Showing posts with label environmental issues. Show all posts
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2:29 AM
forest damaged by acid rain
forest damaged by acid rain

Acid precipitation is rain, snow, or mist which has a pH lower than unpolluted precipitation. Increased levels of acid precipitation have significant effects on food chains and ecosystems.

Precipitation—rain, snow, hail, sleet, or mist—is naturally acidified by carbonic acid (H2CO3). Carbon dioxide (CO2) in the atmosphere reacts with water molecules, lowering the pH of precipitation to 5.6. A pH scale is used to measure a solution’s acidity or alkalinity; pH is defined as the negative logarithm of the concentration of hydrogen ions, H+ . A solution with a pH of 7.0 is neutral. A pH lower than 7 is acidic, and a pH greater than 7 is alkaline.

Other acidic substances are also present in the atmosphere, causing "unpolluted" precipitation to have a pH approaching 5.0. Solutions with a pH of 5.0 or less have concentrations of hydroxyl ion, or OH– , and carbonate ion, or CO3– , approaching zero.


Acid precipitation is the name given to rain or snow contaminated with oxides of sulfur (SOx) and oxides of nitrogen (NOx). These chemicals combine with water droplets to form sulfuric acid and nitric acid. SOx is formed by combustion of materials containing sulfur, and NOx is formed by oxidation of molecular nitrogen in the atmosphere during combustion. SOx sometimes arises from natural sources such as volcanoes and geyser fields, and NOx is formed by lightning.

Downwind of smelting facilities, hydrochloric acid (HCl) and hydrofluoric acid (HF)may also contribute to acid precipitation. Acid precipitation may detrimentally change soil chemistry, either by stripping nutrients, especially magnesium and calcium, or mobilizing phytotoxic trace elements (elements toxic to plants).

Geographic Extent of Damage

Acid precipitation is a regional problem. SOx and NOx can travel many thousands of kilometers in the atmosphere after being emitted by large, stationary sources, especially those that have very high smoke stacks.

How acid rain is formed
How acid rain is formed

These pollutants are slowly transformed into sulfuric and nitric acid aerosols and are incorporated into precipitation, which eventually makes contact with the earth’s surface. Acid precipitation in the eastern United States contains more SOx than precipitation in the western United States, which contains more NOx.

In North America, acid precipitation and dry deposition (of acid aerosol particles) are major environmental problems in New England and New York State and in Ontario and Quebec. These regions attribute much of their acid precipitation to emissions from large coal-burning plants in the American Ohio Valley.

Scandinavian activists blame coal-burning power plants and factory emissions in the British Isles for that region’s acid rain problems. Central Europe—including Poland, the Czech Republic, Slovakia, and eastern Germany—has many power plants and factories that burn high-sulfur coal. Acid-laden pollution plumes stretch thousands of kilometers downwind from smokestacks in that region.

Controlled Studies

Controlled experiments on individual plant species have revealed short-term damage to a limited number of those species. Experiments using simulated acid rain (SAR) are difficult to extrapolate to field conditions, where the specific pollutants and pH levels vary widely over time.

Air Pollution
Air Pollution

In controlled conditions, studies showed no link between SAR and yield in Amsoy soybeans. However, field studies demonstrated that acid deposition does decrease yield in Amsoy soybeans.

Acid precipitation influences plant diseases by acting on both pathogens and host organisms. Seedlings of Pinus rigida, Pinus echinata, Pinus taeda, and Pinus strobus exposed to SAR of pH 3.0 had a 100 percent mortality rate because of fungal damping-off, a diseased condition of seedlings marked by wilting or rotting.

Red spruce seedlings subjected to dilute sulfuric acid mist developed brown lesions on their needles, followed by needle drop. Studies showed a reduction in the growth of sugar maple seedlings following exposure to low pH moisture, and that seedling survival decreased with increasing acidity.

Crop and Forest Decline

In field experiments, soybeans have shown reduced yields with decreasing pH (increasing acidity) of moisture applied. Yields of seed and seed protein are both reduced in soybeans exposed to high acidity. A lower number of seed pods were found in plants exposed to high acidity, compared to control plants.

Acid precipitation causes detrimental long-term effects in most ecosystems, especially forests. Root systems under acidic stress show great variability in tolerance and injury. Acidic stress on roots decreases root growth, measured by a reduction in root length, and severely damaged trees have more fine roots with opaque tip zones than do slightly damaged trees. Some scientists have suggested that the radical growth rate in yellow pines in the southeastern United States may be reduced by acid precipitation.

Since the 1960’s Central European soils have been progressively acidified, altering soil buffering capacities. Acid rain containing nitrates (which are not immobilized in soil) played an important role in this soil acidification.

Acidification has reduced the magnesium, calcium, and potassium available for nutrient uptake by plants and has affected root growth. One-quarter of European forests are moderately or severely damaged by acid precipitation, with dry deposition believed (by scientists and politicians) to be largely responsible.

This pattern of damage, first detected in the 1980’s, has been called neuartige Waldschäden (literally, "new-type forest decline"). It has been detected throughout Central Europe at all elevations and on all soil types. Waldschäden is most pronounced downwind of major air pollution sources.

