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| Titel |
Tracing groundwater salinization processes in coastal aquifers: a hydrogeochemical and isotopic approach in the Na-Cl brackish waters of northwestern Sardinia, Italy |
| VerfasserIn |
G. Mongelli, S. Monni, G. Oggiano, M. Paternoster, R. Sinisi |
| Medientyp |
Artikel
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| Sprache |
Englisch
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| ISSN |
1027-5606
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| Digitales Dokument |
URL |
| Erschienen |
In: Hydrology and Earth System Sciences ; 17, no. 7 ; Nr. 17, no. 7 (2013-07-24), S.2917-2928 |
| Datensatznummer |
250018945
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| Publikation (Nr.) |
 copernicus.org/hess-17-2917-2013.pdf |
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| Zusammenfassung |
| Throughout the Mediterranean, salinization threatens
water quality, especially in coastal areas. This salinization is the result
of concomitant processes related to both seawater intrusion and water–rock
interaction, which in some cases are virtually indistinguishable. In the
Nurra region of northwestern Sardinia, recent salinization related to marine
water intrusion has been caused by aquifer exploitation. However, the
geology of this region records a long history from the Palaeozoic to the
Quaternary, and is structurally complex and comprises a wide variety of
lithologies, including Triassic evaporites. Determining the origin of the
saline component of the Jurassic and Triassic aquifers in the Nurra region
may provide a useful and more general model for salinization processes in
the Mediterranean area, where the occurrence of evaporitic rocks in coastal
aquifers is a common feature. In addition, due to intensive human activity
and recent climatic change, the Nurra has become vulnerable to
desertification and, in common with other Mediterranean islands, surface
water resources periodically suffer from severe shortages. With this in
mind, we report new data regarding brackish and surface waters (outcrop and
lake samples) of the Na-Cl type from the Nurra region, including major ions
and selected trace elements (B, Br, I, and Sr), in addition to isotopic data
including δ18O, δD in water, and δ34S and
δ18O in dissolved SO4. To identify the origin of the
salinity more precisely, we also analysed the mineralogical and isotopic
composition of Triassic evaporites. The brackish waters have Cl contents of
up to 2025 mg L−1 , and the ratios between dissolved ions and Cl, with the
exception of the Br / Cl ratio, are not those expected on the basis of simple
mixing between rainwater and seawater. The δ18O and δD
data indicate that most of the waters fall between the regional meteoric
water line and the global meteoric water line, supporting the conclusion
that they are meteoric in origin. A significant consequence of the meteoric
origin of the Na-Cl-type water studied here is that the Br / Cl ratio,
extensively used to assess the origin of salinity in fresh water, should be
used with care in carbonate aquifers that are near the coast. Overall,
δ34S and δ18O levels in dissolved SO4
suggest that water–rock interaction is responsible for the Na-Cl brackish
composition of the water hosted by the Jurassic and Triassic aquifers of the
Nurra, and this is consistent with the geology and lithological features of
the study area. Evaporite dissolution may also explain the high Cl content,
as halite was detected within the gypsum deposits. Finally, these Na-Cl
brackish waters are undersaturated with respect to the more soluble salts,
implying that in a climate evolving toward semi-arid conditions, the
salinization process could intensify dramatically in the near future. |
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