Freshwater pouring into the Gulf of Mexico after weeks of flooding in Texas has created an oxygen-depleted "dead zone" that threatens sea life, a researcher said Tuesday.
Steve DiMarco, a professor of oceanography at Texas A&M University, said freshwater runoff from the swollen Brazos River left an area 1,750 square miles depleted of oxygen, or hypoxic. Sea life is threatened about 35 miles offshore.
"This can definitely have an effect on organisms living there - fish and shrimp, crabs, clams," DiMarco said. "All these things need oxygen in order to live. If you have this phenomenon occurring, depending on the severity and how long it lasts, you can have mass mortality."
It's the first extensive dead zone detected off Texas, he said. The zone is strongest at the river delta off Freeport and San Luis Pass, just west of Galveston, then extends down the coast and dissipates at Matagorda Bay.
The phenomenon has been more identified with the Mississippi River's runoff into the Gulf off Louisiana. The Texas zone is about a quarter of the size of this year's Louisiana zone.
In a dead zone, freshwater on the surface caps the oxygen below, affecting organic material at the bottom. The duration of the dead zone depends on currents and winds.
"The storms come through and the wind mixes up the ocean and breaks down this capping of the freshwater," he said.
DiMarco based his findings on data collected recently by researchers aboard a ship from the National Oceanic and Atmospheric Administration National Marine Fisheries Service.
Nancy Rabalais, chief scientist for the Northern Gulf of Mexico Hypoxia Studies, said it may not be a long-term problem.
"That area doesn't usually doesn't have hypoxia but also doesn't usually have heavy rains like that," she said. "The system off Texas is just not conducive for formation of hypoxia."
Rabalais said that once the sediments and organic matter that came with the freshwater subside, researchers are likely to find the new dead zone is temporary.