Biosphere. Mass Extinctions

Smog
Smog is an urban problem caused by combustion of fuels. Pollutants react with sunlight to cause more than 100 secondary pollutants that can cause respiratory problems (asthma and such) in humans. Most problems with acid rain and smog are caused by the use of fossil fuels. The U.S. gets 90% of its energy from fossil fuels, more than half of which is wasted. Conservation measures, more fuel efficient vehicles, mass transit, and alternative energy sources are possible measures to be taken. World supplies of petroleum are estimated to run out in 50-100 years.

Photochemical smog is air pollution that contains nitrogen oxides (NOx) [where the x is a 2 or 3] and hydrocarbons (HC), that react together in the presence of sunlight to produce ozone (O3) and peroxylacetyl nitrate (PAN). Both NOx and hydrocarbons result from the burning (or combustion) of fossil fuel. Additional hydrocarbons come from various other sources as well, including paint solvents and pesticides.

Breathing O3 affects both the respiratory and nervous systems, resulting in respiratory distress, headache, and exhaustion. Ozone is damaging to plants, resulting in leaf mottling and reduced growth.

Carbon monoxide (CO) is a gas that comes from burning of fossil fuels in the industrial regions. High levels of CO increase the formation of ozone (O3). CO combines preferentially with hemoglobin and prevents hemoglobin from carrying oxygen. The amount of CO over the Southern Hemisphere, produced by the burning of tropical forests, is equal to that over the Northern Hemisphere, produced by industrial activity..

Thermal inversions are local occurrences of polluted air being trapped close to the surface. This is a major problem in cities located in a valley, like the Phoenix (Arizona) metropolitan area. Warm air near the ground usually rises and dissipates into the upper atmosphere. Air pollutants, including smog and soot, can be trapped near ground due to a thermal inversion. A thermal inversion occurs when a layer of dense cold air is trapped under a layer of warm air. Areas around hills are susceptible because air stagnates, with little mixing. At certain times of the year, usually in winter, thermal inversions in Phoenix can cause difficulty in breating for some individuals who has asthma and other respiratory diseases.

Water Pollution Is Altering the Hydrosphere
Air pollutants will eventually precipitate into the hydrosphere. During cooler periods, ice acts as a water reservoir, forming glaciers that lower sea-level and affect climate. Global warming will melt this reservoir, raising sea level (or sinking coastlines). The hydrosphere can be directly altered by water polluted by human wastes. There are three basic sources of water pollutants: municipal sewage, industrial discharges, and agriculture/mining/logging discharges of sediment.

Freshwater is required for domestic purposes, including drinking, crop irrigation, industrial use, and energy production. Freshwater resources include surface water from lakes and rivers, and underground aquifers. Pollution contributes to the shortage of freshwater. Solid wastes include household trash, sewage sludge, agricultural residue, mining refuse, and industrial waste. Pollution comes from either a point source, an identifiable source of the pollution, or a nonpoint source, a broad area of pollution with no single idetifiable source, such as runoff. The United States spends more than $9 billion a year on cleanup (including the Superfund) compared to a mere $200 million per year to prevent pollution. Recycling may save industry money, extend the life of increasingly scarce resources, and prevent or lessen pollution.

Sewage treatment plants degrade organic wastes, which would otherwise cause oxygen depletion in lakes. Human feces contain pathogens (viruses, bacteria) that cause cholera, typhoid fever, and dysentery. Sewage treatment plants use bacteria to break down organic matter into inorganic nutrients. The treated water can then be used for various purposes, depending on state and local laws governing sewage treated water. During the spring of 2000, Los Angeles made national news because of the city''s plans to reintroduce treated sewage water to the home water supply.

