The Mississippi cuts through America’s mid-section and often serves as a delineator between east and west. As the longest river in the United States, the potential exists for a great deal of pollution between its headwaters in Minnesota and its basin in the Gulf of Mexico.
Water pollution is an important topic because the earth has a finite supply of fresh water, and that supply is being depleted rapidly. Additionally, with rivers, pollution spreads downstream and affects a far greater number of people than other types of pollution.
The two types of pollution that have affected the Mississippi River the most are from industry and agriculture. The primary type of pollution from industry is from metal deposits. Some of these metals are harmless at low concentrations, but are toxic at high concentrations. Other metal deposits can be toxic to humans even at low concentrations.
Agriculture run-off deposits fertilizers into the water, which can affect the ecological balance of the river and lead to nitrification. This upsets the ecological balance of a water source and can lead to hypoxia, or a lack of oxygen.
Concern over the water quality of the Mississippi River first came to public view following World War II. An increase in population and the resulting increases in agriculture and industry to support that population led to harmful water pollutants (http://www.seagrantfish.lsu.edu/pdfs/missriver_waterquality.pdf)
Pollution in the Mississippi River has increased in severity since the alarm was first sounded several decades earlier. Nitrogen pollution diminished coastal wetlands; this fragile ecosystem was then battered by Hurricane Katrina in 2005 (“What impacts to teach?”).
Nitrogen pollution has increased in the Mississippi River in part due to run off from fertilizer for agriculture. This type of pollution is considered non-point source, because it cannot be attributed to a single location. This type of pollution can be difficult because of its widespread nature, and the inability to pinpoint who major polluters are.
“The seasonal patterns in nitrate and silicate concentration have also changed during this century. There was no pronounced peak in nitrate concentration earlier this century, whereas there was a spring peak from 1975 to 1985, we think due to fertilizer application” (Eugene and Rabalais).
Fertilizer run off, which contains nitrates, creates an excess of nutrients in the Mississippi River and in the Gulf of Mexico. The consequences of hypoxia include excessive algal growth, reduced sunlight penetration, degradation of habitat for bottom-dwelling species, and decreased oxygen content in the water (http://www.seagrantfish.lsu.edu/pdfs/missriver_waterquality.pdf).
Although the problem of excessive nutrients in the Mississippi River can be difficult to contain because of its widespread nature, nitrate pollution has decreased since its peak in the 1980’s. “Nitrogen and phosphorus fertilizer use in the United States began in the mid-1930s and climbed coincidentally and dramatically to a peak in approximately 1980 ... Nitrogen fertilizer use in the United States appears to have reached a plateau in the last ten years, whereas phosphorus fertilizer use stabilized in 1980 and then dropped slightly ” (Eugene and Rabalais).
Another main source of pollution in the Mississippi River is from metallic elements contained in the sediment of the riverbed. Metals are divided into two general categories, those that are approximately five times the weight of water, such as lead, iron, and copper, are referred to as heavy metals, and those metals that are less dense, such as sodium, magnesium, and potassium are referred to as light metals (http://pubs.usgs.gov/circ/circ1133/heavy-metals.html).
Many light metals are essential to human function in small quantities, but can be harmful in large quantities. Other metals can be toxic even in small concentrations. This type of pollution is considered point source pollution because the factory where the metal deposits originate from can be directly identified.
“On the average, the USEPA estimates that 81 percent of the metals introduced into wastewater treatment plants comes from various regulated industries that dispose of their wastes into municipal sewer systems … Cadmium, chromium, copper, lead, and mercury are used extensively in industries along the Mississippi River” (http://pubs.usgs.gov/circ/circ1133/heavy-metals.html).
The Mississippi River divides the United States roughly in half, stretching from Minnesota to the Gulf of Mexico. With this great expanse also comes pollution. The types of pollution that have most affected the Mississippi River since concerns over the River’s water quality arose following World War II are nitrification from agricultural fertilizer run off, and metal deposits in riverbed sediment from industry.
While the water quality of the Mississippi River has improved significantly in the last few decades, there is still much more to be done in order to ensure that this major waterway remains ecologically viable for decades to come.
Sources
http://www.seagrantfish.lsu.edu/pdfs/missriver_waterquality.pdf
"Which impacts to teach?" Environment 48.7 (2006): 6. Expanded Academic ASAP. Web. 30 Apr. 2010.
Turner, R. Eugene, and Nancy N. Rabalais. "Changes in Mississippi River water quality this century." BioScience 41.3 (1991): 140+. Expanded Academic ASAP. Web. 8 May 2010.
