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Puruvesi

Puruvesi

Puruvesi is a lake in Eastern Finland. Part of Kerimäki, Kesälahti and Punkaharju municipalities. Known for its pure water. It is regarded as 7th cleanest large lake on the planet and has uniquely good underwater visibility for a Finnish lake, easily extending to 6-10 meters from surface on calm and sunny days. Part of the Saimaa lake system, it borders on the sub-lake system of Pihlajavesi to the south. Category:Lakes of Finland

Lake

A Lake is a body of water surrounded by land. The majority of lakes are fresh water, and most lie in the northern hemisphere at higher latitudes. Large lakes are sometimes referred to as "inland seas" and small seas are sometimes referred to as lakes. The term lake is also used to describe a feature such as Lake Eyre, which is dry most of the time but becomes filled under seasonal conditions of heavy rainfall. Many lakes are artificial and are constructed for hydro-electric power supply, recreation (swimming, wind surfing,...), water supply, etc. Finland is known as The Land of the Thousands Lakes (actually there are 187,888 lakes in Finland, 60,000 of them are big ones) and Minnesota is known as The Land of Ten Thousand Lakes. The Great Lakes of North America originated in the ice age. Over 60% of the world's lakes are in Canada; this is because of the deranged drainage system that dominates the country.

Origin of natural lakes

Most lakes are young, as the natural results of erosion will tend to wear away one of the basin sides containing the lake. There are a number of natural processes that can form lakes. A recent tectonic uplift of a mountain range can create bowl-shaped depressions that accumulate water and form lakes. The advance and retreat of glaciers can scrape depressions in the surface where lakes accumulate. Such lakes are common in Scandinavia, Siberia and Canada. Lakes can also form by means of landslides or by glacial blockages. An example of the latter occurred during the last ice age in the state of Washington, when a huge lake formed behind a glacial flow. When the ice retreated, the result was an immense flood that created the Dry Falls Monument at Sun Lakes, Washington. Saline lakes can form where there is no natural outlet or the water evaporates rapidly, and the drainage surface of the water table has a higher than normal salt content. Examples of salt lakes include the Great Salt Lake, the Caspian Sea and the Dead Sea. Small, crescent-shaped lakes called oxbow lakes can form in river valleys as the result of meandering. The slow-moving river forms a sinuous shape as the outer side of bends is torn away more rapidly than the inner side. Eventually a horseshoe bend is formed and the river cuts through the narrow neck. This gap now forms the main passage for the river and the ends of the bend become silted up. Lake Vostok is an under-ice lake in Antarctica, possibly the largest in the world. The pressure from ice and the internal chemical composition means that if the lake were drilled into, it may result in a fissure and spraying in the same manner as a shaken can of soda. Some lakes, like Lake Baikal and Lake Tanganyika are volcanic in origin, and lie on geological fault lines. The Crater Lake in Oregon is a lake located within the caldera of an extinct volcano. Some lakes come into existence as a result of sinkhole activity.

Characteristics

The change in level of a lake is controlled by the difference between the sources of inflow and outflow, compared to the total volume of the lake. The significant input sources are precipitation onto the lake; runoff carried by streams and channels from the lake's catchment area; groundwater channels and aquifers, and man-made sources from outside the catchment area. Output sources are evaporation from the lake; surface and groundwater flows, and any extraction of lake water by humans. As climate conditions and human water requirements vary, these will create fluctuations in the lake level. Lakes can be categorized on the basis of their richness of nutrients, which typically effects plant growth. Nutrient poor lakes are said to be oligotrophic, and are generally clear, having a low concentration of plant life. Mesotropic lakes have good clarity and an average level of nutrients. Eutrophic lakes are enriched with nutrients, resulting in good plant growth and possible algal blooms. A hypertrophic lake is a water body that has been highly enriched with nutrients. These lakes typically have poor clarity and are subject to algal blooms. Lakes typically reach this condition due to human activities, such as heavy use of fertilizers in the lake catchment area. Such lakes are of little use, and have a poor ecosystem.

