If Maryland experiences heavy snowfall this winter, biologists predict the Chesapeake Bay could experience above-average levels of bacteria and toxic algae blooms during the summer.
While human pollution can cause bacteria growth and algae blooms, natural factors, such as climate conditions, dictate their frequency. The amount of snowfall each winter is linked to algae bloom instances in the summer, since spring snowmelt causes runoff, and more nutrients to enter the bay.
“Some relation does exist between higher harmful ... blooms and increased runoff related to the amount of snow, rather than just winter temperatures,” University of Maryland Atmospheric and Oceanic Science Professor Raghu Murtugudde said. Maryland is expected to experience warmer than normal temperatures this winter, but also excess amounts of snowfall, so “harmful algal blooms may well turn out to be above normal next summer.”
Water temperature, the bay’s salt content, and nutrient levels determine bacterial growth.
“Warmer temperatures mean more growth,” Maryland Department of Health and Mental Hygiene’s Environmental Health Bureau Director Clifford Mitchell said, so the summer is generally the most high-risk time of the year for contamination. However, “hundreds of thousands of people ... [enjoy] the bay every year completely safely… I don’t discourage people from going in the bay.”
Potential for infection and toxic exposure is generally not worrisome, although Maryland residents could benefit from avoiding recreational activity in the bay during certain high-risk periods when bacteria and algae blooms are high in frequency and toxicity, Mitchell said.
In certain situations however, the state health department issues swimming warnings because of higher risks of bacterial infections. Heavy downpours lead to increased sewage run off, which could potentially contain strains of E. coli or promote toxic algae blooms, Mitchell said.
According to Mitchell, although “a little consumption of bay water isn’t worrisome … we do worry about infections that come from exposure.”
There’s a chance of exposure to bacteria and toxins for people who do recreational activity in the bay with open wounds, especially for those with compromised immune systems. Even people “who are otherwise healthy but get puncture wounds from contaminated crab or shellfish” can develop infections, though only a few cases a year develop into significant or serious infections, Mitchell said. Raw seafood consumers are also at a small risk of exposure.
As for bacteria that grow naturally in the bay, Vibrio is the Department of Health’s main concern, but of all the people who swim in the bay each year, only about 30 to 50 individuals develop cases of Vibrio, which in its mildest form causes skin infections and stomach ailments.
The Department of Health doesn’t directly monitor individual bacterial levels in the bay, but looks out for warning signs such as algae blooms.
“Although not common, we have had cases across the country where blooms contain relatively high concentrations of toxins,” Mitchell said.
According to Allen Place, marine biologist at the Institute of Marine and Environmental Technology, blooms occur when algae encounters its optimum growth factors, and natural predators like viruses and grazers don’t exist in high enough levels to suppress growth.
Blooms are fed by nutrients, mostly from human sources. Human waste and agricultural production are two of the main culprits of creating nutrient pollution, Place said.
“In the Chesapeake Bay, we are fortunate that most algae blooms have very little direct effects on human health,” Place said, citing possible skin irritation as one of the worst consequences.
The bay’s freshwater lakes and upper parts of the tributaries sometimes have Cyanobacteria blooms however, that produce toxins that damage liver cells, which can cause cancer in humans and death for dogs when ingested, he said. To be safe, Mitchell said the public is advised to avoid the bay and its tributaries’ affected regions until any bloom clears.
According to Place, Maryland isn’t alone in this phenomenon: “General trend worldwide is greater frequency of algal blooms with longer duration,” he said.