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Hurricanes destroy homes and flood neighborhoods but they can also tip entire ecosystems out of balance, according to a new study published in today's Proceedings of the National Academy of Sciences. Several major hurricanes that hit the North Carolina coast in 1999 flooded Pamlico Sound, the nation's largest lagoonal estuary, flushing nutrients and sediment into the ecosystem and diluting the salty water. "Within six weeks, the entire water content of Pamlico Sound was replaced by the flood," lead author Hans Paerl from the University of North Carolina at Chapel Hill says. "Normally that would take a year because the sound has only four small inlets, restricting exchange with the sea."
As a result, the salinity of the water in the sound dropped by two-thirds and the nitrogen levels soared by over 50 percent. Such a boost of fertilizer lets algae and other microorganisms flourish, creating a low-oxygen environment that threatens other wildlife like crab, shrimp and fish. In Pamlico Sound, it led many species to migrate out of the area. Last spring and summer, winds in the lagoon kept the water well-mixed and oxygen-levels within limits. Because water stays in the sound for a long time before running off into the ocean, though, most of the nitrogen is still in the lagoon estuary. Scientists fear that if the winds subside this year, the algae will choke the finfish and shellfish that have remained.
There are indications that the ecosystem is slowly recovering for now, but even if the summer winds return, it may take several years for the estuary to return to normal. Paerl is also concerned about the effects of future storms: "The real question is: if we're going to have 20 or more years of more frequent hurricanes as our meteorologist friends predict," he says, "how many times can the system bounce back?"