Types of lakes

A periglacial lake is one in which part of its margin is formed by an ice sheet, ice cap or glacier, the ice having obstructed the natural drainage of the land. A subglacial lake is one which is permanently covered by ice. They can occur under glaciers and ice caps or ice sheets. There are many such lakes, but Lake Vostok in Antarctica is by far the largest. The are kept liquid because the overlying ice acts as a thermal insulator retaining energy introduced to its underside by friction, water percolating through crevasses, by the pressure from the mass of the ice sheet above or by geothermal heating below. Because of the unusual relationship between water's temperature and its density, the water in lakes in temperate climates mixes twice a year. Fresh water is most dense at about 4 degrees Celsius. When the temperature of the water at the surface of a lake reaches the temperature at which water is most dense all the water in the lake can mix, bringing oxygen starved water up from the depths, and bringing oxygen down to decomposing sediments. When the density of surface water differs from that of the deeper water there is a marked barrier layer, the thermocline, that prevents mixing. Deep Temperate lakes can maintain a reservoir of cold water year-round. The reservoir of deep, cold water allows cities to tap that reservoir for deep lake water cooling. Since the water of deep tropical lakes never reaches the temperature where water reaches its maximum density, there is no process that makes the water mix. The deeper layer becomes oxygen starved, and can become saturated with carbon dioxide, and possibly other gases, like sulfur dioxide, if there is even a trace of volcanic activity. Exceptional events, like earthquakes or landslides, which do cause mixing, that brings up the deep layers, can release a vast cloud of toxic gas. The amount of gas that can be dissolved in water is pressure related. As the water surfaces, and the pressure drops, a vast amount of gas cab comes out of solution. Under these circumstances even carbon dioxide is toxic. Carbon dioxide is heavier than air, and the released carbon dioxide flows down the river valley.

Artificial lakes

A reservoir (French: réservoir) is an artificial lake created by flooding land behind a dam. Some of the world's largest lakes are reservoirs. Artificial lakes can also be made deliberately by digging one or by flooding an open-pit mine.

Abiotic and biotic limnology

mine Limnology divides lakes in three zones: littoral zone, which is a sloped area that is close to land; open-water zone, where sunlight is abundant; and deep-water zone, where little sunlight can reach. The depth which light can reach in lakes depends on the density and motion of particles. These particles can be sedimentary or biological in origin and are responsible for the color of the water. Decaying plant matter for instance is responsible for a yellow or brown color, while algae result in greenish water. In very shallow water bodies, iron oxides make water reddish brown. Biological particles are algae and detritus. A sediment particle is in suspension if its weight is less than the random turbidity forces acting upon it. The turbidity is a decisive factor in the transparency of the water. Bottom-dwelling detritivorous fish are responsible for turbid waters, because they stir the mud in search for food. Piscivorous fish eat plant-eating (planktonivorous) fish, thus increasing the number of algae (see aquatic trophic cascade). The light depth or transparency is measured by using a Secchi disk. This is a 20 cm disk with alternating white and black quadrants. The depth at which the disk is no longer visible, is the Secchi depth, and is a measure for transparency. It is commonly used to test eutrophication. A lake moderates the surrounding region's temperature and climate because water has a very high specific heat capacity (4186). In the daytime, the lake can cool the land beside it with local winds, resulting in a sea breeze; in the night, it can warm it, forming a land breeze.

How lakes disappear

A lake may be infilled with deposited sediment, and gradually, the lake becomes a wetland, such as a swamp or marsh. An important difference exists between lowland and highland lakes: lowland lakes are more placid, are less rocky/more sedimentary, have a less sloping bottom, and generally contain more plant life. Large water plants (typically reeds) accelerate this closing process significantly because they trap sediment. Turbid lakes, and lakes with much plant-eating fish, tend to disappear slower. A "disappearing" lake (barely noticeable on a human timescale) typically has a water's edge with extensive plant mats. They become a new habitat for other plants (like peat moss, when conditions are right) and animals, many of which are very rare. Gradually, the lake closes, and young peat may form, forming a fen. In lowland river valleys (allowing the river to meander), the presence of peat is explained by the closing of historical oxbow lakes. In the very last stages of succession, more trees would grow in, eventually turning the wetland into a forest. Some lakes can also disappear seasonally; they are called Intermittent lakes and are typical of karstic terrain. A prime example of this is Lake Cerknica in Slovenia. On June 3, 2005 in Bolotnikovo, Russia, a lake called White Lake vanished in a short period of time (minutes). News sources reported government officials theorized that this strange phenomena may have been caused by a shift on soil underneath the lake which drained water to channels leading to Oka River. Neusiedler See, located in Austria and Hungary, dried up several times for a of number years during the past centuries. As of 2005, it is again rapidly losing water, giving rise to the fear that it will be completely dried up by 2010.

