"We have come to look at our planet as a resource for our species, which is funny when you think that the planet has been around for about five billion years, and Homo sapiens for perhaps one hundred thousand. We have acquired an arrogance about ourselves that I find frightening. We have come to feel that we are so far apart from the rest of nature that we have but to command."
Ecologists and environmental scientists study different aspects of organisms on Earth. Ecology is the study of interrelations of living organisms and how they affect one another within a system of living things. Environmental science is a broader study of living systems, or environments. Environmental scientists use concepts of geology, chemistry, meteorology, agriculture, and many other fields, along with biology. In addition to studying the relationships between living things and their environments, environmental science addresses the human influence on living systems.
Why do forest managers use controlled burns?
Smokey the Bear began warning us about forest fires in the 1940s, and has been doing it ever since. His message has changed a bit over the years, however. At the time Smokey first appeared, the goal of forest management was to prevent all fires and to put out any fire that did start. Today, the National Park Service and other forest agencies start hundreds of fires every year. Why would the message about forest fires change over time?
An ecosystem is a community of organisms—plants, animals, microorganisms, fungi—that interact with one another, along with the physical factors that make up their environment. Physical factors include soil, water, light, and temperature that are interrelated with the organisms.
Ecologists have learned that fire is an important part of many ecosystems. Since the first forests developed on land, fires have been started by lightning, volcanoes, and even by the decay of dead plant material. We now know that many species depend on fire in order to thrive, or even to survive and reproduce. In addition, many uncontrolled fires have been made worse, in terms of damage to human and natural resources, by earlier policies of preventing all fires.
The benefits of fire to an ecosystem include improvement to wildlife habitat, control of tree disease, removal of invasive species, and removal of fuels that can cause a fire to burn out of control if they are allowed to accumulate. In fact, the seeds of some species of conifers, including the sequoia, will not germinate unless they have been activated by the heat of a fire.
Even so, fires are not always desirable. Many forests and grasslands have changed substantially since they were allowed to burn freely. Human habitations and other structures are now an integral part of many areas where natural fires once burned. Controlled or prescribed burns are now used extensively to manage forests. In a controlled burn, excess fuel is often removed to prevent a fire from burning too hot. The fire is started when wind direction and speed make it easiest to control and crews stand by to prevent the fire from burning beyond the planned boundaries. Fire has become an important tool in maintaining forest health.
In the summer of 1998, the driest in the history of Yellowstone Park, fires burning out of control affected more than one-third of the park. Most of the fires were caused by lightning. Although human life and property were protected by a massive fire-fighting effort, there was no way to prevent the spread through the forest.
The Park Service was widely criticized for allowing natural fires to burn to the point that control was lost. Many news reports detailed the "destruction" of the park. Ecologists, however, saw a unique opportunity to study the effects of a large fire on a forest. Their research found that the fire did not destroy the forest and that it was, in fact, healthier within a few years than it had been before the fire.
Among their observations:
♦ Lodge pole pines are growing, reclaiming many areas where they had disappeared.
♦ Aspens have begun reproducing at faster rates than before as the forest floor was cleared.
♦ Grasslands recovered in several years with healthier plants due to increased nutrients in the soil.
♦ The amount of habitat available to some animals, such as bluebirds, has increased.
Many plants that have adapted to succeed in environments that include periodic fires cannot continue to exist without fire. Many wild grasses have very deep roots that easily survive a fire that destroys plants that compete with them. When there are no fires, the grasses of natural prairie ecosystems are replaced by bushes and trees and the prairie no longer exists.
Smokey’s message is not obsolete, however. Although controlled burns are used extensively, uncontrolled fires destroy many homes every year. They can also increase erosion when protective ground cover is removed prior to heavy rains. The message is still: "Only you can prevent wildfires!"
Do flies serve any useful purpose?
On the whole, houseflies seem to be designed to be annoying. They buzz around the room, making noise at a grating frequency, and land on your body and on your food. It is possible that they can transmit a number of diseases and maggots, their larvae, are disgusting. Do flies serve any useful purpose?
