The hydrosphere is the total amount of water present on Earth. The water from water bodies such as lakes, seas and rivers, oceans, the water present under the ground and the water from the air, everything is included in the hydrosphere river and ocean waters. This water can be of any form - solid (in the form of ice), liquid or gas (vapours). The solid water is present in the form of ice sheets, glaciers and icebergs. Liquid water is present in the water bodies such as lakes, river and ocean waters. There is also groundwater which is in liquid form. The gaseous form of water can be found in the form of clouds and fogs.
River and Ocean Waters
Rivers are naturally flowing water bodies, generally freshwater bodies that flow towards another river lake and ocean. The rivers have a starting point from where it starts flowing. This starting point is known as the headwater. This starting point or headwater can be from a snow melting point or rainfall or a bubble up from groundwater or a lake or a pond. The other end of the river is called its mouth. The river empties into a river stream sea ocean through this mouth.
Composition of Ocean Waters
The seawater is more uniform in composition with respect to the river water. Seawater has 3.5% of dissolved salts in it whereas river water has only 0.012% of dissolved salts. If we calculate the average density, the world’s ocean is approximately 2.75% denser than river water.
Of the average of 35 parts per 1000 salts of the seawater, 30 parts are sodium and chlorine and 4 parts are magnesium and sulphate. The remaining 1 part of the saline water is constituted with 0.4 part of calcium and potassium each and 0.15 part of the carbon in the form of carbonate and bicarbonate. Along with these elements, the other nutrients found in the ocean or seawater are phosphorus, nitrogen and silicon.
Composition of River Waters
The water flowing in the rivers is freshwater. It contains less than 1% salt. In this 1% salt, 58 parts are carbon in the form of bicarbonate, 39 parts are calcium, sulfur in the form of Sulphate and silicone as dissolved monomeric silicic acid. The remaining 3 parts are chlorine, sodium and magnesium.
Stream and Lake Waters
Lake waters contribute a small percentage of water in the hydrosphere but it is an important source of freshwater. The lake and stream waters are used for household purposes, agricultural purposes and also for industrial purposes. The composition of stream and lake water varies from place to place and season to season. The main source of the dissolved minerals of the stream and lake waters are the rocks through which this water flows. When slightly acidic water hits the rocks, the minerals start dissolving in them. Another factor affecting the composition of stream and lake water is biomass. The biomass helps in neutralizing the pH of the precipitation. Any biological activity in the stream or lake like photosynthesis can change the pH and dissolved oxygen content. Temperature also influences the number of dissolved gases in the water.
The composition of lake water is influenced by evaporation. When the water evaporates, the dissolved minerals are left behind. The more the evaporation will be, the more will be the concentration of dissolved minerals. And if the evaporation continues, minerals such as calcite (CaCO3) and gypsum (CaSO4.2H2O) can precipitate from the solution.
The factors that influence the surface water such as river lake and ocean, sea, pond water also influence the groundwater. The groundwater is always in contact with the rocks. But they move slowly as compared to the surface waters. The surface water may move at a speed of a few kilometres per hour while the groundwater moves a few centimetres in a day. As a result of this slow movement, the groundwater contains more minerals than the surface water.
The composition of groundwater is influenced by the geological materials through which the water passes, the types of reactions taking place and the contact time. The contact time may be a few days to 10,000 years.
Generally, the groundwater has a total dissolved solids content of less than 250 mg/L. But in some areas, groundwater with a total dissolved solid content of greater than 100000 mg/L has been found. This saline groundwater is found in marine sedimentary rocks and also in ancient metamorphic and igneous rocks. Saline groundwater is formed by the three ways -