Extraterrestrial lakes

At present the surface of the planet Mars is too cold to permit pooling of liquid water on the surface. However geologic evidence appears to confirm that ancient lakes once formed on the surface. It is also possible that volcanic activity on Mars will occasionally melt the subsurface ice, forming large lakes. Under current conditions this water will quickly evaporate or freeze unless insulated in some manner, such as by a coating of volcanic ash. Jupiter's small moon Io is volcanically active due to tidal stresses, and as a result sulfur deposits have accumulated on the surface. Some photographs taken during the Galileo mission appear to show lakes of liquid sulfur on the surface. There are dark basaltic plains on the Moon, similar to lunar maria but smaller, that are called lacus (singular lacus, Latin for "lake"). They were once thought by early astronomers to be literal lakes.

Notable lakes


- The largest lake in the world by surface area is the Caspian Sea. With a surface area of 394,299 sq. km., it has a surface area greater than the next six largest lakes combined.
- The largest freshwater lake, and second largest lake altogether is Lake Superior with a surface area of 82,414 sq. km. It is also the largest lake in North America and is a part of the Great Lakes.
- The deepest lake is Lake Baikal in Siberia, with a bottom at 1,741 m (5,712 ft.) and is the world's largest freshwater lake by volume.
- The highest navigable lake is lake Titicaca, at 3821 m above sea level. It is also the second largest lake in South America.
- The world's highest lake is Lhagba Pool in Tibet at 6,368 m.
- The world's lowest lake is the Dead Sea, at 396 m (1,302 ft.) below sea level. It is also the lake with the highest salt concentration.
- The largest freshwater-lake island is Manitoulin Island on Lake Huron, with a surface area of 2,766 square km.
- The largest lake located on an island is Nettilling Lake on Baffin Island.
- Lake Toba on the island of Sumatra is located in what is probably the largest resurgent caldera on Earth.
- The largest freshwater lake in Europe is Lake Balaton, followed by Lake Geneva.
- Lake Victoria is the largest lake in Africa. It is a part of the Great Lakes of Africa.
- Lake Maracaibo is the largest lake in South America. Lake Titicaca is the largest freshwater lake in South America.
- The largest lake located completely within the boundaries of a single city is Lake Wanapitei in the city of Greater Sudbury, Ontario, Canada. Before the current city boundaries came into effect in 2001, this status was held by Lake Ramsey, also in Sudbury.
- Saimaa is the largest lake in Finland (the land of 187,888 lakes).

See also


- List of lakes
- Loch
- Lough
- Pond
- Limnology
- Lagoon
- Geography
- Tarn

External links


- [http://www.highestlake.com/ Lists of the highest lakes in the US and the world]
- [http://www.mlswa.org/lkclassif1.htm Lake Classification Systems]
- [http://www.uklakes.net/ UKLakes Database]
- [http://www.midwestlakes.org/ Midwest Lakes Policy Center] Category:Bodies of water Category:Landforms ko:호수 ja:湖 simple:Lake th:ทะเลสาบ

Kerimäki

Kerimäki is a municipality of Finland. It is located in the province of Eastern Finland and is part of the Southern Savonia region. The municipality has a population of 5,938 (2003) and covers an area of 875.55 km² of which 281.14 km² is water. The population density is 6.8 inhabitants per km². The municipality is unilingually Finnish. The Church of Kerimäki, built between 1844 and 1847, is the biggest wooden church in the world (45 meters long, 42 meters wide and 37 meters high). There are over 3,000 seats there. Altogether there can be 5,000 people at a time in the church. Category:Municipalities of Southern Savonia Region

Punkaharju

Punkaharju is a municipality of Finland. It is located in the province of Eastern Finland and is part of the Southern Savonia region. The municipality has a population of 4,128 (2003) and covers an area of 748.55 km² of which 250.28 km² is water. The population density is 8.3 inhabitants per km². The municipality is unilingually Finnish. Category:Municipalities of Southern Savonia Region

