Gulf of Mexico's 'dead zone' is 8th largest

(1 Aug 2019) Scientists are back from measuring the Gulf of Mexico "dead zone" and say although Hurricane Barry reduced the size from a predicted near-record 7,800 square miles (20,200 square kilometres) the area is still one of the top 10 largest.
The dead zone refers to an area where there's too little oxygen to sustain marine life in a large underwater area, starting at the sea floor.
But tropical storms roil the water, mixing in oxygen.
Hurricane Barry made landfall July 13 — 10 days before the measurement cruise began.
Louisiana State University scientist Nancy Rabalais returned Wednesday from a week of collecting water samples in the Gulf to measure the size and severity of the dead zone.
Rabalais said the high river levels and higher amount of freshwater flooding the Gulf carry with it fertilizer and other nutrients carried in Midwestern floodwaters to the Mississippi River.
The nutrients feed algae, which die and then decompose on the sea floor, using up oxygen.
"The Mississippi River watershed is a world class river, and it drains a long distance," Rabalais said.
"It drains a lot of water, and there's a lot of activity within that watershed that can cause problems with the nutrient levels.
The bottom area of low oxygen in Louisiana coastal waters west of the Mississippi River was 6,952 square miles (18,000 square kilometres), approaching the land area of New Jersey, but well below the predicted size of 8,717 square miles (22,557 square kilometres) before Hurricane Barry.
Still, the size ranks the eighth largest among the 33 years with similarly mapped areas.
Rabalais said the research trip was nine days, seven of which two teams worked around the clock collecting nearly 100 samples.  
The brown shrimp season, which is at its peak during the summer months, is likely to take a hit – to both the size of the shrimp and the distance fishermen will have to travel to catch them , she said.
The size of this year's dead zone ranks eight in the top 10 in recent history, according to Rabalais.
She also adds the problem of the dead zone is fixable and has only come about in recent decades with the increased use of fertilizer and other nutrients in agricultural runoff, which ultimately ends up in the Mississippi River.
"Other areas in the world when you reduce the nutrients, you improve the water quality," she said.
"And it's not just the Gulf of Mexico. The watershed has the same toxic bacterial blooms – these blue-green algae blooms that are harmful to children, dogs, people. And, nitrate levels in drinking water often exceeds the safe standards."

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