In 1980, after several years of health concerns and protests, the U.S. Government relocated and reimbursed 800 families from the Love Canal housing development built atop a landfill which had “disposed of” 22,000 tons of toxic waste from Hooker Chemical and Plastics Corporation. Increased awareness of the problems of abandoned toxic waste sites led to the passage later that year of Superfund legislation, which holds polluters accountable for effects of toxic waste, and taxes chemical and petroleum industries to pay for cleanup of sites where responsible parties cannot be identified. As of early 2007, the EPA listed 1,245 Superfund sites; 324 are delisted, and 66 new sites are proposed. In general, developing countries lag behind in identification, cleanup, and prevention.
Agriculture, as one of the largest land uses, has altered soils in a number of ways. When we harvest crops repeatedly from soil, we remove basic ions such as Calcium, Magnesium, Potassium, and Sodium. One result is acidification, which lowers soil fertility and productivity. Acid rain and the use of nitrogen fertilizers accelerate acidification, and acid rain can increase soil contamination.
Irrigation can degrade soils through salination – the accumulation of salts. High concentrations of salt make it difficult for plants to absorb water by osmosis, so salination reduces plant growth and productivity, and can lead to desertification (degradation of formerly productive land – usually at least semi-arid) and soil erosion.
Agriculture, deforestation, overgrazing, and development can remove vegetation to cause unnatural levels of erosion by wind and water. In the U.S., erosion forced its way into public awareness during the 1930s after drought compounded exposed soils. The famous Dust Bowl (Figure below) resulted in the loss of at least 5 inches of topsoil from nearly 10 million acres of land and the migration of 2.5 million people out of the Great Plains. Today in the U.S., contour plowing, cover crops, terracing, strip farming, no-till farming, reforestation, and better construction practices prevent some soil erosion (Figure below: conservation practices), but the USDA reports that 1.6 billion metric tons of topsoil were lost annually between 1997 and 2001. Since Great Plains agriculture began some 200 years ago, the U.S. has lost one-third of its topsoil. Alarming rates of slash-and-burn agriculture in tropical forests expose thin soils to erosion, and development in China sends 1.6 billion tons of sediment annually into the Yellow River.
Figure 18.27
Soil erosion in the U.S. peaked during the Dust Bowl years of 1933-1939. Intense dust storms (left) shifted vast quantities of unprotected rich prairie soil (right) much of it all the way into the Atlantic Ocean.
Figure 18.28
Conservation practices such as terracing, contour plowing and conservation buffers (left) and conservation tillage (right) prevent soil erosion and improve water quality.
With – or sometimes without – its soil, land resources are used by humans for agriculture, forestry, mining, industry, waste disposal, and cities. Modification of land for these uses inevitably alters ecosystems, and in many cases, the resulting urban sprawl, pollution, salination, erosion, and/or desertification lead to the loss of species, as well. As you learned in the lesson on biodiversity, habitat loss is the primary cause of extinction. Within the past 100 years, the area of land cultivated worldwide has increased 74%; grazing land increased 113%. Agriculture has cost the United States 50% of its wetlands and 99% of its tallgrass prairies. Land changes also result in fragmentation, yet another threat to biodiversity. Pressures from population growth cause the loss of land for human use, as well: ecologist David Pimental reports that erosion and salination destroy more than 2 million acres of prime agricultural land each year, and urban growth, transportation systems, and industry remove a million additional acres from production. Global increases in cropland and pasture from 1700 to 1990 are shown in Figure below.
Figure 18.29
Changes in land use from 1700 to 1990 show the conversion of forests, grasslands, steppes, shrubland, and savannas to cropland (red) and grazing (pink).
Land use changes affect global processes as well as the ecosystems they directly involve. Deforestation – even if it is replaced by agriculture – reduces photosynthesis, which means that less CO2 is removed from the atmosphere. The result is that CO2 builds up – and as you will see in the fourth lesson of this chapter, an increase in CO2 means an increase in the greenhouse effect and global warming. The International Panel on Climate Change (IPCC) estimates that land use change contributes 1.6 gigatons of carbon (as CO2) per year to the atmosphere. This is highly significant when compared to the better-known fossil fuel-burning carbon contributions of 6.3 gigatons.
Urbanization and industry contribute to yet another land use issue that affects water resources and the atmosphere. Increasingly, impervious surfaces such as parking lots, building roofs, streets and roadways are covering land areas. Impervious surfaces prevent water infiltration and groundwater recharge, increasing runoff and altering waterways. They deprive tree roots of aeration and water, decreasing productivity and increasing CO2. Far more than vegetated surfaces, they absorb solar radiation and convert it to heat, increasing runoff, which eventually degrades streams. In the U.S., impervious surfaces cover an area almost as large as the state of Ohio. Solutions to this harmful impact include the development of porous pavements and green roofs (Figure below).
Figure 18.30
Impervious surfaces (left) fragment habitats, increase runoff, degrade water sources, reduce photosynthesis, and effectively increase CO in the atmosphere. In the U.S., they cover an area of land almost the size of Ohio. Permeable pavements and green roofs (right) are beginning to reverse their effects.