Water

:This article focuses on water as it is experienced in everyday life. See water (molecule) for information on the chemical and physical properties of pure water (H2O, hydrogen oxide). Water (from the Old English word wæter; c.f German "Wasser", from PIE
- wod-or, "water") is a tasteless, odorless, and nearly colorless (it has a slight hint of blue) substance in its pure form that is essential to all known forms of life and is known also as the most universal solvent. Water is an abundant substance on Earth. It exists in many places and forms. It appears mostly in the oceans and polar ice caps, but also as clouds, rain water, rivers, freshwater aquifers, and sea ice. On the planet, water is continuously moving through the cycle involving evaporation, precipitation, and runoff to the sea. Water fit for human consumption is called potable water. This natural resource is becoming more scarce in certain places as human population in those places increases, and its availability is a major social and economic concern.

Molecular properties

Forms of water

potable water] Water takes many different shapes on earth: water vapor and clouds in the sky, waves and icebergs in the sea, glaciers in the mountain, aquifers in the ground, to name but a few. Through evaporation, precipitation, and runoff, water is continuously flowing from one form to another, in what is called the water cycle. Because of the importance of precipitation to agriculture, and to mankind in general, different names are given to its various forms: while rain is common in most countries, other phenomena are quite surprising when seen for the first time. Hail, snow, fog or dew are examples. When appropriately lit, water drops in the air can refract sunlight to produce rainbows. Similarly, water runoffs have played major roles in human history as rivers and irrigation brought the water needed for agriculture. Rivers and seas offered opportunity for travel and commerce. Through erosion, runoffs played a major part in shaping the environment providing river valleys and deltas which provide rich soil and level ground for the establishment of population centers. Water also infiltrates the ground and goes into aquifers. This groundwater later flows back to the surface in springs, or more spectacularly in hot springs and geysers. Groundwater is also extracted artificially in wells. Because water can contain many different substances, it can taste or smell very differently. In fact, humans and other animals have developed their senses to be able to evaluate the drinkability of water: animals generally dislike the taste of salty sea water and the putrid swamps and favor the purer water of a mountain spring or aquifer.

Water in biology

From a biological standpoint, water has many distinct properties that are critical for the proliferation of life that set it apart from other substances. Water carries out this role by allowing organic compounds to react in ways that ultimately allows replication. It is a good solvent and has a high surface tension, and thus allows organic compounds and living things to be transported in it. Fresh water has its greatest density at 4°C, then becoming less dense as it freezes or heats up from this point. As a stable, polar molecule prevalent in the atmosphere, it plays an important atmospheric role as an absorber of infrared radiation, crucial in the atmospheric greenhouse effect without of which, the average surface temperature would be −18° Celsius. Water also has an unusually high specific heat, which plays many roles in regulating global and regional climate, such as the Gulf Stream climate, allowing life to survive. Water is a very good solvent, chemically not unlike ammonia, and dissolves many types of substances, such as various salts and sugar, and facilitates their chemical interaction, which aids complex metabolisms. Some substances, however, do not mix well with water, including oils and other hydrophobic substances. Cell membranes, composed of lipids and proteins, take advantage of this property to carefully control interactions between their contents and external chemicals. This is facilitated somewhat by the surface tension of water. Water drops are stable due to the high surface tension of water caused by the strong intermolecular forces called cohesive forces. This can be seen when small quantities of water are put onto a nonsoluble surface such as polythene: the water stays together as drops. On extremely clean glass the water may form a thin film because the molecular forces between glass and water molecules (adhesive forces) are stronger than the cohesive forces. This property plays a key role in plant transpiration. A simple but environmentally important and unique property of water is that its common solid form, ice, floats on the liquid. This solid phase is less dense than liquid water, due to the geometry of the strong hydrogen bonds which are formed only at lower temperatures. For almost all other substances and for all other 11 uncommon phases of water ice except ice-XI, the solid form is more dense than the liquid form. Fresh water is most dense at 4°C, and will sink by convection as it cools to that temperature, and if it becomes colder it will rise instead. This reversal will cause deep water to remain warmer than shallower freezing water, so that ice in a body of water will form first at the surface and progress downward, while the majority of the water underneath will hold a constant 4°C. This effectively insulates a lake floor from the cold. While this behavior may seem obvious, even intuitive, it should be noted that almost all other chemicals are denser as solids than they are as liquids, and freeze from the bottom up. Life on earth has evolved with and adapted itself to the important features of water. The existence of abundant liquid, vapor and solid forms of water on Earth has been an important factor in the abundant colonization of Earth's various environments by life-forms adapted to those varying and often extreme conditions. Civilizations have historically flourished around rivers and major waterways; Mesopotamia, the so-called cradle of civilization, is situated between two major rivers. Large metropolises like London, Paris, New York, and Tokyo owe their success in part to their easy accessibility via water and the resultant expansion of trade. Islands with safe water ports, like Singapore and Hong Kong, have flourished for precisely this reason. In places such as North Africa and the Middle East, where water is scarcer, access to clean drinking water was and is a major factor in human development.

