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of the saltwater intrusion process. However, in reality, excessive pumping occurs
mostly in arid or semi-arid areas characterized by little or no rain, so that aquifer
restoration is unlikely. In these cases, therefore, we can characterize seawater
intrusion
and
other
salinization
processes,
with
associated
changes
in
the
groundwater chemistry, as irreversible.
17.2 Groundwater Acidification
Acidification of groundwater is the result of diffuse anthropogenic sources, such as
atmospheric industrial emissions or agricultural practices, and of point anthropo-
genic sources, such as leakage from municipal or industrial wastes. Knutsson
(
1994
and references therein) provides a short historical review of human-induced
atmospheric emissions. As early as the 1730s, Carl von Linne reported damage to
vegetation around a copper mine and smelter at Falun, Sweden. The expression
''acid rain'' (due to emissions of, e.g., sulfur dioxide and nitrogen oxides) was used
for the first time by R. A. Smith in 1872 with regard to the acidification of
industrial areas in England. Systematic monitoring of airborne substances depo-
sition following acid rains began in Sweden in the middle of the last century; this
culminated with Oden (
1968
), who showed that acid rain deposition over Scan-
dinavia originated mainly from emissions in central and western Europe and the
British Isles. Subsequent studies on acid precipitation risk on soil and water
environment carried out in North America and Europe showed that the SO
4
2-
emissions were reduced (e.g., Ulrich
1985
; Likens and Bormann
1995
). However,
accumulated storage of acidity in soil, as found for example in Germany (Alewell
et al.
2001
), indicates that groundwater acidification remains a long-term threat.
As a result of acid rain, irreversible changes in groundwater chemistry may
occur. Acid rain depletes the acid neutralizing capacity of the subsurface envi-
ronment and may result in groundwater with low pH and enhanced metal con-
centrations. A few examples follow below. Discussion of acid rain in the context
of changes in soil properties appears in Sect.
18.3.1
.
Jacks et al. (
1984
) reported a tendency to lowering of pH in water from shallow
wells in western and southwestern Sweden, where the bedrock consists of
weathering-resistant minerals and does not act as a buffer on the groundwater acid/
alkali ratio. Acid deposition—via acid rain—is highest in this part of Sweden,
originating mostly from western and central Europe, as well as from local emis-
sions of sulfur oxides. Because hardness—due to the presence of calcium and
magnesium, expressed by equivalent quantity of calcium carbonate—is a routine
parameter for characterization of well waters, a correlation between hardness and
groundwater acidification was examined. Hardness increase indicates elution of
calcium and magnesium ions, which leads to alkalinity decrease and groundwater
acidification. Jacks and Knutsson (
1982
) noted that hardness relative to alkalinity
increased markedly in southern Sweden since acid rains began to be recorded
(Fig.
17.6
).
