Farm Runoff: Down the Mississippi to the Gulf of Mexico

Beneath its sparkling waters off the Louisiana coast, part of the Gulf of Mexico is dying. Nutrients washed into the gulf by the Mississippi River have promoted excessive algae growth, sucking the oxygen out of the water over an area roughly the size of New Jersey and killing off or driving away many plants and animals. The growth of this so-called “dead zone” threatens the future of some Gulf Coast fisheries. Dr. Wayne Skaggs believes the best way to reverse the trend is to turn down the spigot of nutrients flowing down the Mississippi.

A national task force has concluded controlled drainage could help solve nutrient problems in the Mississippi River.

A William Neal Reynolds Professor and Distinguished University Professor in the Department of Biological and Agricultural Engineering (BAE), Skaggs has spent more than three decades designing soil hydrology computer models. His DRAINMOD simulation has become widely accepted for predicting how water drains from various types of soil, from farm fields to wetlands. It could suggest ways to reduce the amount of nutrients spilling into the dead zone of the gulf.

Skaggs initially designed DRAINMOD to help farmers in eastern North Carolina better manage their drainage systems. By crunching data on rainfall, evaporation, and soil composition, the model determines how deep and far apart to place drains or ditches so the water table would be at the proper level for growing crops. Subsequent tweaks to the model led Skaggs and several colleagues to devise a system of controlled drainage to reduce the nutrients lost from farm fields and improve downstream water quality. Temporarily damming the drainage canals in the winter—more nutrients leech from the soil then because they aren’t taken up by crops and there’s less evaporation—cuts the nitrogen carried downstream in half. Structures have been installed on about 450,000 acres of agricultural and forest land in North Carolina to implement controlled drainage.

Temporarily damming eastern North Carolina drainage canals in winter cuts the nitrogen carried downstream in half.

A national task force studying ways to reduce the nitrogen load in the Mississippi River has concluded that controlled drainage could help solve nutrient problems there as well. Dozens of farmers in Illinois and Ohio are using the practice, but many others are slow to change, insisting it won’t work for their soils and drainage needs. To quell such arguments, Skaggs and colleagues like BAE Assistant Professor Mohamed Youssef have developed algorithms to go beyond the water properties of soil to predict nitrogen cycles and other physical and chemical properties as well. “I started with an agricultural management issue, but I’ve spent most of my career applying it to water quality and environmental issues,” Skaggs says. “I’m glad the methods we’ve developed can be used to address both sides of the equation.”

 

Dr. Wayne Skaggs has spent decades studying soil hydrology. His drainage models could help reduce agricultural runoff in the Mississippi River and pollution in the Gulf of Mexico.

NASA satellite photography shows a sedimentation plume the size of Rhode Island extending from the mouth of the Mississippi into the Gulf of Mexico.