Wetlands continue to reduce nitrates

Wetlands created 20 years ago between tile-drained agricultural fields and the Embarras River were recently revisited for a new two-year University of Illinois research project. Results show an overall 62 percent nitrate removal rate and little emission of nitrous oxide, a potent greenhouse gas.

“Slowing down the rate of flow of the water by intercepting it in the wetland is what helps to remove the nitrate,” says Mark David, a University of Illinois biogeochemist in the College of Agricultural, Consumer and Environmental Sciences. “The vegetation that grows in the wetland doesn’t make much of a difference because the grasses don’t take up much nitrogen. It’s just about slowing the water down and allowing the microbes in the sediment to eliminate the nitrate. It goes back into the air as harmless nitrogen gas.”

I’m so glad Illinois is looking into this. We really need to understand the ways to fix our streams. The EPA says that nitrates are leftovers from all the fertilizers and rodenticides farmers use. And that if the get into wells or groundwater they can cause illness in children or cancer at higher levels.

Exposure to nitrates and nitrites at levels above health-based risk values has adverse health effects on infants and children. The health effect of most concern to the U.S. EPA for children is the “blue baby syndrome” (methemoglobinemia) seen most often in infants exposed to nitrate from drinking water used to make formula.

Exposure to higher levels of nitrates or nitrites has been associated with increased incidence of cancer in adults, and possible increased in cidence of brain tumors, leukemia, and nasopharyngeal (nose and throat)

As a rule Americans are against turning our babies blue or giving ourselves cancer. So we really, really want to get rid of nitrates when we can. And it turns out that just slowing down the water by making wetlands is a better way to do that than just about anything else. Even better than plants. Even better than building expensive bioreactors.

“Farmers generally prefer to install bioreactors because they don’t take up much space,” Gentry says. “A wetland requires about 3 to 4 percent of the drainage area. So, for a 100-acre field, you’d need about 4 acres in wetland. Although bioreactors don’t use much land, they also don’t slow the water enough during high flows. Research on their performance is still underway. Because water tends to be in the wetlands for a much longer time period, they are more effective.”

Wow, wetlands work harder for longer and they are supremely effective at getting rid of nitrates. We really need them! The article doesn’t mention it but they also have all these added benefits as a buffer zone for huge storms, and a stopping place for migratory birds, or habitat for wildlife. We should be working hard to protect them since they do this important work. Maybe giving a tax credit to farmers that allow them?

The article also doesn’t mention a certain rodent that actually makes and maintains these valuable wetlands for free. Its name escapes me now. What was it called again?

I think it started with a ‘B’?