Astronomical position of Earth and impact on its water

Mesopotamia The coexistence of the solid, liquid, and gaseous phases of water on Earth is vital to the origin, evolution, and continued existence of life on Earth. However, if the Earth's location in the solar system were even marginally closer or further from the Sun (ie, a million miles or so), the conditions which allow the three forms to be present simultaneously would be far less likely to exist. Earth's mass allows gravity to hold an atmosphere. Water vapor and carbon dioxide in the atmosphere provides a greenhouse effect which helps maintain a relatively steady surface temperature. If Earth were less massive, a thinner atmosphere would cause temperature extremes preventing the accumulation of water except in polar ice caps (as on Mars). According to the solar nebula model of the solar system's formation, Earth's mass may be largely due to its distance from the Sun. The distance between Earth and the Sun and the combination of solar radiation received and the greenhouse effect of the atmosphere ensures that its surface is neither too cold nor too hot for liquid water. If Earth were more distant, most water would be frozen. If Earth were nearer to the Sun, its higher surface temperature would limit the formation of ice caps, or cause water to exist only as vapor. In the former case, the low albedo of oceans would cause Earth to absorb more solar energy. In the second case, a runaway greenhouse effect and inhospitable conditions similar to Venus would result. It has been proposed that life itself may maintain the conditions that have allowed its continued existence. The surface temperature of Earth has been relatively constant through geologic time despite varying solar flux, indicating that a dynamic process governs Earth's temperature via a combination of greenhouse gases and surface or atmospheric albedo. This proposal is known as the Gaia hypothesis.

Human uses of water

Gaia hypothesis All known forms of life depend on water. Water is a vital part of many metabolic processes within the body. Significant quantities of water are used during the digestion of food. (Note however that some bacteria and plant seeds can enter a cryptobiotic state for an indefinite period when dehydrated, and come back to life when returned to a wet environment) About 72% of the fat free mass of the human body is made of water. To function properly the body requires between one and seven litres of water per day to avoid dehydration, the precise amount depending on the level of activity, temperature, humidity, and other factors. It is not clear how much water intake is needed by healthy people. However, for those who do not have kidney problems, it is rather difficult to drink too much water, but (especially in warm humid weather and while exercising) dangerous to drink too little. People do often drink far more water than necessary while exercising, however, putting them at risk of water intoxication, which is frequently fatal. The "fact" that a person should consume eight glasses of water per day cannot be traced back to a scientific source. However, leading dieticians and nutritionists will tell you that this is the RDI (Recommended Daily Intake) of water. [http://ajpregu.physiology.org/cgi/content/full/283/5/R993]. The latest dietary reference intake report by the National Research Council recommended 2.7 liters of water total (including food sources) for women and 3.7 liters for men[http://www.iom.edu/report.asp?id=18495]. Water is lost from the body in urine and feces, through sweating, and by exhalation of water vapor in the breath. Humans require water that does not contain too much salt or other impurities. Common impurities include chemicals and/or harmful bacteria, such as crypto sporidium. Some solutes are acceptable and even desirable for perceived taste enhancement and to provide needed electrolytes.

