UM Bio Station and Karuk Tribe Study Finds Presence of Toxin-Producing Cyanobacteria in Rivers Higher than Previously Thought
In a new study published in the scientific journal, Freshwater Science, a team of scientists led by recent University of Montana Flathead Lake Biological Station (FLBS) PhD graduate Laurel Genzoli working in close partnership with the Karuk Tribe sought to increase understanding of anatoxin-producing cyanobacteria found in lake and river bottoms by surveying sites within the Klamath River watershed in Northern California.
Their research uncovered some surprising results, which may have public health implications for even the most pristine rivers and streams, including those in Montana.
“We didn’t expect to find high anatoxins in rivers with clear, clean water, but that is where they were,” said Genzoli. “In our study, these were the same streams that are used for swimming during the hot summer months.”
Blooms of toxin-producing cyanobacteria (also known as blue-green algae) are an enduring public health threat in lakes and rivers around the world. When ingested, cyanobacterial toxins can cause illness and even death to humans, livestock, pets, and wildlife. Anatoxins are of particular concern because they are neurotoxins that act very quickly. While reports of human illness from anatoxins are rare, if ingested in large quantities they can cause convulsions, paralysis, and death from respiratory failure.
“Poisoning from anatoxin requires eating a large amount of algal material,” said Genzoli. “Which is why dogs and, in some cases, small children are at the biggest risk. Fortunately, it generally requires ingesting a lot of algae to harm people and animals, so most of the risk can be mitigated by watching small kids and dogs closely and not letting them drink or play in areas with attached or floating mats of algae.”
Using a combination of visual surveys, cyanobacteria-dominated mat samples (pictured above), and water samples, scientists were able to quantify benthic cyanobacteria and the extent of the production of anatoxins, which is far more significant than previously thought. Photo courtesy University of Nevada-Reno.
To this point, scientific understanding of the drivers and impacts of toxin-producing cyanobacterial blooms has relied largely on research of planktonic blooms in the open water of lakes. But cyanobacteria also thrive on river and lake bottoms. This is significant, because cyanobacterial mats that develop along riverbeds and lake bottoms—also known as the benthic area of a body of water—can produce anatoxins.
Utilizing visual surveys, cyanobacteria-dominated mat samples, and water samples, scientists were able to quantify benthic cyanobacteria and the extent of the production of anatoxins. The resulting data revealed a widespread prevalence of anatoxins throughout the middle and lower Klamath River watershed, adding to a growing body of evidence that anatoxins from benthic cyanobacteria may be more common than previously thought.
Additionally, sites with higher water quality—including clear, low-nutrient tributaries—supported anatoxin concentrations as high as, and in some cases higher than, the nutrient-polluted mainstem of the Klamath River.
One of the biggest takeaways for scientists was that the widespread detection of anatoxins from benthic cyanobacteria in this study and previous work suggests that benthic habitats, even in large rivers, can drive ecological processes relevant to public health. The team of scientists call for increased monitoring of toxin-producing benthic cyanobacteria.
They also state that further research is needed to identify factors promoting anatoxin production from benthic cyanobacteria, which could help to assess current risks and to forecast trends of anatoxins in rivers, related to public safety.
The scientists note that monitoring for anatoxin-producing benthic cyanobacteria is no easy task. Rivers and streams are dynamic environments and monitoring is logistically challenging in deep, fast rivers. Still, increasing understanding of when, where and how benthic cyanobacteria flourish along the bottoms of rivers and streams can help focus monitoring resources toward times and locations of greatest public health risk.
The resulting data from this study and others have already provided important clues to aid scientists moving forward. As an example, genetic techniques and lab cultures have increasingly identified Microcoleus as the primary benthic anatoxin producer in rivers. Even though anatoxins are not associated with all strains of Microcoleus, visual observation of Microcoleus is an immediate indicator that anatoxins may be present, which means visual surveys of benthic Microcoleus mats can help focus resources when monitoring for anatoxins.
It’s important to note that cyanobacteria are a natural part of river and stream ecosystems, and in small quantities are not a public health concern. Additionally, scientists aren’t sure if high levels of anatoxin-producing benthic cyanobacteria in rivers have been around for a long time, or if they are a more recent phenomenon.
Still, scientists say that informing river users on how to reduce contact with benthic cyanobacteria can go a long way toward mitigating public health issues. Because the highest concentrations of benthic cyanobacteria occurred in clear rivers and streams with higher water quality, there is a higher likelihood that people choosing to swim in moderate-to-high quality water may be at risk for anatoxin exposure.
River and stream users should watch small children closely, making sure that algae are not ingested. Taking extra precautions in the late summer and where mats are floating in the water or easily dislodged from the riverbed will reduce chances of ingesting toxins from benthic cyanobacteria. River users should also be informed about the risk to dogs, which may accidentally ingest or be attracted to cyanobacterial scums or mats.
Continued outreach, monitoring, and research focused on benthic anatoxins will help protect people, pets, wildlife and livestock. Additional research is needed to better understand and predict changes to benthic anatoxins associated with future impacts to the health of the public, wildlife, and ecosystems associated with freshwater streams and rivers.
Additional authors on the study include FLBS stream ecology professor Bob Hall, Bend Genetics principal scientist Timothy Otten, Karuk Tribe Department of Natural Resources scientist Grant Johnson, University of Nevada-Reno assistant professor Joanna Blaszczak, and Aquatic Ecosystems Sciences ecologist Jacob Kann.
For the complete study, visit the Freshwater Science website at https://www.journals.uchicago.edu/doi/full/10.1086/731975?af=R
Banner image: The results of this toxin-producing benthic cyanobacteria study have spurred additional research by Genzoli and a team of researchers from the University of Nevada-Reno, who will work in partnership with the Quartz Valley Indian Tribe. Photo courtesy University of Nevada-Reno.