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water > glossary
GlossaryAlgal bloom: Abnormally increased biomass of algae in a lake or river. Algal blooms occur naturally in spring and early summer, when the rate of reproduction of the algae outstrips that of their consumers. However, the most serious algal blooms are associated with human activities. Phosphates and nitrates carried into waterways in sewage, agricultural fertilisers and detergents, provide the nutrients that cause explosive growth in the algae population.
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Aquifer: A layer or section of earth or rock that contains freshwater, known as groundwater - any water that is stored naturally underground or that flows through rock or soil, supplying springs and wells.
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Aridity: Permanent dryness caused by low average rainfall, often (but not always) in combination with high temperatures. The deserts of the world are permanently arid, with rainfall amounts of less than 100 mm per year, and evapotranspiration rates well in excess of that amount.
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Arsenic: A highly toxic element which exists in three forms � grey, black and yellow arsenic. It occurs naturally in the environment, being released from arsenic-bearing rocks through weathering. Arsenic accumulates in the environment so that small doses, relatively harmless individually, may eventually kill organisms - including people.
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Catchment: A drainage basin, or the area drained by a particular river system. Adjacent drainage basins are separated by watersheds. In North America, the term watershed refers to the entire drainage basin, and the height of land between basins referred to as a divide.
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Cholera: A bacterial disease caused by drinking water contaminated by sewage or eating food that has not been washed or is inadequately cooked. It is common in areas where the growth in population has outstripped the development of facilities for providing clean water or disposing of sewage. The problem is most severe in warm climates where high temperatures encourage the growth of the cholera bacteria.
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Condensation: Condensation in the environment is most frequently associated with the change of water vapour into liquid water in the atmospheric environment. It is generally brought about by cooling, which reduces the ability of the atmosphere to absorb and retain water vapour. If a parcel of air containing a specific volume of water vapour is progressively cooled, it will reach a temperature at which it is completely saturated - the dewpoint temperature of that parcel of air. Any additional cooling beyond the dewpoint will cause the condensation of some of the vapour.
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Conservation (nature): Protection against irreversible destruction and other undesirable changes, including the management of human use of organisms or ecosystems to ensure such use is sustainable.
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Dams: Structures designed to restrict the flow of surface runoff, usually to control flooding or to provide water for irrigation or the production of hydroelectricity. They range from relatively small earth-fill features, pounding back thousands of cubic metres of water, to massive reinforced concrete structures which create reservoirs containing several billion cubic metres of water. All dams, large or small, have an environmental impact on the area in which they are built. The obvious change is in the hydrological cycle, but environmental interrelationships ensure that the effects are felt in the local climatology and in the flora and fauna of the region.
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Delta: A depositional landform created when a river or stream flows into a body of standing water, such as a lake or sea. The sudden reduction in the velocity of the stream which results causes it to deposit the sediment it is carrying.
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Desalination: The removal of dissolved salts from sea water or saline groundwater to provide fresh water for domestic, industrial or agricultural use.
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Development: A process of economic and social transformation that defies simple definition. Though often viewed as a strictly economic process involving growth and diversification of a country's economy, development is a qualitative concept that entails complex social, cultural, and environmental changes. There are many models of what 'development' should look like and many different standards of what constitutes 'success'.
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Distillation: A process in which a liquid is vapourised and the vapour subsequently condensed to produce a purified form of the liquid or one of its constituents. Distillation is a natural part of the hydrological cycle. Energy supplied by the sun causes the water to evaporate. The vapour is carried up into the atmosphere until it is cool enough to condense as water droplets. These droplets are pure water, although the original source may have been salty or polluted. Distillation is the principal method of purifying liquids. It is the most common process used in desalination, and has been used increasingly by domestic consumers to provide fresh drinking-water.
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Ecological balance: Stability in an ecosystem achieved through the development of equilibrium among its various components. This does not imply that the community is static. It is subject to natural variations associated with ecological succession and other influences such as fire, disease and climate change, but the system is normally sufficiently elastic to make the necessary adjustments without major displacement of the balance. Human intervention that includes the introduction or removal of plants and animals, pollution of the environment and destruction of habitat is now a main cause of imbalance in many ecosystems.
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Ecology: Originally defined by Ernst Haeckel in 1866, ecology is the study of the relationships that develop among living organisms and between these organisms and the environment.
