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Lake Erie supplies drinking water to an estimated 11 million people in the United States and Canada, and the project led by Chaffin is geared toward developing toxicity forecasts that best prepare water treatment plant operators for the removal of microcystin. A high concentration of the toxin overwhelmed a Lake Erie water treatment plant in 2014, leading to the three-day Toledo drinking water crisis.
But not all microcystin congeners are alike in terms of toxicity. The most abundant and most studied congener in Lake Erie, known as MC-LR, has been shown in recent research to be somewhere in the middle, in terms of toxicity, compared to other congeners in the lake’s bloom. In this study, Chaffin and colleagues set out to determine the location and abundance of these different congeners to get a better handle on toxicity trends over the busy summer season.
The team collected samples at 15 sites stretching from Maumee Bay to the Central Basin from June through September in 2018 and 2019, focusing on identifying the concentration of specific microcystin congeners present over time and the changing nutrient levels in the water.
Along with the common MC-LR congener, two other congeners were found to dominate the microcystin populations: MC-RR, whose toxicity is about one-fifth of MC-LR, and MC-LA, estimated to be about 2 1/2 times more toxic than MC-LR. MC-RR, which is 17.5% nitrogen, was more dominant early in the season, when the water was rich in nitrogen, and MC-LA, which is 10.8% nitrogen, dominated later in the season, when nitrogen levels had substantially dipped – however, the total microcystin concentration was lower at that time as well, meaning overall toxicity may not have dramatically increased.
Detecting congeners doesn’t come easily – it requires highly sophisticated equipment and is more expensive than the analysis tool ELISA that’s routinely used to measure microcystins in the bloom – which is why current toxicity estimates are probably off, Chaffin said.
“Because ELISA measures overall concentration, basically you’re overestimating the toxicity in early summer when the majority of microcystins are a low-toxicity form, and then as summer progresses, the bloom is making more toxic forms, so you may be underestimating the toxicity,” he said.
An investment in routinely gathering congener data could improve modeling efforts to predict how the toxicity of the HAB in Lake Erie changes each year. Chaffin co-authored another recent study that showed using data on toxin concentrations (from existing ELISA measurements that don’t take congeners into account), water currents and a bloom’s increase in toxin production in a one-week weather map-like simulation improved the accuracy of microcystin forecasting by 79%.
“We took all the data we could find and put it in a hydrodynamic model and ran it under simulations,” Chaffin said. “So if you know where the toxins are today and make a map of the bloom like a weather map, you can watch where it’s going to go in the next seven days. And if you add biology data to the simulation, you can get a better prediction of where the highest toxin concentrations will be.
“The next step would be to merge the bloom location and toxin concentration forecast with different congeners so we could really forecast the toxicity of the bloom. But lab capabilities would need to be improved to make that possible.”
Pengfei Xue, professor of civil, environmental and geospatial engineering at Michigan Technological University, was senior author of the modeling study published in the Journal of Great Lakes Research. Co-authors of the Harmful Algae study include Judy Westrick of Wayne State University, Laura Reitz of Bowling Green State University (now at the University of Michigan) and Thomas Bridgeman of the University of Toledo.