Abnormally high numbers of red spruce have died in the high-elevation northern Appalachian Mountains since the 1960’s. This die-off has been attributed to high rates of acid deposition (up to 4 kilo equivalents of hydronium ions per hectare per year) and exposure to acid fog droplets for up to two thousand hours per year. Very high levels of trace metals (known to be phytotoxic) have accumulated in the region.

Aquatic Ecosystems

Most freshwater ecosystems range from pH 6.0 to pH 8.0. In limestone terrain, acid precipitation is neutralized by dissolution of calcium carbonate. As a freshwater environment becomes acidified, the number of species it supports declines. When conditions are more acidic than pH5.5, dissolved inorganic carbon exists only as dissolved carbon dioxide. Planktonic algae, which can use low levels of dissolved inorganic carbon, are favored in these environments.

Acid environments greatly reduce the numbers of herbivores that graze on aquatic plants; this is thought to explain why filamentous green algae are found in most acidified lakes. Scientists point out that it is difficult to separate the effects that acidification alone produces in an aquatic ecosystem.
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9:20 PM
Modern Agriculture
Modern Agriculture

Many current problems in agriculture are not new. Erosion and pollution, for example, have been around as long as agriculture. However, agriculture has changed drastically within its ten-thousand-year history, especially since the dawn of the Industrial Revolution in the seventeenth century.

Erosion and pollution are now bigger problems than before and have been joined by a host of other issues that are equally critical—not all related to physical deterioration.

Monoculture

Modern agriculture emphasizes crop specialization, also known as monoculture. Farmers, especially in industrialized regions, often grow a single crop on much of their land. Problems associated with this practice are exacerbated when a single variety or cultivar of a species is grown. Such a strategy allows the farmer to reduce costs, but it also makes the crop, and thus the farmand community, susceptible to widespread crop failure.


The corn blight of 1970 devastated more than 15 percent of the North American corn crop. The cornwas particularly susceptible to the harmful organisms because 70 percent of the crop being grown was of the same high-yield variety. Chemical antidotes can fight pests, but they increase pollution.

Maintaining species diversity or varietal diversity—growing several different crops instead of one or two—allows for crop failures without jeopardizing the entire economy of a farm or region that specializes in a particular monoculture, such as tobacco, coffee, or bananas.

Genetic Engineering

Growing genetically modified (GM) crops is one attempt to replace post-infestation chemical treatments. Recombinant technologies used to splice genes into varieties of rice or potatoes from other organisms are becoming increasingly common. The benefits of such GM crops include more pest-resistant plants and higher crop yields.

Genetic Engineering
Genetic Engineering

However, environmentalists fear new genes could trigger unknown side effects with more serious, long-term environmental and economic consequences than the problems they were used to solve. GM plants designed to resist herbicide applications could potentially pass the resistant gene to closely related wild weed species that would then become "super weeds".

Also, pests, just as they can develop resistance to pesticides, may also become resistant to defenses engineered into GM plants. The high cost of recombinant technologies calls into question the feasibility of continuing development of GM plants.

Erosion

Erosion
Erosion
An age-old problem, soil loss from erosion occurs all over the world.As soil becomes unproductive or erodes away, more land is plowed. The newly plowed lands usually are considered marginal, meaning they are too steep, nonporous or too sandy, or deficient in some other way.

When natural vegetative cover blankets these soils, it protects them from erosive agents: water, wind, ice, or gravity. Plant cover "catches" rainwater that seeps downward into the soil rather than running off into rivers. As marginal land is plowed or cleared to grow crops, erosion increases.

Expansion of land under cultivation is not the only factor contributing to erosion. Fragile grasslands in dry areas also are being used more intensively. Grazing more livestock than these pastures can handle decreases the amount of grass in the pasture and exposes more of the soil to wind, the primary erosive agent in dry regions.

Overgrazing can affect pastureland in tropical regions too. Thousands of acres of tropical forest have been cleared to establish cattle-grazing ranges in Latin America. Tropical soils, although thick, are not very fertile. After one or two growing seasons, crops grown in these soils will yield substantially less than before.

Tropical fields require fallow periods of about ten years to restore the soil after it is depleted. That is why tropical farmers using slash-and-burn agriculture move to new fields every few years in a cycle that returns them to the same place years later, after their particular lands have regenerated.

Where there is heavy forest cover, soils are protected from exposure to the massive amounts of rainfall. Organic material for crops is present as long as the forest remains in place.

When the forest is cleared, however, the resulting grassland cannot provide the adequate protection, and erosion accelerates. Lands that are heavily grazed provide even less protection from heavy rains, and erosion accelerates even more.

The use of machines also promotes erosion, and modern agriculture relies on machinery such as tractors, harvesters, trucks, balers, and ditchers. In industrialized nations, machinery is used intensely. Machinery use is on the rise in developing countries such as India, China, Mexico, and Indonesia, where traditional, nonmechanized farming methods are the norm.

Farming machines, in gaining traction, loosen topsoil and inhibit vegetative cover growth, especially when farm implements designed to rid the soil of weeds are attached. The soil is then more prone to erode.

Eco-fallow farming has become more popular in the United States and Europe as a way to reduce erosion. This method of agriculture, which leaves the crop residue in place over the fallow (non-growing) season, does not root the soil in place as well as living plants do.

