Record rainfall totals in many parts of Texas the past few weeks means a record amount of freshwater pouring into the Gulf of Mexico – as high as 10 times the normal rate – and that could lead to huge problems for marine life and commercial fishermen very soon, warns a Texas A&M University oceanographer.
Steve DiMarco, professor of oceanography, says the huge rainfall amounts in the last month mean that such rivers as the Brazos, Trinity, Colorado and others currently are carrying record amounts of water flowing southward to the Gulf, similar to a situation that occurred in 2007 when rivers carried 10 to 20 times the normal seasonal rate of discharge into the Gulf.
“When this happens, the coastal waters become stratified, meaning that the lighter freshwater will stay at the surface and cap the saltier, and heavier, ocean water beneath,” he explains. “Because the salt water is isolated from the atmosphere, oxygen levels in that water will begin to drop.
“That is exactly what is going on right now and in the weeks to come, and when this happens, it almost always means many marine organisms, particularly those that live near and at the ocean bottom, can’t get enough oxygen and they can get sick and die.”
In a “dead zone,” technically called hypoxia, marine life for thousands of square miles become distressed and fish kills can occur. Dead zones have been happening in the Gulf for decades off the Texas-Louisiana coastline, but the record amounts of rain this year could mean a sort of dead zone within a dead zone, DiMarco says.
Such low levels of oxygen are believed to be caused by nutrient pollution from farm fertilizers and other land-based sources as they empty into rivers such as the Mississippi and eventually make their way into the Gulf.
DiMarco has made 28 research trips to investigate the dead zone since 2003.
He says the size of the dead zone off coastal Louisiana has been routinely monitored since 1985. Previous research has also shown that nitrogen levels in the Gulf related to human activities have tripled over the past 50 years.
“Because it has the possibility to extend much further west than in typical years, the dead zone could be more intense and even much larger this year,” DiMarco believes.
“This is very similar to what happened in 2007, when dead zone conditions existed from June to September and the only thing that ended it was a hurricane, Humberto, that provided strong enough winds to mix the freshwater and saltwater and allowed oxygen back into the lower water.
“This year’s flood levels are at least as high as they were back in 2007, and all of that water in the rivers will eventually make its way down into the Gulf. These waters rushing into the Gulf means that fisheries and marine life are at risk, and this has the potential to impact all Texans who rely on products from the Gulf for their livelihood.”
DiMarco is funded by the NOAA Center for Sponsored Coastal Ocean Research to investigate the mechanisms that cause the dead zone of the northern Gulf of Mexico.