Study says algal blooms can be hard to root out

[USA] Once the tiny creatures that create harmful algal blooms become established in a lake, they can change the lake’s conditions and make getting rid of harmful blooms more difficult, says a new study from a scientist at Dartmouth University and other schools.

A local scientist, however, says the study actually underscores that fixing the algal bloom problem in Lake Erie is relatively straightforward.

The new study, “Cyanobacteria as biological drivers of lake nitrogen and phosphorus cycling,” published in the journal “Ecosphere,” has been “sensationalized in the local media” and applies more to Grand Lake St. Marys in Ohio than to Lake Erie, said Justin Chaffin, senior researcher at The Ohio State University’s Stone Laboratory at Put-in-Bay.

The new study, co-authored by five scientists, says that dealing with harmful algal blooms is more than just a matter of reducing the runoff that puts nutrients that feed harmful algal blooms.

The report says that cyanobacteria, popularly known as “blue green algae,” can drive the cycling of nitrogen and phosphorus in lakes, tapping into pools of nitrogen and phosphorus and releasing it into the water.

“We usually think of cyanobacteria as responders to human manipulations of watersheds that increase nutrient loading, but our findings show they can also be drivers of nitrogen and phosphorus cycling in lakes,” says Dartmouth professor Kathryn Cottingham, the study’s lead author.

“This is important because cyanobacteria are on the increase in response to global change — both warming temperatures and land use — and may be driving nutrient cycling in more lakes in the future, especially the clear-water, low-nutrient lakes that are so important for drinking water, fisheries and recreation,” she said.

The Sandusky Register asked scientists at Ohio Sea Grant’s Stone Laboratory on Gibraltar Island, near Put-in-Bay, what they thought of the study and what it means about efforts to battle harmful algal blooms in Lake Erie.

The Register was referred to Chaffin, who has a doctorate in ecology from Toledo University, focusing on the effect of nitrogen concentrations on phytoplankton. For his master’s degree, Chaffin studied microcystis in Lake Erie. Microcystis is the kind of cyanobacteria blamed for Lake Erie’s worst algal blooms.

“That manuscript has been sensationalized in the media,” Chaffin replied. “It has been well-known that cyanobacteria are capable of accessing phosphorus from the lake bottom. They migrate up to the surface for sun light and go down to get nutrients.”

The study has little relevance to Lake Erie, Chaffin said.

“Ninety percent of the summer time cyanobacteria biomass is explained by spring time phosphorus load from the Maumee River. The study and its findings are more applicable to smaller, inland lakes that have a great deal of internal nutrient recycling, such as Grand Lake St. Marys,” Chaffin said.

Chaffin said that Grand Lake St. Marys has a large amount of phosphorus in sediments, and that’s a big part of the problem in that lake, compared to nutrients from rivers flowing into the lake.

“For Lake Erie, I am convinced that the cyanobacterial bloom can be fixed by proper land use practices that reduce nutrients flowing into the lake. For example, in 2011 we had the worst bloom in Lake Erie history, but in 2012 we had a very small bloom and the phosphorus load to Lake Erie during the spring time was about one-tenth that of 2011,” Chaffin said. “Thus, Lake Erie can improve itself within one year if we can keep excess nutrients out of the lake.”

Photo: A Lake Erie algal bloom. ( Jeff Reutter / Ohio Sea Grant and Stone Laboratory)

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