‘Dead Zone’ is largest ever in Gulf of Mexico

From National Geographic

A record-breaking, New Jersey-sized dead zone was measured by scientists in the Gulf of Mexico this week—a sign that water quality in U.S. waterways is worse than expected.

The National Oceanic and Atmospheric Administration (NOAA) announced today that this summer’s dead zone is the largest ever recorded, measuring 8,776 miles. This is more expansive than the nearly 8,200 square-mile area that was forecast in July. Since monitoring began 32 years ago, the average size of the Gulf’s dead zone measured in at 5,309 square miles.

The Gulf of Mexico hypoxic or low-oxygen zone, also called a dead zone, is an area of low to no oxygen that can kill fish and other marine life. It’s primarily caused by an excess of agricultural nutrients that flow downstream and into surface waters, stimulating harmful algae.

To record the new measurements and assess the severity of low oxygen levels in the Gulf, scientists from the Louisiana Universities Marine Consortium (LUMCON) embarked on their 31st mid-summer hypoxia research cruise in July. Even with reported numbers as large as they are, the team of scientists said the entire area of the dead zone couldn’t be mapped due to an insufficient number of workable days on the ship. There was more hypoxia to the west, and the measured size would have been larger if there was more time for researchers to work.

“The results from this year reflect the nitrate flux into the Gulf, which was high,” says Nancy Rabalais, a research professor at LUMCON who helped lead the cruise. “It’s a matter of addressing the sources of the nitrate—where they first start—which is in a field of agricultural crops.”

This year’s large size is mainly due to heavy stream flows in May, Rabalais continued, which were about 34 percent above the long-term average and carried higher-than-average amounts of nutrients through Midwest waterways and into the Gulf. (Read “Heavier Rainfall Will Increase Water Pollution in the Future”)

Preliminary reports from the United States Geological Survey (USGS) align with the observation, estimating that 165,000 metric tons of nitrate–about 2,800 train cars of fertilizer—and 22,600 metric tons of phosphorus flowed down the Mississippi and Atchafalaya rivers into the Gulf of Mexico in May.

There are many alternative ways to farm using sustainable agriculture, Rabalais added. Those types of practices can reduce the flux of nitrogen, and they can be economical and beneficial to farming communities.

“It’s a small-scale effort right now that needs to be addressed more formally by the agricultural community,” she says. “I don’t want to see the dead zone get any larger—it’s large enough, and it’s way higher than the target size we want to see.”

What’s Flowing Downstream

The Gulf’s hypoxic zones are caused by excess nutrient pollution, primarily from human activities such as agriculture and wastewater treatment.

Farmland runoff containing fertilizers and livestock waste is the main source of the nitrogen and phosphorus, which stimulate an overgrowth of algae that sinks and decomposes in the water. The resulting low oxygen levels are insufficient to support most marine life and habitats in near-bottom waters, posing a serious threat to the Gulf’s fisheries.

The Gulf dead zone can slow shrimp growth, leading to fewer large shrimp, according to a study led by Duke University. Additionally, the total catch of shrimp could suffer, meaning higher costs at the marketplace and loss of jobs for fishermen, equating to an economic ripple effect on fisheries.

Read the full story at National Geographic