The hydrosphere is often called the "water sphere" as itincludes all the earths water found in theoceans, glaciers, streams, lakes, thesoil, groundwater, and in the air. The hydrosphereinteracts with, and is influenced by, all the other earthspheres. The water of the hydrosphere is distributedamong several different stores found in the otherspheres. Water is held in oceans, lakes and streams at thesurface of the earth. Water is found in vapor, liquid andsolid states in the atmosphere. The biosphere serves asan interface between the spheres enabling water tomove between the hydrosphere, lithosphere andatmosphere as is accomplished by plant transpiration.The hydrologic cycle traces the movement of water andenergy between these various stores and spheres.
Other hydrospheresA thick hydrosphere is thought to exist around the Jovianmoon Europa. The outer layer of this hydrosphere is almostentirely ice, but current models predict that there is anocean up to 100 km in depth underneath the ice. Thisocean remains in a liquid form because of tidal flexing ofthe moon in its orbit around Jupiter. The volume ofEuropas hydrosphere is 3 × 1018 m3, 2.3 times that ofEarth.It has been suggested that the Jovian moon Ganymedeand the Saturnian moon Enceladus may also possess sub-surface oceans. However the ice covering is expected tobe thicker on Jupiters Ganymede than on Europa.
The Structure of HydrosphereOceans—96.5% Fresh water distribution:of water found •Ice: 1.762%here •Groundwater: 1.7% •Surface Fresh Water: 0.014%Fresh water— •Atmosphere and3.5% of water soil: 0.002%found here
Distribution and quantity of the Earth’s watersOcean waters and waters trapped in the pore spacesof sediments make up most of the present-dayhydrosphere (see Table 1). The total mass of water inthe oceans equals about 50 percent of the mass ofsedimentary rocks now in existence and about 5percent of the mass of the Earth’s crust as a whole.Deep and shallow ground waters constitute a smallpercentage of the total water locked in the pores ofsedimentary rocks—on the order of 3 to 15 percent.The amount of water in the atmosphere at any onetime is trivial, equivalent to 0.013 × 106 cubickilometers of liquid water, or about 0.001 percent ofthe total at the Earth’s surface. Thiswater, however, plays an important role in the watercycle.
Water masses at the Earth’s surface volume (in millionsreservoir percent of total of cubic kilometers)oceans 1,370.0 97.25ice caps and glaciers 29.0 2.05deep groundwater* 5.3 0.38(750–4,000 meters)shallow groundwater 4.2 0.30(less than 750 meters)lakes 0.125 0.01soil moisture 0.065 0.005atmosphere** 0.013 0.001rivers 0.0017 0.0001biosphere 0.0006 0.00004total 1,408. 7 100
At present, ice locks up a little more than 1 percent of the Earth’s water andmay have accounted for as much as 3 percent or more during the height ofthe glaciations of the Pleistocene Epoch (2,600,000 to 11,700 years ago).Although water storage in rivers, lakes, and the atmosphere is small, the rateof water circulation through the rain–river–ocean–atmosphere system isrelatively rapid. The amount of water discharged each year into the oceansfrom the land is approximately equal to the total mass of water stored at anyinstant in rivers and lakes.Soil moisture accounts for only 0.005 percent of the water at the Earth’ssurface. It is this small amount of water, however, that exerts the most directinfluence on evaporation from soils. The biosphere, though primarily H2O incomposition, contains very little of the total water at the terrestrial surface,only about 0.00004 percent. Yet, the biosphere plays a major role in thetransport of water vapor back into the atmosphere by the process oftranspiration.As will be seen in the next section, the Earth’s waters are not pure H2O butcontain dissolved and particulate materials. Thus, the masses of water at theEarth’s surface are major receptacles of inorganic and organic substances,and water movement plays a dominant role in the transportation of thesesubstances about the planet’s surface.
RainwaterAbout 110,300 cubic kilometres of rain fall on landeach year. The total water in the atmosphere is 0.013× 106 cubic kilometres, and this water, owing toprecipitation and evaporation, turns over every 9.6days. Rainwater is not pure but rather containsdissolved gases and salts, fine-ground particulatematerial, organic substances, and even bacteria. Thesources of the materials in rainwater are the oceans,soils, fertilizers, air pollution, and fossil-fuelcombustion.
River and ocean watersRiver discharge constitutes the main source forthe oceans. Seawater has a more uniformcomposition than river water. It contains, byweight, about 3.5 percent dissolvedsalts, whereas river water has only 0.012percent. The average density of the world’soceans is roughly 2.75 percent greater than thatof typical river water. Of the average 35 partsper thousand salts of seawater, sodium andchlorine make up almost 30 parts, andmagnesium and sulfate contribute another fourparts.
