‘Dead Zone’ Area Extends To Lower Texas Coast

The 2010 “dead zone” area has for the first time covered areas from High Island to Port O’ Connor, says Texas A&M University oceanographer Steve DiMarco, who has just completed a research cruise to study the dead zone off Texas waters.

A “dead zone” occurs when there is hypoxia, or oxygen-depleted waters. Off of Louisiana, such low levels of oxygen are believed to be primarily caused by the combined inputs of freshwater and nutrients of the Mississippi River and other sources such as organic material from coastal wetlands as they empty into rivers and eventually the Gulf of Mexico.

Environmental conditions such as winds, waves and currents also impact the size, severity and duration of the dead zone each summer, DiMarco says. Hypoxia off of coastal Texas is less understood and is likely the result of several additional factors including local freshwater sources flowing onto the coast and summer upwelling and the accompanying algal blooms, he adds.

DiMarco and his research team sampled waters from south of Terrebonne Bay, La., to Corpus Christi and found that hypoxia was common throughout the region. The lowest oxygen readings of oxygen concentrations were near zero in regions south of Sabine, Texas and near Lake Charles, La. The team had the ability to sample with ultrahigh spatial resolution (660 feet) spacing, and the use of an extremely fast vessel, capable of more than 20 knots, allowing the researchers to collect more than 19,000 observations across the coastal ocean in less than five days.

Water samples taken near Port Aransas and Corpus Christi were depleted to near 50 percent of normal conditions, but were not considered hypoxic, DiMarco says.

Severe hypoxia levels can result in fish kills and can adversely affect many types of marine life where it is present.

“We found severe hypoxic levels near Galveston to Crystal Beach and High Island, and down the coast to Freeport and Port O’Connor,” DiMarco explains. “The dead zone areas are not as big as they were in 2008 and not as intense as they were in 2007, but they are still there and in most areas of the upper Texas coast, so it is a major concern.”

The team took water samples from 5 to 15 miles off the Texas coast and found most hypoxia level at depths from 24 to 90 feet. Hypoxia was found most often in the water column at from 3 to 24 feet above the ocean floor, DiMarco said.

DiMarco was the first to discover a Texas-created dead zone area off the Texas coast in 2007, a result of unusually heavy rains that poured into the Brazos River. Where the water emptied into the gulf off the Texas coast, it created the first proven dead zone area that originated from Texas rivers.

Dead zone areas frequently occur where major river systems empty into the Gulf, such as the Mississippi River, which drains 40 percent of the land area of the United States and also accounts for almost 90 percent of the freshwater runoff into the Gulf of Mexico. Previous research has shown that nitrogen levels in the Gulf related to human activities have tripled over the past 50 years.

The team surveyed almost 400 miles of Louisiana and Texas coastline on the NOAA (National Oceanic and Atmospheric Administration) research vessel Manta, an 83-foot ship operated by the Flower Garden Banks National Marine Sanctuary Program office in Galveston.

DiMarco’s research is part of a $3.7 million grant from the NOAA Center for Sponsored Coastal Ocean Research to study the dead zone and better understand and predict where and when it will happen each year. They will have two cruises per year through 2014.

Other scientists aboard the ship were Piers Chapman, head of oceanography at Texas A&M; Norman Guinasso, director of Texas A&M’s Geochemical and Environmental Research Group, and five graduate students.