There’s a 6,475-square-mile “dead zone” in the Gulf of Mexico. Roughly the same size as Connecticut and Rhode Island, this area located off the Louisiana coast becomes so polluted that it can’t support the fish and shrimp populations that are vital to southern fisherman. While actions by those living in the bayous play a part, the real cause is located 1,000 miles north: Iowa’s golden cornfields, whose runoff is dirtying the Mississippi River and its tributaries, says Dan Jaynes, a research soil scientist at the U.S. Department of Agriculture’s National Laboratory who’s studying ways to decrease the contamination.
While the prairie’s black soil is extremely fertile — roughly 25 million acres of cropland were harvested last year — the former swampland is also excessively moist. “It’s a fairly flat landscape, so water has no place to go,” Jaynes says. That’s why, beginning a century ago, farmers in the Hawkeye State built artificial drainage systems (that consisted of four-inch-wide clay pipes buried a few feet underground; today, perforated, plastic tubing is used) to shunt water into streams.

Installation of saturated buffer along Bear Creek, Iowa.

Today, these small-scale systems add high levels of nitrates (a form of nitrogen) and phosphorous (additives that largely come from fertilizer) to nearby waterways. During the spring, these nutrients fuel algal growth, presenting a health hazard to the many cities like Des Moines and Cedar Rapids that obtain their drinking water from the rivers. (Des Moines’s water utility has filed a controversial federal lawsuit against drainage districts upstream.)
Jaynes has a simple solution to the problem that’s impacting the entire Midwestern Corn Belt, from Ohio to southern Minnesota: just shift the pipes 30 to 50 feet away from the streams to allow the water to percolate through the vegetated land between the fields’ edge and the riverbed. Grasses and soils retain some of the nitrates or send them back to the atmosphere as harmless gas, and in the process, the water’s nitrate levels drop anywhere from two-thirds to zero, according to several pilot projects of the “saturated buffer,” which was built in partnership with Iowa State University. The fix comes at a reasonable cost: ranging from $3,000 to $5,000 and can be installed within a half hour, Jaynes says.
If citydwellers along the Mississippi River and fisherman in the Gulf of Mexico want to see clearer waters, saturated buffers will have to be implemented, along with other land management practices, Jaynes says. The only alternative? “We can get rid of all the corn or soybeans in the area,” he adds, “but I don’t think that’s very practical.”