This year’s so-called "dead zone" off the coast of Louisiana is much smaller than expected. After monitoring farm runoff from the Midwest, that has some researchers surprised.
This year’s dead zone in the Gulf of Mexico measures 2,720 square miles, or about the size of the state of Delaware. That's half as big as scientists thought it would be, with projections of 6,570 square miles. And despite what researchers call largely similar conditions, the low oxygen zone is markedly smaller than last year's, the largest on record.
Louisiana State University oceanographer Eugene Turner was part of the research team that monitored the hypoxic, or low oxygen, zone off the coast of Louisiana last month. He's said he's "very surprised" by the findings.
“The conditions aren’t that different from last year when we had the really large one, the largest one yet," Turner said. "I’m still a little flummoxed about this.”
The Gulf hypoxia is linked to farm field runoff from Midwestern states, including Iowa, which makes its way downstream. Nutrients like nitrates and phosphorus from crop fertilizers and manure flow into the Mississippi River and ultimately spur algae blooms that deprive fish and shrimp of oxygen.
Turner said the markedly smaller hypoxic zone is surprising because there hasn't been a significant decrease in nutrient runoff, which according to his research is "directly related" to the blooms of phytoplankton.
"The same amount of nitrate was coming down," Turner said. "It just wasn't all that different. I don't know."
Turner said changing ocean currents could account for the higher oxygen levels.
At 2,720 square miles, this year's hypoxic zone is still larger than researchers want it to be. The Gulf Hypoxia Task Force hopes to reduce the average size of the "dead zone" to under 1,930 square miles by the year 2035.
Though the impacts seem smaller this year, Turner said polluters aren’t off the hook.
“Of course they’re not," he said. "Because we have a five year running average. And at least from a science point of view, we’ve always said and continue to say, the environment itself is changing every year.”
According to recent findings from University of Iowa researchers, Iowa contributes disproportionate amounts of nutrients to the Gulf of Mexico. The vast majority of the state's nitrate load is linked to crop lands, which are largely devoted to corn and soybean production.
Iowa leaders and regulators have signed on to a plan to reduce nutrient runoff and improve water quality in the state. But critics say more funding is needed to implement the scale of conservation practices needed to reduce nitrate loading in the Gulf in the long-term.