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Great Lakes Ecological Protection and Restoration

Table of Contents

Chapter 1
Chapter 2
Chapter 3
Chapter 4
Chapter 5
Chapter 6
Chapter 7
Chapter 8


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Great Lakes Report to Congress 1994

REPORT TO CONGRESS ON THE GREAT LAKES ECOSYSTEM

February 1994
EPA 905-R-94-004

Chapter 1
Introduction

America's inventive and productive genius has been amply realized in the Great Lakes region. Early in the last century, steamships and the Erie Canal helped to open a 2,200 mile waterway into the heart of a continent. Through this corridor came timber to build a growing nation and ores to feed the successive industrial ages of iron, then steel. America's first oil refineries were within the Great Lakes watershed, helping to spark the region's automobile industry that grew into the preeminent industry of twentieth century America. The connection of railroads and canals to the Lakes contributed to unprecedented agricultural development in the Midwest and Great Plains.

During the twentieth century, fuels and industrial minerals have been found elsewhere around the world, and modern means of transportation have made them widely accessible. With the spread of industrial economies, the Great Lakes region's disproportionate share of world manufacturing has inevitably eroded. Yet, productive industries, such as forest products, shipping, agriculture, food processing, chemicals, mining, metals, and heavy manufacturing continue to be important. Manufacturing remains the largest sector in the economy of most Great Lakes States.

Before its development, the Great Lakes region was endowed with extraordinary natural abundance--oceans of freshwater, splendid forests, plentiful animals, rich soil, immense wetlands, multitudes of waterfowl. The Great Lakes were an important part of the breeding range of the passenger pigeon, one of the most numerous birds in the world. Waters teemed with fish. Sturgeon up to 6 feet long were common. A fisherman using a dip net could reap many hundreds of whitefish in a day.

Much of the majesty and plenty of the Lakes remain, although human actions have often changed or damaged the ecosystem. The last passenger pigeon died early in the twentieth century, the tragic survivor of a species exterminated by hunting and the loss of oak and beech forest habitat. Today, few sturgeon survive. Lake trout populations are not self-sustaining. A top predator, the bald eagle, breeds with less success along the shores of the Lakes than inland. Habitat available to fish and wildlife is greatly reduced, as are their populations.

To help place today's Great Lakes environmental issues in context, this chapter discusses physical features of the Lakes, their economic development during the past three centuries, and ecological outcomes associated with this development.

The Great Lakes Back to Top

By many measures, the five Great Lakes are freshwater seas. Formed by the melting retreat of mile-thick glaciers 10 to 12 thousand years ago, the Great Lakes water system represents about 18 percent of the world's surface freshwater and 95 percent of the surface freshwater of the United States. If poured over the landmass of the continental United States, the 6 quadrillion gallons of the Lakes would immerse the "lower 48" States to a depth of almost 10 feet. The Lakes and their connecting channels have 7,437 miles of shoreline across eight States and the Province of Ontario. Their 201,000 square mile watershed holds nearly 80,000 small lakes--one-third within the United States--that could collectively cover an area larger than Lake Erie.

By virtue of their size, the Lakes affect the climate of their region. Heat stored in the Lakes during the summer warms adjacent land in the winter. Areas of Michigan, southern Ontario, and western New York have warmer winters than some other parts of North America at similar latitudes. These same areas, however, receive heavy snowfalls as prevailing winds from the west pick up moisture over the Lakes. In spring and summer, the Lakes are slow to warm, cooling nearshore land.

As would be expected across such a large area, the physical characteristics of the Great Lakes watershed vary. In the north, the land is heavily forested, particularly by conifers. The soil is generally thin and acidic, covering an ancient bedrock called the Laurentian Shield. The climate is cold. Principal industries are timber, mining, and hydroelectric power. In the south, soils are deeper and fertile, rocks sedimentary and nutrient rich, temperatures warmer, the density of human population greater. Vast wetlands and deciduous forests have generally been replaced by agricultural, industrial, and residential uses.

By surface area, Lake Superior is the largest freshwater lake in the world. It is the second largest in water volume, trailing only the immensely deep Lake Baikal in Siberia. Superior holds just over one-half of the water in the Great Lakes system. Because of its huge volume, Superior has a water retention time of 173 years, which is the longest of the Lakes. The St. Marys River, which flows southeasterly into Lake Huron, is Superior's outlet.

