‘Dead zone’ off Texas coast growing in size

Headlines this month bring grim news of a massive “dead zone” in the Gulf of Mexico.

Is this something Texas should be worried about?

Yes and no.

Most of those headlines refer to a recent study from Louisiana State University, which forecast a dead zone in the Gulf one-third larger than average this summer. That’s big. It forms from chemical runoff in the Mississippi River, and it kills a lot of marine life.

But that’s Louisiana. Texas is different. It has a different kind of dead zone, said Steve DiMarco, an oceanographer and veteran dead zone researcher with Texas A&M, and it’s also hitting record size this year after a rainy spring.

When you put the two contiguous zones together, that’s a 600-mile swath of uninhabitable sea from Gulfport, Miss., to south of Corpus Christi.

“The dead zone that’s off Texas right now has nothing to do with the Mississippi,” DiMarco said. “It has everything to do with the Brazos, the Colorado, the Guadalupe, the Trinity.”

All rains eventually flow to the sea. Sometimes, that creates dead zones. Image via Texas Water Development Board

As the name suggests, it’s an area of the ocean where life withers for lack of oxygen. Specifically, it happens in the bottom 6 to 9 feet of shallow coastal waters for various reasons.

In Louisiana, it’s largely due to the runoff of chemical fertilizers from the vast central swath of the country that drains into the Mississippi River. The high-tech, nutrient-rich fertilizers farmers spray over tens of thousands of square miles of Midwestern farms eventually wash into the Gulf.

There, hungry algae have a feeding frenzy on the nutritious muck, and their population explodes. Until the food is gone, that is. Then they all die together and sink to the bottom, where microbes await to decay them.

Microbes, unlike algae, breathe oxygen. Like the algae, their population booms when a food source — algae — becomes rapidly abundant. But eventually the microbes breathe all the oxygen. Then they also all die. And so do most other creatures down there without oxygen to breathe.

Unlike the Louisiana zone, DiMarco said, Texas’ has much less to do with pollution runoff and more to do with rain. And Texas has sure had a lot of rain this season.

Almost everything that falls on the state then flows out to sea, and floods on the land became floods atop the water, which are harder for people to see.

Saltwater and freshwater, though similar in appearance, don’t mix. They just stack like water and oil.

So when billions of gallons pour down Texas rivers and into the Gulf, it smothers the saltwater beneath, blocking it from the oxygen in the air above. Then a dead zone — also called hypoxia — begins to form, and it stays in place until late summer storms bring waves to mix the water.

The National Oceanographic and Atmospheric Administration sends vessels out to track these zones. Nelson May helped lead the most recent expedition in June, when researchers found dead zone oxygen levels (less than 2 milligrams of oxygen per liter of water) more than 55 miles south of Corpus Christi.

“This is the farthest south that we've detected hypoxia since the beginning (2001) of the Hypoxia Watch Project,” he said.

The Texas dead zone was first described in the 1970s, DiMarco said, though evidence suggests it’s been occurring for more than 100 years, which predates most chemical fertilizers and many chemical pollutants.

Still, it has effects. DiMarco said dead bottom-feeding sea life is washing ashore along parts of the Texas coast now, creating bad smells and offending tourists.

Peter Thomas, a marine scientist at the University of Texas Marine Science Institute in Port Aransas, said, “We have found that a very large dead zone causes widespread reproductive impairment in Atlantic croaker, an indicator species, with potential long-term serious impact on their populations.”

Atlantic croaker are studied to assess the broader health of their environment.

Thomas’ research showed that croaker populations in dead zones experienced “masculinization.” Male reproductive cells were found in female reproductive parts, and the overall population saw a greater ratio of males to females. The reasons are complicated.

Research by the Smithsonian Institution in 2014 found that dead zones worldwide were increasing in frequency and severity. Researchers attributed that mostly to an increase in fertilizer runoff, like in the Louisiana case.

But they also cautioned that a warming climate — the planet broke annual temperature records for both of the last two years — would exacerbate the problem. Warm water becomes more buoyant than cool water.

So as a warmer atmosphere slowly heats the ocean surface, the top layer, rich with oxygen, will become less likely to mix into the depths beneath, where the dead zone occurs.