Ecosystems are made of many organisms that depend on one another. It makes more sense to talk of the role of an organism in an ecosystem rather than the purpose of the organism. Although flies seem, on first glance, to have no value, they play important roles in nature.
A female housefly deposits about 100 to 150 eggs on something that can provide food for the larvae that will hatch from the eggs. This food is decaying material, such as garbage, animal droppings, or grass clippings. Between 8 hours and 2 days later, the maggots hatch and begin to feed. Eventually they form pupae and change into adult flies, restarting the cycle. Fly larvae are efficient disposers of garbage and other dead matter. Along with bacteria and other decomposers, they convert the material into other forms. Imagine how dead plant and animal materials and animal and human wastes would accumulate if there were no way to destroy them.
Throughout their life cycle, flies also play another role in their ecosystem—food for other organisms. Foraging insects, lizards, and small mammals feed on fly eggs, larvae, and pupae. Fish and other aquatic organisms feed on flies throughout their life cycle, as do many birds and other land animals. Although flies may be an annoying part of the world around us, they would be missed if they did not exist.
What is biodiversity and why is it important?
One of the goals of conservationists is to maintain the biodiversity of an ecosystem in order to protect the health of the system. What is biodiversity and why is it important?
Biodiversity refers to the variation in life forms within an ecosystem, or on Earth as a whole. There are three parts to biodiversity in a system:
♦ Genetic diversity is the variability in the genetic makeup of individuals in a particular species.
♦ Species diversity is the variety of species within an ecosystem.
♦ Ecological diversity is the variety of biological communities (e.g., forest, desert, grassland, tidal marsh, lake) that interact with one another.
You may often see the term ecosystem used to refer only to the "natural" world, excluding humans. Humans are actually part of the ecosystems in which they live. For example, your home is an ecosystem that includes people, houseplants, bacteria, dust mites, houseflies, a spider or two, and maybe a mouse. Each part of the ecosystem interacts with other parts.
Biodiversity at all levels is important for the general health of a system and the different species within it, including humans. Every species of living thing depends on other species for its existence. Herbivores need a variety of plants to provide all their needs; carnivores need a variety of prey species; plants depend on animals for pollination, seed distribution, and nutrients—the list of interactions is too extensive to list.
From a human viewpoint, biodiversity is important to provide for human needs. All of our food comes from plants or animals in our environment. At least 40,000 species are used by humans for food, shelter, clothing, and building materials. Diversity provides different materials for specific needs. Most of the medicines that we use come either directly or indirectly from a chemical compound that occurs in nature. We have only explored a small fraction of the available compounds that could be medically useful. In addition to material uses, the biodiversity of the planet provides us with leisure and cultural activities.
In a population of a single species, genetic diversity is a protection against disease. Individuals are able to react differently to different genetic diseases or infections. The diversity of species within an ecosystem protects the system in the same way. Some species are susceptible to specific stresses and attacks, while others are resistant. By having a wide range of species, an ecosystem can adapt and resist threats.
The value of biodiversity is most evident when a catastrophe strikes a monoculture (nondiverse environment). The Irish Potato Famine of the nineteenth century occurred because the population relied overwhelmingly on one crop for sustenance. When disease destroyed that crop, people were unable to adapt by turning to another source of nourishment.
Tropical rainforests are among the most diverse ecosystems. Tall trees reach high above the ground for access to light. Other species below them have adapted to lower light levels. Many of these plants and animals use the tall trees for shelter and food. At the ground level, still other plants live in low light conditions, obtaining nourishment from material dropped by plants and animals above them. On and under the ground, fungi, bacteria, and other decomposers break down leaves and other materials, making their nutrients available to the next generation of plants.
"Man will survive as a species for one reason: He can adapt to the destructive effects of our power-intoxicated technology and of our ungoverned population growth, to the dirt, pollution and noise of a New York or Tokyo. And that is the tragedy. It is not man the ecological crisis threatens to destroy but the quality of human life."