Lake Michigan is the only Great Lake that lies wholly within the United States. The second largest Lakes in terms of water volume, Michigan holds 21 percent of the water in the system. Lake Michigan has the second longest water retention time, 62 years. Water from Lake Michigan primarily flows out through the Straits of Mackinac into Lake Huron. A much smaller outflow is artificially diverted into the Mississippi River system via the Chicago Sanitary and Ship Canal.

Lake Huron, the second largest Great Lake in terms of surface area, is slightly larger than Lake Michigan. Huron holds about 16 percent of the water in the Great Lakes and has a water retention time of 31 years. Huron's outlet, the St. Clair River, flows into shallow Lake St. Clair (average depth 11 feet).

Lake Erie is the smallest in water volume, having an average depth of only 62 feet. Erie has three distinct basins, as defined by water depth and underwater ridges. The shallow western basin averages 24 feet in depth. The central basin is deeper; its waters stratify by temperature, and its narrow bottom layer is vulnerable to depletion of dissolved oxygen. The eastern basin is the deepest; its bottom layer is thicker and less vulnerable. Erie has the shortest water retention time, 2.7 years, making it the Lake most responsive to both environmental abuse and cleanup.

Erie is the southernmost of the Lakes. Its waters are the warmest in summer and most productive biologically, supporting abundant fisheries. Because of its shallowness, Erie is the Lake most affected by air temperature. As a result, it regularly has 95 percent ice cover in the winter, in contrast to deeper Lake Ontario, which has an average cover of only l5 percent. Erie's watershed is the most agricultural, most urban, and least forested; about two-thirds of it is used for farming. Erie has the highest rate of sedimentation, receiving soil particles from the rich farmlands of its watershed.

Lake Ontario is the smallest in surface area but contains more than three times Erie's water volume. The Canadian population within Lake Ontario's watershed is about twice that of the United States and has increased significantly during the 1970s and 1980s, while the U.S. population has remained stable. Canada's largest industrial region lies along the western and northwestern shores of Lake Ontario and includes Toronto, a metropolitan area of three million people.

The major source of water to Lake Ontario is the Niagara River flowing from Lake Erie. Lake Ontario is about 325 feet lower in elevation than Erie, causing the river to cascade at the famous Niagara Falls. Ontario's outlet is the St. Lawrence River, which has an annual flow that represents less than one-half of one percent of the water volume of the entire Great Lakes system.

This relatively small outflow is a notable characteristic of the Great Lakes. The system does not flush contaminants quickly. This attribute makes the Great Lakes ecosystem especially sensitive to environmental stresses. Another important characteristic of the Lakes is their clarity. Before intense European settlement of the region began around 1800, the Lakes contained little phosphorus, were rich in oxygen, and, with the exception of shallow waters, were very clear. One reason for these phenomena was that shorelines were rimmed by forests and wetlands, allowing little nutrient runoff to stimulate production of microscopic plants (i.e., phytoplankton, such as algae). Although phytoplankton are the foundation of the Great Lakes food web, excessive algal growth clouds water. Despite today's level of development, most of Superior and Huron remain very clear, as do parts of the northern basin of Lake Michigan.

The most biologically productive areas are Green Bay, Saginaw Bay, and western Lake Erie, relatively warm shallow waters that are fed, respectively, by the Fox, Saginaw, and Maumee Rivers The Lakes sustain a rich diversity of birds and other wildlife. Following the Atlantic and Mississippi flyways, an estimated three million waterfowl migrate through the Great Lakes each year, relying on them for food and shelter. During their spring and fall migrations, up to 25,000 birds of prey can be observed each day from Whitefish Point in eastern Lake Superior. The Lakes host multitudes of cormorants, egrets, gulls, herons, and terns. Native animals include deer, fox, moose, wolves, and fur-bearing mammals-- beaver, mink and muskrat--that fueled the early development of the region by European settlers.

Economy in Historical Perspective  Back to Top

During the past 300 years, various industries have boomed in the Great Lakes region. Fur trapping, especially of beavers, thrived from the last half of the seventeenth century until the early nineteenth century. As trapping depleted beaver populations in the region, the fur trade expanded westward to California, Oregon, the Arctic Ocean. Even after trapping had moved west, the Lakes remained vital to the industry for waterborne transportation. The Lakes and St. Lawrence River provided a pathway for canoes laden with animal pelts to the Atlantic coast where furs were shipped to customers in Europe. Many early settlements in the region were fur-trading posts, including Chicago, Detroit, Duluth, and Green Bay. Chicago's first non-Native American settler, Jean Baptiste Pointe du Sable, a Haitian of African and French descent, was a fur trader who built a cabin beside the Chicago River in 1779.