As a result, some erosion continues. Additionally, eco-fallow methods require heavy use of chemicals, such as herbicides, to "burn down" weed growth at the start of the growing season. This contributes to increased erosion and pollution.

Pollution and Silt

Besides causing resistance among harmful bacteria, insects, and weeds, pesticides inevitably wash into, and contaminate, surface and groundwater supplies. Chemicals, although problematic, are not as difficult to contend with as the increasingly heavy silt load choking the life out of streams and rivers.

Accelerated erosion from water runoff carries silt particles into streams, where they remain suspended and inhibit the growth of many forms of plant and animal life.

The silt load in American streams has become so heavy that the Mississippi River Delta is growing faster than it once did. Heavy silt loads, combined with chemical residues, are creating an expanded dead zone. By taxing the capabilities of ecosystems around the Delta, sediments are filtered out slowly, plant absorption of nutrients is decreased, and salinity levels for aquatic life cannot be stabilized.

Most of the world’s population lives in coastal zones, and 80 percent of the world’s fish catch comes from coastal waters over continental shelves that are most susceptible to this form of pollution.

Pesticide Resistance

Pesticide Resistance
Pesticide Resistance
With the onset of the Green Revolution, the use of herbicides, insecticides, and other pesticides increased dramatically all over the world. An increasing awareness of problems caused by overuse of pesticides extends even to household antibacterial cleaning agents and other products. Mutations among the genes of bacteria and plants have allowed these organisms to resist the effects of chemicals that were toxic to their ancestors.

Use of pesticides leads to a cycle wherein more, or different combinations of, chemicals are used, and more pests develop resistance to these toxins. Additionally, the development of herbicide-resistant crop plants enables greater use of herbicides to kill undesirable weeds on croplands.

Increasing interest in biopesticides may slow the cycle of pesticide resistance. Types of biopesticides include beneficial microbes, fungi, and insects such as ladybugs that can be released in infested areas to prey upon specific pests. Biopesticides used today include naturally occurring and genetically modified organisms. Their use also avoids excessive reliance on chemical pesticides.

Fertilizers and Eutrophication

Increased use of fertilizers was another result of the Green Revolution. Particulate amounts of most fertilizers enter the hydrologic cycle through run-off. As a result, bodies of water become enriched in dissolved nutrients, such as nitrates and phosphates.

The growth of aquatic plants in rivers and lakes is overstimulated, and this results in the depletion of dissolved oxygen. This process of eutrophication can harm all aquatic life in these ecosystems.

Water Depletion

With an increasing reliance on irrigation, groundwater resources are mismanaged and overtapped. The rate of groundwater recharge is slow, usually between 0.1 and 0.3 percent per year. When the amount of water pumped out of the ground exceeds the recharge rate, it is referred to as aquifer overdraft. An aquifer is a water-bearing stratum of permeable rock, sand, or gravel.

In Tamil Nadu, India, groundwater levels dropped 25 to 30 meters during the 1970’s due to excessive pumping for irrigation. In Tianjin, China, the groundwater level declines 4.4 meters per year. In the United States, aquifer overdraft averages 25 percent over the replacement rate.

The Ogallala aquifer under Kansas, Nebraska, and Texas represents an extreme example of overdraft: Depletion is 130 to 160 percent above the replacement rate annually. At this rate, this aquifer, which supplies water to countless communities and farms, has been projected to become nonproductive by 2030.

Soil Salinization

In addition, continued irrigation of arid regions can lead to soil problems. Soil salinization is widespread in the small-grained soils of these regions, which have a high water absorption capacity and a low infiltration rate.

Some irrigation practices add large amounts of salts into the soil, increasing its natural rate of salinization. This can also occur at the base of a hill slope. Soil salinization has been recognized as a major process of land degradation.

Although surface and groundwater resources cannot be enriched by technology, conservation and improved environmental management can make the use of precious freshwater more efficient. In agriculture, for example, drip irrigation can reduce water use by nearly 50 percent. In developing countries, though, equipment and installation costs often limit the availability of these more efficient technologies.

Urban Sprawl

Urban Sprawl
Urban Sprawl
As more farms become mechanized, the need for farmers and farm workers is being drastically reduced. From a peak in 1935 of about 6.8 million farmers farming 1.1 billion acres, the United States at the end of the twentieth century counted fewer than 2 million farmers farming 950 million acres.

Urban sprawl converts a tremendous amount of cropland into parking lots, malls, industrial parks, and suburban neighborhoods. If cities were located in marginal areas, then concern about the loss of farmland to commercial development would be nominal.

However, the cities attracting the greatest numbers of people have too often replaced the best cropland. Taking the best cropland out of primary production imposes a severe economic penalty.
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6:56 AM
Biological Invasions
Biological Invasions

Biological invasions are the entry of a type of organism into an ecosystem outside its historic range. In a biological invasion, the "invading" organism may be an infectious virus, a bacterium, a plant, an insect, or an animal.

Species introduced to an area from somewhere else are referred to as alien or exotic species or as invaders. Because an exotic species is not native to the new area, it is often unsuccessful in establishing a viable population and disappears.

