Living on Lake Erie, people become familiar with the bright green paint look of Microcystis harmful algal blooms in the water, and management efforts have been focused on this nuisance for a while now. However, in Lake Erie’s Sandusky Bay, another cyanobacterial species is more prevalent, as Planktothrix blooms stain the bay’s water a dark olive green.
Both Microcystis and Planktothrix produce microcystin, a powerful toxin that can affect the liver, nervous system, and skin. However, the two species seem to prefer different nutrients: Microcystis uses phosphorus, while Planktothrix prefers nitrogen. Both types of algae also come in toxin-producing and non-toxic varieties, and little is known about what causes their blooms to become toxic.
Ohio Sea Grant researchers Dr. George Bullerjahn and Dr. R. Michael McKay, Professors of Biology at Bowling Green State University, along with graduate student Taylor Tuttle, are planning to examine what makes Planktothrix in Sandusky Bay tick. The project, which stems from ongoing work done with Sue Watson and Tim Davis of Environment Canada, will look into two aspects of Planktothrix blooms in the bay: the basic science of what drives the algae’s bloom in a relatively low-nitrogen environment, and the applied science of managing Planktothrix blooms and the associated toxin, which can contaminate drinking water.
“On an applied science level, here we have a nasty cyanobacterial bloom producing a toxin that we want to reduce,” Bullerjahn says. “But on a basic science level it really intrigues me because if you go from the open lake into Sandusky Bay, you go from a Microcystis bloom to a Planktothrix bloom in about a mile. Why is that, what is it about the bay that supports a Planktothrix bloom versus Microcystis in the open lake? Is it temperature, is it nutrients, is it a combination of both, and we really don’t know. That’s a fundamental scientific problem I find interesting.”
Phosphorus and nitrogen mostly enter the Lake Erie environment through fertilizer runoff from agricultural fields and discharge from sewage treatment and septic systems. Current management efforts focus on Microcystis blooms by reducing phosphorus use in the watershed – fertilizer manufacturer Scott’s has removed phosphorus from all of its lawn care products – but studies show that controlling nitrogen could also play a big role in reducing blooms of other potentially toxic cyanobacteria.
Bullerjahn and McKay have previously tested this hypothesis in the lab: samples of water from Sandusky Bay that received added phosphorus did not change much, while algae in the water grew visibly when nitrogen was added. This suggests that Planktothrix is always present in the bay, scavenging nitrogen wherever it can when the nutrient is present in very low concentrations. However, an influx of nitrogen from the landscape allows the cyanobacteria to grow quickly and enter a bloom stage.
“This is a situation in which you can never ignore the importance of phosphorus, but nitrogen is playing a bigger role here,” Bullerjahn says. “It points to management strategies in which you would control nitrogen as well as phosphorus.”
However, more research is needed to confirm this hypothesis, and also to find out what drives the change from non-toxic to toxic algal blooms. Previous studies have shown that there are multiple genotypes – different varieties of the same blue-green alga – of Microcystis, with some genotypes producing toxins while others don’t. Bullerjahn and McKay plan to determine whether the same is true in Planktothrix, and under which conditions toxic genotypes become predominant in Sandusky Bay.
“What we don’t know about Sandusky Bay is really how many different genotypes of Planktothrix there are,” Bullerjahn says. “Are there toxic and non-toxic genotypes? Is it one single genotype? My guess is it isn’t, but we don’t know. And if you have non-toxic and toxic genotypes, how do they interact? Is one genotype better suited for a particular set of nutrients or temperature over another? So there’s a lot of basic work that needs to be done.”
To help with that work, the researchers will use a Sandusky Bay metagenome, which is created by sequencing all of the DNA in a water sample. The metagenome can be used to determine the microorganisms present in the water, which in turn lets researchers identify the biochemical reactions carried out by those organisms.
“One thing we know about the bay is that it’s a nitrogen-limited environment and if you go and sample the bay in June when the blooms are just starting, there’s virtually undetectable nitrate,” says Bullerjahn. “So somehow Planktothrix appears to be very good at scavenging nitrogen, and it’s not a nitrogen fixer.”
Some cyanobacteria, such as Anabaena, are nitrogen fixers and can support their nitrogen needs by taking in atmospheric nitrogen and making ammonia, but Planktothrix isn’t one of those species. Yet it lives in an environment where there is very little free nitrogen available for its growth.
“So what is it about this environment where they can survive in low nitrogen conditions? Maybe they’re better at scavenging nitrogen than Microcystis is, or maybe they’re benefiting from the presence of other nitrogen fixers, that’s what we need to figure out,” Bullerjahn explains.
Once they have a better idea of what drives the Planktothrix blooms in Sandusky Bay, the researchers will also be able to make recommendations about its management. Once they know the role of nitrogen, and they can use lab evidence to document that it triggers both enhanced blooms and toxin formation, they can emphasize the importance of managing nitrogen from nonpoint sources like agriculture to control the extent of the Sandusky Bay blooms.
“The citizen science components of these projects teach students how to collect that impactful data, so it can go toward real scientific findings, not just lab exercises.” Dr. Chris Winslow
Bullerjahn and McKay will also incorporate education and outreach components into their project. Students from Perkins and Sandusky elementary schools will help to collect water samples for nutrient analysis as part of a STEM (science, technology, engineering, and mathematics) program called iEvolve, based at BGSU and funded by the National Science Foundation.
“We want to make sure that students realize they can collect and analyze relevant data while being guided by professional research scientists,” explains Ohio Sea Grant Assistant Director Dr. Chris Winslow, who is also part of the iEvolve project. “The citizen science components of these projects teach students how to collect that impactful data, so it can go toward real scientific findings, not just lab exercises.”
In addition, Dr. Kathy Durham, a former student of Bullerjahn’s, and her molecular biology students at Lorain County Community College will help the research team sequence environmental DNA from the different Lake Erie environments being studied. With field sampling already underway to determine nutrient concentrations before spring runoff begins to add nitrogen to Sandusky Bay, the researchers have a busy two years ahead of them.
“What we want to do is look at nutrient levels in the bay throughout the year,” says Bullerjahn. “So we’re actually getting water samples even under the ice right now, looking at nitrogen and phosphorus, and seeing how the ratios change as seasons change.” Final results are expected in February 2016.