As the beaver industry declined because of the scarcity of beavers and whims of fashion, early settlers began harvesting trees on a large scale. Three principal types of forests surrounded the Lakes. Spruce and fir trees grew in the north on the Laurentian Shield above Superior and down the eastern shore of Huron. Birch, hemlock, and pines ranged south of Lake Superior to northern Michigan, north of Lake Erie, and around Lake Ontario. Hardwoods, such as ash, oak, maple, and dogwood, grew south of this region. Settlers cleared land for agriculture and buildings. Commercial logging began in the l830s, after the opening of the Erie Canal and the advent of steamships, which provided access to eastern markets. Logging began in Michigan and soon extended to Minnesota and Wisconsin. Loggers cut softwoods first, chiefly white pine, often hundreds of years old and more than 100 feet high. Softwoods framed homes and ships. Hardwoods became barrels and furniture.

The heyday of lumbering was from 1850 to 1900. Grand Rapids, today Michigan's second largest city, was a sawmill boom town in the 1850s; later it earned renown as a center for furniture-making. During the 1890s, there were 100 sawmills adjacent to the Saginaw River; by tonnage shipped, Saginaw was the largest port on the Lakes. Tugboats pulled enormous floating trains of trees from Canada to Saginaw mills. Around Muskegon Lake, beside Lake Michigan, there were 50 active sawmills in 1900. By 1910, there were none.

The Great Lakes lumber industry ran out of trees early in the twentieth century. The climate and soils of the North Woods and the Laurentian Shield are generally not conducive to farming. With the passage of time, forests have now returned to much of their former domain in the northern half of the region, though trees are much younger and smaller than their predecessors. Today, these woods are harvested for paper. The paper-making industry, which started in the 1860s, remains important in both the United States and Canada. In 1982, the forest industry of Michigan, Minnesota, and Wisconsin employed about 150,000 people and had sales of $15 billion. An additional 80,000 persons were employed in forest recreation.

The mining industry grew concurrently with the lumber industry and remains important today. In 1845, rich iron ore was found in the Marquette Range of Michigan's upper peninsula. Additional iron ranges were later discovered in Minnesota and Wisconsin. In 1855, completion of the Sault Canal opened Lake Superior to shipping and permitted mining of these ranges.

Iron ore from the mineral-rich Lake Superior watershed helped to make the Great Lakes region a center of iron-making, steel-making, and heavy manufacturing. Ore was shipped to lakeside cities, such as Buffalo, Cleveland, Detroit, Gary, and, in Canada, Hamilton and Sault-Sainte Marie. Another key ingredient for steel-making, limestone, was quarried near the northeast shore of Michigan peninsula. Coal from Illinois, Ohio, and Pennsylvania fired industrial hearths.

Oil became another significant industry. The world's first oil well was tapped in the northwestern Pennsylvania town of Titusville in 1859. Oil was later found near the Lakes in such locations as Midland, Michigan; Toledo, Ohio; and north-east of Lake St. Clair. Cleveland, Ohio, already an industrial hub in part because it was the terminus of a canal that linked the Lakes to the Ohio River, became the Nation's oil-refining center. In 1863, a 23-year old bookkeeper, John D. Rockefeller, invested $4,000 in a Cleveland oil refinery. By 1880, his Standard Oil Company refined 95 percent of the Nation's oil.

Since iron ore, limestone, coal, oil, and waterborne transportation were readily available, the Great Lakes region became an industrial heartland of both the United States and Canada. The automotive industry was born in a Michigan triangle bounded by Lansing, Flint, and Detroit, supplanting the carriage industry that had been thriving there. Detroit's population soared by almost 400 percent between 1890 to 1920 as Ford Motor Company began mass production of automobiles. The Ford, Chrysler, and General Motors corporations were producing eight million vehicles a year by 1950.

Industries associated with the automotive business, such as tool and die, machining, aluminum and rubber, were drawn to the area. By the 1920s, Akron, Ohio, where Benjamin Goodrich had open a rubber factory in l871, was processing almost half the world's rubber. Proximity to the steel industry attracted appliance and agricultural equipment manufacturers. Proximity to industrial customers attracted chemical manufacturers. Brine wells in southeastern Michigan were appealing to chemical firms. To draw on these wells, Herbert Dow founded what became one of America's largest chemical firms, Dow Chemical Company, in Midland, Michigan, in 1891.

