Is the water preserved on earth

Water resources

1 water and life

Water was the prerequisite for the creation of life on earth. Water has only existed in liquid form since the earth cooled down around 4 billion years ago. The primordial building blocks of life were created around 3.5 billion years ago on the bottom of the primordial ocean, which then formed. Life in the country would not have been possible at that time, as there was no ozone layer to protect the cells from the sun's UV radiation. This task was performed by seawater for long periods of the earth's history. Settlement of the mainland only started about 400 million years ago. But the creatures on the land have also remained attached to the water. The body of most plants and animals consists of 50 to 80% water. Without water, plants would not be able to absorb their nutrients. Within the organisms, water serves as a means of transport for nutrient salts, enzymes and hormones and is involved in almost all important life processes. An adequate water supply is therefore also essential for human existence on earth. He can only produce the food he needs with water, and he can only sustain himself through constant consumption of water.[1]

Amounts of water on earth and various freshwater reservoirs

2 amounts of water on earth

Even if people live almost exclusively in the countryside, their home planet and life on it is primarily shaped by water. Three quarters of the earth's surface is covered with water in liquid and solid aggregate states, approx. 71% by the oceans, about 3% by ice surfaces and 1% by lakes and rivers. The total amount of water on earth is 1.4 billion km3 (Cubic kilometers) estimated.[2] By far the largest part of it (97.5%) is found as salt water in the oceans. The fresh water reserves are mainly bound in the ice (approx. 35 million km3 or 2.5%) or are located under the earth's surface as groundwater (approx. 1%). Only a minimal fraction of less than 1% of total freshwater resources is available as surface water in lakes and rivers and only 0.001% is present in the atmosphere.[3]

3 water resources

Without special treatment, the world's largest water pool, the ocean, cannot be used because of its relatively high salt content. Man is dependent on fresh water for himself and the production of his food. But even of this, only a small proportion of the earth's total fresh water supply is available for use. This is divided into three main reservoirs: 1. the surface waters, 2. the groundwater and 3. mountain glaciers.

3.1 Surface waters

Surface waters consist of lakes and rivers. However, almost half of the inland lakes are salt lakes and therefore cannot be used. The world's freshwater lakes contain 125,000 km3 Water, the rivers on the other hand only 1200 km3. Both are constantly losing water through seepage, runoff and evaporation and are fed by precipitation. The amount of runoff is important because it is a measure of the renewable water potential. Worldwide the discharge is 41,000 km3. However, this potential is very unevenly distributed regionally. In arid and semi-arid climates in particular, only small amounts of water are available. While in Kuwait 10 m per person per year3 are available, it is 2000 m in Germany and 10,000 m in Austria3. Almost everywhere the missing amount is covered by the use of fossil groundwater resources.

The extent to which water resources can actually be used also depends on the quality of the water available. Lakes and rivers are heavily polluted in many regions, especially where water is scarce. Nitrogen compounds, heavy metals and pesticides can find their way into water reservoirs via the soil and tributaries, acids and other pollutants via precipitation. For the concentration of the pollutants, the renewal rate due to precipitation and inflow, but also the water volume of the reservoirs is decisive. With a high renewal rate and water-rich lakes and rivers, the concentration of pollutants is lower than in the opposite case.[4]

3.2 groundwater

Groundwater resources by continent

30% of all freshwater on earth consists of groundwater. The proportion of readily available freshwater resources is even estimated to be over 90%, since the other large freshwater reservoir, the large ice masses at higher latitudes, is difficult to access and the surface water only accounts for around 1% of global freshwater resources. The quality of the groundwater is also usually better than that of the surface water.

A distinction is made between fossil and newly formed groundwater. Fossil groundwater was formed in earlier geological times and is no longer renewed today. Part of this groundwater may have arisen under completely different climatic conditions than today, such as the groundwater resources under the Sahara. Because of the long contact times with the surrounding rock, fossil groundwater can be heavily polluted by salts and other minerals.