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Endangered species: Species of plants or animals threatened with extinction because their numbers have declined to a critical level as a result of overharvesting or because their habitat has drastically changed. That critical level is the minimum viable population (MVP), and represents the smallest number of breeding pairs required to maintain the viability of species.
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Environment: A combination of the various physical and biological elements that affect the life of an organism. Although it is common to refer to �the� environment, there are in fact many environments eg, aquatic or terrestrial, microscopic to global, all capable of change in time and place, but all intimately linked and in combination constituting the whole earth/atmosphere system.
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Environmentally-sound: The maintenance of a healthy environment and the protection of life-sustaining ecological processes. It is based on thorough knowledge and requires or will result in products, manufacturing processes, developments, etc. which are in harmony with essential ecological processes and human health.
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Eutrophication: The occurrence of high nutrient levels in freshwater and marine ecosystems, usually resulting in excessive plant growth and the death of animal and some plant life due to oxygen deprivation.
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Evapotranspiration: The exchange of water between trees, soil and the atmosphere.
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Flood: The inundation of normally dry land by water. Flooding causes millions of dollars'-worth of property damage and takes hundreds of lives each year. It is most common in river valleys or along the coastal areas of lakes, seas and oceans. River floods are caused when a river channel is incapable of carrying the volume of water added to it, and the excess spills over on to the adjacent floodplain. Heavy and prolonged precipitation, snowmelt, channel constrictions, dam failures and alterations to drainage basins may produce or contribute to flooding. Global warming through the increased melting of glaciers and ice sheets, and the subsequent rise in sea level, has the potential to increase the frequency and extent of coastal flooding.
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Floodplain: An area of limited relief bordering a river inundated when the river overflows its bank during a flood. Floodplains are generally low and flat, but possess some relief in the form of the levées which border the main channel and the abandoned channels which indicate the former course of the river as it meandered across the floodplain.
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Glacier: Large, usually moving mass of ice formed in high mountains or in high latitudes where the rate of snowfall is greater than the melting rate of snow. Glaciers can be divided into four well-defined types � alpine, piedmont, ice cap, and continental � according to the topography and climate of the region in which the glacier was formed.
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Grey water: Waste water which does not contain the products of bodily functions, being mainly the product of bathing showering, dishwashing and similar activities. It is generally considered suitable for lawn and garden irrigation, and in areas such as the US south-west where water is scarce, it is seen as a simple way of increasing the efficiency of water use.
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Groundwater: The water that accumulates in the pore spaces and cracks in rocks beneath the earth's surface. It originates as precipitation and percolates down into sub-surface aquifers. The upper limit of groundwater saturation is the water table. Groundwater moves under the influence of gravity, although usually only slowly, and may return to the surface naturally - for example, through springs. Increasingly, it is pumped from wells and boreholes for human use. The rate of withdrawal commonly exceeds the rate the rate of recharge, and in many areas the groundwater supply is simply declining.
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Hydrological cycle: The natural cycle by which water evaporates from the oceans and other water bodies, accumulates as water vapour in clouds, and returns to oceans and other water bodies as precipitation. Precipitation over land has two components: runoff and moisture from evapotranspiration.
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Hydrology: The scientific study of water in the earth or atmosphere system. It includes not only surface water, but also water in the atmosphere and in the groundwater system. Physical hydrology focuses on the distribution and circulation of water, while applied hydrology is more concerned with water and human activities, and includes consideration of water quality, irrigation, drainage and erosion and flood control.
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Irrigation: The provision of water for crops in areas where the natural precipitation is inadequate for crop growth. The water may be obtained from natural or artificial surface storage systems (such as lakes or reservoirs) or from the groundwater system. Irrigation takes many forms from the total flooding associated with paddy-rice production to various sprinkler systems that attempt to emulate precipitation.
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National conservation strategies: Plans that highlight country-level environmental priorities and opportunities for sustainable management of natural resources, following the example of the World Conservation Strategy published by the World Conservation Union (IUCN) in 1980. Though governments may support preparation for the strategies, they are not bound to follow IUCN's recommendations.
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Non-renewable water: Water in aquifers and other natural reservoirs that are not recharged by the hydrological cycle or are recharged so slowly that significant withdrawal for human use causes depletion. Fossil aquifers are in this category: They recharge so slowly over centuries that they are, in effect, a non renewable resource.