The fossil record, as well as historical documentation, indicates that this is the fate of many species in new environments as they move from their native habitats. Occasionally, however, an invading species finds the new environment to its liking.


In this case, the invader may become so successful in exploiting its new habitat that it can completely alter the ecological balance of an ecosystem, decreasing biodiversity and altering the local biological hierarchy. Because of this ability to alter ecosystems, exotic invaders are considered major agents in driving native species to extinction.

Biological invasions by notorious species constitute a significant component of earth’s history. In general, large-scale climatic changes and geological crises are at the origin of massive exchanges of flora and fauna. On a geologic time scale, migrations of invading species from one continent to another are true evolutionary processes, just as speciation and extinction are.

On a smaller scale, physical barriers such as oceans, mountains, and deserts can be overcome by many organisms as their populations expand. Organisms can be carried by water in rivers or ocean currents, transported by wind, or carried by other species as they migrate seasonally or to escape environmental pressures.

Humans have transplanted plants since the beginning of plant cultivation in pre-Columbian times. The geological and historical records of the earth suggest that biological invasions contribute substantially to an increase in the rate of extinction within ecosystems.

Invasive Plants

Invasive Plants
Invasive Plants

In modern times, most people are not aware of the distinction between native plants and exotic species growing in their region. Recent increases in intercontinental invasion rates by exotic species, brought about primarily by human activity, create important ecological problems for the recipient lands. Invasive plants in North America include eucalyptus trees, morning glory, and pampas grass.

It would seem logical to assume that invading species might add to the biodiversity of a region, but many invaders have the opposite effect. In all ecosystems the new species are often opportunistic, driving out native species by competing with them for resources.

For example, Pueraria lobata, or kudzu, is a vine native to Japan. Introduced in the United States at the 1876 Philadelphia Exposition, kudzu was planted to control erosion on hillsides and for livestock forage. By the end of the twentieth century, it could be found from Connecticut to Missouri, extending south to Texas and Florida.

Kudzu covers everything in its path and grows as much as 1 foot (0.3 meter) per day. Similarly, English ivy (Hedera helix), a native of Eurasia, is considered a serious problem in West Coast states. It forms "ivy deserts" in forests and crowds out native trees and shrubs that make up essential wildlife habitat.

The invasion of an ecosystem by an exotic species can effectively alter ecosystem processes. An invading species does not simply consume or compete with native species but can actually change the rules of existence within the ecosystem by altering processes such as primary productivity, decomposition, hydrology, geomorphology, nutrient cycling, and natural disturbance regimes.

Invasive Insects and Microorganisms

The invasion of native forests alone by nonnative insects and microorganisms has been devastating on many continents. The white pine blister rust and the balsam woolly adelgid have invaded both commercial and preserved forest lands in North America. Both exotics were brought to North America in the late 1800’s on nursery stock from Europe.

The balsam woolly adelgid attacks fir trees and causes their death within two to seven years from chemical damage and by feeding on the trees’ vascular tissue. The adelgid has killed nearly every adult conebearing fir tree in the southern Appalachian Mountains.

The white pine blister rust attacks five-needle pines; in the western United States fewer than 10 pine trees in 100,000 are resistant. Because white pine seeds are an essential food source for bears and other animals, the loss of the trees is having severe consequences across the food chain.

Since the 1800’s the deciduous trees of eastern North America have been attacked numerous times by waves of invading exotic species and diseases. One of the most notable invaders is the gypsy moth, which consumes a variety of tree species. Other invaders have virtually eliminated the once-dominant American chestnut and the American elm.

Tree species that continue to decline because of new invaders include the American beech, mountain ash, white birch, butternut, sugar maple, flowering dogwood, and eastern hemlock. It is widely accepted that the invasion of exotic species is the single greatest threat to the diversity of deciduous forests in North America.

Effects on Humans and Humans as Invaders

Some introduced exotic species are beneficial to humanity. It would be impossible to support the present world human population entirely on species native to their regions. Humans, the ultimate biological invaders, have been responsible for the extinction of many species and will continue to be in the future.

At the beginning of the twenty-first century, the United States was spending $4 billion annually to eradicate invasive plant species, a figure that does not take into account loss of biodiversity or wildlife habitat.
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7:01 PM
Biomass Related to Energy
Biomass Related to Energy
The relationship between the accumulation of living matter resulting from the primary production of plants or the secondary production of animals (biomass) and the energy potentially available to other organisms in an ecosystem forms the basis of the study of biomass related to energy.

Biomass is the amount of organic matter, such as animal and plant tissue, found at a particular time and place. The rate of accumulation of biomass is termed productivity. Primary production is the rate at which plants produce new organic matter through photosynthesis.

Secondary production is the rate at which animals produce their organic matter by feeding on other organisms. Biomass is an instantaneous measure of the amount of organic matter, while primary and secondary production give measures of the rates at which biomass increases.

Plant and animal biomass consists mostly of carbon-rich molecules, such as sugars, starches, proteins, and lipids, and other substances, such as minerals, bone, and shell. The carbon-rich organic molecules are not only the building blocks of life but also the energy-rich molecules used by organisms to fuel their activities.


