A new report released Jan. 9 from the Upper Mississippi River Basin Association found that although water quality has generally improved in the upper river in past decades, new threats, such as road salt and lead, are emerging.
The report tracked 19 indicators of water quality — including phosphorus, nitrogen, chloride, heavy metals and total suspended solids — over 30 years across the entire upper river, which stretches from the headwaters in northern Minnesota to Cairo, Ill.
It also included the Illinois River, which is a major tributary of the Mississippi and part of the upper Mississippi River system.
The first version of the report was released in 1989, when the Mississippi was just beginning to recover from a heavily polluted era before t he passage of the Clean Water Act in 1972. At the time, the river’s biggest problems included heavy metals and sediment. Today, while those concerns have abated some, the report describes new problems, like increasing nutrient pollution and chloride levels.
Here are five takeaways.
The upper Mississippi River is getting saltier: Chloride concentrations in the upper Mississippi increased by an average of 35% between 1989 and 2018, the report found.
Chloride is a component of road salt — which is a major driver of the increases in the river, according to the report. Water softener salt can also be a contributor. It’s nearly impossible to remove chloride from water, meaning that this salt has accumulated in the river over decades.
Increasing salt content can wreak havoc on a freshwater ecosystem like the Mississippi River — killing aquatic plants and animals, raising the risk for harmful algal blooms, and seeping into groundwater and corroding pipes and other infrastructure. It also increases the river’s electric current, degrading the overall environment.
Lauren Salvato, who coordinates the water quality program for the Upper Mississippi River Basin Association, called the chloride finding “a really scary trend.”
She said we need to prevent salt from getting in the water in the first place. That could be accomplished by fine-tuning cities’ winter salting techniques and educating the public about how much salt is needed to keep an area ice-free. It’s not as much as you might think — about a 12-ounce coffee mug’s worth of salt for a 12-foot driveway or 10 sidewalk squares.
Mixed progress on reducing nitrogen and phosphorus, which cause algae blooms: The Mississippi River has long suffered from excess phosphorus and nitrogen, which end up in the Gulf of Mexico where they produce the dead zone, a massive area where nutrient pollution chokes off oxygen for fish and plants. Pollution from farming and industry have driven these trends.
But the report shows in the last few decades, some improvements have been made.
On average, phosphorus has declined 34% above Pool 13, which begins near Bellevue, Iowa — but there was no clear trend south of there. Phosphorus was increasing in Pool 26, near Alton, Ill. The picture of nitrogen pollution was harder to tease out, and the report wasn’t able to confidently pinpoint a trend above Pool 13. There was a 14% decrease in total nitrogen at the La Grange Pool on the Illinois River, which is part of the Upper Mississippi s ystem.
Phosphorus reductions, the report notes, are the result of years of work from states getting in compliance with the Clean Water Act, regulating so-called “point sources” of pollution, like wastewater treatment plants; and farm conservation work to keep nutrients in the soil, such as cover cropping.
But challenges still stand in the way of reducing these nutrients in the river. Among them: Nonpoint sources of pollution, like farm runoff and urban stormwater, are not regulated by the federal government; and more water dumping into the river due to climate and land use changes is diminishing water quality gains.
Sediment in the water decreased, creating better habitat for plants and animals: The report notes a significant decrease in total suspended solids, which include sediment, algae and other particles . Water with high amounts of total suspended solids is m urky and provides poor habitat for aquatic animals and plants.
In the past 30 years, total suspended solids have decreased up to 66% in the upper river, according to the report.
Salvato said she finds this trend encouraging, particularly because agricultural runoff has been a major source of total suspended solids in the river. The decrease shows that conservation practices on the land have been paying off, she said. The report also pointed to successes from regulating wastewater treatment plants and similar facilities.
Metal concentrations decreased, aside from some hot spots: Lead levels in pools 15 and 17, near Davenport and Muscatine, Iowa, have increased in the 30 years that the report analyzed.
Although the increases are numerically small and the lead concentration in both pools is still well below what the U.S. Environmental Protection Agency considers “chronic,” Salvato said it’s a finding to keep tabs on — particularly because it’s unclear what’s causing it.
Lead in surface water typically comes from the combustion of leaded fuels, coal emissions and discharges from mining and industrial sites, as well as lead emissions from burning gasoline and coal that drop onto soils and are carried as runoff into the water, according to the report.
But Salvato said her organization examined point sources and didn’t find any answers.
She raised a similar question about arsenic, which increased by 40% in Pool 26 — though the report notes that arsenic levels are so low in the upper Mississippi River that that represents an increase of less than one part per billion.
Still, most metal concentrations have decreased in the upper river.
Aluminum, zinc, copper and cadmium concentrations have all dropped, the report found. Only two sites included in the analysis had data on mercury, for which there was no significant trend.
The Clean Water Act significantly reduced the amount of trace metals from industrial pollution and fossil fuel emissions ending up in the water, according to the report.
Data gaps make it tougher to tease out trends: One drawback of the report is that it relies on water quality data collected by each state — and every state does things differently. Some track mercury and some don’t, for example.
These data gaps make it hard to identify problems and potential solutions, the report notes.
Some states monitor just a handful of pools on the river, others have more extensive systems, and two states — Iowa and Missouri — don’t conduct monitoring on the Mississippi at all, Salvato said.
She believes it will be important to develop a monitoring system that is used by all states and consistent in its frequency and what it measures. Her organization is piloting such a system, but it’s in early stages and wasn’t used in this report.
“We really do want these federal, interstate waters to be valued and treasured. And some of that is through investing in monitoring,” Salvato said.
This story is a product of the Mississippi River Basin Ag & Water Desk, an independent reporting network based at the University of Missouri in partnership with Report for America.
Indicators of water quality tracked in new report
How much salt is needed — about a coffee mug’s worth — to de-ice 10 sidewalk squares
Increase in chloride concentration in upper Mississippi
Decrease in suspended solids