If spring is here, can algae blooms be far behind?
Every year, as flowers bloom and trees leaf out, algae — microscopic plants — begin to flourish in the water.
Most algal blooms are innocuous, but some can be harmful, poisoning fish, birds and other animals. Others suffocate fish by depleting the water of oxygen they need to survive, contributing to the "dead zone" that forms every summer in the Chesapeake Bay.
A recent study by researchers with the University of Maryland Center for Environmental Science finds that there have been increases in two of the more common strains of harmful algae that often plague the bay. Though they tend to flare up at different times, they share a common source, the study notes: the deluge of plant-nourishing nutrients that pours into the bay from sewage, farm and urban runoff, and air pollution.
Reviewing data gathered by the state from 1991 to 2008, the center's scientists found the median annual number of blooms of one type of algae, Prorocentrum minimum, grew from 13 in the 1990s to 23 in the 2000s. It tends to pop up in May, turning the water red in what locals often refer to as a "mahogany tide."
Researchers saw a sixfold increase in another troublesome algae, Karlodinium veneficum, which often appears later in the summer when temperatures are warmer. The number of blooms reported grew from five in 2003 to more than 30 in 2008. Scientists were unable to look back beyond that because, until recently, experts often had trouble distinguishing it from other species of algae.
"This is consistent with the pattern we are seeing in many parts of the world," said Pat Glibert, co-author of the study and a professor at the center's Horn Point laboratory near Cambridge. "Globally, we see more harmful bloom events more often in more places, and often lasting longer when they do occur."
According to the National Oceanic and Atmospheric Administration, virtually every state is threatened by toxic or harmful algae. Nationwide, they cost an estimated $82 million annually in closed shellfish beds and lost seafood sales, in health impacts on bathers affected by waterborne toxins and in depressed tourism for beaches or waters infested by blooms.
The UM researchers found no clear trend in a third type of bloom, involving cyanobacteria. Often called blue-green algae, it's limited to freshwater stretches of bay tributaries, lakes and ponds. Outbreaks of cyanobacteria varied from 50 to 150 a year.
But even in "quiet" years, cyanobacteria blooms generally occur more frequently around the bay than the other two, Glibert noted. And they are particularly troublesome, as some strains release a toxin that can kill birds and even harm dogs and people who come in contact with it.
"The fact they are not increasing in occurrence should not be taken as a positive sign," Glibert said.
The UM study only looked at harmful blooms through 2008. Catherine Wazniak, a biologist with the Maryland Department of Natural Resources, said they've been more sporadic of late.
"We've gone into a pretty quiet period for both Prorocentrum and Karlodinium, where we haven't seen as much of them in the last four or five years as we had earlier," said Wazniak, who tracks the blooms.
Three years ago, though, Prorocentrum virtually blanketed Baltimore's Inner Harbor and local creeks during a warm spell, killing tens of thousands of fish and filling the air with a noxious stench of rotting flesh and microscopic plants. And Microcystis aeruginosa, a type of cyanobacteria that releases a toxin, pops up fairly regularly in the Sassafras River and in a couple of lakes on the Eastern Shore.
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Some have questioned whether the apparent increase in harmful algal blooms is real, or if people are just noticing them more.
But Allen Place, a UMCES biochemist who specializes in harmful algae, said he's convinced increasing levels of nutrient pollution are stimulating more blooms.
"It's not just a question of our looking," said Place, who was not involved with the recent study. He pointed out that Toledo, Ohio, had to shut down its water system last year after winds blew a large bloom of Microcystis into the treatment plant intake on Lake Erie.
Whether harmful blooms have increased a lot, a little or not at all, at least some scientists think that unless nutrient pollution is scaled back significantly, they're likely to break out more frequently in the future as climate change raises water temperatures, creating more favorable conditions for them.
With Baltimore-area temperatures reaching into the summer-like 80s, a smallish bloom of Karlodinium veneficum has been spotted recently in the lower Patapsco River, just beyond the Key Bridge, according to the DNR's "Eyes on the Bay" website.
"The bottom line for the public is we're still having algal blooms," said Robert E. Magnien, who oversees harmful algae research at NOAA. "We're still not in the condition we'd like to be in."