Water-rock interactions as determining river water compositionGenerally speaking, the composition of river water, and thus that oflakes, is controlled by water–rock interactions. The attack of carbondioxide-charged rain and soil waters on the individual minerals incontinental rocks leads to the production of dissolved constituents forlakes, rivers, and streams. It also gives rise to solid alteration productsthat make up soils or suspended particles in freshwater aquaticsystems. The carbon dioxide content of rain and soil waters is ofparticular importance in weathering processes. The pH of rainwaterequilibrated with the atmospheric carbon dioxide partial pressure of10−3.5 atmosphere is 5.7. In industrial regions, rainwater pH valuesmay be lower because of the release and subsequent hydrolysis ofacid gases—namely, sulfur dioxide and nitrogen oxides (NOx) from thecombustion of fossil fuels. After rainwater enters soils, itscharacteristics change markedly. The usual few parts per million ofsalts in rainwater increase substantially as the water reacts. The upperpart of the soil is a zone of intense biochemical activity. The bacterialpopulation near the surface is large, but it decreases rapidly downwardwith a steep gradient
Lake watersAlthough lake waters constitute only a small percentage of the waterin the hydrosphere, they are an important ephemeral storagereservoir for fresh water. Aside from their recreational use, lakesconstitute a source of water for household, agricultural, andindustrial uses. Lake waters are also very susceptible to changes inchemical composition due to these uses and to other factors.In general, fresh waters at the continental surface evolve from theirrock sources by enrichment in calcium and sodium and by depletionin magnesium and potassium. In very soft waters the alkalines maybe more abundant than the alkaline earths, and in the moreconcentrated waters of open river systems Ca > Mg > Na > K. Forthe anions, in general, HCO3− exceeds SO 2/4−, which is greater inconcentration than Cl−. It is worthwhile at this stage to considersome major mechanisms that control global surface watercomposition. These mechanisms are atmospheric precipitation, rockreactions, and evaporation-precipitation.
The mechanism principally responsible for waters of very low salinity isprecipitation. These waters tend to form in tropical regions of low relief andthoroughly leached source rocks. In these regions rainfall is high, and watercompositions are usually dominated by salts brought in by precipitation. Suchwaters constitute one end-member of a series of water compositions for whichthe other end-member represents water compositions dominated bycontributions of dissolved salts from the rocks and soils of their basins. Thesewaters have moderate salinity and are rich in dissolved calcium andbicarbonate. They are, in turn, the end-member of another series that extendsfrom the calcium-rich, medium-salinity fresh waters to the high-salinity, sodiumchloride-dominated waters of which seawater is an example. Seawatercomposition, however, does not evolve directly from the composition of freshwaters and the precipitation of calcium carbonate; other mechanisms thatcontrol its composition are involved. Such factors as relief and vegetation alsomay affect the composition of the world’s surface waters, but atmosphericprecipitation, water–rock reactions, and evaporation–crystallization processesappear to be the dominant mechanisms governing continental surface waterchemistry.Continental fresh waters evaporate once they have entered closed basins, andtheir constituent salts precipitate on the basin floors. The composition of thesewaters may evolve along several different paths, depending on their initialchemical makeup.
Water distribution..WatershedsRiver systemsLakes and pondsAquifersIcebergs and glaciers
The water or hydrologic cycle is thecontinuous movement of water fromoceans and freshwater sources tothe air, land, and back to the bodiesof water which results in fresh watercontinuously being renewed.
Evaporation is when the sun heats up waterin rivers or lakes or the ocean and turns itinto vapor or steam. The water vapor orsteam leaves the river, lake or ocean andgoes into the air.
Condensation:Water vapor in the air gets cold and changes back into liquid, formingclouds. This is called condensation.You can see the same sort of thing at home... pour a glass of cold water on a hotday and watch what happens. Water forms on the outside of the glass. Thatwater didnt somehow leak through the glass! It actually came from theair. Water vapor in the warm air, turns back into liquid when it touches the coldglass.
Precipitation:Precipitation occurs when so much water has condensed that theair cannot hold it anymore. The clouds get heavy and water fallsback to the earth in the form of rain, hail, sleet or snow
Collection:When water falls back to earth asprecipitation, it may fall back in theoceans, lakes or rivers or it may endup on land. When it ends up onland, it will either soak into the earthand become part of the ―groundwater‖ that plants and animals use todrink or it may run over the soil andcollect in the oceans, lakes or riverswhere the cycle starts.