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The waters of the Mississippi River carry dissolved contaminants and bacteria that originate from a variety of municipal, agricultural, and industrial sources. This map shows the amounts of water discharged by the Mississippi River and its tributaries during an average year. About 2 percent of the average discharge of the Mississippi River comes from municipal and industrial point sources. The distribution of contaminants along the Mississippi River depends on the nature and locations of their sources, the degree of wastewater treatment, and the stability of the contaminants and their dilution by receiving waters. The graphs show the concentrations of contaminants dissolved in the Mississippi River between Minneapolis–St. Paul, Minn., and the Gulf of Mexico. The data in the graphs are generalized from chemical analyses of representative samples of water collected at between 10 and 15 sites along the Mississippi River on as many as 10 separate occasions from 1987 to 1992 in the lower river and on 3 separate occasions during 1991 and 1992 in the upper river.

As the Mississippi River flows southward from its headwaters in the northern States of the Midwest, its discharge is more than doubled by the waters it receives from the Illinois and Missouri Rivers. This combined discharge is more than doubled again as it is joined by the waters of the Ohio River. About 500 kilometers upriver of its principal mouth, the Mississippi River bifurcates, and a quarter of its discharge is diverted by way of the Atchafalaya River to the Gulf of Mexico.

A. Fecal coliform bacteria derived from human and animal wastes survive only briefly in river water, but their averaged concentrations exceed the maximum contaminant level of 2,000 per liter for recreational use in much of the Mississippi River because of incomplete wastewater treatment.

B. Linear alkylbenzene sulfonate (LAS) is a biodegradable detergent primarily derived from domestic sewage. Its presence in high concentrations in the Mississippi River in the St. Louis metropolitan area corresponds with elevated counts of coliform bacteria and probably reflects the incomplete treatment of wastewater discharged into the river.

C. Caffeine is a stimulant chemical in coffee and soft drinks. Because it is consumed only by humans, it serves as an indicator of domestic sewage and illustrates the extent to which sewage is diluted by the river. Concentrations of caffeine in municipal wastewaters usually range between 20 and 300 micrograms per liter. The much lower concentrations of less than 1 microgram per liter of caffeine shown in the graph indicate that munici

pal wastewaters may be diluted as much as a thousand fold after they are well mixed into the Mississippi River.

D. E. Agricultural chemicals enter the rivers from mostly nonpoint sources, usually as runoff from croplands during spring and summer. Nitrate in the Mississippi River (D) comes mostly from fertilizers. Its concentration in the river fluctuates seasonally, depending on when it is applied to farmlands and the timing of rainfall and runoff. Nitrate concentrations generally are smaller in the Mississippi River below the confluence of the Ohio River; the major portion of nitrate in the Mississippi River is derived from tributaries that drain intensively farmed regions in Illinois, Iowa, and Minnesota. Atrazine (E) is a preemergent herbicide that is used mostly on corn fields and is nearly ubiquitous in the Mississippi River. Atrazine concentrations usually are greatest near St. Louis because of inputs from the Missouri and Illinois Rivers and other rivers that drain the farming regions of the Corn Belt. Concentrations usually are smaller in the lower Mississippi because of dilution by water from the Ohio River. Atrazine concentrations vary seasonally and occasionally exceed the maximum contaminant level of 3 micrograms per liter during spring runoff in the Mississippi River between St. Louis and the Ohio River confluence.

F. Ethlenediaminetetraacetic acid (EDTA) is the dissolved organic chemical contaminant present at the greatest concentration in the Mississippi River. Generally considered nontoxic, this chemical is a general indicator of industrial contamination and is found in the Mississippi River at about onefourth of the concentration found in some European rivers.

G. H. Two examples of contaminants from industrial point sources are tris-2-chloroethylphosphate (TCLEP) and 1,3,5-trimethyl-2,4,6triazinetrione (TTT). TCLEP (G) is a flame retardant that is added to polyurethane foams and textiles; in the Mississippi River system, it is derived almost exclusively from the Illinois River Basin. Its exclusive source and its persistence in solution make TCLEP a useful tracer and indicator of waters from the Illinois River as they mix down the Mississippi River with waters from other tributaries. TTT (H) is a byproduct of the manufacture of methylisocyanate. Its overwhelmingly singular source in the Mississippi River system is the basin of the Kanawha River of West Virginia, which is a tributary of the Ohio River. Proportions of TTT dissolved in the water can be used to follow the mixing of the Kanawha River with the Ohio River and the Ohio with the Mississippi River.

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0 100 200 kilomet ERs - l OKLAH TENNESSEE i OMA - ExPLANATION o 100 200 MILES 35 – ~ l -- Suspended-sediment - - - - I 0 100 200 discharge, in millions w of metric tons ALABAMA Concentrations in - - tributaries 15 T T Jay-os- Ill R - inois River : to \A o: * Nowomen. C - -5 s H - - o Missouri River a- o l l O Ohio River

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Gulf of Mexico

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“– The suspended sediments that are transported by

the Mississippi River and its tributaries adsorb and carry pollutants. Organic pollutants, such as polychlorinated biphenyls (PCB's), and inorganic pollutants, such as lead, are many times more likely to adhere to sediment particles than they are to remain in the dissolved state. The map shows the amounts of suspended sediment discharged by the Mississippi River and its tributaries during an average year near 1990. The graphs show the Concentrations of the constituents adsorbed on the sediments in suspension in the Mississippi River between Minneapolis–St. Paul, Minn., and the Gulf of Mexico. The data in the graphs are generalized from chemical analyses of representative samples of suspended sediment collected at between 10 and 15 sites along the Mississippi River on as many as 10 separate occasions from 1987 to 1992 in the lower river and on 3 separate occasions during 1991 and 1992 in the upper river.