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Onchocerciasis: Also known as river blindness; common in tropical regions of Africa and America; caused by infestation by a filarial worm (especially Onchocerca volvulus), transmitted by various species of blackfly, and characterised by subcutaneous nodules and very often blindness.
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Pathogen: Agent causing disease.
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Percolation: Vertical movement of water downwards through soil or rock in the unsaturated zone immediately beneath the surface.
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Pesticides: Chemical products designed to kill or restrict the development of pests. They include fungicides, herbicides and insecticides. Pesticides range from relatively simple elements such as sulphur (S) to complex chemical compounds such as chlorinated hydrocarbons and may be broad-spectrum or narrow-spectrum agents. Pesticides also vary in their persistence in the environment, and in general, the longer they remain chemically stable the greater is their potential for environmental damage. The use of pesticides has undoubtedly benefited society, by preventing disease and improving the food supply. At the same time, ignorance of the environmental impact of pesticides, the indiscriminate use of certain products and inadequate control of the production and use of pesticides has created problems for wildlife and natural vegetation and has threatened human health.
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Precipitation: Any solid or liquid water particles falling to the earths' surface from the atmosphere. It includes rain, snow, hail and sleet, but 'precipitation' and 'rain' are often treated as synonyms.
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Proper resource pricing: The pricing of natural resources at levels which reflect their combined economic and environmental values.
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Rain: Precipitation in the form of liquid water droplets. Droplets vary in size but exceed 0.5mm in diameter. Smaller droplets are considered to be drizzle.
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Renewable water: Freshwater that is continuously replenished by the hydrological cycle for withdrawal within reasonable time limits, such as water in rivers, lakes or reservoirs that fill from precipitation or from runoff. The renewability of a water source depends both on its natural rate of replenishment and the rate at which the water is withdrawn for human use.
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Runoff: Water originating as precipitation on land that then runs off the land into rivers, streams, and lakes, eventually reaching the oceans, inland seas, or aquifers, unless it evaporates first. That portion of runoff that can be relied on year after year and easily used by human beings is known as stable runoff.
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Sahel: A semi-arid to arid area, subject to seasonal and long-term drought, in West Africa south of the Sahara Desert. Named from the Arabic word 'border', since it borders the desert, the Sahel proper consists of six nations - Senegal, Mauretania, Mali, Burkina Faso, Niger and Chad - but the name has come to include adjacent nations that suffer from problems of drought, famine and desertification that are characteristic of the Sahel.
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Salinisation: The build-up of salts in soil as a result of the capillary flow of saline water towards the surface. Salinisation is a common problem in areas where agriculture requires irrigation. There, the natural process is exacerbated by the evaporation of irrigation water that not only adds salts directly to the soil, but also encourages sub-surface water to be drawn from deeper levels to the surface where it is evaporated. At best, it can lead to a reduction in crop yields; at worst, it made the land sterile and unsuitable for agriculture.
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Schistosomiasis: A tropical or subtropical intestinal disease of humans caused by parasitic flatworms or flukes. Using snails as intermediate hosts, the flukes are spread from person to person through polluted water and insanitary living habits. Deteriorating health and reduced resistance usually cause those infected to die of secondary diseases rather than schistosomiasis itself. Schistosomiasis is prevalent in Africa, South America and tropical Asia, where as many as 200 million people are infected.
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Sustainable development: Sustainable development has as many definitions as subscribers. In essence, it refers to economic development that meets the needs of all without leaving future generations with fewer natural resources than those we enjoy today. It is widely accepted that achieving sustainable development requires balance between three dimensions of complementary change:
- Economic (towards sustainable patterns of production and consumption)
- Ecological (towards maintenance and restoration of healthy ecosystems)
- Social (towards poverty eradication and sustainable livelihoods)
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Utility: A public or private company that supplies a basic service to the general public, such as electricity, gas, or water.
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Water: Pure water is a colourless, odourless liquid that is a compound of hydrogen and oxygen (H20). Natural water in the environment is never pure, but contains a variety of dissolved substances. Sea water, for example, is a solution of sodium chloride (NaCl - common salt) and other salts; rainwater can be acidic because of the carbon dioxide (CO2) that it contains and the water in rivers may include minerals dissolved from the rocks over and through which it has flowed. Water can exist as a solid (ice), liquid (water), or gas (water vapour) and changes readily from one to the other, either releasing or taking up energy as it does so.
