could understand the size and scale of the water beneath the ground, but that’s apparently some time off. At the moment we’re like blind people poking a stick at an elephant trying to guess what sort of animal it is.

At least we now understand the importance of groundwater. In the last 20 years, we’ve recognised the existence of groundwater dependent ecosystems (GDEs). These can be terrestrial – the woodlands and forests where the plants have their roots extending into that groundwater. Then we have aquatic GDEs, which are the rivers and wetlands and springs, where the groundwater is either completely or partially the main water source. And then we have subterranean GDEs – the underground ecosystems. These are the ones that I’ve become very excited about.

At the moment we’re like blind people poking a stick at an elephant trying to guess what sort of animal it is.

One of the first things we need to know about groundwater is its age. All groundwater was originally rain, obviously. But when did it fall?

We use a technique where the isotopes of hydrogen and oxygen are measured in a water sample, and you then compare the results with what’s called a local meteoric (rainfall) line. This technique can indicate whether water in a spring is from recent rain or whether it has fallen sometime in the past. There are other techniques – for example, if you detect tritium which was released into the atmosphere with the detonation of nuclear bombs in WW2, and nuclear tests in 1950s and early 1960s, it means that water was in rain that has fallen since that time – it’s a chemical marker. And there are other techniques that can tell you if it’s much older water.

Why do we want to know the age? Well, if it’s recent rain, that means that system you’re studying – say, waterholes along a river – will refill with the next lot of rain, and that the flora and fauna that occurs there are well adapted to a dry-wet-dry cycle. But if it’s much older water and you start pumping it, it’s never going to be replaced: it’s rain that fell long in the past, when Australia had a different climatic regime. Effectively, you’re going to be mining that water.

Once you know the age of the water, you’ve got a good idea of how a particular development might impact it. If a system is going to be completely pumped dry of rain that fell a very long time ago, the chances are that some the plants and animals existing there can’t ever come back. They will be very finely adapted to that particular environment because they’ve always had constant water. Other systems – Lake Eyre would be the great example – can be completely dry for decades, then fill with water, and soon the birds turn up, the invertebrates hatch out, and the whole system comes to life.

If it’s much older water and you start pumping it, effectively, you’re going to be mining that water.

Some of the water we have measured from these remote springs will have last fallen as rain hundreds of thousands of years ago, and the fauna living in it has Gondwana origins. We’ve also found a whole new subterranean ecosystem right here in the karst limestone in the Beetaloo.

The invertebrates we’re finding in these subterranean systems are blind and colourless, because they went underground at a time when the Australia continent was moving northwards, and surface water sources became both unreliable and warmer. They have persisted in the very constant conditions that the underground environment provides.

Range of subterranean creatures labelled a-o
Subterranean fauna collected from NT aquifers. A-C: Decapoda: Atyidae: Parisia unguis. D-F: Amphipoda: Melitidae G: Syncarida: Bathynellaceae: Brevisomabathynella sp. H-J: Ostracoda: Podocopida: Candonidae K: Harpacticoida: Ameiridae: Nitokra lacustris L: Gastropoda: Caenogastropoda M-N: Cyclopoida: Cyclopidae O: Annelida: Aeolosomatidae: Aeolosoma sp.

These organisms are sort of living dinosaurs – only they don’t look like dinosaurs. But they have a role, and we need to value them because they’re part of our biodiversity and, as grazers of the subterranean microbial communities, they provide what is known as an ecosystem service – in this case, they maintain good quality water. 

And that’s the fear with fracking. If you get a crack in a bore, and the fracking chemicals spread out into this underground limestone, you will kill off this fauna, and that will have ramifications for not only the biodiversity within this area, but for the people who are dependent on the freshwater that the aquifer provides.

Water is incredibly important to us. My interest is very much in the biodiversity space, but I’m well aware that we have to share that water with multiple human activities – which could be agriculture, horticulture, mining, tourism and fishing. And of course indigenous cultural associations with groundwater are very strong – very strong. So there’s lots of different uses and values for this water, and developments in science are giving us the opportunities to finally understand how these systems work in a detailed and comprehensive way.

As told to Graem Sims for Cosmos Weekly.

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