Beneath fields of corn and soybeans across the U.S. Midwest lies an unseen network of underground pipes. These systems, which are known as tile drainage networks, channel excess water out of soil and carry it to lakes, streams and rivers. There are over 38 million acres of tile drainage in the Corn Belt states.
These networks play a vital role in farm production. They allow farmers to drive tractors into fields that would otherwise be too wet and make it possible to plant early in spring. And they boost crop growth and yield by preventing fields from becoming waterlogged.
But drainage systems are also major contributors to water pollution. The water they remove from fields contains nitrogen, which comes both from organic matter in rich Midwestern soil and from fertilizer. This nitrogen over-fertilizes downstream water bodies, causing blooms of algae. When the algae die, bacteria decompose them, using oxygen in the water as fuel.
The result is hypoxic zones, also known as dead zones, where nothing can live. Some of these zones, such as the one that forms in the Gulf of Mexico every year fed by Midwestern farm drainage water, cover thousands of miles.