Why were phosphates removed from most detergents?
Soaps and detergents do not always break down in the environment and their residues cause problems in sewage treatment plants and waterways. In the 1950s many streams and rivers had an almost constant covering of foam that was toxic to many of the small organisms necessary for the health of the aquatic ecosystem. Materials were added to detergents to make them biodegradable. Other materials were added to make detergents work better in hard water. Several phosphorus-containing materials served both of these purposes. If they were useful in the 1950s, why have phosphates now been removed from detergents?
Biodegradable means that a material can be broken down by biological organisms called decomposers. Most decomposers are bacteria or fungi.
While phosphorus-containing compounds in the detergents helps with their performance and biodegradability, phosphates in the water can also create problems. The breakdown of detergents by bacteria, which was one of the desired results, created an oversupply of an essential nutrient, available phosphates. These compounds act as a natural fertilizer in waterways, with results that can cause deterioration of the natural ecosystems.
Algae are an important part of aqueous ecosystems, decomposing organic matter and providing food to other organisms. Algae population is usually regulated by the amount of phosphates available in the water, which is generally introduced by the slow breakdown of soil and rocks. When phosphates were introduced by the disposal of detergents, however, the control on algae population was removed.
Unfortunately, the result in many waterways was an algae bloom, a rapid increase in the population of algae. As their population exploded, the algae used more and more oxygen. Other organisms that need oxygen die during a bloom, providing still more food for algae growth. Eventually, the oxygen in the water is completely depleted. No insects or fish can survive and the result is a dead area in the waterway. Algae blooms can occur in streams, lakes, and even in large areas of the ocean.
Most detergents today do not include phosphates, but it is important to keep in mind the lesson that ecosystems are extremely complex and sensitive systems of interdependent parts. Sometimes the solution to one problem creates a new, unexpected problem.
Fast Facts
Many "dead zones" have formed in the waters off the coasts of most continents. These are areas at the bottom of the ocean where there is no oxygen. An excessive population of plankton near the surface drops large amounts of organic material to lower levels as the plankton die. Bacteria decomposing this material use all of the available oxygen, making the area uninhabitable by marine animals. Most of the dead zones form near the mouths of rivers that carry large amounts of agricultural runoff that is high in fertilizers that nourish the plankton. A dead zone of more than 8,000 square miles has formed in the Gulf of Mexico below the mouth of the Mississippi River.
Why are wetlands important?
Many environmental laws have been written in the past half century that are designed to protect wetlands. Federal and state laws define flood plains and the development that is permitted in them. Local regulations use zoning to control building near streams and marshes. What are wetlands, and why do they need protection?
According to the Clean Water Act, wetlands are areas that are inundated or saturated by surface water or groundwater at a frequency and duration sufficient to support vegetation typically adapted for life in saturated soil conditions. This definition does not require that wetlands have water on the surface all the time and, in fact, wetlands are often identified by their native plants rather than by standing water. Usually, wetlands are places where water, sediments, and dissolved minerals collect as they flow from higher elevations. Because of this collection of resources in one place, they serve as home to an amazing variety of living things.
Although the ecosystems of wetlands vary from one place to another depending on conditions such as temperature and rainfall, they generally provide homes to a wide variety of plants, insects, microbes, and amphibians which thrive in the moist environment. Birds, reptiles, and mammals are abundant because of the availability of food. Decaying plant material feeds many aquatic insects and other invertebrates, shellfish, and small fish living in surface waters.
Wetlands are often portrayed as places overrun with mosquitoes, one reason that neighbors oppose rebuilding wetlands. Mosquitoes breed in still, warm water, and wetlands such as swamps and marshes can provide habitat for them. However, in many wetlands, water passes through in a constant flow. This does not provide breeding places for mosquitoes. In general, even wetlands with mosquito habitat tend to also provide good habitat for their predators, such as dragonflies.
