Summary: A cyanobacterium caused by blue-green algae blooms has been identified in the waters of Lake Erie. The cyanobacterium is capable of producing a neurotoxin that can attack the central nervous system in humans.
Source: Ohio State University
Harmful algal blooms pose a unique toxic threat in Lake Erie’s central basin, new research has found.
Not only do blooms routinely occur in this area, they can also produce types of cyanobacterial toxins that aren’t typically detected through routine water-safety monitoring, according to a study published in the Journal of Great Lakes Research.
“The cyanobacteria we found in the central basin are completely different from what we’ve seen in the Toledo area in the western basin,” said lead researcher Justin Chaffin, a senior researcher and research coordinator at The Ohio State University’s Stone Laboratory.
“That’s troubling because water treatment plants aren’t typically set up to look for this bacteria or the toxins they create. It requires more expensive, more sophisticated equipment.”
Harmful blue-green algal blooms and the toxic microcystins that accompany them have been a persistent threat in the lake’s western basin. But until this study, bloom-related toxins hadn’t been formally documented and analyzed in the central basin.
Several years ago, environmental scientists began hearing reports of harmful algal blooms in the central basin, in the waters just west of Cleveland. This was surprising at the time, because the experts thought these environmental threats were concentrated primarily near Toledo, Chaffin said.
The water in the central basin hadn’t been thought of as friendly to cyanobacteria because it isn’t as warm or nutrient-rich as in the western basin, where nitrogen and phosphorous is plentiful because of agricultural runoff brought in by the Maumee River.
The research team sampled the water in four areas from 2013 to 2017 and analyzed satellite images taken before then for evidence of blooms. They found a cyanobacterium called Dolichospermum in the central basin during early-season blooms in July. This cyanobacterium is capable of producing a toxin that can attack the central nervous system in humans, and the researchers found genetic evidence that the bloom has the potential for the neurotoxin.
“What this means is that if you’re a water plant operator in Cleveland, you have to be ready by late June or early July for cyanobacteria because they do have the potential to produce a really potent toxin. It could also be a problem for beachgoers if there’s a north wind and these blooms gather along the Ohio shoreline,” Chaffin said.
Researchers have shared these findings with the Ohio Environmental Protection Agency and with water plant operators, he said.
Later in the season, the researchers found the cyanobacterium Microcystis – the chief troublemaker in the western basin, which feeds off of excess phosphorous – in the central basin. The toxins, called microcystins, that it produces are most harmful to the liver and also a threat to the kidneys and reproductive system. Water plant operators routinely look for microcystins.
Figuring out precisely what is causing these unexpected algal blooms in the central basin will require more work, Chaffin said.
“We still can’t pinpoint what’s really causing these blooms because it’s a complex interaction of several factors,” he said.
But the new study did find evidence that it’s a combination of low levels of iron (which decreases nitrogen availability), muddy water and a strain of Dolichospermum adapted to cooler waters.
The researchers found an association between central basin blooms and lower water clarity – meaning that when the water is muddier, the likelihood of harmful blue-green algae goes up. There’s also evidence that iron plays a role. If there’s not enough iron, beneficial algae’s growth is suppressed, but the harmful algae found in this study likely flourish because they are efficient at capturing iron when the nutrient is in short supply, Chaffin said.
Continual work to reduce sediments, which lead to lower water clarity, is important, he said. And though phosphorous and nitrogen – which have driven blooms in the western basin – aren’t present in high concentrations in the central basin, minimizing them is important to Lake Erie’s overall health, he said.
About this neuroscience research article
Source: Ohio State University Media Contacts: Misti Crane – Ohio State University Image Source: The image is credited to Ohio State University.
Cyanobacterial blooms in the central basin of Lake Erie: Potentials for cyanotoxins and environmental drivers
Lake Erie western basin (WB) cyanobacterial blooms are a yearly summer occurrence; however, blooms have also been reported in the offshore waters of the central basin (CB), and very little is known about what drives these blooms or their potential for cyanobacterial toxins. Cyanobacteria Index was quantified using MODIS and MERIS data for the CB between 2003 and 2017, and water samples were collected between 2013 and 2017. The goals were to 1) quantify cyanobacteria, 2) determine environmental drivers of CB blooms, and 3) determine the potential for cyanobacterial toxins in the CB. Dolichospermum (Anabaena) occurred in the CB during July before the onset of the WB bloom, and then in August and September, the cyanobacteria community shifted towards Microcystis. The largest Dolichospermum blooms (2003, 2012, 2013, and 2015) were associated with reduced water clarity (Secchi disk depth < 4 m), whereas large CB Microcystis blooms (2011 and 2015) were associated with large WB blooms. Dolichospermum blooms occurred in high nitrate concentrations (>20 μmol/L) and high nitrogen-to‑phosphorus ratios (>100), which indicate nutrient concentrations or ratios did not select for Dolichospermum. Additionally, the sxtA gene, but not mcyE or microcystins, were detected in the CB during July 2016 and 2017. The mcyE gene and microcystins were detected in the CB during August 2016 and 2017. The results indicate the CB’s potential for cyanotoxins shifts from saxitoxins to microcystins throughout the summer. Continued monitoring of cyanobacteria and multiple cyanobacterial toxins is recommended to ensure safe drinking water for CB coastal communities.