Geoscience Reference
In-Depth Information
et al.
2000
; Spoor
1998
). In Australia, soil salinization is the most severe envi-
ronmental problem on the continent, causing dramatic changes in landscape,
industry, and the future of farmland (e.g., Dehaan and Taylor
2002
).
3.3.2 Impacts on Water Usage
The salt content of groundwater, surface water, and soils is a major factor in
determining their benefit to the community, the economy, and the environment. In
many areas around the globe, increasing demand for water has created tremendous
pressures
on
water
resources,
which
resulted
in
lowering
water
levels
and
increasing salinization.
Both natural and anthropogenic changes result in surface water salinization, and
in many cases, a combination of the two processes enhances the phenomenon.
Natural processes include discharge of saline groundwater to surface water and the
dissolution and transport of salts accumulated in the partially saturated zone (James
et al.
1996
; Kolodny et al.
1999
). Additionally, saline feed streams can result from
runoff water that dissolved salts during transport, which then are drained to surface
water. These natural processes are more pronounced in semiarid and arid zones,
where high evaporation rates often exceed transport rates. Anthropogenic changes
also affect the water-salt balance, especially in more heavily populated areas. Some
examples of such anthropogenic interventions include
1. Diversion of rivers or constriction of dams, which causes decreases in flow and
available water, amounts for natural washing of salts (e.g., Funakawa et al.
2000
; Spoor
1998
).
2. Directed deposition of saline solutions by disposal of effluents, drainage of
saline solutions (containing, e.g., agricultural waste), or migration of road
deicing salts after dissolution and transport of the resulting brine (e.g., Cardona
et al.
2004
; Thunqvist
2004
).
3. Land use changes that eliminate natural vegetation and increase drainage and
recharge rates (e.g., Gordon et al.
2003
; Leaney et al.
2003
).
Groundwater salinization is caused mainly by saltwater intrusion and recharge of
saline solution. Natural processes involved in these phenomena include advection
and diffusion of saline fluids entrapped in aquitards connected to an aquifer, dis-
solution of soluble salts (such as gypsum and halite minerals) within the aquifer,
intrusion of underlying or adjacent saline groundwater, and flow from adjacent or
underlying aquifers. Population growth (especially near coastal zones, where
approximately two-thirds of the world's population lives) and dense urbanization
increasingly cause groundwater to become the most important source of freshwater.
Furthermore, large water volumes from domestic industrial and agricultural use are
recharged to the subsurface as saline wastewater effluents. Rising water demand
leads to extensive (over)pumping of fresh groundwater. This, in turn, reduces or
reverses the natural offshore flow that otherwise counters the invasion of saline