Solar Energy and Photosynthesis

Ultimately, all energy used by organisms to produce the building blocks of life and to drive life processes originated as solar energy captured by plants. Only a small fraction, less than 2 percent, of the total solar light energy received by a plant is absorbed and transformed by photosynthesis into energy-containing organic molecules.

The rest of the sun’s energy passes out of the plant as heat. The rate at which plants capture light energy and transform it into chemical energy is called primary production.

Because plants do not rely on other organisms to provide their energy needs, they are referred to as primary producers, or autotrophs (meaning “self-feeding”). In addition to light energy, plants must absorb water, carbon dioxide gas, and simple nutrients, such as nitrate and phosphate, to produce various organic molecules during photosynthesis. Oxygen gas is also produced.

Sugars are the first energy-containing organic molecules produced in photosynthesis, and they can be changed to other, more complex, molecules, such as starches, proteins, and fats.

The energy in the sugar molecules can be used immediately by the plants to maintain their own respiration needs, stored as starches and fats, or can be converted to new plant tissue. It is the stored organic matter plus new tissue that contributes to the growth of plants and to biomass.

Because the energy-containing products of photosynthesis can be used either immediately in respiration or in the formation of new plant biomass, two types of primary production can be distinguished. Gross production refers to the total amount of energy produced by photosynthesis.

It includes both the energy used by the plant for respiration and the energy that goes into new biomass. Net production refers only to the amount of energy that accumulates as new biomass. It is only the energy in net production that is potentially available to animal consumers as food.

The rate of primary production varies directly with the rate of photosynthesis; therefore, factors in the environment that affect the rate of photosynthesis affect the rate of primary production. These factors most often include light intensity, temperature, nutrient concentrations, and moisture conditions.

Each species of plant has a specific combination of these factors that promotes maximum rates of primary production. If one or more of these factors is in excess or is in short supply, then the rate of primary production is slowed.

Primary Production

Primary Production
Primary Production
On land, the rate of primary production by plants is determined largely by light, temperature, and rainfall. The favorable combination of intense sunlight for twelve hours per day, warm temperatures throughout the year, and considerable rainfall make the tropical rain forests the most productive ecosystems on land.

In contrast, Arctic tundra vegetation is exposed to reduced light intensity, very cold winters, and cool summers. Primary production there is very low. In deserts, the lack of water severely limits primary production even though light and temperature are otherwise favorable.

In aquatic habitats, rates of primary production by algae, such as phytoplankton, are determined by nutrient concentration and light intensity. As sunlight penetrates water, it is quickly absorbed by the water molecules and by small suspended particles.

Thus, all primary production occurs near the surface, as long as nutrients are available. Although thewaters of the open ocean are very clear, and sunlight can penetrate to great depths, the scarcity of nutrients reduces the rate of primary production to less than one-tenth that of coastal bays.

Secondary Production

The energy and material needs of some organisms are met by consuming the organic materials produced by others. These consumer organisms are called heterotrophs; there are two types. Those that obtain their food from other living organisms are called consumers and include all animals. Those that obtain their energy from dead organisms are called decomposers and include mostly the fungi and bacteria.

The energy available to each type of consumer becomes progressively less at each level of the food chain. Each consumer level uses most of its food energy, about 90 percent, to fuel its respiratory activities. In this energy-releasing process, most of the food energy is actually converted to heat and is lost to the environment.

Only 10 percent or less of the original food energy is used to form new biomass. It is only this small amount of energy that is available for the next consumer level. The result is that food chains are limited in their number of links or levels by the reduced amount of energy available at each higher level.

Generally, the greater the amount of primary production, the larger the number of consumer organisms and the longer the food chain. Most food chains consist of three levels; rarely are there examples of up to five levels. It should be noted that the food chain concept is a simplified view of a more complex network of energy pathways, known as food webs, that occur in nature.

Another outcome of the reduction in energy flow up the food chain is a progressive decrease in production and biomass. The most productive level, and the one with the greatest biomass, is therefore the primary producers, or plants.

Human Threats to Primary Production

Human Threats to Primary Production
Human Threats to Primary Production
The total natural primary production of the earth is limited, and human efforts to increase total world primary production much beyond its present levels may be futile. One reason for this is that much of the earth’s surface lacks optimal conditions for plant growth. The open ocean, which covers about 71 percent of the earth’s surface, has very little plant growth.

On land, the Arctic, subarctic, and Antarctic regions are very unproductive most of the year. Human attempts to increase primary production in the form of food or fuel crops usually involve changing the characteristics of the land, converting forests into croplands, for example, and adding large quantities of nutrients and water.

It has been estimated that humans are currently utilizing most of the easily workable croplands and that the development of additional lands for agriculture would require major changes to currently unworkable habitats, changes that would be expensive and demand much fuel energy.

The study of production processes is vitally important in understanding the ecology of natural ecosystems. Such information is necessary to manage and conserve habitats and their organisms in the face of human pressures.

These processes provide insight into the general health of ecosystems. Pollutants, such as acid rain or industrial toxic wastes, are known to reduce the primary and secondary productivity of forests and lakes.

