CORVALLIS, Ore. - Hurricane Katrina left a swath of destruction along the Gulf Coast landscape, and now a team of scientists is heading to the Gulf of Mexico to see what effects the storm may have had on the water quality, biology and sediment deposits in the shallow coastal waters.
Researchers from several institutions will take part in a series of cruises aboard different research vessels as part of a major interagency effort to mobilize the scientific community to study the aftermath of one of the country's most devastating natural disasters. Their projects, which began this week, are federally funded by the National Science Foundation, the National Oceanic and Atmospheric Administration and the Department of Defense.
Oregon State University chemical oceanographer Miguel Goni leaves for Louisiana this week to study the effects of Katrina on sediment deposits. Goni, who has spent much of the last eight years researching sediment in Gulf waters off the Mississippi delta, says sediment often shifts during storms, but the immense tidal surge of Katrina has the potential to create major changes in "an unnatural system."
"Human engineering has completely changed the delta and the Mississippi River, in fact, drains into an area of the Gulf that it probably wouldn't, left to its own devices," Goni said. "Since those human activities began, we've annually seen sediments about 2-3 centimeters deep build up in the spring when the river has its highest discharge, and then wash out to deeper water during winter storms."
"When Hurricane Lili hit the Louisiana coast in 2002, there was a very large shift of sediments into areas not normally affected," Goni added. "We saw deposits of between one and 30 centimeters of very fine sediment in areas that don't really see that kind of activity. And Lili was a category-2 storm that pales compared to Katrina."
As a result of their cyclonic wind circulation, hurricanes such as Katrina often bring sediments onto shore on the east side of the storm's eye, while they transport them offshore on the west side, said Goni, who is an associate professor in OSU's College of Oceanic and Atmospheric Sciences.
"The larger, coarser sediments are left on shore, while the smaller, finer material is washed out to sea," he said. "This offshore transport can help the sub-aqueous part of the delta grow."
The sediment shifts are of concern to the shrimp industry, Goni says, although Gulf Coast shrimp historically have weathered sediment changes because they thrive in the soft, muddy bottom. But the shrimp also depend on algal matter for food, and the region has been struck by several hypoxia events, creating a "dead zone" that virtually snuffs out all marine life.
"In a complex ecosystem, any change in the environment is a cause for concern," Goni said.
Shifting sediments may alter currents and contribute to additional algal blooms. When these blooms die off, the organisms sink to the bottom and suck the oxygen out of the water column, suffocating shellfish, fish and other life forms.
Goni said the sediment also may bury oil pipelines and communication cables - and though they may not damage them, the layers of silt make it difficult to access and repair them.
"One of the things we're looking at with the sediment, in addition to its volume and location, is its composition," he said. "We can tell if the organic matter in the sediments is natural or if it is petroleum-based, which could indicate that some of the underwater pipes may have been damaged and are leaking."
Both the oil pipelines and communication cables are in more danger from underwater landslides that may occur as sediment is washed out into the deeper Gulf waters of the Mississippi Canyon.
Goni said it is sometimes hard for people from other regions to visualize the Gulf of Mexico, which has shallow coastal waters that "really feel the impact of storms." Goni and his colleagues estimated that Hurricane Lili dropped more sediment into those waters than the entire output of the nearby Atchafalaya River did for an entire year.
"Much of the broad shelf west of the Mississippi delta is very shallow, with water depths of five to 20 meters," Goni said. "I've been out there when there have been two-meter waves and the entire ocean turns chocolate brown. Hurricane Katrina had a six-meter surge and even larger waves. The impact on the seafloor must be immense."
Goni will join other researchers aboard the Cape Hatteras, which is the research vessel of Duke University, for a series of projects that will examine water quality, pollutants, navigation hazards, and the marine food chain, as well as the area's sediment deposits.