Pollution also causes extinction. Many toxic substances that are released inadvertently or in the process of waste disposal are very similar to pesticides. They have similar impacts on living systems, including the eggshell thinning in birds. PCBs have contaminated organisms from the Antarctic penguins to ourselves. Its production was stopped in the USA in 1977, but 750,000 million tons have ended up in dumps and landfills.
One of the greatest public alarms at toxic dumping concerned the Love Canal affair in Niagara, New York (United States), where toxic substances were dumped into a landfill. An elementary school was built on the site and houses constructed next to it. Not only this, but the public soon learned that there were thousands of "Love Canals" scattered around the nation, and probably in other countries as well. They were afraid of the possibility of developing emphysema or heart disease from the air pollution, diarrhea from the water pollution, or cancer from the chemicals leaching from old dumps.
The sulfur dioxide gas that is produced when coal and fuel oil are burned can cause diseases in humans. In broad-leaved and evergreen plants, sulfur oxides inhibit growth and cause cells in the leaves to collapse or become distorted. Air pollution has wiped out vegetation, and with the plants, of course, go all of the animal populations dependent on them. The oxides of sulfur and nitrogen released into the atmosphere from factories and car exhausts undergo chemical reactions that convert them into nitric and sulfuric acids. As a result, rains over large parts of North America and Europe are ten to a thousand times as acidic as rains from unpolluted skies. On April 10, 1974, in Pitlochry, Scotland, a downpour of rain as acid as vinegar drenched the land.
In the Adirondack mountains of North America, the rains are acidifying the water and the nitric acid is reacting with the soil to release large amounts of aluminum, which is then washed into the lakes. These acids build up during the winter, and in the spring, when the snow melts, they pour into lakes in concentrations lethal to fishes. After this initial acid water rush, a flush of aluminum pollution follows. As a result, all fish populations in three hundred Adirondack lakes are now extinct, and the Brook Trout and other species may have been wiped out over the entire area.
Further north, Canadian scientists have isolated 48,000 lakes that will not be able to support life in two decades if the current trends continue. Spotted Salamanders no longer live in snowmelt ponds in upstate New York because the winter snows are too acid. Acid rains have already ruined a third of the Nova Scotia spawning rivers of the Atlantic Salmon, adding to the pesticides, dams, other pollution, overfishing, and poaching that are already pushing the species toward extinction.
Acid rains are also damaging to microorganisms in the soil, including those involved in the nitrogen cycle. Acid accumulation may also worsen the effects of other pollutants. In 1871, a killing blow came when the flow of the Chicago River in the US was reversed to carry the city's sewage into the Illinois River system rather than into Lake Michigan, the source of its drinking water. Sewage, because it contains toxins and organic wastes, can overwhelm the decomposing capacity of natural ecosystems. The Illinois River system was destroyed, and along with it commercial fishing for such species as turtles, mussels, and fishes. Between 1900 and 1920, the northern 100 miles of the river became a biological desert with almost no dissolved oxygen in the water, glaring evidence of organic pollution overload.
This same story is repeated in freshwater systems all over the world. The Rhine river is loaded with poisons and has suffered massive fish kills. In the Danube, populations of many important fish species have been greatly reduced. Lake Baikal is under threat, despite efforts to stop pollution. Rivers in Central America are filled with silt as the soil washes off denuded uplands. Japan's rivers are full of industrial wastes. Streams in Queensland, Australia, are polluted with wastes from the sugar mills. A steady movement of feces, chlorinated hydrocarbons, mercury, cadmium, chromium, acids, alkalis, fertilizers, waste oil, detergents, pulp wastes, carbamate insecticides, and silt roll toward the sea, passing through vital estuaries, and threatening countless populations with extinction.
DIGGING, LEAKING, AND FLOODING
Mining and development of minerals and energy have had wide-ranging effects on habitats both through direct attacks and pollution. Mining has the greatest variety of effects, for many of its wastes contain toxic substances. These poisons get into freshwater ecosystems, and, as in the case of acid rains, the impact on aquatic organisms can be severe.
Heavy-metal pollution is also common, especially with mercury, copper, lead, cadmium, chromium, and zinc. Its influences on the environment can be long-lasting and profound. For example, lead mines in Cardiganshire, Wales, were closed in 1921, but the rivers only gradually regained their diversity. Mine effluents can lead to a dramatic reduction of dissolved oxygen in lakes and streams, leaving a lethal effect on many animals. Moreover, cleaning up water pollution from mines can extremely difficult.
Oil leaking is another frequent problem. The oil spills threaten the coastal ecosystems and wildlife. Oil pollution continually assaults the populations of the South African Blackfooted Penguin. Populations have been reduced several hundredfold by these accidents. In 1974 populations of the Magellanic penguin species suffered heavy losses when the Shell supertanker Metuchen went aground in the Strait of Magellan. It was the second largest oil spill up to that time, and thousands of birds died. On March 24, 1989, the Exxon Valdez spilled over 11.2 million gallons of oil into the waters off the Oregon coastline, coating many birds and seals with petroleum. It was and remains one of the greatest ecological disasters of all time.
The construction of dams, surprisingly, also creates many ecological difficulties. Two of the most famous endangered species in North America are endangered by dams. The Snail darter fish is threatened by the Tellico Dam in Tennessee, and the Furbish Lousewort, a yellow-flowered plant in the snapdragon family, has eighteen known populations in the United States. Thirteen were flooded out by the construction of the Dickey-Lincoln Dam. The hydroelectric project would also destroy the habitat of species such as the Bald Eagle, Osprey, Lynx, Bobcat, Otter, Marten, Moose, and Blueback Trout. It would flood 140 square miles of valuable timber, and the construction of high-voltage lines radiating from the dam would scar another 400 square miles of wilderness. All over the US, dams flood out natural populations and divert waters from their natural courses, modifying or destroying riverine habitats that are centers of biological diversity in otherwise dry and less diverse areas. In addition, more than 3,000 miles of irrigation canals built by the Bureau of Reclamation form death traps that drown birds, snakes, coyotes, badgers, Bighorn Sheep, antelopes, and deer.
In India, a Hubbardia grass is thought to be extinct because a dam diverted water from the waterfall that provided it with life-giving spray. On the island of Mauritius, a Crinum Lily became extinct when the leaks in a dam were plugged and its lake fully flooded. In Russia, so many dams have been built on the Volga that is has been described as "not so much a river as a 2,300 mile chain of reservoirs, created by hydroelectric power dams." And three famous species of Caspian sturgeon were cut off from their spawning grounds by the dams. The sturgeon species went into severe decline.
Indirect Causes - Agriculture
