There are two ways by which humanity can change the basic quality and natural distribution of water: by introducing materials and organisms into a body of water (including the atmosphere)—commonly known as pollution—and by intervening in any phase of the hydrologic cycle in such a way that the cycle is altered. Dams, irrigation, and hydroelectric plants are examples of alterations.
Pollutants That Degrade Water Quality
For centuries, the world's lakes, rivers, and oceans have been dumping sites for many of the undesirable byproducts of civilization. People have dumped indiscriminately, believing that bodies of water had an inexhaustible capacity to disperse and neutralize any amount of waste. What was not dissolved or dispersed settled to the bottom, where it could not be seen.
Dumping waste into the oceans and waterways led to few apparent problems as long as waste products were few and consisted mainly of naturally occurring materials. As the world's population grew and technology began introducing huge numbers of new products and processes, however, this natural disposal system began breaking down under an overload of natural and synthetic contaminants. Fish and marine animals died; "dead zones," where no life could survive, developed in harbors and oceans; drinking water became contaminated; and beaches became littered with garbage.
According to an article in WaterNews (EPA, April 1, 2003), G. Tracy Meehan III of the EPA's Office of Water announced approximately $10 million in grants for eligible states and territories to improve their water testing and to notify the public of health risks during the coming summer season. Data from the EPA's National Health Survey of Beaches for the 2002 swimming season showed one-quarter (25%) of beaches surveyed (a total of 2,823) had issued at least one swimming advisory or closure during the summer of 2002. Although 43% of causes for closings were unknown, 25% were due to elevated bacteria levels caused by sewage overflows or storm water runoff. Another 3% of closings were caused by discharge from boats ("EPA's BEACH Watch Program: 2002 Swimming Season," May 2003).
Concern over water pollution helped launch the environmental movement of the 1970s. The 1972 Federal Water Pollution Control Act (PL 92–500), commonly known as the Clean Water Act, was the first major piece of environmental legislation enacted by Congress. Since then, many laws and regulations designed to protect, preserve, and clean up the national waters have been passed. Although substantial progress has been made, many problems remain to be solved.
There are many sources and types of water pollution. Every day, industrial byproducts and household wastes such as nutrients, toxic chemicals, metals, plastics, medical refuse, radioactive waste, and sludge (the solid material left after water is extracted from raw sewage) are deposited into the nation's rivers, lakes, harbors, and oceans. Septic tanks, landfills, and mining operations often produce hazardous contaminants that seep into the soil and then into underground aquifers (aggregates of water that flow through rocks and soil, and eventually into surface rivers or oceans). Table 1.1 lists the most common sources of pollution. Figure 1.7 shows how bacteria, viruses, and other microorganisms can be introduced into water.
Reducing Water Pollution
The term "water pollution" is very broad. Water is often classified into different categories: drinking water, wastewater, coastal waters, surface water, groundwater, freshwater, estuarine, and salt water. In nature, however, all water is part of the hydrologic cycle. When it rains, a pesticide applied to a cornfield may run off into a nearby stream and from there into the ocean. It can seep into the earth and contaminate underlying groundwater, which, in turn, feeds into a lake or reservoir. While a heavy buildup of contaminants in any one area is a local concern,
TABLE 1.1
Pollution source categories
| Category | Examples |
| Industrial | Pulp and paper mills, chemical manufacturers, steel plants, metal process and product manufacturers, textile manufacturers, food processing plants |
| Municipal | Publicly owned sewage treatment plants that may receive indirect discharges from industrial facilities or businesses |
| Combined sewer overflows | Single facilities that treat both storm water and sanitary sewage, which may become overloaded during storm events and discharge untreated wastes into surface waters |
| Storm sewers/urban runoff | Runoff from impervious surfaces including streets, parking lots, buildings, and other paved areas |
| Agricultural | Crop production, pastures, rangeland, feedlots, animal operations |
| Silvicultural | Forest management, tree harvesting, logging road construction |
| Construction | Land development, road construction |
| Resource extraction | Mining, petroleum drilling, runoff from mine tailing sites |
| Land disposal | Leachate or discharge from septic tanks, landfills, and hazardous waste sites |
| Hydrologic modification | Channelization, dredging, dam construction, flow regulation |
| Habitat modification | Removal of riparian vegetation, streambank modification, drainage/filling of wetlands |
increased sources and types of pollutants have also made water pollution a global problem.