Wetlands also provide valuable services to human populations. Many communities rely on groundwater for drinking supplies. The plants and soils of the wetland filter out contaminants from water as it enters the ground. They are primary sources of clean underground water. In addition, they act as natural sponges that trap rainwater and even floodwater from overflowing rivers and streams. Mats of vegetation and tree roots slow the water, releasing it gradually. Salt marshes provide the first barrier against massive sea storms. Areas in which the marshes are intact tend to suffer much less damage during hurricanes than areas where the swamps have been drained and developed.
While swamps and marshes were once thought to be wastelands, filled with dangerous animals and disease-bearing insects, environmental studies have shown that they are key elements to healthy ecosystems. Besides improving water quality and providing flood and erosion control—all very pragmatic uses from the human viewpoint— wetlands are keys sources of food and shelter for animals ranging from the smallest insects to large predators.
What is the ozone hole and how was it formed?
During the 1980s, there was a lot of concern about a hole in the ozone layer of the upper atmosphere. Chemicals in air-conditioners, aerosol cans, and certain types of fire extinguishers were replaced with other materials in order to protect the ozone layer. A truly worldwide environmental initiative was successful, leading to a slow but steady improvement. But how did the hole exist in the atmosphere in the first place?
The first step to answering the question is to describe the "ozone layer" and its usefulness to living things on Earth, including humans. Ozone is colorless gas that reacts very easily with most other substances. The sharp, acrid smell that is sometimes detectable around high voltage electrical equipment is ozone. Near the surface, it is considered to be a pollutant because it is toxic to plants and animals.
The stratosphere is the second layer of the atmosphere from the surface, extending from about 6 miles to 30 miles above the surface. Because of absorption of ultraviolet radiation near the top of the stratosphere, the temperature at the top is higher than the temperature at the bottom. Large airplanes often fly in the lower part of the stratosphere because it tends to be very stable and calm.
However, in the stratosphere, ozone is a naturally occurring substance and an important atmospheric component. The so-called "ozone layer" is not really a layer at all. Ozone normally occurs as part of the atmosphere at altitudes between 7 and 25 miles above sea level. The concentration of ozone in this region averages about 1 molecule of ozone per 10,000 molecules of nitrogen and oxygen, so it is very dilute even in the ozone layer.
Ozone in the stratosphere absorbs ultraviolet light that damages living organisms, so a change in the ozone layer is a major concern to humans. Observations of the amount of ozone in the atmosphere have shown that, beginning in the 1970s, the amount of ozone in the atmosphere above Antarctica dropped substantially in the spring (September to December in the Southern Hemisphere). At its worst, the level of ozone in this "hole" dropped to about one-third of the normal level. Scientists found that the drop was caused by chlorine atoms from gases called chlorofluorocarbons (CFCs). These gases were used as propellants in aerosol sprays and refrigerants in air conditioners.
When CFCs escape into the atmosphere, they rise to the stratosphere, where they are stable for many years.
The combination of cold temperatures in the stratosphere and spring sunlight causes a chemical reaction that destroys ozone faster than it can be replaced by natural processes. A smaller ozone depletion occurs in the Arctic during the northern spring.
Although the overall decrease in the global amount of ozone was fairly small (about 4 percent), its discovery was a cause for concern. The amount of ozone destroyed was increasing from year to year, and there was a concern that holes could begin appearing elsewhere. In addition, only a small fraction of the CFC molecules in the atmosphere were destroyed, so their concentrations continued to grow.
Harmful effects of an increase in UV light could include an increase in skin cancers and cataracts in humans, reduced yields of some grain crops, and a disruption of photoplankton populations in the oceans. These concerns led to a worldwide ban on the use of CFC in 1989. Since the late 1990s, scientists have observed that destruction of ozone has decreased slightly each year.
Two separate problems related to the atmosphere are often confused with one another. Global warming is not at all related to the depletion of ozone in the stratosphere. Ozone depletion is caused by the release of certain compounds that contain chlorine. It creates problems by allowing ultraviolet radiation to reach the Earth’s surface but does not affect weather or climate. Global warming is caused by excess greenhouse gases, such as carbon dioxide. It is unrelated to ultraviolet radiation but traps heat so it cannot be radiated into space.
