Water covers almost 70% of our Earth. The largest body of water is the ocean, while the remaining bodies of water can be subdivided into categories like glaciers and ice caps, groundwater, freshwater, and atmospheric water. In fact, about 97% of our water resources are saltwater, 2% is stored in glaciers and ice caps, and only 1% is freshwater. Of this 1% being freshwater, 97% is in the form of groundwater, often stored in aquifers deep below the soil surface. The rest is stored in rivers and lakes and is more or less directly usable by humans. Only 0.001% of the total water resources is in the atmosphere.
Oceans- The Earth’s ocean is the largest and most apparent body of water. All the oceans of the Earth are connected to each other but we often distinguish five distinct oceans through geopolitical rationale: the Pacific Ocean, Atlantic ocean, Indian ocean, Southern ocean, and Arctic ocean. The oceans are a vital part of the Earth ecosystem; they contain the Earth’s highest biodiversity, from sharks to phytoplankton, to jellyfish, and not to forget the coral reefs that are themselves living organisms. Oceans determine the wind and climate patterns and are responsible for about 90% of the Earth’s natural oxygen production, mainly transpired by phytoplankton. There is still a limitless frontier to explore in the oceans, as half of the world’s oceans are over 3000 meters (9,800 ft) deep, and nearly entirely inaccessible. The deepest point is the Marianas Trench in the Pacific Ocean, east of the Philippines and Japan. In 1960 Don Wolsh and Jacques Piccard became the first and only people to reach the bottom of the trench, which has a maximum depth of 10.923 meters (35,838 ft).
Ice- After the oceans, the ice caps and glaciers are the biggest category. This means that an enormous amount of the Earth’s water is stored in ice. When one looks at the immense ice sheets of Antarctica, however, it doesn’t sound so strange. The Antarctic ice sheet is the largest mass of ice by far and covers an area of almost 14 million km2 (5,400,000 sq mi). In comparison, both Europe and the USA are less than 10 million km2 (3,860,000 sq mi). This ice sheet, including the surrounding frozen sea, contains such a large amount of water that sea levels worldwide would rise more than 60 meters if this would melt. The other two largest ice storages are the North Pole and Greenland. The North Pole is actually a large ice pack floating on the sea. It is two or three meters thick on average. The Greenland ice sheet covers the larger part of Greenland and has an area of 1,755,637 km² (677,676 sq mi). Though smaller than Antarctica it still amasses an area one fifth the size of Europe. Other smaller ice bodies are glaciers and ice caps in the high mountains and in the far North.
Groundwater- A lot of water is stored in the ground. The size of groundwater reserves is often underestimated because water under the ground cannot be seen. Nevertheless, groundwater is the body of water where most of our planet’s freshwater is stored, as well as a similar amount of saltwater. The simplest definition of groundwater is “water stored in the ground.” Water that infiltrates the soil can fill in the soil pores, the spaces between soil particles. This becomes evident when we dig a hole in the ground, and, at some point or another, we watch as groundwater inevitably starts to fill the bottom of the pit. This is the groundwater table, all the voids and soil pores below this point are saturated with water. The groundwater table is the dividing surface between atmosphere and water. The depth of the groundwater table is often defined in relation to the soil surface, or by NAP, the Amsterdam Ordinance level.
The groundwater table is the upper limit of groundwater. The lower limit is defined as the limit to which water is still circulating through subterranean channels. This is called the hydrological base, or impermeable base. Although there can still be layers of water below this base, this water is no longer considered part of the water cycle, and is therefore often not taken into consideration. Between the water table and the hydrological base there are different soil layers in which groundwater is stored. Some soil layers can contain a lot of water while other layers contain hardly any water. An aquifer is a porous and permeable layer which contains a lot of water. The boundaries of an aquifer are either the surface or other soil layers that are more difficult to permeate. Aquifers where water can flow directly to the surface of the aquifer and vice-versa are called unconfined aquifers. Aquifers that do not have a direct connection with the surface, but are, for instance, trapped under impermeable soil layers, are called confined aquifers. Some of the deepest groundwater aquifers lie hundreds of meters below the surface and contain fossil water, water that has remained in an aquifer for thousands of years.
Freshwater- The abundant fresh surface water bodies on Earth are the centre of human civilizations and rich biodiverse nature systems. The most important surface water bodies are rivers and lakes. Lakes function as water storage facilities and can regulate the sometimes erratic run-off of rivers. Rivers describe water run-off at the surface and are often the product of melting snow and ice in the mountains, supplemented by run-off from rainfall. Rivers can be subdivided into three zones: the production zone, the transport zone, and the deposition zone. The production zone is a network of small streams merging together to form a river. The transport zone is the zone where the river forms one big stream with smaller sub-streams branching to it. In the deposition zone, the river starts to branch again, forming a delta and deposing sand and clay that have been transported from higher altitudes.
The morphology and dynamics of rivers are fascinating, the apparent chaos and randomness of flowing water is immensely well structured when observed close up. One of these structural jewels is the dendrite structure and the related geomorphologic laws of Horton.
- The watercourse of most rivers follows a dendrite structure. This is a transport system that is often used in nature: for instance in trees, in blood vessels, in lightning, and in the lungs. It is the most efficient way of transporting goods. For the sake of scientific conformity, the branches of the dendrite structure are often ordered according to location. The outer branches are labeled as order-1. As soon as two branches of order-1 come together they form a stream of order-2. An order-2 stream that is joined by an order-1 stream remains order-2. However, when two order-2 streams join, they continue as an order-3 stream. This is illustrated in the picture on the right. This structure is irrelative to the size of the system; it is the same for the stream in your backyard as for the currents in the sea.
- The geomorphologic laws of Horton describe the universal traits of dendrite structures. The first geomorphic law of Horton describes the number of branches of a certain order in a dendrite system. It appears that there is a perfect relation between the number of branches in one order, compared to the number of branches in a higher order. This is called the bifurcation number. For example, if the bifurcation number of one river system is 3, and there are nine streams of order-1, it follows that there are three order-2 and one order-1 streams. Worldwide, the range of bifurcation numbers is between 3 and 5, which is surprisingly small for something that seems so random. The bifurcation number for blood vessels, for instance, is 3.4, and for lightning it is 3.2. Apart from the bifurcation number, similar relationships are found in other laws of Horton, e.g. the average length of each order, the average slope, and the average drainage area.
- This is only one example of the structure of river; also the meandering of rivers, sediment transport, drainage area, and river bed profiles are described by a perfect scientific logic.
Atmospheric water- Although the amount of atmospheric water is relatively small, it supplies all the water for surface and groundwater reserves in the form of precipitation. Beside this it also has a protective function: clouds can reduce extreme heat and cold that makes the climate more bearable for living beings. Because precipitation is so crucial to the very sustenance of life itself, we give different names to its various forms. While rain is probably the most common form of precipitation across the globe, other phenomena can be quite fascinating when seen for the first time, such as hail, snow, fog, mist, or dew. In many African countries, snow is a rare phenomenon. The combination of sunlight and atmospheric water furnishes stunning skies and sunsets that have at some time inspired every human being. And on the threshold between rainy and sunlit weather water drops in the air refract the stunning colors of our visual spectrum in the form of a rainbow.