The area of low oxygen that forms each summer off Louisiana’s coast should be about average size this year, according to the National Oceanic and Atmospheric Administration.
This “dead zone,” where oxygen levels are too low to support marine life in the lower water column, is forecast to be 5,898 square miles this year, about the same it has been for the past several years.
The forecast is based on river flows and levels of nutrients caused primarily by agricultural runoff as well as other pollution that ends up in the Gulf of Mexico.
Last year’s forecast was 5,483 square miles of low oxygen and the measured amount was 6,474 square miles.
NOAA sponsors the forecast work done by a team of researchers, including those from LSU and the Louisiana Universities Marine Consortium (LUMCON).
The overall NOAA forecast uses the Louisiana-based forecast combined with forecasts from three other university teams around the country to come up with an average based on information provided by the U.S. Geological Survey’s river and nutrient information.
LSU and LUMCON’s forecast calls for a larger dead zone at 6,824 square miles on the assumption there will be no tropical storms in the two weeks before the monitoring cruise. This is 29 percent larger than the average size and much larger than the goal set by the national Hypoxia Action Plan of less than 1,930 square miles.
In May, the Geological Survey estimated a higher than average amount of nitrate and phosphorus — 146,000 metric tons of nitrate and 20,800 metric tons of phosphorus — flowed down the Mississippi and Atchafalaya rivers into the Gulf of Mexico.
These nutrients help feed the growth of small organisms that use oxygen in the water as they die and decompose. This lower level of oxygenated water grows from the water bottom up as freshwater from the rivers overlays the Gulf’s saltwater. This dead zone can grow until a storm or hurricane helps mix the two layers of water.
The big lesson from the forecast is that no progress has been made on reducing the amount of nitrates getting into the river systems and eventually into the Gulf of Mexico, said Gene Turner, author of the Louisiana-based forecast and professor in the LSU Department of Oceanography and Coastal Sciences.
“I admit the problems are huge,” Turner said, but so far the efforts to reduce nitrates in the river from agricultural fertilizer runoff have all been voluntary. Although there are efforts such as the use of cover crops and other means to keep fertilizer on the fields, it’s not being done on a large scale.
“We’ve been measuring this since 1985,” Turner said. It’s been clear what needs to happen to make a change, but there are social and political hurdles.
Follow Amy Wold on Twitter, @awold10.