Throughout the world, humans are reducing the biomass of the world’s primary producers through deforestation. This is particularly true in the tropics, where high population pressures have necessitated that land be cleared for agriculture and development. There is a world wide demand for lumber. One obvious consequence is the dramatic reduction in the primary and secondary production of these areas.

The clear-cutting (removal of all the trees) of tropical forests allows unprotected soils to wash away quickly during the heavy tropical rains. It will take hundreds of years for new soils to develop and for the forest to return—if it can return at all.

Deforestation is also harmful in that tropical forests form a major part of the world’s life-support system. For millions of years these forests have buffered the earth’s atmosphere by producing the oxygen gas needed by animals and by removing carbon dioxide and other toxic gases.

The low level of carbon dioxide in the atmosphere is believed to have moderated the earth’s temperature, counteracting the so-called greenhouse effect. It is therefore of great importance to understand and preserve these forests and other primary producers of the world.
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9:46 PM
Biopesticides
Biopesticides
Biopesticides are biological agents, such as viruses, bacteria, fungi, mites, and other organisms used to control insect and weed pests in an environmentally and ecologically friendly manner.

Biopesticides allow biologically based, rather than chemically based, control of pests. A pest is any unwanted animal, plant, or microorganism. When the environment provides no natural resistance to a pest and when no natural antagonists are present, pests can run rampant.

For example, spread of the fungus Endothia parasitica, which entered New York in 1904, caused the nearly complete destruction of the American chestnut tree because no natural control was present. Viruses, bacteria, fungi, protozoa, mites, insects, and flowers have all been used as biopesticides.

Advantages of Biopesticides

Many plants and animals are protected from pests by passive means. For example, plant rotation is a traditional method of insect and disease protection that is achieved by removing the host plant long enough to reduce a region’s pathogen and pest populations.


Biopesticides have several significant advantages over commercial pesticides. They appear to be ecologically safer than commercial pesticides because they do not accumulate in the food chain.

Some biopesticides provide persistent control, as more than a single mutation is required to adapt to them and because they can become an integral part of a pest’s life cycle. In addition, biopesticides have slight effects on ecological balances because they do not affect nontarget species. Finally, biopesticides are compatible with other control agents.

The major drawbacks to using biopesticides are the time required for them to kill their targets and the inefficiency with which they work; also, if the organism being used as a biopesticide is a nonnative species, it may cause unforeseen damage to the local ecosystem.

Viruses and Bacteria

Viruses and Bacteria
Viruses and Bacteria
Viruses have been developed against insect pests such as Lepidoptera (butterflies and moths), Hymenoptera (bees, wasps, and ants), and Dipterans (flies).Gypsymoths and tent caterpillars, for example, periodically suffer fromepidemic virus infestations, which could be exploited and encouraged.

Many commensal microorganisms (microorganisms that live on or in other organisms causing no direct benefit or harm) that occur on plant roots and leaves can passively protect plants against microbial pests by competitive exclusion (that is, simply crowding them out). Bacillus cereus has been used as an inoculumon soybean seeds to prevent infection by fungal pathogens in the genus Cercospora.

Some microorganisms used as biopesticides produce antibiotics, but the major mechanism in most cases seems to be competitive exclusion. For example, Agrobacterium radiobacter antagonizes Agrobacterium tumefaciens, which causes the disease crown gall.

Species of two bacterial genera—Bacillus and Streptomyces—when added as biopesticides to soil help control the damping-off disease of cucumbers, peas, and lettuce caused by Rhizoctonia solani. Bacillus subtilis added to plant tissue also controls stem rot and wilt rot caused by species of the fungus Fusarium.

Mycobacteria species produce cellulose degrading enzymes, and their addition to young seedlings helps control fungal infection by species of Pythium,Rhizoctonia, and Fusarium. Species of Bacillus and Pseudomonas produce enzymes that dissolve fungal cell walls.

Bacillus thuringiensis Toxins

The best examples of microbial insecticides are Bacillus thuringiensis (B.t.) toxins, which were first used in 1901. They have had widespread commercial production and use since the 1960’s and have been successfully tested on 140 insects, including mosquitoes.

Insecticidal endotoxins are produced by B.t. during sporulation, and exotoxins are contained in crystalline parasporal protein bodies. These protein crystals are insoluble in water but readily dissolve in an insect’s gut.

Once dissolved, the proteolytic enzymes paralyze the gut. Spores that have been consumed germinate and kill the insect. Bacillus popilliae is a related bacterium that produces an insecticidal spore that has been used to control Japanese beetles, a corn pest.

The gene for the B.t. toxin has also been inserted into the genomes of cotton and corn, producing genetically modified, or GM, plants that produce their own B.t. toxin. GM cotton and B.t. corn both express the gene in their roots, which provides them with protection from root worms.

Ecologists and environmentalists have expressed concern that constantly exposing pests to B.t. will cause insects to develop resistance to the toxin. In such a scenario, the effectiveness of traditionally applied B.t.would decrease.

Fungi and Protozoa

Saprophytic fungi can compete with pathogenic fungi. There are several examples of fungi used as biopesticides, such as Gliocladium virens, Trichoderma hamatum, Trichoderma harzianum, Trichoderma viride, and Talaromyces flavus. For example, Trichoderma species compete with pathogenic species of Verticillium and Fusarium.

