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TEHRAN, August 7 -Heavy Midwest rains will wash more destructive fertilizer into the water, scientists say.
TEHRAN, Young Journalists Club (YJC) -Scientists expect the size of the Gulf of Mexico's massive dead zone to be larger in coming years as changing global weather patterns pound the Midwest with heavier rains and more severe flooding.
The Gulf's dead zone is an area that spans thousands of square miles just off the coast and where no fish can survive. It is created mainly year after year by fertilizers that run off Midwestern agricultural fields.
The fertilizers travel to the Gulf down the Mississippi River. Once there, they stimulate intense algae growth. That overly thick algae consumes all the oxygen in the water, choking out the other marine life.
"Just like people, anything living in the water requires oxygen to breathe," said David Kidwell, a lead scientists with the National Oceanic and Atmospheric Administration's National Centers for Coastal Ocean Science. "That oxygen is dissolved in the water. And when that dissolved oxygen level is low, it causes things to die off."
Thousands of species of marine plants and animals live in the Gulf, including shrimp, crabs, oysters, squid, octopus and corals. Animals that can swim, like fish or shrimp, simply leave the zone once the oxygen is depleted. Those that cannot swim usually die.
This low-oxygen -- or hypoxic -- area has existed in the Gulf for decades. Scientists began measuring it in the 1980s.
On average, the dead zone has not changed much for decades, said Dan Obenour, an assistant professor of civil, construction and environmental engineering at North Carolina State University, who works with a team of scientists to predict the dead zone's annual size.
"The nutrient load ... plateaued in the late 1980s, and we haven't had much success at changing that," Obenour said.
But things could change for the worse now, because, while the amount of fertilizer applied to America's cropland hasn't changed, the percentage of that fertilizer carried into the Gulf is expected to increase, said Craig Cox, the senior vice president for agriculture and natural resources at the Environmental Working Group.
The latest climate models, produced by the federally mandated U.S. Global Change Research Program, predict that springtime in the Midwest will become wetter. The rains will arrive in heavy downpours that will cut through fields, washing away tons of fertilizer-dense soil -- far more than over the previous decades.
It already has started. This year, historically heavy rains and flooding inundated the entire Midwestern region, delaying or preventing farmers from planting millions of acres of agricultural fields.
"All the climate models predicted what is happening now," Cox said. "Across the Midwest, it is going to be wetter. And, more importantly, most of the rainfall will come in heavy downpours."
When the water is delivered in a downpour, it creates more-intense erosion, Cox said. Instead of washing off the fields in a more level sheet -- as happens with gentle rain -- the water creates a channel through the dirt.
"They look like small streams flowing through the fields," Cox said. "And that creates much more erosion. The estimated amount of soil and material that erodes is anywhere from two to four times more than what happens in a normal year. It's tons and tons and tons of soil and fertilizer."
It's already having an impact. Scientists this spring predicted that the Midwestern flooding would create a larger-than-average dead zone.
On June 10, NOAA released a forecast predicting the zone to span more than 7,829 square miles -- well above the five-year average size of 5,770 square miles, and nearing the record set in 2017 of 8,776 square miles.
"A major factor contributing to the large dead zone this year is the abnormally high amount of spring rainfall in many parts of the Mississippi River watershed, which led to record high river flows and much larger nutrient loading to the Gulf of Mexico," a statement from NOAA said. "This past May, discharge in the Mississippi and Atchafalaya rivers was about 67 percent above the long-term average between 1980 and 2018."
NOAA scientists measured the zone in late July at 6,952 square miles -- nearly 1,000 square miles smaller than predicted. But, the agency was quick to warn that the area probably would grow substantially.
The scientists measured the zone shortly after Hurricane Barry swept through the Gulf in mid-July. The storm churned up the water, bringing more oxygen into the dead area.
"Tropical storms will mix up the water and make the hypoxia go away," Obenour said. "But it is a temporary effect. It only lasts a couple weeks. So, the size they measured was a little smaller than what we predicted, probably because of the storm. It was kind of bad luck because now we don't have a clear picture of the zone's size."
The scientists who measured the area were already seeing evidence that it was growing, Kidwell said.
The forecast may look bleak, but there are efforts being made to reduce the dead zone's size over in the coming years, Kidwell said.
Source: upi
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