Some 97 per cent of the world's water is in the oceans, while a further 2 per cent is in the form of ice and snow, which leaves only 1 per cent available as freshwater for plants and animals. Survival on such small amount is made possible by the natural recycling of the water in the hydrological cycle, which not only replaces the water once is has been used, but also cleans it.
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Water consumption: Use of water that results in its evaporation or transpiration (through plants) or that otherwise makes it unavailable for subsequent human use.
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Water quality: The definition of water quality will vary to some extent depending upon the proposed use. Water intended for irrigation or for certain industrial purposes will not have to meet the same quality standards as water intended for drinking, for example. However, there are certain factors that determine water quality whatever the use. They can be classified as physical properties, chemical properties and biological properties.
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Water quality standards: Acceptable standards for water quality have been developed at both the national and international level. The World Health Organisation (WHO) has published guidelines for drinking-water quality, for example, and the European Commission has produced a directive which applies to the quality of water intended for human consumption. Elsewhere all developed nations have established standards for water quality, and some progress has been made among the developing nations. Published standards typically include maximum allowable concentrations (MACs) of specific toxic elements - for example, heavy metals - and guide levels (GL) for those considered less harmful - for example, acidity or calcium (Ca).
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Water scarcity: According to a growing consensus among hydrologists, a country faces water scarcity when its annual supply of renewable freshwater is less than 1,000 cubic meters per person. Such countries can expect to experience chronic and widespread shortages of water that hinder their development.
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Water stress: A country faces water stress when its annual supply of renewable freshwater is between 1,000 and 1,700 cubic meters per person. Such countries can expect to experience temporary or limited water shortages.
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Water table: The upper level of the saturated or groundwater zone in the rocks beneath the earth's surface. In the general, the shape of the water table follows that of the surface, but in places it may reach the surface, creating ponds or natural springs. The depth of the water table in any one area varies with such factors as input from precipitation, loss through sub-surface flow and pumping of groundwater from wells.
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Water vapour: Water in its gaseous state, produced from liquid water by evaporation or by respiration from animals and transpiration from plants. Its presence in the atmosphere contributes to humidity and through subsequent condensation to precipitation. Water vapour is also a greenhouse gas.
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Water withdrawal: Removal of freshwater for human use from any natural source or reservoir, such as a lake, river or aquifer. If not consumed, the water may return to the environment and can be used again.
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Water-washed diseases: Diseases spread from one person to another due to inadequate supplies of water for personal hygiene. These include infections of the skin and eyes (e.g. trachoma) and infections carried by lice, e.g. louse-borne epidemic typhus.
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Watershed: A watershed is an area of land that is drained by a river system and its tributaries. Watersheds can be visualised as physical basins, the "rims" of which are ridges of high land that separate adjacent watersheds.
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Wetlands: Swamps, marshes, fens, tidal marshes, peatlands and other ecosystems which are dominated by water. The presence of water may be permanent, temporary or seasonal and it may by fresh or salt, but the plant and animal organisms in wetlands have adapted to that situation to create unique communities that reflect the conditions at a specific site. Wetlands provide habitat for fish and wildlife, act as staging areas for migrating wildfowl, filter sediments and control flooding in stream systems and protect the shore from erosion in coastal areas.
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WHO (World Health Organisation): A UN agency created in 1948 to deal with global health issues and to achieve as high a level of physical, mental and social well-being as possible for peoples of the world. It is involved in a variety of environemental studies, including the impact of climate change and ozone depletion on health, in conjunction with other agencies such as the World Meteorological Organisation (WMO) and the United Nations Environment Program(UNEP).
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World Commission on Environment and Development: Established by the United Nations General Assembly in 1983 to examine international and global environmental problems and to propose strategies for sustainable development. Chaired by Norwegian Prime Minister Gro Harlem Brundtland, the independent commission held meetings and public hearing around the world and submitted a report on its inquiry to the General Assembly in 1987.
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World Summit on Sustainable Development (WSSD): The World Summit on Sustainable Development takes place from 26 August - 4 September 2002 in Johannesburg, South Africa. Governments, UN agencies, and civil society organisations will come together to assess progress since the UN Conference on Environment and Development held in Rio in 1992 (hence the title 'Rio + 10' for the Johannesburg meeting). Sustainable development is defined in the report from the Rio meeting as being 'economic progress which meets all of our needs without leaving future generations with fewer resources than those we enjoy'.
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