Agricultural and industrial wastes present a number of water pollution problems. Intensive animal farming or the presence of many septic tanks releases ammonium (NH4+) from wastes. This ammonium is converted by bacteria to soluble nitrate that moves through the soil to water supplies. Between 5-10% of all wells in the United States have nitrate levels higher than the recommended maximum. Industrial wastes include heavy metals and organochlorides, such as some pesticides. These are not degraded in nature or in normal sewage treatment, and accumulate in deltas. When these wastes enter water, they are subject to biological magnification. Decomposers are unable to break down these wastes, and they are not excreted. The molecules, therefore, remain in tissues and are passed up the food chain to the next consumer. They become more concentrated at each level in the food chain. Since aquatic food chains have more links, biological magnification is greater. Where humans are the final consumers, human milk can contain detectable amounts of DDT and PCBs.

Aquifer pollution is an increasingly significant health threat. Prior to environmental regulations enacted during the 1970s, many industries ran wastewater into a pit from which pollutants could seep into the ground Much of this material eventually made its way to the groundwater in various aquifers below the surface. Wastewater and chemical wastes were also injected into deep wells. Both practices are being phased out; there are few alternatives for industry to dispose of wastes, other than to reduce the volume or develop a long-term containment facility.

The oceans are the final recipients of wastes deposited in rivers and along the coasts. Waste dumping occurs at sea, and ocean currents sometimes transport both trash and pollutants back to shore. Solid pollutants cause death of birds, fish, and marine mammals that mistake them for food and get entangled. Offshore mining and shipping add pollutants to the oceans. Five million metric tons of oil a year, over one gram per 100 square meters of ocean surface, ends up in oceans. Large oil spills kill plankton, fish larvae, and shellfishes, as well as birds and marine mammals. The Exxon Valdez oil spill in Alaska''s Prince William Sound leaked 44 million liters of crude oil. During the Gulf War, 120 million liters were released from damaged onshore storage tanks in the Persian Gulf. Petroleum is biodegradable; takes a long time because low-nutrient content does not support bacteria. Some species of fish are in dramatic decline from combined effects of pollution and overfishing.

Desertification and Deforestation
In 1950, 20 % of the world''s population lived in cities. Predictions of this number rising to 60% by 2000 have been made. The trend of growth of urban areas began with the Industrial revolution of the 1800s, but greatly accelerated after World War II. Buidling new housing around new (or enlarging) cities, removes land from agricultural uses. Change of land use can alter heat distribution patterns and surface water runoff. Expanded urbanization also degrades the environment. Estrella Mountain Commmunity College, my college, was built in 1991 (opened in 1992) in an old cotton field. When we opened our campus the nearest houses were over one mile away.

In agricultural areas, wind and rain carry away about 25 billion tons of top soil yearly, worldwide. At such a rate, it is estimated that practically all top soil will be lost by the middle of the next century. Soil erosion causes a loss of productivity; it is compensated for by fertilizers, pesticides, and fossil fuel energy. One solution is to employ strip-cropping and contour farming to control soil erosion. Desertification is transformation of marginal lands to desert conditions due to overgrazing and overfarming. This is most evident along the southern edge of the Sahara Desert in Africa. Over 240,000 square miles of once-productive grazing land has become desert in the last fifty years. A similar process can occur if U.S. rangeland is overgrazed. The Dust Bowl, shown in Figure 18, was an area of the southern Great Plains that experienced several years of drought, coupled with poor farming techniques and economic hard times. Was the area becoming a desert before soil conservation and improved farming methods halted the trend?

Canada has seen immense stands of trees cut down for paper, wood products and particleboard. Tropical rain forests are more biologically diverse than temperate forests. U.S. temperate forests contain about 400 species of trees; a typical 10-hectare rain forest contains 750 species. The loss of U.S. forests is shown in Figure 19. South American streams contain about twice the species found in all of the U.S. and Canada. A N.A.S. study estimates a million species are in danger of disappearing in 20 years due to deforestation. Lost species that have never been studied may have been sources of food or medicine. Logging in tropical forests meets the demand for furniture and also the desire of local people to farm the land. Slash-and-burn agriculture also contributes to the destruction of tropical rain forests. The ashes provide temporary nutrients to raise crops. After a few years, the fertility of the land is insufficient to raise crops and farmers move on. Cattle ranching usually takes over from farming. Pig-iron industry in Brazil also requires wood charcoal to smelt the pig iron.

