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To understand GW-SW interactions, it is necessary to understand the effects of the hydrogeological environment on GW flow systems, that is the effects of topography, geology, and climate as these factors are the major influences on the type of techniques use to determine GW-SW interactions (see figures 1, 2 & 3) (USGS, 2008). Ground-water flow paths vary greatly in length, depth and travel time from points of recharge to points of discharge in the ground-water system (USGS, 2008) Many studies of GW-SW interactions involve the use of more than one technique in attempting to determine nature of exchanges.
Environmental tracers are naturally occurring dissolved constituents, or physical properties of water that can be used to track water movement through water sheds.
Previous review articles have occasionally summarised the use of CFC's as tracers for dating pristine groundwater as a failure due to local CFC contamination in excess of the equilibrium with modern air.
However, CFCs do provide hydrogeological tracers and dating tools for young groundwater on a time-scale of 50 years (Hohener et al, 2003).
In addition, stable isotopes of oxygen and hydrogen, which are part of the water molecule, are used to determine the mixing of waters from different sources (USGS, 2008; Rodgers et al, 2004).
This is successful because of the differences in the isotopic composition of precipitation among recharge areas, the changes in the isotoic composition of shallow subsurface water caused by evaporation and temporal variability in the isotopic composition of precipitation relative to groundwater.
Since the mid 1970's, CFCs have been used routinely by hydrologists and various disciplines, for dating and tracing water masses.
Strontium isotopes used in combination with more conventional tracers such as deuterium and 18O have helped to establish the sources of differing groundwater types entering lakes (Rodgers et al, 2004).Although chemical, biological and physical properties of surface water and groundwater are indeed different, they are not isolated components of the hydrologic system, but instead interact in a variety of physiographic and climatic landscapes.Therefore development or contamination of one commonly affects the other (Kalbus et al, 2006). Subaqueous springs resulting from ground water flow through highly permeable sediments (USGS, 2008) (USGS, 2008) Figure 3.These methods include several tracers used to identify the exchange of surface and groundwater, such as heat, ion chemistry, isotopes and viruses.
Potential surface aquifer interactions have also been quantified using remote sensing and models (USGS, 2008; Kalbus et al, 2006).Several studies have documented that radon can be used to identify locations of significant groundwater input into a stream, such as from springs.In France a study was conducted where radon was used to determine stream-water loss to groundwater as a result of ground-water withdrawals (USGS, 2008).The water on the Earth's surface - surface water - occurs as streams, lakes, rivers as well as bays and wetlands.