Water as a precious resource

:See water resources for information about fresh water supplies. fresh water Because of the growth of world population and other factors, the availability of drinking water per capita is shrinking. The issue of water shortage can be solved through more production, better distribution and less waste of it. For this reason, water is a strategic resource for many countries. Many battles and wars, such as the Six-Day War in the Middle East, have been fought to gain access to it. Experts predict more trouble ahead because of the world's growing population, increasing contamination through pollution, and global warming. UNESCO's World Water Development Report (WWDR, 2003) from its World Water Assessment Program indicates that, in the next 20 years, the quantity of water available to everyone is predicted to decrease by 30%. 40% of the world's inhabitants currently have insufficient fresh water for minimal hygiene. More than 2.2 million people died in 2000 from diseases related to the consumption of contaminated water or drought. In 2004, the UK charity WaterAid reported that a child dies every 15 seconds due to easily preventable water-related diseases. Some have predicted that clean water will become the "next oil", making Canada, with this resource in abundance, possibly the richest country in the world.

Regulating water distribution

Drinking water is often collected at springs or extracted from artificial borings in the ground, or wells. Building more wells in adequate places is thus a possible way to produce more water assuming the aquifers can supply an adequate flow. Other water sources are the rainwater and river or lake water. This surface water, however, must be purified for human consumption. This may involve removal of undissolved substances, dissolved substances and harmful microbes. Popular methods are filtering with sand which only removes undissolved material while chlorination and boiling kill harmful microbes. Distillation does all three functions. More advanced techniques exist, such as reverse osmosis. Desalination of abundant ocean or seawater is a more expensive solution used in coastal arid climates. The distribution of drinking water is done through municipal water systems or as bottled water. Governments in many countries have programs to distribute water to the needy at no charge. Others argue that the market mechanism and free enterprise are best to manage this rare resource, and to finance the boring of wells or the construction of dams and reservoirs. Reducing waste, that is using drinking water only for human consumption, is another option. In some cities, such as Hong Kong, sea water is extensively used for flushing toilets citywide in order to conserve fresh water resources. Polluting water may be the biggest single misuse of water; to the extent that a pollutant limits other uses of the water, it becomes a waste of the resource, regardless of benefits to the pollutor. Pharmaceuticals consumed by humans often end up in the waterways and can have detrimental effects on aquatic life if they bioaccumulate and if they are not biodegradable.

The impact of water on human culture

Water is considered a purifier in most religions, including Christianity, Islam, Judaism, and Shinto. For instance, baptism in Christian churches is done with water. In addition, a ritual bath in pure water is performed for the dead in many religions including Judaism and Islam. In Islam, the daily Salah can only be done after ablution (Wodoo), that is, washing parts of the body in clean water. In Shinto, water is used in almost all rituals to cleanse a person or an area. Water is often believed to have spiritual powers. In Celtic mythology, Sulis is the local goddess of thermal springs; in Hinduism, the Ganga is also personified as a goddess. Alternatively, gods can be patrons of particular springs, river or lakes: for example in Greek and Roman mythology, Peneus was a river god, one of the three thousand Oceanids. The Greek philosopher Empedocles held that water is one of the four classical elements along with fire, earth and air, and was regarded as the ylem, or basic stuff of the universe. Water was considered cold and moist. In the theory of the four bodily humours, water was associated with phlegm. Water was also one of the Five Elements in traditional Chinese philosophy, along with earth, fire, wood, and metal. A common misconception about water is that it is a powerful conductor of electricity. Any electrical properties observable in water are due to the ions of mineral salts and carbon dioxide dissolved in it. Water does self-ionize (two water molecules become one hydroxide anion and one hydronium cation), but only at a very slight, almost immeasurable level. Pure water can also be electrolized into oxygen and hydrogen gases but without any dissolved ions, this is a very slow process and thus very little current is conducted. Many bottled water companies exploit another common misconception, advertising both purity and taste, even though pure water is tasteless.