During the 1970s and early 1980s, foreign competition and rising energy costs caused red-ink and job losses in Great Lakes heavy industry, especially in the United States. By that time, foreign economies devastated by the Second World War had developed strong competitors to Detroit's automobile manufacturers. The demand for fuel-efficient cars made lighter materials, such as plastics and aluminum, desirable alternatives to steel. During the 1970s, Detroit lost 20 percent of its residents. About one million manufacturing jobs disappeared in the early 1980s in just five Great Lakes States.

Yet heavy industries, including mining, steel, machine tools, and cars, remain important. Today, manufacturing continues to be the largest sector in the economy of most Great Lakes States. In 1991, five Great Lakes States made 61 percent of the cars produced in America. Mining and manufacturing are also major elements in the economy of the Province of Ontario. The Sudbury area produces the largest quantity of nickel in the world. Ontario is a major producer of gold, silver, platinum, uranium, zinc, iron, copper, salt, and gypsum. The province produces nearly 50 percent of Canada's manufactured goods. Employment in Ontario's manufacturing sector has increased over the last 20 years.

Agriculture is another productive element of the regional economy. During the nineteenth century, cheap land blessed with ample top soil, flat terrain, and railroads that brought crops to distant markets contributed to extraordinary agricultural productivity in the American Midwest. After 1914, combustion engines supplanted horses in powering farm machinery. Since 1950, farm yields have soared further because of developments in biology, chemistry, and engineering. Breeding plants has provided varieties with higher yields. Fertilizers, especially nitrogen, have raised soil productivity, and pesticides have abated crop losses to weeds, fungi, and insects. Farm machines have become vastly more effective.

As a result of these developments, agricultural output within the U.S. Great Lakes watershed has increased during the last 40 years, although farm acreage has actually decreased by one-third. Cropland accounts for 18 percent of the land in the U.S. counties of the watershed, predominantly in the south. Corn is the largest crop (42 percent of farm acreage), followed by soybeans (24 percent), and small grains, especially wheat (17 percent). Dairy products, fruits, vegetables, and tobacco are also important.

Convenient waterways have abetted the regional economy. The Erie Canal, completed in 1825, connected Buffalo to the Hudson River at Albany. At the same time, Canada constructed the Lachine Canal to bypass rapids on the St. Lawrence and the first Welland Canal between Lakes Ontario and Erie to bypass Niagara Falls. The 27-mile long Welland has been enlarged a number of times.

The five parallel locks at Sault-Sainte Marie, connecting Lakes Superior and Huron, are among the busiest in the world. In 1990, 5,000 vessels carried 90 million tons of cargo (including 50 million tons of iron ore) through these locks. Many commercial vessels are headed to or from the port of Duluth/Superior, which ranked 14th in the United States by tonnage shipped in 1987, and Thunder Bay, Ontario, the port of embarkation for one-half of Canada's grain production.

The St. Lawrence Seaway connects Lake Ontario to Montreal and provides the final link in a 2,200 mile commercial waterway between Duluth and the Atlantic Ocean. Completed in 1959, the Seaway is 27 feet deep, as are the shipping channels that cut through the St. Marys, St. Clair, and Detroit Rivers, and Lake St. Clair. This inland waterway is navigable by one-third of the world's saltwater fleet. In 1989, 40 million tons of cargo passed through the Seaway.

The waters of the Lakes provide other economic benefits. They are a source of drinking water to millions. Industries use water to make products (as in the beer for which Milwaukee is famous) and to cool manufacturing processes. Some rivers are harnessed to generate electricity; up to one-half the natural flow of the Niagara River is diverted for this purpose.

Another large element of the Great Lakes economy is recreation, including sight-seeing, fishing, boating, camping, and hiking. In 1988, Michigan had more registered boat owners than any other State. The Lakes sustain both sport and commercial fisheries, although recreational fishing is more important today. As the value of recreational fishing has increased, some jurisdictions have established policies that favor sport fishing. The Great Lakes Fisheries Commission has estimated that five million sport fisherman on the Great Lakes spent $2 billion in 1985; during the same year, the value of the commercial fish catch was just $41 million. The largest recorded commercial harvests were in 1889 and 1899. By weight, the commercial yield in recent years has been about two-thirds of these peak years, yet the value is small since the size and species harvested are less desirable.

