| dc.description.abstract | The Earth's water is always in movement, and the water cycle (hydrologic cycle) describes the continuous movement of water on, above, and below the surface of the Earth. Water can change states among liquid, vapor, and ice at various places in the water cycle, with these processes happening in different time scales. Thus, the water cycle describes the processes that drive the movement of water throughout the hydrosphere, whilst a reservoir represents the water contained in different steps within the cycle. The largest reservoir is the collection of oceans, whereas the third is groundwater. The average time a water molecule will spend in a reservoir is the residence time, which usually ranges from 100 to 200 years in shallow groundwater but over 10,000 years in deep groundwater. In general, there is a relationship between the mineral composition of natural water and that of the solid minerals with which the water has been in contact. This relationship may be comparatively simple and uncomplicated, as in the case of an aquifer receiving direct recharge by rainfall and from which water is discharged without contacting any other aquifer or other water. Or the situation may be rendered very complex by influence of one or more interconnected aquifers of different composition, mixing of unlike waters, chemical reactions such as base exchange, adsorption of dissolved ions, and other factors like anthropogenic inputs. This chapter reports how different techniques can be utilized to investigate the water movement in different aquifer systems occurring in Brazil. Conventional methods to determine the hydraulic conductivity will be described, as well the use of the natural uranium isotopes 238U and 234U to investigate the groundwater flow and hydrogeochemical reactions taking place along it. © 2011 Nova Science Publishers, Inc. | |