Reducing water pollution is a complex issue as all substances have the potential to be contaminants and to cause harmful effects, thereby demonstrating "toxicity." The mere presence of a substance does not mean a threat exists either to humans or to other species. Not all contaminants are harmful, or the contaminant may be harmful only at certain levels or in certain waters. For example, salt is not a problem in ocean and estuarine environments but can be highly toxic to aquatic life in freshwater rivers and streams. Whether or not a substance exerts toxicity depends on the characteristics of the particular environment, its concentration in the environment, its particular chemical composition, the dose experienced by humans or other species, and the duration of exposure. Reducing water pollution is further complicated by the many pathways by which contaminants reach water, and the limits on our ability to identify and minimize or eliminate these pathways.
The issues of water pollution and waste disposal are interrelated. Because there are only three options for disposing of waste (placement in land, water, or air), water will continue to be used as a depository for waste for the foreseeable future. While the concept of "zero discharge" of pollutants is a laudable goal, it is terribly expensive and, in most cases, not technologically achievable. Zero discharge means that the wastewater is treated to remove all traces of any substance present in the water. In many cases, low levels of the pollutants would either occur naturally in the water, or their presence would do no harm.
FIGURE 1.7
Sources of bacteria
Several approaches are used to minimize or in some cases eliminate the effects of contaminants on water. These include introducing new processes or techniques that require the use of fewer contaminants, thereby reducing the amount of contaminants that reach water; treating the wastewater to remove contaminants; water reuse; and land disposal of waterborne wastes. The effectiveness of these approaches varies in each situation depending on the amount and complexity of the waste, the cost of waste treatment or the alternate method of disposal, and the effects of the alternate disposal method on land and air environments. In some cases, the public refuses to accept alternative methods because of cost, fear, or cultural bias. For example, some communities object to having highly treated wastewater used to water their golf courses, while several large cities, such as San Diego, California, routinely use treated wastewater to water lawns and landscaping.
Recognizing that there is a continued need to discharge wastes into water, the Federal Water Pollution Control Act and its amendments, such as the Clean Water Act, established the National Pollutant Discharge Elimination System, which uses water quality standards and discharge permits to regulate contaminant discharge. Water quality standards establish the upper limit for the amount of contaminant that will not cause an adverse effect on humans or other species. Cities, companies, and other entities that want to discharge into water apply for permission and if approved receive a permit. The permit specifies the amount and type of contaminants that may be discharged and not cause a violation of the water quality standard. Dischargers are required to monitor what they release and report the results. When limits are exceeded, fines and other penalties are imposed, including requirements for additional treatment and cleanup.
Human Intervention Processes That Degrade
Water Quality
People alter the environment by directly or indirectly intervening in the hydrologic cycle. The purpose of this intervention is to increase or divert water from surface water or groundwater supplies for household use (including drinking), irrigation, industrial uses, flood control, hydro-electric power generation, and other uses. Sometimes the environment absorbs the modification with little or no perceptible change. In other cases the intervention may be disruptive on a local scale. In extreme cases the intervention may completely change the environment in a large area.
Modern technological developments allow massive quantities of water to be pumped out of the ground for use as drinking water and irrigation of crops. When large amounts of water are removed from the ground, underground aquifers can become depleted much more quickly than they can naturally replenish themselves. In some areas, this has led to the subsidence, or sinking, of the ground above major aquifers. Removing too much water from an aquifer in coastal areas can result in saltwater intrusion into the aquifer, rendering the water too brackish (salty) to drink. The natural filtering process that occurs as water travels through rocks and sand is also impaired when aquifer levels become depleted, leaving the aquifer more vulnerable to contamination.
Building dams has also changed the hydrologic cycle. The huge dams built in the United States just before and after World War II have substantially changed the natural flow of rivers. By reducing the amount of water available downstream and slowing stream flow, a dam not only affects a river but also the river's entire ecological system. For example, wetlands have the ability to clean water by trapping and filtering pollutants. This water cleansing process can be stopped or reduced if dams cause wetlands to dry up.
Deforestation and overgrazing worldwide have destroyed thousands of acres of vegetation that play a vital role in controlling erosion. Erosion is the process by which a material is worn away by a stream of water or air, usually because of the abrasive particles in the water or air. Erosion results in soil runoff into rivers and streams, causing turbidity (cloudiness or discoloration), siltation, and disruption of stream flow. Removal of vegetation reduces the amount of water released into the atmosphere by transpiration. In some areas, less water in the atmosphere can mean less rainfall, causing fertile regions to become deserts.
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