In the spring of 2011, Nicole Khan, a doctoral student in the Department of Earth and Environmental Science in the School of Arts & Sciences, was wrapping up a few weeks of field work in Puerto Rico. She had been studying the island’s mangrove forests in an attempt to reconstruct ancient sea levels. Her plan was to return to Philadelphia for a few days before setting off for nearly a month in England to perform specialized laboratory analyses. But then a unique research opportunity presented itself: The Mississippi River flooded in one of the largest such events ever recorded.
Khan’s advisor, Benjamin Horton, an associate professor in Earth and Environmental Science, urged her to go, so Khan rebooked her flight from Puerto Rico to take her directly to Lafayette, La. Her aim, working alongside researchers from the U.S. Geological Survey, was to sample the state’s coastal wetlands to see how much new sediment had been carried down the Mississippi.
“I went out on helicopter surveys to sample in different areas,” says Khan. “It was very interesting to get that perspective because you could see the whole expanse of the marshes and how they’re declining.”
The Gulf of Mexico’s wetlands are shrinking due to rising sea levels, increasing human development, dams and levees on the Mississippi that divert its flows, and subsidence, or sinking, of coastal lands. Not only are these factors eliminating valuable ecosystems for wild creatures, but they are also reducing the protective effect that wetlands can have for coastal communities in the event of a hurricane.
The researchers hypothesized that the floods might help counteract these effects by partially rebuilding the wetlands with sediment carried by the floodwaters. To test this idea, Khan and her colleagues took sediment cores from 45 sites across four wetland basins.
“The flood sediments had a different color and a loose consistency compared to the older sediments, which were more compact,” Khan says.
Khan also found that the sediments deposited by the flood had other unique characteristics, including a higher ratio of a particular type of diatom, or photosynthetic algae, than older sediments.
The scientists’ findings, published online in the journal Geology this month, indicate that the flooding—though terribly damaging to human life and property—actually benefited Louisiana’s wetlands by carrying above-average amounts of new sediment to the marshes. The floodwaters brought nearly a year’s worth of sediment deposition to some areas of the wetlands.
“This sets the stage for us to go back to those sites in the future and see whether the flood actually helped in terms of lasting effects on these marshes,” says Khan.
Originally published on February 21, 2013