Algal blooms: a colourful danger
Algal blooms cause serious, even fatal, problems in our waterways, but we know little about what causes them.
IT STARTS SMALL, just a few cells cycling through the water column, invisible to the casual observer. But it's not long before the proliferating blue-green algae, or cyanobacteria, become a bright green quagmire of deadly toxins.
Using gas-filled bags, the cyanobacteria - the oldest forms of life on Earth and the ancestor to modern plants - float towards sunlight to photosynthesise until the sugar-heavy cells sink back to the watery depths.
But at some point, usually between February and April, favourable conditions cause the cells to proliferate until those on top can't sink and those beneath can't surface. This internal war on the water surface manifests as a thick scum of cells resembling green sawdust or paint. With prolonged UV exposure, the cells die, releasing toxins, sucking oxygen from the water and killing any animal life unlucky enough to be in the vicinity.
This natural scourge afflicts every mainland state in Australia and causes an estimated $200 million of damage yearly. In an endless struggle against nature, scientists and water managers are developing better tools of detection, treatment and management of blooms, which experts predict will become even worse with the world's changing climate.
Long history of algal blooms in Australia
According to Associate Professor Mike Burch from SA water, a world expert in the management of cyanobacteria, these blooms are "not a new phenomenon in Australia."
In fact, Australia was home to the world's first recorded cyanobacterial bloom, which occurred in 1878 in Lake Alexandrina, South Australia. But it is likely that Australia has a much longer history of blooms. "Anecdotal reports show that local Aboriginal people were aware the lake could be toxic before 1878," says Mike.
Since then, Australia has been plagued with regular episodes of cyanobacterial outbreaks, including the infamous bloom of late 1991, which tinted 1000km of the Darling-Barwon river system pea-green, caused the deaths of 1600 sheep, and catalysed a surge of research into cyanobacterial blooms. About 18 years later, similarly extensive blooms occurred in the Murray River for two consecutive years.
"We had contamination starting from Albury and continuing over 1000km downstream in both 2009 and 2010," recalls Lee Bowling, state algal coordinator with the NSW Office of Water.
Algal blooms a serious threat
In Australia, algal blooms hit hardest in the continent's southeast corner - New South Wales, Victoria, south-east Queensland, and the south-east corner of South Australia - where conditions are wetter and human populations are higher. "More people in this area leads to greater land use pressures and hence more pollution flowing into waterways, which exacerbates algal blooms," says Lee.
But besides undesirable tastes, odours and unsightly scums, there can be serious human impacts if algal blooms reach important waterways. "Larger blooms cause major problems for water supplies and incur an economic cost as tourism suffers from closure of recreational water bodies," says Lee.
To a lesser extent, toxins produced by some types of cyanobacteria can also be dangerous to health. "There are well-documented reports of animal and human poisonings from drinking water contaminated with cyanobacteria," says Mike, who was responsible for developing the current Australian drinking water and recreational guidelines for cyanobacteria for the NHMRC, WHO and UNESCO.
In humans, the toxins can cause nerve and liver damage, gastroenteritis, or skin and eye irritation. Long-term exposure to microcystin - the most common toxin in cyanobacterial blooms - may possibly promote tumour growth.
Causes of this environmental scourge unknown
Although our understanding of cyanobacterial toxicity has improved, we do not know exactly what causes them to bloom and, says Professor Brett Neilan of UNSW, "we still cannot predict it."
A combination of environmental conditions is associated with blooms - a stable water column, sunlight and nutrients - but no single factor can ever be implicated as the sole perpetrator. "People often have this idea that algal blooms are nutrient-driven events, but it's not the case," says Professor Gary Jones, chief executive of water management company, eWater CRC, and former algal expert for CSIRO. "It's far more complex than that."
This complexity is why, when it comes to mitigating blue-green algal blooms, "there aren't too many silver bullets," says Gary.
Long-term solutions focus on maintaining vegetation to minimise erosion, and therefore nutrient run-off, within a catchment. But of all the short-term solutions, which include methods like stripping phosphorus out of the water, Gary says that only 'thermal destratification' - artificially mixing water to prevent cyanobacteria from collecting in the warm upper layers - comes close to being successful.
However, he concedes that although it works in theory, mixing large water bodies is "difficult, or prohibitively expensive, to do properly."
Treating algal bloom symptoms rather than the cause
For cyanobacterial researcher Brett Neilan, successful algal mitigation will only come with an understanding of the entire ecosystem. "We don't think the story is just about cyanobacteria anymore," says Brett. "We know there's a whole community of microbes - other bacteria, small algae and viruses - that are interacting with cyanobacteria. Future research is about understanding how the organisms exist in nature so we can develop alternate management strategies, where instead of stopping the cyanobacteria growing, you can inhibit the growth of something else that will in turn make them decline."
The difficulty in preventing blooms means that Lee Bowing at NSW Office of Water chooses to focus instead on protecting the public, through closing water bodies and advising recreational users, water utilities and landholders about risks.
Gary agrees that prevention is a near-impossible dream. "In Australia, we're up there with the best in the world in how we respond to blooms, but to this day, all we've been able to do is manage the symptoms, and this is probably what we'll be doing forever."
So it seems this ancient, single-celled organism still has the upper hand. And with 3 billion years of evolution behind it, that's hardly surprising.
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