Researcher: Texas 'Dead zone' shrinking

The first detected "dead zone" off Texas in the Gulf of Mexico, a 1,700-square-mile patch of oxygen-depleted water that could threaten sea life, is shrinking as fresh water pouring into gulf from the rain-swollen Brazos River subsides, a Texas A&M University researcher said Thursday.

"It's really hard in one day to get an assessment of an area that size, but based on what we saw, it's likely a lot smaller and dispersed," Steve DiMarco, a professor of oceanography, said after he and 24 graduate students in four boats took oxygen readings a day earlier from the waters off Freeport.

"The most concentrated area seems to be right where the Brazos River empties into the gulf," he said. "The dead zone area extends at least 10 miles offshore, and it appears it is pretty much driven directly by waters from the Brazos River."

The phenomenon is caused when salt water loses large amounts of oxygen, a condition known as hypoxia that is typically associated with an area off the Louisiana coast at the mouth of the Mississippi River. The fresh water and salt water don't mix well _ like oil and water _ and keeps oxygen from filtering through to the sea bottom, causing problems for fish, shrimp, crabs and clams.

Scientists who study the Louisiana dead zone characterized the Texas event as temporary.

DiMarco said his team found no immediate evidence of a large fish kill or other significant loss of marine life in their testing Wednesday.

"There's nothing on the surface," he said. "So it's really hard to know. Sometimes in severe hypoxic conditions, you can see marine life at the surface that's at the bottom and it's a sign they're trying to escape. But we didn't see any of that."

Water levels on the Brazos have been falling after heavy rains earlier this summer inundated vast areas of North and Central Texas. The river flows more than 900 miles through most of the main regions of the state.

Researchers last month who detected the first-ever Texas dead zone estimated it was about one-fourth the size of the annual Louisiana zone, which is described as about the size of New Jersey. It's the largest such area in the world and has been studied for years.

"We have a fairly large program to look at the processes that occur off Louisiana, and what we were seeing off Texas was consistent to the August conditions off Louisiana," DiMarco said. "We see the same kind of physical processes there that work to break up the low oxygen waters at the end of the summer."

Hypoxia is defined as sea water having less than 2 milligrams of oxygen per liter. Only a couple of the two dozen stations tested by the Texas A&M team found levels below that threshold although several others were close, DiMarco said.