Record-high water temperatures and a March sewage leak are contributing to a large algae bloom in the Baltimore harbor, bringing what is known as a "mahogany tide" of reddish-brown algae to the Middle Branch of the Patapsco River.
The bloom is somewhat earlier and more severe than usual, scientists say, despite the fact that a developing drought has limited runoff pollution from feeding algae growth.
Water testing conducted by the Maryland Department of Natural Resources shows skyrocketing levels of chlorophyll, the molecule plants use to turn sunlight into energy, and plummeting levels of oxygen in waters near Brooklyn and Cherry Hill. Both are classic signs of algae blooms.
The blooms threaten aquatic plant and animal life because when they die, the bacteria that decompose them suck oxygen from the water, creating dead zones. The algae also block sunlight from reaching underwater grasses, and the type that has developed in this bloom can also be toxic at high enough levels, scientists said.
"They're already existing in a less-than-pristine environment," National Aquarium interpretive specialist Susan Bitter said of the marine wildlife. "Add another stressor, and they might struggle a little bit."
Organizers of clean-water advocacy group Blue Water Baltimore first noticed water in the Middle and Northwest branches of the Patapsco turn murky during a weekly visit for samples April 25, said David Flores, water-quality manager for the group's Baltimore harbor waterkeeper program. While their test results haven't come back yet, Department of Natural Resources' monitoring shows high levels of Prorocentrum minimum, a potentially harmful form of algae that crops up every spring.
But a few factors are different this spring, scientists said. Spring rain typically pours fertilizers into the bay, spawning the algae blooms, but this year rainfall totals are about 5 inches below normal. In some parts of the bay, that is showing how much water quality can improve if anti-pollution policies limit fertilizer runoff, said Beth McGee, a senior water quality scientist with the Chesapeake Bay Foundation.
"It is one more argument that we need to keep up pollution reduction," McGee said.
But lack of rain is also keeping sewage leaks stagnant. On March 27, a pipe that transports about 17 million gallons of untreated sewage from western Baltimore County to the Patapsco Treatment Plant in Southwest Baltimore ruptured, flowing the sewage into the Middle Branch near Cherry Hill. Tom Parham, director of the DNR's tidewater ecosystem assessment division, attributed much of the algae around Baltimore to the leak.
Warmth of the bay water is further exacerbating the algae growth, scientists said. Testing sites showed 61-degree temperatures in the Patapsco and Back rivers in April, 6 degrees above normal and 2 degrees above the previous record high dating back to 1985. Record-high water temperatures are being recorded up and down the Chesapeake.
That is a problem because it makes the algae-eating bacteria more active, drawing more oxygen out of the water, McGee said. Warm water also holds less oxygen than cooler water, she said.
Elsewhere, an even larger algae bloom has developed in the South River, according to state testing sites. Algae levels there are nearly three times as high as in the Patapsco.
Water-quality advocates fear the conditions could mean an active algae-bloom season this summer. If rainfall levels remain below normal, it could mean less nitrogen and phosphorus pollution running into the bay, limiting algae growth. But the waters may also already be loaded with algae food because of a flood of runoff into the bay from Hurricane Irene in August and remnants of Tropical Storm Lee in September.
"It'll be an interesting summer," McGee said.