Peniophora gigantea antagonizes the pine pathogen Heterobasidion annosum by three mechanisms: It prevents the pathogen from colonizing stumps and traveling down into the root zone, it prevents the pathogen from traveling between infected and uninfected trees along interconnected roots, and it prevents the pathogen from growing up to stump surfaces and sporulating.

Nematodes are pests that interfere with commercial button mushroom (Agaricus bisporus) production. Several types of nematode-trapping fungi can be used as biopesticides to trap, kill, and digest the nematode pests.

The fungi produce constricting and nonconstricting rings, sticky appendages, and spores, which attach to the nematodes. The most common nematode-trapping fungi are Arthrobotrys oligospora, Arthrobotrys conoides, Dactylaria candida, and Meria coniospora.

Protozoa have occasionally been used as biopesticide agents, but their use has suffered because of slow growth and the complex culture conditions associated with their commercial production.

Mites, Insects, and Flowers

Well-known “terminator” bugs include praying mantis and ladybugs as well as decollate snails, which eat the common brown garden snail. Fleas, grubs, beetles, and grasshoppers often have natural nematode species that prey on them, which can be used as biocontrol agents.

Predaceous mites are used as a biopesticide to protect cotton from other insect pests such as the bollwe evil. Parasitic wasps of the genus Encarsia, especially E. formosa, preyon whiteflies, as does Delphastus pusillus, a small, black ladybird beetle.

Dalmatian and Persian insect powders contain pyrethrins, which are a toxic insecticidal compounds produced in Chrysanthemum flowers. Synthetic versions of these naturally occurring compounds are found in products used to control head lice.
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6:48 PM
Biosphere Concept
Biosphere Concept

The term "biosphere" was coined in the nineteenth century by Austrian geologist Eduard Suess in reference to the 20-kilometer-thick zone extending from the floor of the oceans to the top of mountains, within which all life on earth exists.

Thought to be more than 3.5 billion years old, the biosphere supports nearly one dozen biomes, regions of climatic conditions within which distinct biotic communities reside.

Compounds of hydrogen, oxygen, carbon, nitrogen, potassium, and sulfur are cycled among the four major spheres, one of which is the biosphere, to make the materials that are essential to the existence of life.


The other spheres are the lithosphere, the outer part of the earth; the atmosphere, the whole mass of air surrounding the earth; and the hydrosphere, the aqueous vapor of the atmosphere, sometimes defined as including the earth’s bodies of water.

The Water Cycle

The most critical of these compounds is water, and its movement among the spheres is called the hydrologic cycle. Dissolved water in the atmosphere condenses to form clouds, rain, and snow. The annual precipitation for any region is one of the major factors in determining the terrestrial biome that can exist.

The precipitation takes various paths leading to the formation of lakes and rivers. These flowing waters interact with the lithosphere (the outer part of the earth’s crust) to dissolve chemicals as they flow to the oceans. Evaporation of water from the oceans then supplies most of the moisture in the atmosphere. This cycle continually moves water among the various terrestrial and oceanic biomes.

The Water Cycle
The Water Cycle

Solar Energy

The biosphere is also dependent upon the energy that is transferred from the various spheres. Solar energy is the basis for almost all life. Light enters the biosphere as the essential energy source for photosynthesis.

Plants take in carbon dioxide, water, and light energy, which is converted via photosynthesis into chemical energy in the form of sugars and other organic molecules.

Oxygen is generated as a by-product.Most animal life reverses this process during respiration, as chemical energy is released to do work by the oxidation of organic molecules to produce carbon dioxide and water.

Incoming solar energy also interacts dramatically with the water cycle and the world wide distribution of biomes. Because of the earth’s curvature, the equatorial regions receive a greater amount of solar heat than the polar regions.

Convective movements in the atmosphere—such as winds, high- and low-pressure systems, and weather fronts—and the hydrosphere—such as water currents—are generated during the redistribution of this heat. The weather patterns and climates of earth are a response to these energy shifts. Earth’s various climates are defined by the mean annual temperature and the mean annual precipitation.
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7:44 AM
Biotechnology
Biotechnology
Biotechnology is the use of living organisms, or substances obtained from those organisms, to produce processes or products of value to humanity, such as foods, high-yield crops, and medicines.

Modern biotechnological advances have provided the ability to tap into a natural resource, theworld gene pool,with such great potential that its full magnitude is only beginning to be appreciated.

Theoretically, it should be possible to transfer one or more genes from any organism in the world into any other organism. Because genes ultimately control how any organism functions, gene transfer can have a dramatic impact on agricultural resources and human health in the future.

History of Biotechnology

Although the term “biotechnology” is relatively new, the practice of biotechnology is at least as old as civilization. Civilization did not evolve until humankind learned to produce food crops and domestic livestock through the controlled breeding of selected plants and animals. Eventually humans began to utilize microorganisms in the production of foods such as cheese and alcoholic beverages.


During the twentieth century, the pace of modification of various organisms accelerated. Through carefully controlled breeding programs, plant architecture and fruit characteristics of crops have been modified to facilitate mechanical harvesting. Plants have been developed to produce specific drugs or spices, andmicroorganisms have been selected to produce antibiotics and other medicinal or food products.

