Each summer, a hypoxic dead zone forms in the Gulf of Mexico, making some marine habitats unlivable. The dead zone is caused by nutrients—primarily from agricultural fertilizers—flowing into the Gulf from the Mississippi River. Restoring wetlands at field margins has been proposed to intercept some of the runoff, as wetland plants and soils are capable of absorbing nutrients like a living sponge. But estimates of nutrient removal by restored wetlands have varied widely.