At the onset of the twentieth century, the human population of the watershed was slightly more than 10 million. According to 1986 census data, the region has 35 million residents--27.5 million U.S. citizens and 7.5 million Canadians. The Lake Superior and Lake Huron watersheds are sparsely inhabited. The south and southwestern shoreline of Lake Michigan, the Canadian shore of Lake Ontario, and the U.S. side of Lake Erie are heavily populated. The third and sixth most populated U.S. metropolitan areas (Chicago and Detroit) and the largest Canadian metropolitan area (Toronto) are situated near the Lakes. Native American tribes also reside in the region. Five U.S. Indian reservations lie adjacent to the shores of the Great Lakes; 14 do so on the Canadian side.

Some Ecological Impacts of Development

Intense development of the Great Lakes region has wrought vast changes to its ecosystem. Humans have altered habitat, introduced exotic (i.e., nonnative) species, and contaminated the Lakes.

Some effects have been dramatic. Through discharge of raw sewage into the Lakes, cities infected their water supplies with typhoid and cholera during the late nineteenth and early twentieth centuries. By the mid-195Os, nonnative sea lamprey (parasitic eel-like fish) decimated lake trout to the extent that commercial catches in Lakes Huron and Michigan fell to 1 percent of the yield obtained 20 years before. By the 1960s, mats of algae fouled Lake Erie beaches and water intakes. In 1967, millions of another exotic fish, alewife, washed up on the Lake Michigan shore, victims of the combined effects of cold weather and starvation. Overpopulation, related to the decline of alewife predators, such as lake trout, contributed to the massive die-off. In 1969, a stretch of the Cuyahoga River in Cleveland was so laden with oil products, chemicals, and debris that it caught fire. Since the 1960s, researchers have noted reproductive problems in birds, such as double-crested cormorants, which have been born with grotesquely crossed beaks. These problems are probably caused by bioaccumulative toxic chemicals.

Many of these once acute problems have abated. Treatment of both drinking water and sewage ended water- related epidemics. Application of a toxicant to spawning grounds slashed the population of sea lamprey, although this exotic species is firmly established as a resident of the Lakes. Stocking of lake trout bolstered their numbers; however, the species generally is unable to sustain itself. Reductions in loadings of phosphorus have lessened many problems associated with nutrient over-enrichment, such as excessive algae. Stocking of salmon and trout has helped to control alewife numbers. Since the passage of the Clean Water Act in 1972, the reduction in pollutant loadings has greatly improved overall water quality, allowing fish to return to some harbors from which they had disappeared. The health of many fish and wildlife populations has improved as their burdens of contaminants have declined.

Yet the Great Lakes ecosystem has been pervasively changed in other, less dramatic ways, many of which are permanent. The decline in the beaver population resulted in fewer beaver dams, which had impeded tributaries and helped to create wetlands. In their absence, river flows increased; faster rivers captured and carried more silt, burying the spawning grounds of fish.

Harvesting trees exposed soil to direct sunlight, causing drying, and to wind and water, causing erosion. This, in turn, added silt to rivers. Forests had provided shade along tributaries. In their absence, the temperature of streams increased, further modifying the fish habitat. Forest clearance also increased seasonal variation in tributary flow. Low wintertime flow exposed streambeds, freezing fish eggs.

Agriculture also increased soil erosion. Since 1950, eroding soil particles and rainfall runoff have carried agricultural chemicals--pesticides and fertilizers. The over-enrichment of Lake Erie was partly the result of increased nutrient use by farmers.

The growth of human population has imposed further ecological change. Roads, sidewalks, roofs, and parking lots distort natural infiltration of water into the ground. Rain that would otherwise seep into the soil is caught by drainage systems and discharged to streams. As a result, tributaries have become more variable in their flow and less hospitable to fish.

The Lakes have been extensively altered for shipping and flood control. River mouths, critical habitat for fish and wildlife, have especially attracted development. Hundreds of them have been dredged and surrounded by breakwaters. Dredging and the wash from ship propellers injure organisms in bottom sediments upon which fish feed. Canals and ships have introduced nonnative species. Unchecked by natural predators, some of these have profoundly damaged native species.

Wetlands and sand dunes are two other habitats modified by humans. Wetlands have vital ecological functions, serving as nursery, resting, and breeding habitat for fish and wildlife. Perhaps two-thirds of the region's wetlands have been drained or filled since 1800. The downtown areas of Chicago, Detroit, and Milwaukee largely rest on filled-in wetlands. In fact, Chicago takes its name from an Indian word for the wild garlic that once grew there in marshlands beside Lake Michigan.