Extinctions occur when environments change too fast. Local extinctions can occur, as can mass extinctions: they differ in scale, scope and the numbers of species involved. There have been five environmental changes (mostly cooling) of global proportions that resulted in the five mass extinctions in Earth history. Recovery from these extinctions took millions of years. A spectacular exception was the large meteorite strike sixty-six million years ago near the Yucatán peninsula in Mexico that either caused the extinction of dinosaurs and 75% of all marine species, or was the nail in the coffin of the dinosaurs.

There have been several natural mass extinctions in the history of earth followed by recovery. Human activities that reduce biodiversity began about 30,000 years ago with development of social and language skills to apply increasingly better stone tool technology to trap and kill the largher animals. Hunting contributes to the estimated extinction of 15,000 to 30,000 species a year. Fish stocks are being depleted by overfishing. Commercial trade causes exploitation of tigers, cheetahs, leopards, jaguars, etc. for furs; sharks for fins; rhinoceros for rhino horn powder; elephants for tusks for ivory; and cacti for gardeners.

A major cause of extinction is the loss of habitat to support a species. The habitat for a species may be totally destroyed through natural events or human activities. Habitats may be fragmented into small pieces that cannot support the population. By 2010, very little undisturbed rain forest will exist outside of national parks.

Accidental or purposeful introduction of new species can cause extinction of endemic species. Introduction of brown tree snake to Guam has resulted in extinction of nine of eleven native bird species. The carp, an Asian fish that can tolerate polluted waters, is now more prevalent than our native fish. Kudzu, a plant native to Asia, has beome a major pest throughout the south. Water hyacinth escaped from captivity and has become a hazard to navigation, as well as disrupting the local environment.

Global climate change may be so rapid that many species cannot adjust. Biological magnification of pesticides has reduced predatory bird populations. Acid deposition is implicated in the worldwide decline in amphibian populations.

Conservation biology is a discipline that brings together many fields to attempt to solve biodiversity problems. It attempts to develop practical approaches to preventing extinction of species and destruction of ecosystems. Most conservation biologists believe biological diversity is good and each species has a value all its own. Sustainability is concept that it is possible to meet economic needs while protecting environment. Some economists argue that as per capita income increases, environmental degradation first increases, then decreases as people become affluent enough to begin to protect the environment.

Development in Tropical Regions
Human-caused environmental changes and extinctions are accelerating in the tropics. If this pace continues nearly half all species could be extinct by 2050. Development in tropical areas causes more extinctions due to the great diversity found in tropical rain forests (half all species on Earth). Tropical reefs are also under siege by water pollution, leading to even more extinctions. Nearly half the rain forests are gone already. By as early as 2010 (less than 15 years!) all rain forests will be gone if present trends of exploitation and human population growth continue.

Species are not equally likely to suffer extinction. Cockroaches hav e been around for 300 million years essentially unchanged and probably will be around for millions more. Island species, species with limited habitats, low reproductive rates, high territory requirements, susceptibility to pollution, predators, and having economic value: all make species susceptible to extinction.

What Does Extinction Mean to Me?
We migh ask ourselves, why should we try to save species from extinction? One answer is that wildlife is a curiosity for which humans have no need. Others seek to preserve nature for its own sake. There are some economic reasons to save species from extinction: food and non-food uses.

Approximately 7000 plant species have historically been used by humans as food. Today, thirty of these species provide 95% of all human food. Just four -wheat, corn, rice, and potatoes- provide most of the world''s food. Nearly 75,000 edible plants species exist, many superior in nutrition and quality to the 30 we favor today. Low genetic diversity, resulting from centuries of selective inbreeding, make crops especially susceptible to pests and parasites. During the 1970s the U.S. corn crop was almost completely wiped out by a leaf fungus. The corn crop was saved by interbreeding it with a rare species of wild corn from Mexico. Genetic engineering may also offer some hope by facilitating transfer of genes between species. This increases the value of wild strains which can be used as sources for new traits to be introduced into crops.

At current rates, 25,000 plant species will become extinct by the year 2000, before we have a chance to study them. Gene banks t