How do we know about ancient climates?
About 15,000 years ago, the climate in North America was cold and icy. In fact, much of the continent was covered by huge glaciers. From 1575 to 1585, southern Arizona suffered a severe drought, worse than any droughts in recent times. This is the type of information that environmental scientists use to analyze and predict changes in environmental conditions and climates and make predictions. How do scientists find details about weather and climate from prehistoric times?
The study of climate change over the history of Earth is called paleoclimatology. It uses a variety of methods to find out what climates have existed in the past and to chart changes in climate over time.
Tree rings provide one of the most accurate ways to find out about rainfall in the past 2,000 years or so. In a rainy year, a tree grows much faster than in a dry year, so the growth ring in its trunk is wider. Because you can get an accurate date by counting the rings, this is one of the most reliable tools for studying past climates.
Glaciers and ice sheets hold a wide range of climate information, extending as far as 800,000 years into the past. An ice core is removed by drilling straight down into the sheet. Layering in the ice is used to relate the depth of the ice to its age and the thickness of a layer gives information about annual precipitation. Scientists use pollen trapped in the ice to estimate relative plant growth for different years and ash residues to track volcanic eruptions. Small differences in the ratios of hydrogen and oxygen isotopes in the ice track changes in ocean temperature.
Although information from tree rings is generally limited to the past few thousand years, there are some cases in which they can provide much older information. Many petrified trees retain the ring information. Although it is not possible to correlate these rings to particular years, the fossils do provide information about cycles of precipitation in ancient times.
For data beyond what is locked up in the ice, paleoclimatologists turn to sediments and sedimentary rocks. Layer after layer of sediments in oceans, lakes, and desert floors reveal preserved animal and plant material, such as bones and pollen. Sedimentary rock layers do not give us information about year-to-year changes because the information has been compressed into layers that span long periods. They do, however, record climate in long sweeps and show periods of major change.
How does the greenhouse effect work?
Many factors affect the temperature at any particular place on Earth, but the average temperature depends on a balance of energy that reaches the planet and energy that radiates into space. If the planet receives more energy as sunlight than it radiates, the average temperature increases. One of the controlling factors in radiation of energy into space is a phenomenon called the greenhouse effect. What is the greenhouse effect and how does it work?
Energy from the sun arrives at Earth in the form of electromagnetic radiation, including visible light and ultraviolet radiation. About 30 percent of this energy is reflected back into space, mostly by clouds. Some energy is absorbed by the atmosphere, but most of the electromagnetic radiation reaches the surface, where it is absorbed by soil and water, which then become warmer.
Warm objects radiate electromagnetic energy as infrared radiation. The amount of energy radiated increases as a surface becomes warmer. When the Earth’s surface radiates energy, some of it is absorbed by the atmosphere and some is radiated into space, effectively cooling the planet. If the amount of solar radiation coming in is balanced by the amount of infrared radiation going out, the average temperature of the planet does not change. Currently, Earth’s average surface temperature is about 59°F and it is pretty stable.
Most of the molecules in the atmosphere do not absorb infrared radiation very easily. That’s why it can be radiated into space. Other molecules, including water and carbon dioxide, do absorb the infrared energy. The term "greenhouse effect" refers to the action of these molecules. They absorb the energy that is radiated from the surface and trap it in the atmosphere, preventing its radiation into space. The name comes from a comparison to the glass of a greenhouse trapping heat radiated when light passes through the glass and heats the inside of the greenhouse. (Interestingly, the mechanism by which a real greenhouse traps heat is very different from that of the atmosphere, but the name has been applied and that’s that.)
The greenhouse effect is important to humans and other living things. If all the infrared radiation were lost in space instead of some of it being trapped, the average temperature would be 0°F instead of 59°F.
