Sky high view of a huge flood
Floods from hurricane Floyd and follow-on rains did more than damage the works of humans. They hit North Carolina marine life hard.
For scientists who continue to monitor this potential ecological disaster, the recently released satellite image to the right represents a revolution. For the first time, they have the big picture of what is going on. It gives them the perspective they need to grasp what close-up aircraft surveillance and ship-based sampling are telling them.
The image, produced Sept. 23, shows the massive stain of sediments and pollutants that flowed down into estuaries and out across Pamlico Sound to slosh over Cape Hatteras and the barrier islands. Discolored water around Cape Hatteras reveals sediment the islands trapped.
Oceanographer Pat Tester says this unprecedented overview shows that "we were lucky" the floods came when they did. Nutrients they flushed into coastal waters overfeed microscopic plants called phytoplankton. The burst of plant growth depletes oxygen dissolved in the water. That can be bad for everything living there, including fish. There would have been massive suffocation if this had happened during the summer when the off-shore water is relatively calm. However, Dr. Tester explains, the autumn weather is stirring the sound enough to mix in undepleted water and air and thus replenish dissolved oxygen. "So far," she says, "I think we're doing OK."
Tracking floods' effects
Tester works at the National Oceanic and Atmospheric Administration's Center for Coastal Fisheries and Habitat Research in Beaufort, N.C. It's one of several federal and state agencies that are tracking the floods' ecological effects on rivers and estuaries as well as the sea.
Not all habitats are in as good shape as Pamlico Sound. Ecologist Gene Feldman at NASA's Goddard Space Flight Center in Greenbelt, Md., notes that "rivers and tributaries along the Atlantic are choked, and major ecological changes are happening." He explains, "Periodically, levels of dissolved oxygen in the water have dropped dramatically as organic matter decomposes, and aquatic life has been threatened in dozens of estuaries and peripheral habitats, commonly referred to as 'dead zones.' " He adds that these changes "may have lasting repercussions for hundreds of thousands of people."
It will take many months, perhaps years, of detailed monitoring on the ground and from space to know what these repercussions will be.
An instrument dedicated to this kind of surveillance on NASA's SeaStar satellite produced the image shown above. Called SeaWiFS (Sea Viewing Wide Field of View Sensor), it is designed to look at colors that reflect environmental changes. Later images show some improvement in Pamlico Sound.
Laser measures "grass" of the sea
The big question now, Tester says, is how the situation the floods created differs from normal and what will happen in the future. To pursue this question in Pamlico Sound, aircraft use a laser system to check out the abundance and health of microscopic plankton. Scientists call this the "grass" of the sea. It is the base of the marine food change, just as grass on land underlies many food chains.
Green laser pulses penetrate the water and are absorbed by the plants. Some of the green light reflects off the water surface. Meanwhile, the plankton, having absorbed laser light, gives off red pulses. The differences in arrival times of red and green pulses at the aircraft receiver let the instrument detect how the plankton is distributed in depth. This gives a three-dimensional view of how widespread and abundant the plankton is.
Meanwhile, the SeaWiFS instrument orbiting 438 miles overhead is "watching" for color changes, as well as giving an environmental overview. Changes in sea surface color can reflect changes in the phytoplankton. Tester says she is spot-checking the laser and SeaWiFS data by direct measurements from boats - an exercise she calls "sea-truthing." Put all this together, she adds, and scientists now have "a three-tiered look at the area from space, air, and sea."
(c) Copyright 1999. The Christian Science Publishing Society