Freshwater plants invade Louisiana coast

Linda Benedict, Bogren, Richard C.  |  12/22/2010 2:40:40 AM

An unintended consequence of the Deepwater Horizon oil spill, which occurred on April 20, 2010, has been the expansion of invasive freshwater plants into the intertidal zone along Louisiana’s Gulf Coast.

"In the course of my regular salvinia survey work, I have noted and documented to the Louisiana Department of Wildlife and Fisheries a huge environmental change," said Dearl Sanders, LSU AgCenter weed scientist.

To keep the oil at bay, the U.S. Army Corps of Engineers has operated the freshwater diversions at maximum capacity since shortly after the spill, said Sanders, who has been instrumental in the AgCenter’s program to control invasive plants in Louisiana’s freshwater lakes, rivers and bayous.

What was normally brackish water became fresh as a result of the diversions, which kept the oil at bay, Sanders said. But that apparently has allowed normally freshwater plants to move south 20 miles farther than normal.

This year, the Corps ran the Davis Pond Diversion at maximum or near maximum capacity from May until September, a time that it usually operates at minimum to low capacity, Sanders said.  

"An explosion of freshwater invasive plants has occurred," he said. "Hydrilla, salvinia and water hyacinth have taken over areas where minimal saltwater levels have kept them in check for decades."

For example, Sanders has documented the movement of hydrilla from the fringes of lakes Des Allemands, Salvador, Catawatche and others so that the plants now cover hundreds of acres of what had been clear, brackish waters.

"Unless this is reversed, we may lose these lakes – or parts of them – like we have lost lakes Boeuf and Henderson," Sanders said. "I have discussed this with the Department of Wildlife and Fisheries, and they, too, are aware of the problem."

Rick Bogren

(This article was published in the fall 2010 issue of Louisiana Agriculture.)

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