Fast Facts
Right now, we are in the middle of one of Earth’s "ice ages." While people generally think of ice ages as periods when glaciers cover much of the land surface, that is only part of the story. The first ice age occurred about 2.5 billion years ago. The second lasted from 850 million years ago to 630 million years ago. Another occurred from about 460 to 260 million years ago. The current ice age began about 40 million years ago. During the periods between ice ages, the polar ice caps melt completely. There are cycles of warm and cool climate within an ice age that correspond to shrinking and expanding of glaciers. Right now, we are in a warm period within an ice age and the big glaciers have shrunk in Greenland and Antarctica. Earth is still much cooler now than during the truly warm periods, however. There is concern that global warming could drastically increase the rate of melting. While Earth is expected to warm as part of the long cycle, global warming may cause changes to occur more rapidly than we are able to adapt to them.
Remember that there is a balance involved. What would happen if the amount of carbon dioxide in the atmosphere were to change? Then the amount of radiation from the planet would change, altering the balance of radiation in and radiation out.
This is the concern of environmental scientists. An increased concentration of carbon dioxide in the atmosphere would be expected to absorb more infrared radiation, increasing the temperature of the planet, and the effect known as global warming.
Measurements from ice cores show that the level of carbon dioxide has varied from 180 parts per million (ppm) to 270 ppm over the past 800,000 years. Times of low concentration correspond to the cooler temperatures of the ice ages and higher concentration to warmer periods. In 1960, scientists measured the carbon dioxide level in the atmosphere as 313 ppm. It has since increased to more than 375 ppm. Most of the change is attributed to the burning of fossil fuels and deforestation.
Climatologists predict that the global average temperature will increase by several degrees over the next few decades as a result of the change in the greenhouse effect. This increase could lead to drastic changes of Earth’s climates.
What causes acid rain?
Since the beginning of the Industrial Revolution, limestone and marble statues have had a shorter lifetime. Their features tend to erode and blur due to reactions of acid with the stone. This acid falls out of the sky as rain, snow, and sleet. What is the source of acid precipitation?
Normal, unpolluted rain is slightly acidic because carbon dioxide from the atmosphere reacts with water to form carbonic acid. Acid rain contains much stronger acids, nitric acid and sulfuric acid. The amount of acid in this rain is generally between 10 and 100 times that of normal rain.
Acid rain forms as a result of burning fossil fuels, such as coal and gasoline. These fossil fuels are composed primarily of carbon and hydrogen, but, because they were formed from living organisms, the fuels also contain compounds that have other elements, including sulfur and nitrogen. When these compounds react with oxygen during combustion, they form sulfur dioxide and nitrogen oxides. These oxides react with water molecules in the air to form acids.
In addition to its effects on statues and buildings, acid rain can have devastating effects on natural systems. The insects and invertebrates in streams, which form the base of the aquatic food chain, are killed in significant numbers by the acid. Even moderate acidification can prevent fish eggs from hatching and, in severe cases, it kills adult fish as well.
The acidity of acid rain is sometimes compared to that of lemon juice or vinegar, making the point that acid rain is not really dangerous. This argument misses the point that the problem with acid rain is its effect on the environment, not whether the acid is strong enough to be harmful on human skin. Would you expect a fish to thrive if you placed it in a tank of vinegar?
In forests, especially those in high altitudes where trees are often surrounded by acid fog, plants can be damaged or killed by the acid. High acidity also makes it impossible for plants to take up some minerals from soil, stunting their growth.
The main control for acid rain is preventing the nitrogen and sulfur compounds from entering the atmosphere. Power plants that burn coal have placed systems on the smokestacks that remove sulfur dioxide before releasing combustion gases into the air. The emission-control system in a car engine is designed to prevent the release of nitrogen oxides from the exhaust.
"However fragmented the world, however intense the national rivalries, it is an inexorable fact that we become more interdependent every day. I believe that national sovereignties will shrink in the face of universal interdependence. The sea, the great unifier, is man’s only hope. Now, as never before, the old phrase has a literal meaning: We are all in the same boat."
