When heavy rainfall sweeps the countryside, waterways are flooded with peak levels of the nutrient phosphorus, which can trigger algal blooms and create dead zones in rivers, lakes, and coastal waters, says a newly published study.
This past spring, Louisiana-based professor Dr. Nancy Rabalais, perhaps the world’s most renowned researcher on marine dead zones, predicted that the summer of 2017 would see the largest hypoxic area in the Gulf of Mexico in recorded history. Last month she was proven right.
Marine scientists estimate the low-oxygen "dead zone" in the Gulf of Mexico covers a record 8,776 square miles, or one-seventh of the basin. "This large dead zone size shows that nutrient pollution, primarily from agriculture and developed land runoff in the Mississippi River watershed, is continuing to affect the nation’s coastal resources and habitats in the Gulf," said NOAA.
A mandated interstate "pollution diet" intended to reduce nutrient runoff into the Chesapeake Bay is paying off, while voluntary measures to reduce nitrogen levels in Mississippi River have failed, writes a University of Michigan professor at the site The Conversation. "From my perspective, when we compare these two approaches it is clear that voluntary measures are not even making modest dents in nutrient pollution," says professor Donald Scavia, who has worked on the issue of "dead zones" for four decades.
The harmful effects of fertilizer runoff are likely to be exacerbated by climate change, as more extreme precipitation washes excess nutrients into U.S. waterways, causing dead zones, says a study published in Science. “The authors found that future climate change-driven increases in rainfall in the United States could boost nitrogen runoff by as much as 20 percent by the end of the century,” says The New York Times.
Heavy rainfall in May washed the equivalent of an estimated 2,800 rail cars of nitrogen fertilizer down the Mississippi River and will create the third-largest fish-killing "dead zone" in the Gulf of Mexico in 32 years of monitoring, say federal scientists. They forecast a low-oxygen dead zone of 8,185 square miles, about the size of New Jersey.