'Legacy' phosphorus delays water quality improvements in Gulf of Mexico

The same phosphorus that fertilizes the thriving agriculture of the Midwest is also responsible for a vast 'dead zone' in the Gulf of Mexico near the Mississippi Delta. Efforts to reduce the amount of phosphorus that enters the Mississippi River system are underway, but research suggests that remnants of the contaminant are left behind in riverbeds for years after introduction and pose an overlooked -- and lingering -- problem.