Page 10 - Barrocu_2003

ITALIA
Figure 2. Water balance of the hydrogeological units of Apulia.
P= average yearly rainfall (mm); ET =average yearly
evapotranspiration (mm); average yearly recharge inflow
(m3/s); possible average yearly withdrawal(m 3/s) After
Tulipano, 2001).
Owing to the heterogeneity of the carbonate
sequence and also to the discontinuities generated
by intense fracturing and karstification, the
hydrogeological characteristics are very complex
and diversified (Grassi et al. 1977).
Gargano behaves almost as an island,
because of the length of its coast in relation to
total land area. The majority of the terrains near
the water table are highly permeable, hence thick-
ness of the fresh water lens is limited because of
its low hydraulic head. The well developed karst
system favours the mixing of waters with differ-
ent salt content. The cretaceous karstic limestones
between Foggia and the Gargano are almost all
invaded by seawater, which at low depth is pres-
ent throughout the area owing to low groundwa-
ter head.
In Murgia, seawater has encroached to a
depth of several hundred metres below sea level
and in Salento the lens-shaped aquifer tapers
towards the Adriatic and Ionian coasts of the
peninsula. Preferential flow lines are at different
levels, depending on the karst (Tulipano, 1976).
Actually, from the lithological point of view Mur-
gia and Salento form one substantially similar
system consisting of Mesozoic carbonate rocks,
but permeability is lower in Murgia, so that two
distinct aquifer units have been distinguished
(Alaimo et al. 1988). The "Soglia Messapica"
represents the morphological, structural and
hydrogeological boundary between Murgia and
Salento within the same carbonate platform
(Grassi & Tulipano, 1983). In fact throughout
Apulia fresh groundwater floats on top of seawa-
ter and discharges into the sea through subaerial
and subaqueous springs (Brondi et al. 1983).
Figure 3. Contour lines representing saltwater content (g/l) in
Apulian aquifers (After Tulipano, 2001).
Since the early seventies, the equilibrium
conditions between fresh and saltwater have been
changing as groundwater abstraction increases,
to the extent that vertical flow has been detected
in wells piercing groundwater levels with differ-
ent salinity at various depths. Water head, tem-
perature and salinity variations over time versus
depth have been measured over a long period in
a number of observation wells drilled for
research purposes and in many other irrigation
wells. These measurements have enabled to iden-
tify the main sources of saline contamination.
Contamination is also related with the high
degree of vertical anisotropy. Temperature
proved to be an excellent tracer in recognising
the main hydrogeological pathways and their
interconnections, as well as in the identification
of those factors strongly influencing the evolu-
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