Austin pilots new tactics to tackle toxic algal blooms: toxin found at Sculpture Falls poses greater risk to humans – News



A sign posted at Sculpture Falls warns people and pets to avoid swimming in the water (Photo by John Anderson)

Toxic algae is nothing new to Austin’s waterways. In 2019, at least five dogs died from ingesting a toxin produced by certain types of freshwater cyanobacteria, or blue-green algae, in Lady Bird Lake, followed by more harmful blooms the following year at Red Bud Isle and Festival Beach. Toxins were also found in Highland lakes, including Travis and Austin lakes earlier this year.

Dogs seem particularly vulnerable to toxins produced by these algal blooms, but another type of algal neurotoxin that poses a greater risk to humans has now emerged in Austin. Last month, after receiving a report that someone fell ill after swimming in Barton Creek, the city found regarding the levels of the cylindrospermopsin toxin at Barton Creek near the popular Sculpture Falls swimming hole. Unlike previous incidents, in which the toxin was detected in the algae itself, at Sculpture Falls, the toxin had entered the water, meaning there is a greater possibility of human exposure to recreational purposes. “People are unlikely to eat large handfuls of coarse seaweed,” said Brent Bellinger, a senior environmental scientist in the city Watershed Protection Department, but “your average swimming child is probably swallowing water.” At this time, people and pets are not recommended to swim in Sculpture Falls.

Cylindrospermopsin, like other neurotoxins found in Austin’s waterways – dihydroanatoxin and homoanatoxin-a – can cause nausea, diarrhea, headaches, and, with long-term exposure, failure of internal organs. Toxins aren’t always present, but algae are, especially in hot, standing water conditions, typically around June or July in Austin, while receding in winter. The algae found in 2019 were there before, Bellinger said, but that year new “Goldilocks” conditions gave it the ability to produce toxins. A change in nutrients, caused either by runoff from the heavy rains of 2018, or by the arrival of the dreaded zebra mussel, led to these conditions.

“I don’t see it as a coincidence that within two years of the zebra mussels coming into the system, we have toxic algae,” Bellinger told the the Chronicle. Mussels are a “human calamity”, traveling from lake to lake hitchhiking on boats that have not been properly cleaned, eating good phytoplankton that rivals toxic algae and excreting nutrients like phosphorus that lead to growth of cyanobacteria. Boats are not allowed at Sculpture Falls, so it’s unclear how the toxic algae got there.

Poisonous blue-green algae mats like the one pictured have become more common in Austin’s waterways since 2019 (Courtesy of the City of Austin)

The type of flowering that occurs in Austin – called benthic mats – are much less studied than other types of algae that affect larger bodies of water, Bellinger explained. Yet global observations are increasing, finding “strong links to climate change, due to changes in our precipitation patterns.” Droughts cause stagnant water, heavy rains spilling unfamiliar nutrients and fertilizers, and unusually warm temperatures for the season lead to “cyanobacteria. [being] in their optimal environment for a longer period of time, ”said Bellinger.

The goal is to be like Alice in Wonderland, Bellinger said. “Alice runs and runs, and she still doesn’t move away from the Red Queen. We want to get away from the Red Queen – the Phoslock is what we’re trying to help us do that.

Since the algae cycle is for the most part predictable, monitoring can detect harmful blooms before anyone comes in contact with them. Bellinger and his team test toxin levels every two weeks at Lady Bird Lake, Lake Austin, and Lake Travis. Tests will decrease with blooms, returning monthly in winter, unless there is a seasonal anomaly. The Lower Colorado River Authority, which monitors the Highland lakes, strongly encourages people and pets to avoid contact with algae in one of the Highland lakes after the agency received reports of several dogs becoming ill and a dog dying after swimming in Lake Travis in the weeks following winter storm Uri.

Earlier this summer, the city contracted with a company called EutroPhix for a pilot of 4 to 5 years of a possible mitigation tactic thanks to a clay product called Phoslock. Phosphorus in freshwater systems is a “limiting nutrient,” which means that too much leads to the production of algae. Phoslock buries the phosphorus, Bellinger explains. “It settles on the surface of the sediment and binds the phosphate ions irreversibly. We are trying to speed up this process in the hope that it will starve the cyanobacteria.” As of June 21, the city treated 21 acres of water around Red Bud Isle with a total of 120,000 pounds of Phoslock, collecting samples before and after three treatments. “The last sampling event, the data looked pretty positive,” Bellinger said.

But Phoslock is expensive: $ 300,000 for 2021 alone, including hardware, application, and lab tests. Bellinger said the next phase would be back in the spring to check phosphorus levels against fall: “Do we still have a strong processing effect? Can we add less around Red Bud next year, and maybe target another part of the tank? Or is there so much organic matter going in that we have to keep adding a lot to Red Bud Isle? Which then makes this mitigation strategy not really feasible in the long term. You want to roll back the system, you don’t I don’t want to run in place. “

The goal is to be like Alice in Wonderland, Bellinger said. “Alice runs and runs, and she still doesn’t get away from the Red Queen. We want to get away from the Red Queen – the Phoslock is what we’re trying to help us do that.

“The hope is that during the winter, with different rainy events, the Red Queen does not come close to us.”

A version of this article appeared in print on October 15, 2021 with the title: Austin tries new tactics to tackle toxic algae blooms


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