Water Quality of the Mississippi River 

Background Data

The Mississippi River Basin extends from western Montana to eastern Pennsylvania, from southern Canada to the Gulf of Mexico. It drains 41 percent of the US and contains 27 percent of the US population. It encompasses part of twenty seven states and two Canadian provinces. The Mississippi River serves as a water supply for 70 towns and cities.

The flow of the Mississippi gradually increases with its southward flow, each tributary adding to the flow. During its travel along Illinois, its flow is more than doubled. It doubles again as the Ohio enters it at Cairo. Flow peaks just as it leaves the Mississippi State border. There the old river channel, the Atchafalaya River, diverts about 20 percent of the flow. Before this diversion the flow averages around 17,000 cubic meters per second. That is roughly the daily flow of water used in Carbondale passing in one second!

The Mississippi River has changed dramatically since Europeans settled America. Some of the activities that have brought about these changes are:

1. Channeling the river for barge traffic
2. Damming the river for barge traffic and hydroelectric power
3. Levee construction to control flooding
4. Industrial discharges
5. Agricultural runoff
6. Municipal sewage discharges
7. Surface runoff from mining activity
8. Surface runoff from municipalities

Background Information

The Mississippi River discharges approximately 200 million tons of sediment into the Gulf of Mexico each year. That is equivalent to about 10,000 railroad cars each day loaded with sediment! And, that is less than half of what it was when Samuel Clemens traveled the Mississippi. Why? Dams on the upper Mississippi and the Missouri trap much of their sediment. These areas historically provided most of the sediment the Mississippi River transported.

Total dissolved solids (TDS) is a measure of the amount of matter dissolved into the water. It measures anything present that will not volatilize as the water sample is dried at about 100C. In the case of the Mississippi River, TDS increases at almost every sampling point from the headwaters in Minnesota where is it about 170 mg/L to Thebes, Illinois where it has increased to about 300 mg/L. The influx of water at Cairo decreases TDS to about 200 mg/L. It remains relatively constant throughout the remainder of its travels.

Industrial Contamination

Lead mining and smelting are common in several areas along the Mississippi River. Lead is mined in southwest Wisconsin, northwest Illinois, eastern Iowa, and both western and eastern Missouri. Lead smelting is associated with many of these locations. Throughout the length of the Mississippi River, there is substantial heavy industry. The amount of lead the Mississippi River transports gradually increases from its headwaters to the sampling station at Vicksburg, Mississippi, where about one ton of lead passes each day. After than the levels decrease to the Gulf.

A plethora of other industrial contaminants are also detected in the Mississippi River, ranging from zinc, chromium, and mercury to various organic solvents.

Agricultural Contamination

Agriculture adds a variety of pollutants to the Mississippi River. There has been a marked increase in sediments in the Ohio River basin due to agriculture. (This is in contrast to a reduction in natural sediments in the western tributaries.)

Almost any organic pesticide you can name or find reference to, is present in the waters of the Mississippi River. Everything from Atrazine (widely used in Illinois and Iowa) to DDE, a degradation product of DDT which was banned decades ago. Most pesticides are present in the waters of the Mississippi River in concentrations ranging from parts per trillion to parts per billion. Low concentrations, but if this is your drinking water source. . . . . . .

Nitrate, normally associated with agricultural runoff, but also present in most treated wastewaters, ranges from near zero to less than three milligrams per liter.

Municipal Sewage

Thank you St. Louis! Until last year, the Bissell Point wastewater treatment plant in St. Louis, Missouri discharged roughly 150 to 200 million gallons of primary settled wastewater into the Mississippi River every day. That is essentially untreated sewage. They now have added secondary treatment to the facility.

Fecal coliform bacteria are commonly used as indicators of municipal wastewater contamination. Fecal coliform bacteria reside in the intestinal tract of mammals, including humans. Their level in the Mississippi River gradually rises, peaking in St. Louis, Missouri. Then, declining to the Gulf. The median value in the St. Louis area, prior to improvements at Bissell Point, were around 6000 coliforms per 100 mL. That's about 60,000 in a quart of water!

Good News, Bad News

As a general trend, surface water quality has been gradually improving in the US during the past two decades. Many of the tributaries to the Mississippi River have experienced markedly improved water quality during this period. Microbial contamination and oxygen demanding organic wastes have been substantially reduced. It can be expected that this trend will continue.

The bad news is that there is a long way to go with non-point source pollution. That is, surface water runoff from municipalities and agriculture. The good news in this is that the US EPA has begun to look more closely at this problem in the past few years. Permits are currently required for industries, construction sites, and municipalities that discharge surface water runoff. Many of the worst offending pesticides have been banned. Most of the others have substantial controls placed on their use.

Have we done enough? Will we do enough? Time will tell.

The source of most of the information in this article is: Contaminants in the Mississippi River 1987-92, US Geological Survey Circular 1133.