Water Resources
At the intersection of land and water resources are wetlands: swamps, marshes and bogs whose soil is saturated (Figure below). Historically, humans have viewed wetlands as wasted land; the U.S. has lost as much of 50% of its wetlands to agriculture, development, and flood control. Recently, wetland loss and the loss wetland species has taught us the importance of this ecosystem. Ecosystem services provided by wetlands include:
water storage and replenishment of aquifers
protection of coastlands from tides and storms
flood control
water purification I: slowing of water flow allows sedimentation to remove particulates
water purification II: denitrification of excess nutrients
rich habitat for wildlife
rich habitat for plants (30% of U.S. plant diversity)
recreation: hunting, fishing, ecotourism (e.g., The Everglades)
In the U.S., at least, recognition of the economic value and biodiversity of wetlands has led to restoration efforts and requirements for replacement of those lost through development. The Ramsar “Convention on Wetlands of International Importance, especially as Waterfowl Habitat,” signed by 18 nations in 1971, works to conserve wetlands throughout the world for their ecological services and their economic, scientific, cultural, and recreational values. Signatories today number 157, and they meet every 3 years.
Figure 18.31
Wetlands such as this area in Cape May, New Jersey, filter water both physically and chemically, protect coastal lands from storms and floods, and harbor an exceptional diversity of plants and animals.
Water is the quintessential resource of life; its unique physical, chemical and biological properties make it difficult for us to imagine life on any planet which lacks liquid water. For human use, however, water must be fresh. About 97% of Earth’s water is found in the oceans. Of the 3% which is fresh water, over 2/3 is locked in ice. The 1% which is fresh liquid water is mostly below ground, leaving just 0.3% as surface water in lakes and rivers (Figure below). The atmosphere contains just .001%.
Figure 18.32
Earth is a watery planet, but only 3% is fresh water, and 2/3 of that is locked in ice. A little less than 1/3 is groundwater (GW), leaving 0.3% in surface water the bright blue in the diagram above.
As industry, agriculture, development, an
d a growing world population use more water, fresh water supplies are shrinking due to over-drafting of groundwater and pollution of surface and groundwater. Over-drafting has lowered water tables in Texas, California, and India, leaving many wells dry. New Orleans is below sea level, and San Jose, California dropped 13 feet, because over-pumping caused the land to subside. The UN and others have labeled the current state of water resources throughout the world a Water Crisis (Figure below). You might wonder why we don’t tap the oceans; the answer is that desalination is extremely costly in terms of energy and economics. The UN estimates that 1.1 billion people worldwide are without adequate fresh water, and that 2.6 billion lack enough water for sanitation to protect from disease. Water conflicts in the Middle East, Eastern Europe, and Korea have threatened regional political stability.
Figure 18.33
International Water Management Institute predicts expanding water shortages by 2025. The UN suggests a worldwide Water Crisis already exists. This map may oversimplify water problems; in the US, at least, drought and overdraft already threaten municipal and agricultural water supplies.
Water pollution, especially from nonpoint sources or runoff, threatens vital freshwater and marine resources in the U.S. and throughout the world. A single example dramatically illustrates the potential for disruption of natural cycles and loss of biodiversity. Runoff of fertilizers applied to vast expanses of agricultural land and other sources such as wastewater have led to what ecologists say is a doubling of the amount of nitrogen available to plants and animals, and that amount could increase by another 60% by 2050. At first glance this may seem like a benefit to life, but it is not. Especially in aquatic ecosystems, excessive nutrients lead to overgrowth of algae, creating algal blooms. Some species are toxic in themselves, but more often, this eutrophication - literally, “feeding too well” - leads to such high levels of respiration (recall that photosynthesizers must respirate – especially at night!) that dissolved oxygen levels plummet, resulting in the death of fish and other species. Death results in decomposition and further nutrient input – compounding the problem. Eutrophication threatens one of the most diverse habitats on earth – coral reefs, which cover just 1% of the earth’s surface yet harbor 25% (over 4000) - of marine fish species. Adapted to low-nutrient environments and characterized by tight nutrient cycles, reefs in the pathway of excess nutrient runoff from agriculture and development become overgrown with algae, which block light from coral polyps. The Nature Conservancy predicts that 70% of Earth’s coral reefs will have disappeared by 2050 if current rates of destruction continue.
Among the most devastating consequences of eutrophication are at least 146 dead zones, where low oxygen levels caused by eutrophication have extinguished all ocean life. The most notorious extends into the Gulf of Mexico at the mouth of the Mississippi River, which brings fertilizer runoff from the U.S. corn belt (Figure below). In July of 2007, this dead zone covered an area of ocean the size of New Jersey and affected shrimp and fishing industries as well as countless species of marine organisms. Interestingly, a similar zone in the Black Sea disappeared between 1991 and 2001, after political changes in the Soviet Union and Eastern Europe made fertilizers too expensive to use for most agriculture. Unfortunately, most are growing, and the nitrogen cycle disruption affects many bodies of freshwater throughout the world, as well.
