"Mahogany tides" seen in the bay
It isn't just Baltimore's Inner Harbor that's been plagued lately with fish-killing algae blooms. Scientists with the Department of Natural Resources say they've been seeing "extensive algal blooms" this month across Maryland's portion of the Chesapeake Bay.
The scientists say they've detected especially high concentrations of Prorocentrum minimum, a type of algae with little whiplike arms that enable it to move in the water. Here's a blown-up image of one cell, courtesy of DNR. Scientists say this year's big blooms covering vast stretches of the bay likely have been sparked by unusually heavy runoff of fertilizer and other nutrients during this wet spring. Though generally considered not toxic, these blooms can kill fish by consuming all the oxygen in the water when they die and decay. That's the same type of algae found in the harbor earlier this week, along with more than 3,000 dead fish, mostly menhaden.
Such blooms also can stunt the growth of beneficial bay grasses, discoloring the water and blocking out sunlight needed by the underwater vegetation. A similar surge in 2000 led to a die-back of bay grasses in the mid-bay, according to DNR. It would be unfortunate if that happened again, as bay grasses have been spreading and growing thicker lately. The grasses are important nursery and shelter for crabs and fish, and they're considered a basic indicator of the bay's health.
The good news, probably, is that Prorecentrum blooms tend to dissipate after May, so DNR scientists say. Go here to see a map showing where harmful algal blooms have been spotted so far this year around the bay. Go here to learn more about the blooms.
Comments
Yep, all that fertilizer, read Farms in the Magothy, Patapsco and Pax Rivers are causing the problems. Not many farms in those watersheds, cept the Pax and that is diminishing every day.
Tim, it's obvious this springs blooms are from urban runoff more than ag, so why put the "fertilizer" tag in there at all?
That's right, it's the easiest to point the finger at.
Nutrients as a universal term, regardless of source is much more accurate. But not nearly as accusatory.
Posted by: Dooright | June 3, 2009 9:16 AM
Dooright, I used the term "fertilizer" generically.
You're right that there aren't many farms left in the watersheds of the Western Shore tributaries you mention. If the algae blooms were only occurring in them or at their mouths, I should have amended that to say LAWN fertilizer.
The algae bloom in Baltimore's Inner Harbor no doubt got its nutrients from sewage overflows, nitrogen fallout from vehicle and power plant emissions, runoff of lawn fertilizer and other organic material, including pet droppings. Urban and suburban runoff are a significant problem and one that has been growing largely unchecked to date.
But the DNR map I referenced in the original post indicates blooms have occurred throughout the mid-Bay in May.
Those hugging the Western Shore are likely heavily influenced by urban/suburban runoff, but also by the Susquehanna, source of 50 percent of the freshwater entering the bay. The Susquehanna's nutrients come from sewage treatment plants and from farm runoff of animal manure, mostly.
Those blooms occurring closer to the Eastern Shore also are likely to have agricultural influences as well.
Don't mean to be accusatory, but bay scientists tell us the largest share of nutrients affecting water quality baywide still comes from agriculture.
Posted by: Tim Wheeler | June 3, 2009 1:43 PM