Developments in Biotechnology

Since the mid-twentieth century, the ability to utilize artificial media to propagate plants has led to the development of a technology called tissue culture. The earliest formof tissue culture involved using the culture of meristem tissue to produce numerous tiny shoots that can be grown into full-size plants, referred to as clones because each plant is genetically identical.

Developments in Biotechnology
Developments in Biotechnology
More than one thousand plant species have been propagated by tissue culture techniques. Plants have been propagated via the culture of other tissues, including the stems and roots. In some of these techniques, the plant tissue is treated with hormones to produce callus tissue, masses of undifferentiated cells.

The callus tissue can be separated into single cells to establish a cell suspension culture. Callus tissue and cell suspensions can be used to produce specific drugs and other chemicals. Entire plants can also be generated from the callus tissue or from single cells by addition of specific combinations of hormones.

Afar more complex method of cloning of plants and animals from the deoxyribonucleic acid (DNA) of a single cell is amore recent development. Proponents of this method of producing copies of organisms have suggested that cloning technology might be used to improve agricultural stock and to regenerate endangered species.

These ideas have had their detractors, however, as critics have noted the potential dangers of narrowing a species’ gene pool. The July, 1996, birth in Scotland of Dolly, a sheep cloned and raised to adulthood, demonstrated that the cloning of animals had left the realm of science fiction and become a matter of scientific fact.

Recombinant DNA Technology

In practice, recombinant DNA methodology is complex, but in concept, it is fairly easy to comprehend. The genes in all living cells are composed of the same chemical, DNA. The DNA of all cells, whether from bacteria, plants, or animals including humans, is very similar. When DNA from a foreign species is transferred into a different cell, it functions exactly as the native DNA functions; that is, it "codes" for protein.

The easiestway to manipulate genes is using bacterial cells (most often Escherichia coli) and a vector, an agent that can be used to pass the gene fromone cell to another. Plasmids, small extra circular DNA molecules found in many bacterial cells, are commonly used for this purpose. Plasmids are replicated along with the bacterial cell’s own DNA every time the cell reproduces. Plasmids can be easily isolated from bacterial cells.

Recombinant DNA Technology
Recombinant DNA Technology
When a specific gene has been isolated, it can be fused, using restriction endonucleases, with a plasmid to produce a recombinant plasmid. These recombinant plasmids can then be put into bacterial cells by a process called transformation. Special plasmids called expression vectors allow expression of inserted genes once they are inside a bacterial cell.

Although expressing foreign genes in bacterial cells is relatively simple, inserting theminto plants and getting them expressed is more complicated. The Ti plasmid is a widely used vector that works well in dicots but has never worked for monocots. Consequently, the first successful transgenic plants were dicots, while success with the most important food crops, monocots such as rice and corn, took more time and effort.

Many alternative methods for inserting genes into plant cells have been developed that work on both monocots and dicots. Microinjection can be used to insert a gene into individual cells. A less laborious method is called biolistic, for biological ballistic, where millions of copies of the gene are attached to tiny projectiles that are then fired into groups of plant cells. Using these and other methods, genetic modification of plants is becoming more routine.

Future of Biotechnology in Agriculture

This new technology could have a tremendous impact on agriculture. As the human population grows, biotechnology will most likely play an important role in producing an increase in food production. Such an increase will require developments such as crop plants that will produce higher yields under normal conditions and crops that will produce higher yieldswhen grown inmarginal environments.

Biotechnology provides a means of developing higher-yielding crops in much less time than it takes to develop them though traditional plant-breeding programs. Genes for the desired characteristics can be inserted directly into the plant without having to go through repeated controlled selection and breeding cycles to establish the trait.

There are also economic advantages in diversifying agriculture production in a given area. A producer might wish to grow a particular high-value cash crop in an area where soil or climate conditions would prevent such a crop from thriving. Biotechnology can help solve these types of problems. For example, high value crops can be developed to grow in areas that heretofore would not have supported such crops.

Plants also can be developed to produce new products such as antibiotics, drugs, hormones, and other pharmaceuticals. Crop plants bioengineered to produce novel products mean that pharmaceuticals and other valuable products could be grown in farm environments rather than in laboratories.

While there will be a growing pressure for agriculture to produce more food in the future, there will also be pressure for crop production to be more friendly to the environment. Biotechnology has the potential to play a major role in the development of a long-term, sustainable, environmentally friendly agricultural system. For example, the development of crop varieties with improved resistance to pests will reduce the reliance on pesticides.

Methods of crop production and harvestwith less environmental impact will also have to be developed. Because agriculture will continue to have an impact on the environment, the need to remediate polluting agents will continue to exist. Hence biotechnology will play an important role in the development of bioremediation systems for agriculture as well as other industrial pollutants.

Ownership Issues

There will be many difficult ethical and economic issues surrounding the use of this new biotechnology. One of the major questions concerns ownership. Patent laws in the United States read that ownership over an organism can be granted if the organism has been intentionally genetically modified through the use of recombinant DNA techniques.

In addition, processes that utilize genetically modified organisms can be patented. Therefore one biotechnology firm may own the patent to an engineered organism, but another firm may own the rights to the process used to produce it.
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