Suspended-sediment discharges in the upper Mississippi River are fairly small when compared with those of the major tributaries. The sediment discharge of the upper Mississippi is increased 5 to 10 times by the sediment discharge of the Missouri River. The average sediment load is increased by another significant increment by the Contribution from the Ohio River.

A. Organic carbon (expressed here as a weight percentage of dried suspended silt and clay) is proportionately greater in the uppermost Mississippi River, and its proportion decreases downriver. Particulate organic carbon in the Mississippi River is mostly natural, but it affects the ways in which pollutants, especially organic pollutants, are adsorbed by suspended sediment. The Missouri and Illinois Rivers transport suspended sediment in which organic carbon is somewhat less concentrated; where these two tributaries enter the Mississippi (near kilometer 1850), the organic carbon percentages are decreased by dilution. Organic

carbon percentages in the suspended sediment of the Ohio River, however, are typically greater than those in the Missouri and Illinois Rivers, and the organic carbon in suspended sediment is increased slightly where the Ohio River joins the Mississippi (kilometer 1535).

B. PCB’s, which are pollutants that were once widely used in industrial applications, are typically most concentrated on the suspended sediments in the upper Mississippi River near Minneapolis– St. Paul. The difference between PCB concentrations on the suspended sediments near Minneapolis and those near St. Louis is the result of the greater amounts of suspended sediment in the river at St. Louis rather than an indication that Minneapolis– St. Paul contributed 5 to 10 times more PCB's to the river than St. Louis did. The high concentrations in the upper river decrease rapidly downriver, and they are increased significantly only as the suspended sediment from the Ohio River, which usually contains more PCB's than the middle reaches of the Mississippi River do, enters and mixes.

C. Hexachlorobenzene, another organic pollutant of industrial origin, is predominantly derived from two main sources in the Mississippi River basin— the Ohio River, which enters the Mississippi at kilometer 1535, and the industrial corridor that lines the lowermost 400 kilometers of the Mississippi River.

D. Lead and other heavy metals are associated with the suspended sediments along the length of the Mississippi River. Spatial variations in their concentrations are less pronounced than in those of PCB's and hexachlorobenzene. However, they do tend to be most concentrated on the suspended sediments in the river just downstream from Minneapolis– St. Paul (as in the case of PCB’s, because of the relative scarcity there of suspended sediment), and they show slight increases related to more concentrated inputs from the Ohio River.

Hydrogen ion (acidity) levels in the Rocky Mountain snowpack at the end of the 1992–93 snow season. The greatest concentrations are in and near the Mount Zirkel Wilderness Area, Colorado.

Effects of EnergyResource Development on Lakes: What Do We Need to Know?

he alpine and subalpine zones of the

Rocky Mountains constitute one of the largest undisturbed ecosystems in the United States. The Wilderness Act and the Clean Air Act gave congressionally designated Wilderness Areas special protection from anthropogenic change. However, many Wilderness Areas of the Rocky Mountains are located near to and downwind from developed or economic deposits of fossil fuels, which include coal, petroleum, natural gas, and oil shale. The need for abundant and reliable new energy sources likely will result in increased use of fossil fuels in the Rocky Mountains and other areas in the West. To use these energy minerals without damaging nearby Wilderness Areas and other Federal lands, we need to understand the present status of the Wilderness Areas and the potential risk associated with projected atmospheric emissions from energy-resource development.

Very little is known about the aquatic chemistry and biology of Rocky Mountain Wilderness Areas, which are characterized by

Inset of Mount Zirke wilderness Area

range = 1.7 to 17.4 microeduivalents per liter

a lack of roads, steep terrain, and a seasonal snowpack that lasts about 9 months. Most information regarding these areas consists of a few synoptic samplings and some monitoring and research at only a few small watersheds. Lack of information on Rocky Mountain Wilderness Areas hampers both their protection and the development of fossil fuels. Without the information necessary to predict the effects of new emissions sources, the Federal land manager is required by law to err in the direction of assuring that damage is not done. As a result, worst-case estimates of potential risks posed by proposed energyresource development commonly are used. Most knowledge of the present status of the aquatic chemistry and biology of Rocky Mountain Wilderness Areas and of the risk of damage to them comes from studying acid rain and related problems. The National Atmospheric Deposition Program monitors the chemistry of rain and snow at about a dozen sites in the Rocky Mountain area. No sites are located in Wilderness Areas, and few are located at high elevations. The U.S. Geological Survey (USGS) has conducted a survey of snowpack chemistry throughout the Rocky Mountains. Generally, the smallest concentrations of fossil-fuel combustion products, such as sulfate, nitrate, and acidity in rain or snow and the snowpack, are found in Montana. Concentrations progressively increase in Wyoming and Colorado. Some of the largest concentrations of sulfate, nitrate, and acidity were measured at several sites in an area in northern Colorado downwind (east) of the Yampa River Valley, an area of energy development (especially coal mining and electrical generation from coal). The Western Lake Survey, which was conducted by the U.S. Environmental Protection Agency in 1985, and numerous smaller surveys have indicated that the median acid neutralizing capacity, which is a measure of a lake's ability to neutralize acidity, is smallest in Wyoming and southern Montana and greatest in Colorado. Thus, the lakes that have the smallest median acid neutralizing capacity and thus are the most sensitive to acidification tend not to be in the area where concentrations of sulfate, nitrate, and acidity in wetfall and in snowpack are greatest. Effects of energy development on wilderness hydrologic systems of median sensitivity are of secondary concern to the Clean Air Act and the Wilderness Act; instead, concern is greatest for those systems that are considered to be the most sensitive. Even though median acid neutralizing capacity differs

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