Saturday, June 12th, 2021
Algae from 2010 reappears on lake
Toxin readings remain within safe levels
By Sydney Albert
A thick algae scum coats the surface of Grand Lake at Pullman Bay on Thursday.. . .
CELINA - Colorful clumps of algae that have appeared at several locations around Grand Lake have stoked fears of a repeat of 2010, when the same blue-green algae carpeted the lake in thick mats.
Lake goers and residents recently have noticed patches of thick algae, particularly in some shallow, back channels. The sight has caused heightened emotions regarding the lake's water quality only a few weeks after the state removed no-contact advisories from local beaches for the first time in 12 years.
The distinctive mats of algae reportedly are the result of three different types of cyanobacteria, more commonly referred to as blue-green algae, with which Grand Lake has historically struggled. They are planktothrix, aphanizomenon and microcystis. Stephen Jacquemin, a professor at Wright State University-Lake Campus who studies the lake's water quality, clarified that microcystis is not to be confused with microcystin, a toxin produced by various types of cyanobacteria.
Jacquemin said Friday he'd been investigating the algae sightings. While portions of the 13,500-acre lake remain clear, with good water quality, various pockets of algal blooms are appearing around the lake.
"Lots of the back channels are starting to show this," he said, referring to the brightly-colored clumps of algae.
For most of the past few years, Grand Lake has been host to a virtual monoculture of planktothrix. Jacquemin said that during the last nine years, almost 100% of the lake's algal population consisted of planktothrix, which gave the lake its distinctive cloudy, greenish color many have become familiar with.
What people are seeing now in the patches of blue, green and white-colored mats is a combination of planktothrix, aphanizomenon and microcystis - the same three types of algae present during the bloom of 2010, Jacquemin said.
"Is this year going to be a repeat of 2010? It's unclear. But it's not good to see," Jacquemin said.
In spring and early summer, the lake's algal blooms typically are fed by external nutrient loading, primarily from farmland runoff. This year, low precipitation and resulting runoff in combination with years of conservation practices, including restrictions on the amount of manure and manmade fertilizers farmers can apply to their fields and adding manmade wetlands along lake tributaries to help filter incoming nutrients, resulted in the clearest water Grand Lake has seen in years.
Moving into mid-summer, algae tends to depend more on internal nutrient loads made up of nutrients already present in the lake, particularly in the lake's sediment. When temperatures rise, nutrients held in the lake's sediment are released, Jacquemin said. Types of healthy algae, including green algae, diotoms and dinoflagellates, also decrease.
Without the dominating presence of planktothrix, and the population of healthy algae falling due to rising temperatures, the door was open for a more varied mixture of cyanobacteria to grow again, Jacquemin said.
Even so, current cyanobacteria levels in the lake are roughly 10-15% of what they were last year, Jacquemin said. The latest water samples collected Wednesday by the Ohio Department of Natural Resources show toxin levels have risen, but still are below the state threshold to trigger a water advisory. The area with the highest microcystin levels was West Beach at 4.97 micrograms per liter, while the area with the lowest levels was Windy Point at 0.31 micrograms per liter.
The state threshold for a recreational public health advisory due to microcystin levels is 8 micrograms per liter.
Jacquemin noted microcystin levels could "change on a dime," however. He advised common sense, and that people avoid contact with obvious algal blooms.
He also does not consider a recent heavy rain event in the area as a potential cause for the current blooms. He asserted the cause is internal loading, nutrients that had accumulated in Grand Lake for more than a century, which he said demonstrates the continued need for conservation efforts around the lake.