Newly formed groundwater is created by the seepage of precipitation or from surface water. In the temperate climate, 30-50% of the precipitation goes into the formation of new groundwater, in the Mediterranean climate 10-20%, in the arid climate 0-2%. This groundwater is usually most suitable as drinking and industrial water, as the seeping water goes through various purification processes. On the other hand, it can be contaminated by human influences, such as fertilizers and pesticides from agriculture, fuels from industry or faeces from households.[5]

3.3 Mountain glaciers and snow

Glaciers and ice sheets store 70% of the world's fresh water.

The glaciers and snow cover in mountains represent a special water resource. Mountains are of great hydrological importance because their height means that they receive a relatively large amount of precipitation. In addition, in winter and at higher altitudes, depending on the latitude, precipitation falls as snow all year round and is stored in glaciers for longer periods of time. The winter precipitation does not flow off directly, but with a seasonal delay in spring and summer. The water not only benefits the mountain regions themselves, but also to a considerable extent the surrounding areas. In this respect, high mountains are also referred to as "water castles". The water resources of the glaciers and snow cover are all the more valuable, the drier these areas are and the higher the population density in them.

As a source of water, the Alps are only of limited importance for the foreland because there is sufficient rainfall here. The situation is different in the continental climate of Central Asia. Here, the mountain runoff is the most important source of water supply in the lower elevations. The mountain ranges usually receive sufficient rainfall because of their exposed location. In the upstream basins, however, there is very little precipitation, so that deserts and semi-deserts predominate here. The water supply of over 100 million people in countries such as Kazakhstan, Kyrgyzstan, Tajikistan, Turkmenistan, Uzbekistan and in northwest China is highly dependent on the mountain rivers, whose water is made up of glacier water in the summer up to 75%.[6] The water supply of the Andean state of Peru is also highly dependent on glaciers. More than 50% of the country's inhabitants live in the dry, largely desert-like coastal region of the Andean foothills, where the capital Lima is also located. The annual mean precipitation here is little more than 10 mm, so that around 80% of the water resources in the coastal region consist of glacial melt water.[7]

In the mountainous regions in the western USA, in the Sierra Nevada and the Rocky Mountains as far as Canada, it is above all the snow in the higher elevations that supplies many millions of people with water. Here, too, the surrounding area is characterized by dry summers, in which often only 10% of the precipitation falls. Melting snow accounts for up to 75% of water runoff, especially in spring and summer.[8]

4 individual proofs

  1. ↑ Lozán, J.L., S. Meyer and L. Krabe: Water as the basis of life, in: Lozán, J.L. i.a. (ed.): Warning signal climate: Enough water for everyone? Scientific facts, Hamburg 2004, pp. 19-24
  2. ↑ UNEP / GRID-Arendal (2002): Total global saltwater and freshwater estimates
  3. ↑ Lozán, J.L. i.a. (ed.): Warning signal climate: Enough water for everyone? Scientific facts, Hamburg 2004; Wikipedia: Water (accessed on May 1, 2008)
  4. ↑ Tilzer, M. M. (2004): Natural surface waters as a reservoir for the global supply of fresh water, in: Lozán, J.L. i.a. (ed.): Warning signal climate: Enough water for everyone? Scientific facts, Hamburg 2004, pp. 19-24
  5. ↑ Kohfahl, C., G. Massmann and A. Pekdeger (2004): Fossils and new groundwater as part of the total water, in: Lozán, J.L. i.a. (ed.): Warning signal climate: Enough water for everyone? Scientific facts, Hamburg 2004, pp. 68-73
  6. ↑ Wilfried Hagg (2003): Effects of glacier retreat on water donation of high alpine areas, comparison Alps - Central Asia, Diss. Munich
  7. ↑ WBGU (2007): Security Risk Climate Change, pp. 83-98
  8. ↑ Service, R.F. (2004): As the West Goes Dry, Science 303, 1124-1127

5 literature

  • Lozán, J.L. i.a. (ed.): Warning signal climate: Enough water for everyone? Scientific facts, Hamburg 2004

6 web links

7 License notice