NOAA this week released the latest survey of the “dead zone” just off the Gulf Coast. The dead zone results from fertilizer pollution brought down from midwest farms and cities by the Mississippi River. That nutrient influx fuels phytoplankton blooms. The subsequent decomposition of dead plankton consumes oxygen, leaving the levels of dissolved oxygen in the dead zone’s waters too low to support aquatic life.
The good news in this year’s survey is that at 3,000 square miles, the dead zone is much smaller than the 7,500 – 8,500 square miles that had been forecast. The survey is only semi-good news, though, because researchers attribute this year’s improved conditions to favorable weather, which has kept the waters more thoroughly mixed than usual, rather than to any reduction in nutrient inputs. As University of Maryland marine science professor Donald Boesch points out in this Reuters story, no limits have been set on nutrient pollution in the Mississippi basin. In other words, while things look better than expected this year, that’s just dumb luck. There’s no reason to expect similarly good news next year.