Algal blooms more frequent in Chesapeake

Scientists at the University of Maryland Center for Environmental Science have shown that the frequency of harmful algal blooms in the Chesapeake Bay has been increasing over the past 20 years, fed by excess nitrogen runoff from the watershed.


Harmful algal blooms in the western part of Lake Erie, August 2014 (NOAA)

Findings were published in the February edition of the journal Harmful Algae. The current research looks at algal blooms that occur in addition to the typical temperature-dependent blooms that swell up every spring and summer.

These blooms arise as a result of

  • growing population in the Baltimore-Washington corridor
  • development of animal and plant agriculture in the bay watershed

“The increasing frequency and intensity of these harmful algae blooms will impact our ability to achieve the ultimate goal of restoring a healthy ecosystem in the Bay and put a premium on effective methods to reduce nutrient pollution,” said Don Boesch, president of the University of Maryland Center for Environmental Science. “This study points to the need for continued efforts to reduce the amount of nitrogen running off the land and into the Chesapeake Bay and its tributaries.”

The increase in harmful algal blooms isn’t just happening in the Chesapeake Bay, either. Scientists are finding increased bloom activity off the coast of China, in Europe, and other places.

“We’re seeing this all over the world—more blooms, more often, lasting longer,” said study author Pat Glibert, professor at the UMCES’s Horn Point Laboratory. “In many places these trends are consistent with increased nitrogen loads.”

Here’s the remainder of the press release from the University of Maryland:

The study focused on three of the most common microscopic algae in the Chesapeake Bay that can produce toxic or nuisance conditions when they become very abundant. These are commonly known as harmful algal blooms, or HABs. Two are caused by dinoflagellate species, Prorocentrum minimum and Kalrodinium veneficum, and the third by cyanobacteria, sometimes called blue-green algae.

The study examined water quality data collected by the Maryland Department of Natural Resources from 1991 through 2008. During this period, the average number of P. miminum bloom events observed per year doubled. The blooms were more likely in May and resulted in the reddish waters most commonly known as “mahogany tide.” Such blooms are of increasing global concern and can severely reduce the amount of oxygen available to living things, kill fish, and alter food webs.

The annual occurrences of K. veneficum blooms have increased significantly from fewer than five events per year to more than 30 in the five-year time period from 2003 to 2008. These blooms, also found worldwide, are more likely in the summer, produce a toxin that has been implicated in fish-kill events in the Chesapeake Bay, and is associated with failure of oyster spawning and development.

The frequency of blooms of cyanobacteria in the tidal waters of the Chesapeake estuary has increased from about 13 per year in the 1990s to 23 in the 2000s. Cyanobacteria are the major causes of HABs in freshwater environments, a rapidly expanding global problem that threatens human and ecosystem health. It was cyanobacteria blooms in Lake Erie that last year required shutting down the water supply in Toledo, Ohio. [The New York Times reported last August that cyanobacteria were “far from just Toledo’s problem.”]

This study aids in the broader understanding of the complex mechanisms that influence harmful algal bloom progression in bodies of water rich in organic nutrients such as phosphorus and nitrogen. It points to the direct need to reduce nutrient pollution in the face of both urban and agricultural development.

“There is a relationship with nutrients—as we change the nitrogen-to-phosphorus ratio, we tend to create opportunities for these species to bloom,” said Glibert. “We need to pay more attention to reducing nitrogen. We’ve made some progress but still have efforts to go.”