Researchers in Australia have found a lake that has defied the odds by showing a remarkable resilience to climate change.
Blue Lake, the second largest lake on North Stradbroke Island just off the coast of Queensland, has been relatively untouched by changes in climate for the past 7,000 years, and has so far also resisted the impact of human beings, according to a new study. This makes it a rarity among lakes in Australia and around the world.
I’ve been writing in Water Currents this past year about the effects of climate change on lakes, so naturally I thought that a lake showing such resilience was interesting news. I was surprised to find that the story had been picked up by so many media outlets and suspect the reason had something to do with one of the researchers saying the lake was like “God’s bathtub” in a story published in The Australian. Even I couldn’t resist learning more after reading a comment like that!
It turns out that the reference was “just a slip of the tongue,” said Cameron Barr of the University of Adelaide in an email. He was trying to find a way to describe the lake’s rare and unusual qualities, and he’s not the first lake scientist, or poet for that matter, to struggle to find words befitting the beauty of his study site.
He says his “mates” are already giving him “a lot of stick about it,” but I applaud him for his spontaneous cleverness. The catchy phrase helped get their important research noticed.
Blue Lake was the subject of a study by a team of researchers led by John Tibby. They wanted to learn more about how ecosystems respond to climate change at different time scales, from days to millennia. The University of Adelaide team reconstructed the lake’s ecological history by looking at stable isotopes, pollen, and diatoms. They combined this with historical and more recent data on water depth, chemistry, and temperature to determine how the lake has changed over time.
The results of their study, published online in the journal Freshwater Biology, show that “Blue Lake has remained relatively stable and resilient for millennia.”
“We know that there have been variations in climate in the region including North Stradbroke Island over recent decades, but during that time the depth, shoreline, and water chemistry of Blue Lake has displayed little variation. This is in stark contrast to other changes in the region due to shifts in climate,” said Barr.
The same region experienced a significant shift to a drier climate around 4,000 years ago, but even over this longer time period, the lake has exhibited little change.
The lake’s resilience has a lot to do with it being a groundwater “window lake” – a place where a large, unconfined aquifer flows out to form a lake. It was created when a sand dune blocked the natural drainage, creating a lake basin. Water in the lake is replenished every 36 days on average, making water clarity very high – you can see the bottom 33 feet (10 meters) down.
“This constant replenishment by chemically stable water is the source of the lake’s stability,” he said.
The wetlands on the island support significant biological diversity, including two endemic plants and “distinct genotypes of many aquatic animals that are evolutionarily significant units,” according to the study. A number of threatened and endangered species, protected under Australian law, depend on these ecosystems. Blue Lake also supports a population of endangered Oxleyan Pygmy Perch (Nannoperca oxleyana), is recognized as a site of “high conservation significance,” and has been designated a wetland of national and international importance.
“It appears that Blue Lake has been an important climate ‘refuge’ for the freshwater biota of the region, and is in the same condition now as it was 7,500 years ago. With appropriate management, the lake could continue relatively unchanged for hundreds, possibly thousands of years to come,” Barr said.
Why are researchers worried about managing a lake that has survived this long without the need for human intervention? “Our study suggests that increased extraction of ground water represents one of the few obvious threats to the stability of Blue Lake. The threat this could pose to the lake’s status as a stable freshwater refuge needs serious consideration if the regional aquifer of North Stradbroke Island is to be contemplated,” Tibby says.
The aquifer that feeds Blue Lake serves as a source of freshwater for the communities on the island and suburbs on the mainland. Located less than 30 miles (48 kilometers) from Brisbane, one of the most rapidly growing areas in Australia, the aquifer and lake are expected to come under increasing pressure.
During the decade-long drought that began in 2000, Barr says that water resources in the region were stretched and the aquifer was being considered as a source of drinking water for the mainland. “The drought broke with record-breaking La Ninas, which resulted in significant (and fatal) flooding,” he said, “and the issue of water shortages has left the public (and political) conscience. However, the likelihood of future droughts and further water shortages is almost certain.”
It’s ironic in some ways that climate change, coupled with increased population pressures in the region, poses the greatest threat to a lake that has remained stable until now. Contrary to some of the commentary last week, the sunscreen from people swimming in the lake is not likely to be its undoing.
We may never know whether the lake has or will be used as a sacred bathing pool, but thanks to this new research, local authorities possess the information they need to make wise decisions about protecting the lake (and aquifer) for the next several thousand years at the very least.
Lisa Borre is a lake conservationist, freelance writer and sailor based in Annapolis, Maryland. With her husband, she co-founded LakeNet, a world lakes network, and co-wrote a sailing guide called “The Black Sea” based on their voyage in 2010. A native of the Great Lakes region, she served as coordinator of the Lake Champlain Basin Program in the 1990s. She is now an active member of the Global Lake Ecological Observatory Network.