Figure 18.34
Eutrophication destroys marine and freshwater habitats and threatens biodiversity. Left: Nutrients and sediment flow from the Mississippi River watershed - into the Gulf of Mexico, creating a dead zone literally devoid of life. Right: A satellite photo of the Caspian Sea shows overgrowth of algae in the northern region where the Volga River brings excess nutrients from agricultural fertilizer runoff. Respiration by the algae and their bacterial decomposers lowers levels of dissolved oxygen so that most aquatic life dies.
Conserving Water and Other Natural Resources
Can you imagine what the expression “virtual water” could mean? It is an important concept in the conservation of water resources.
Virtual water is the water used in the production of a good or service. Although it is no longer contained in the product, its use is a part of the cost of production, and as such should be factored into the product’s value. Here are some estimates of virtual water “contained” in various products, from the United Nations Education, Scientific, and Cultural Organization (UNESCO) Institute for Water Education:
1 kg wheat:1,300 liters
1 kg beef:15,000 liters
1 pair of jeans: 10,850 liters
The more water we use, the more likely we are to draw down wells and rivers beyond the hydrologic cycle’s power to recharge them. The more water we use, the more we are likely to pollute the 1% of Earth’s waters which are fresh (as well as the oceans). Protecting soils and lands (especially wetlands and watersheds) is a critical part of protecting water resources, because the hydrologic cycle integrates terrestrial and aquatic ecosystems.
Thus, as for all conservation (wise use) or sustainable use (meeting needs of the present without impairing those of future generations), the first step is to reduce our use of water. This and other strategies to protect our water resources are summarized below. Don’t forget the list of what you can do as an individual, at the end of the lesson on biodiversity!
1. Reduce the use of water, and the abuse of soil, land, and wetlands.
Landscape with native, drought-resistant vegetation.
Use low-flow toilets, faucets, and showerheads. Check out possible local government subsidies for installing these water saving mechanisms.
Purchase foods from water-efficient crops which do not require irrigation.
2. Reuse water where appropriate.
Gray water, which has been used for laundry or washing, can be used to water gardens or flush toilets.
On a municipal level, sewage water can be used for fountains, watering public parks or golf courses, fire fighting, and irrigating crops that will be boiled or peeled before consumption.
3. Catch runoff, which will also slow non-point source pollution and erosion.
Place rainbarrels adjacent to buildings.
Recharge pits which will re-fill aquifers.
4. Support legislation that reduces pollution.
For example in the U.S., the 1977 Clean Water Act, through the EPA, regulates industrial discharge of contaminants and sets standards for water quality.
5. Work locally, nationally and internationally to make clean fresh water available.
The United Nations Depart of Economic and Social Affairs has initiated a second Decade for Water for Life, 2005-2015 to increase awareness of water shortages and work toward sustainable use of freshwater resources.
The World Water Council unites 300 member organizations from 60 countries to work to “build political commitment and trigger action on critical water issues at all levels... to facilitate the efficient management and use of water …on an environmentally sustainable basis.”
Lesson Summary
One’s definition of natural resources clarifies human relationships and responsibilities to the Earth.
Robert Hartwell’s definition defines natural resources as: “something supplied by nature which supports life on this planet.” This definition includes ecosystems, ecosystem services, biodiversity, energy sources and raw materials.
Renewable resources are replenished by natural processes as fast as, or faster than humans consume them.
A non-renewable resource is not regenerated or restored on a time scale comparative to its consumption. Fossil fuels are a classic example of nonrenewable resources.
In practice, pressure from growing populations and increasing industrialization can lead to overconsumption and/or degradation, changing a renewable resource into a non-renewable resource.
According to the Laws of Energy, energy resources are not renewable because they get used up, but materials or matter is constant because it can theoretically be recycled.<
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The concept of sustainable use – the use of resources at a rate which meets the needs of the present without impairing the ability of future generations to meet their needs – may be more helpful in decision making.
The world’s current energy use is unsustainable, especially if increases in developing countries are considered.
Soils are complex mixtures which evolved over thousands of years to support terrestrial ecosystems.
Humans use soils for agriculture, forestry, and waste disposal.
Although soils have been considered renewable resources, human activities have changed them through:
Contamination with heavy metals and toxins
Acidification
Erosion
Salination
Conversion to cropland, cattle production, forestry, and urban centers
Despite soil conservation practices, the U.S. continues to lose topsoil to erosion, and developing countries are losing even more.
Land resources are used for agriculture, forestry, industry, mining, waste disposal, and urban areas.
In the process of converting land resources, the U.S. has lost:
99% of tallgrass prairies
at least 50% of wetlands
an area the size of Ohio to impervious surfaces
Worldwide, conversion of forests to other uses, especially by slash-and-burn, adds CO2 to the atmosphere and reduces the potential for absorption of CO2 by photosynthesis, adding to greenhouse gases.
CK-12 Biology I - Honors Page 85