See also


- Dehydration
- Desalination
- Dihydrogen monoxide hoax
- Double distilled water
- Drought
- Ecohydrology
- Evapotranspiration
- Flood
- Flume
- Fountain
- Fresh water
- Heavy water
- Holy water
- Hydrography
- Hydrology
- Irrigation
- Mineral water
- Precipitation (meteorology)
- Rain
- Sea water
- Spring water
- Transvasement
- Wastewater
- WaterAid
- Water (molecule)
- Water industry
- Water ionizer
- Water quality
- Water quality modelling
- Water resources
- World Ocean Day
- World Water Day

External links


- [http://www.lsbu.ac.uk/water/phase.html Phase diagrams of water]
- [http://www.publicforuminstitute.org/issues/oceans/index.htm Oceans and Water Issues Page]
- [http://www.greenfacts.org/water-disinfectants/index.htm Scientific Facts on Water disinfectants] A faithful summary by GreenFacts of a leading scientific consensus report on Drinking Water Disinfectants published by the International Programme on Chemical Safety of the WHO.
- [http://www.hkc22.com/residentialwater.html Residential water problems and markets] Study paper from Helmut Kaiser Consultancy
- [http://www.hkc22.com/watermarketsworldwide.html Water markets worldwide] Study paper from Helmut Kaiser Consultancy
- [http://www.worldwaterforum.org/ World Water Forum]
- [http://www.unesco.org/water/wwap/ World Water Assessment Program]
- [http://unesdoc.unesco.org/images/0012/001295/129556e.pdf United Nations' World Water Development Report]
- [http://www.gemswater.org/ United Nations GEMS/Water Programme]
- [http://www.lsbu.ac.uk/water/ Water Structure and Behaviour]
- [http://www.wateraid.org/ WaterAid]
- [http://www.sahra.arizona.edu/newswatch/ SAHRA—Global Water Newswatch]
- [http://www.siwi.org/ Stockholm International Water Institute] (SIWI)
- [http://www.c-win.org/ California Water Impact Network (C-WIN)]
- [http://news.bbc.co.uk/2/hi/science/nature/3752590.stm BBC: The water debate]
- [http://www.geocities.com/tapvsbottled/ Tap Water Vs Bottled Water] - Interesting site providing facts about tap and bottled water.
- [http://www.emagazine.com/september-october_2003/0903feat1.html E the Environmental Magazine piece on bottled water] (Oct 2003).
- [http://www.iapws.org/ International Association for the Properties of Water and Steam]
- [http://ga.water.usgs.gov/edu/watercycle.html US Geological Survey: Comprehensive discussion of the water cycle, in many languages]
- [http://www.dartmouth.edu/~etrnsfer/water.htm Why is water blue?]
- [http://www.water.org.uk/home/resources-and-links/water-for-health/ask-about/adults Water requirements in adults]
- [http://www.hkc22.com/environmentaltechnology.html/ Climate change raises markets for environmental technology, drinking water and clean energies]

References


- OA Jones, JN Lester and N Voulvoulis, Pharmaceuticals: a threat to drinking water? TRENDS in Biotechnology 23(4): 163, 2005
- Category:Beverages Category:Hydrology Category:Materials Category:Natural resources Category:Nutrition zh-min-nan:Chúi als:Wasser ko:물 ja:水 ms:Air simple:Water th:น้ำ

Surface

:For other senses of this word, see surface (disambiguation). surface (disambiguation) In mathematics (topology), a surface is a two-dimensional manifold. Examples arise in three-dimensional space as the boundaries of three-dimensional solid objects. The surface of a fluid object, such as a rain drop or soap bubble, is an idealisation. To speak of the surface of a snowflake, which has a great deal of fine structure, is to go beyond the simple mathematical definition. For the nature of real surfaces see surface tension, surface chemistry, surface energy, roughness.

Definition

In what follows, all surfaces are considered to be second-countable 2-dimensional manifolds. More precisely: a topological surface (with boundary) is a Hausdorff space in which every point has an open neighbourhood homeomorphic to either an open subset of E2 (Euclidean 2-space) or an open subset of the closed half of E2. The set of points which have an open neighbourhood homeomorphic to En is called the interior of the manifold; it is always non-empty. The complement of the interior, is called the boundary; it is a (1)-manifold, or union of closed curves. A surface with empty boundary is said to be closed if it is compact, and open if it is not compact.

