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Cation Exchange in Groundwater

Groundwater often contains dissolved minerals in the form of ions, such as dissolved calcium, or magnesium, which come from the weathering of surface rocks as well as dissolved organic compounds such as detritus, animal waste, or human contaminants.

As this water percolates through an aquifer, it may be modified and changed. Material comprising the aquifer may contain material which has a strong natural tendency to exchange one ion for another. In such an aquifer, calcium or magnesium in the water may be exchanged for sodium.

After awhile excess accumulation of one particular ion in the soil of the aquifer may force a chemical change in the rock which form the aquifer leading to metamorphism in that rock.

Eventually dissolved minerals are carried to the sea where these ions form salts. Thus sea water, the repository of dissolved material, especially carbonates, tends to be salty.


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Aquifer

An aquifer is the name for a layer of rock which is capable of holding a large amount of water. Some layers are better at holding water than others, for example a layer of sandstone can hold a good deal...more

Carbonates

Carbonate is a name for rocks and minerals which contain a molecule made of both carbon and oxygen known as CO32-. (CO32- is also known as the molecule carbonate). Limestone is an example of a calcium...more

Deep Water and the CO2 cycle

The deep ocean waters are under pressure and are much colder than layers of the ocean which are closer to the surface. Dissolved carbon dioxide seems to be absent from the deep ocean water and as a result...more

Evaporation

One process which transfers water from the ground back to the atmosphere is evaporation. Evaporation is when water passes from a liquid phase to a gas phase. Rates of evaporation of water depend on things...more

Surface Ocean Currents

The water at the ocean surface is moved primarily by winds that blow in certain patterns because of the Earth’s spin and the Coriolis Effect. Winds are able to move the top 400 meters of the ocean creating...more

Rivers

Rivers are very important to Earth because they are major forces that shape the landscape. Also, they provide transportation and water for drinking, washing and farming. Rivers can flow on land or underground...more

Salinity

About 70% of the Earth is covered with water. Over 97% of that water is found in the oceans. Everyone who has taken in a mouthful of ocean water while swimming knows that the ocean is really salty! Dissolved...more

Windows to the Universe, a project of the National Earth Science Teachers Association, is sponsored in part by the National Science Foundation and NASA, our Founding Partners (the American Geophysical Union and American Geosciences Institute) as well as through Institutional, Contributing, and Affiliate Partners, individual memberships and generous donors. Thank you for your support! NASA AGU AGI NSF