Before parks were established to preserve the remaining sand dunes at the base of Lake Michigan, home to a rich diversity of wildlife, were mined for glass production and for railway bed fill. Cheap lakefront land and a large nearby labor force in Chicago also made the dunes and adjacent wild rice swamps attractive to heavy industry. Standard Oil Company (now Amoco) established a refinery in Whiting, Indiana, in 1889. Inland Steel Company opened in East Chicago in 1901. The city of Gary took its name from the surname of the chairman of United States Steel when America's first billion dollar corporation opened a huge works there in 1906. Bethlehem, National, and LTV steel companies followed. Today, northwestern Indiana is home to numerous metal, oil, and petrochemical facilities. In places, large amounts of oil float on the groundwater, during drought, the sinking water table lowers oil into municipal drainage systems. The Grand Calumet River meanders through this region receiving most of its waters from industrial and municipal dischargers. Its riverbed holds many toxic contaminants.

Manufacturing firms have contributed a broad range of contaminants to the Lakes. One of the most injurious is the family of organic chemical compounds called polychlorinated biphenyls (PCBs). PCBs were widely used from 1929 until EPA prohibited their manufacture in 1977. They are highly stable, which made them useful as hydraulic fluids and lubricants in high temperature or pressure processes. Tests have shown that PCBs may cause reproductive disorders, birth defects, and cancers in laboratory animals. The stability that made PCBs desirable in commercial applications has undesirable environmental consequences; they magnify up the Great Lakes food web and do not degrade. PCB contamination is the most frequent grounds for health advisories regarding consumption of Great Lakes fish.

Though the practice ceased during the 1970s, some chloralkali plants and some pulp and paper mills released mercury that was later detected in fish from Lake Huron, Lake St. Clair, western Lake Erie, eastern Lake Ontario, and the St. Lawrence River at levels that required closure of some commercial fisheries. In the 1980s, EPA also recognized that pulp and paper mills, particularly those using the bleached kraft process, discharge very low concentrations of chlorinated dibenzodioxins and dibenzofurans as byproducts of pulp and paper bleaching with chlorine. Dioxins and furans represent a family of 210 related chemical compounds. The most infamous of the dioxin compounds, 2,3,7,8-TCDD, produces a variety of toxic effects in laboratory animals at very low doses.

The pulp and paper industry also continues to be a significant source of conventional pollutants to the Lakes, particularly to Lake Superior. According to a 1989 report by the International Joint Commission, pulp and paper mills in the Province of Ontario generally do not use secondary (i.e., biological) processes to treat their wastewater. Secondary treatment, usually practiced by U.S. mills, decreases both conventional pollutants and 25 to 60 percent of toxic organic byproducts. In 1993, the Province of Ontario announced a multiyear phase-in of enhanced discharge requirements for this industrial sector.

Chemical companies have left a toxic heritage in the groundwater, bottom sediments, and soils of the region. American chemical companies were attracted by hydroelectric power generated from the Niagara River situated near its banks. Canadian chemical companies similarly clustered along the St. Clair River. Waste sites along the U.S. side of the Niagara have been a source of contamination to Lake Ontario. Since the inception of the Superfund program, cleanup efforts have focused on these sites, substantially reducing their loadings to the Niagara River.

In addition, metals-based industries have been a significant source of pollutants. Many presently used steel-making technologies generate byproducts, including ammonia, cyanide, coal tar, zinc, lead and a range of air pollutants, including fly ash, sulfur compounds, and the volatile chemicals benzene toluene, and xylene. Steel mills emit benzo(a)pyrene, the most toxic member of the family of polyaromatic hydrocarbons (PAHs). Like other PAHs, benzo(a)pyrene is produced by incomplete combustion of fossil fuels and is suspected of causing lip and liver tumors in bottom-dwelling fish. PAHs are common in bottom sediments of the Great Lakes.

Conclusion

This chapter has tried to convey that environmental damage cannot be attributed solely and simplistically to a few leading industries. Damage to the Great Lakes ecosystem during the past three centuries has been caused by the collective actions of society--by individuals and the public sector as well as by industry and agriculture. The prominent industries mentioned in this chapter, especially productive sectors, such as farming, forest products, metals, and manufacturing, continue to make vital contributions to our National economy.

In addition, this chapter has suggested that the changes to the Great Lakes ecosystem during the last three centuries have been vast and that a long-term perspective is useful to appreciate the magnitude of damage to once abundant fish and wildlife populations. The next chapter discusses current challenges facing the Great Lakes ecosystem that are the focus of government programs, discussed later in this report.


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