Classification of closed surfaces

There is a complete classification of closed (i.e compact without boundary) connected, surfaces up to homeomorphism. Any such surface falls into one of two infinite collections:
- Spheres with g handles attached (called g-fold tori). These are orientable surfaces with Euler characteristic 2-2g, also called surfaces of genus g.
- Spheres with k projective planes attached. These are non-orientable surfaces with Euler characteristic 2-k. Therefore Euler characteristic and orientability describe a compact surfaces up to homeomorphism (and if surfaces are smooth then up to diffeomorphism).

Compact surfaces

Compact surfaces with boundary are just these with one or more removed open disks whose closures are disjoint.

Embeddings in R3

A compact surface can be embedded in R3 if it is orientable or if it has nonempty boundary. It is a consequence of the Whitney embedding theorem that any surface can be embedded in R4.

Differential geometry

A simple review of the embedding of a surface in n dimensions, and a computation of the area of such a surface, is provided in the article volume form. Metric properties of Riemann surfaces are briefly reviewed in the article Poincaré metric.

Some models

To make some models of various surfaces, attach the sides of these squares (A with A, B with B) so that the directions of the arrows match: Image:SphereAsSquare.png|sphere Image:ProjectivePlaneAsSquare.png|real projective plane Image:KleinBottleAsSquare.png|Klein bottle Image:TorusAsSquare.png|torus

Fundamental polygon

Each closed surface can be constructed from an even sided oriented polygon, called a fundamental polygon by pairwise identification of its edges. This construction can be represented as a string of length 2n of n distinct symbols where each symbol appears twice with exponent either +1 or -1. The exponent -1 signifies that the corresponding edge has the orientation opposing the one of the fundamental polygon. The above models can be described as follows:
- sphere: A A^
- projective plane: A A
- Klein bottle: A B A^ B
- torus: A B A^ B^ (See the main article fundamental polygon for details.)

Connected sum of surfaces

Given two surfaces M and M', their connected sum M # M' is obtained by removing a disk in each of them and gluing them along the newly formed boundary components. We use the following notation.
- sphere: S
- torus: T
- Klein bottle: K
- Projective plane: P Facts:
- S # S = S
- S # M = M
- P # P = K
- P # K = P # T We use a shorthand natation: nM = M # M # ... # M (n-times) with 0M = S. Closed surfaces are classified as follows:
- gT (g-fold torus): orientable surface of genus g, for g \ge 0.
- gP (g-fold projective plane): non-orientable surface of genus g, for g \ge 1.

Algebraic surface

This notion of a surface is distinct from the notion of an algebraic surface. A non-singular complex projective algebraic curve is a smooth surface. Algebraic surfaces over the complex number field have dimension 4 when considered as a real manifold.

See also


- minimal surface
- Riemann surface
- algebraic surface
- Klein bottle
- torus
- sphere
- cylinder
- Möbius strip
- projective plane

External links


- [http://xahlee.org/surface/gallery.html Math Surfaces Gallery, with 60 ~surfaces and Java Applet for live rotation viewing] Category:Surfaces Category:Geometric topology ja:表面

Saimaa

Saimaa, or Saimen in Swedish, is a lake in southeastern Finland. At 1,147 square km (443 square miles), it is the largest lake in Finland, and the fifth largest in Europe. Major towns on the lakeshore include Lappeenranta, Imatra, Savonlinna and Mikkeli. The river Vuoksi flows from Saimaa to Lake Ladoga. The Saimaa Canal from Lappeenranta to Vyborg binds Saimaa to the Gulf of Finland. Other canals bind Saimaa to smaller lakes in Eastern Finland and form a network of waterways. These waterways are mainly used to transport wood, minerals, metals, pulp and other cargo, but also tourists use the waterways. One of the two fresh water seal species, the Ringed Seal lives in Saimaa.

External link


- [http://virtual.finland.fi/netcomm/news/showarticle.asp?intNWSAID=25710&LAN=ENG Saimaa - Finland´s largest lake] category:Lakes of Finland ja:サイマー湖

Wartość bezwzględna

Wartość bezwzględna (lub moduł) liczby rzeczywistej to odległość tej liczby od zera na osi liczbowej. Na przykład wartość bezwzględna liczby 4 to 4, zaś wartość bezwzględna liczby -5 to 5. Można powiedzieć, że wyliczanie wartości bezwzględnej liczby rzeczywistej polega na odrzuceniu znaku liczby. Algebraicznie określamy to tak: |a|=\left\

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