Study points to increasing nitrate problem in the Mississippi
Go Deeper.
Create an account or log in to save stories.
Like this?
Thanks for liking this story! We have added it to a list of your favorite stories.
[image]
Sediments in the Gulf of Mexico are shown in a September 2002 file photo. (AP Photo/NASA)
A new study from the U.S. Geological Survey has found that by at least one measure, pollution in the Mississippi River has gotten worse since 1980, despite efforts to curb runoff.
When measuring nitrate--a nutrient that causes oxygen depletion and can come from sewage treatment plants and farm fields--researchers found that the overall amount flowing to the Gulf of Mexico has grown by 10 percent in the last three decades.
Turn Up Your Support
MPR News helps you turn down the noise and build shared understanding. Turn up your support for this public resource and keep trusted journalism accessible to all.
Using a new technique that controls for changes in natural water flow in order to identify the impacts of nitrogen management, the study considered data from a series of testing stations along the Mississippi. The highest nitrate concentrations were found at the northernmost station, at Clinton, Iowa, where the water largely comes from Minnesota and Wisconsin.
At that site, according to researchers, "annual flow-normalized nitrate concentrations increased 76 percent from 1980-2008," compared to decreases or small increases from some stations farther south.
Cities and farmers have been working to improve water quality through measures like wetland filtration and state-of-the-art sewage treatment plants. The new study questions whether these efforts are enough. "While conservation practices may have decreased nitrate levels in some portions of the basin, we aren't seeing widespread effects at larger scales," says Lori Sprague, a USGS hydrologist who was the report's lead author.
On a more hopeful note, the study suggests that current conservation measures may have an impact down the line: "Because nitrate moves slowly through groundwater to rivers, the full effects of management strategies designed to reduce nitrate movement to groundwater may not be seen in these rivers for many years."