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| Titel |
Controls of evaporative irrigation return flows in comparison to seawater intrusion in coastal karstic aquifers in northern Sri Lanka: evidence from solutes and stable isotopes |
| VerfasserIn |
Rohana Chandrajith, Saranga Diyabalanage, Mahinda Premathilake, Christian Hanke, Robert van Geldern, Johannes A. C. Barth |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250127616
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| Publikation (Nr.) |
 EGU/EGU2016-7512.pdf |
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| Zusammenfassung |
| Groundwater in Miocene karstic aquifers in the Jaffna Peninsula of Sri Lanka is an important
resource since no other fresh water sources are available in the region. The subsurface is
characterized by highly productive limestone aquifers that are used for drinking and
agriculture purposes.
A comprehensive hydrogeochemical study was carried out to reveal the processes
affecting the groundwater quality in this region. Major and trace element composition and
environmental isotope ratios of oxygen and hydrogen (δ18OH2O and δ2HH2O) were
determined in 35 groundwater samples for this investigation. The ion abundance of
groundwater in the region was characterized by an anion sequence order with HCO3¯ >Cl¯
>SO4¯ >NO3¯ . For cations, average Na++K+ contents in groundwater exceeded those of
Ca2++Mg2+ in most cases. Ionic relationships of major solutes indicated open system calcite
dissolution while seawater intrusions are also evident but only close to the coast. The solute
contents are enriched by agricultural irrigation returns and associated evaporation. This was
confirmed by the stable isotope composition of groundwater that deviated from the local
meteoric water line (LMWL) and formed its own regression line denoted as the local
evaporation line (LEL). The latter can be described by δ2HH2O=5.8 ×δ18OH2O - 2.9.
Increased contents of nitrate (up to 26 mg/L), sulfate (up to 430 mg/L) and fluoride (up to 1.5
mg/L) provided evidences for anthropogenic inputs of solutes, most likely from
agriculture activities. Among trace elements Ba, Sr, As and Se levels in the Jaffna
groundwater were higher compared to that of the dry zone metamorphic aquifers in Sri
Lanka.
Solute geochemistry and stable isotope evidences from the region indicates that
groundwater in the area is mainly derived from local modern precipitation but modified
heavily by progressive evaporative concentration rather than seawater intrusion.
The currently most imminent vulnerability of groundwater in the region occurs
through anthropogenic pollution, and particularly so due to agricultural activities.
Extensive groundwater use in the peninsula may also further add concerns of active
seawater intrusion after intense abstraction. The area should remain under close
monitoring for both quality and quantity in order to protect groundwater as a vulnerable
resource.
Reference
Chandrajith, R., Diyabalanage, S., Premathilake, K.M., Hanke, C., van Geldern, R. and
Barth, J.A.C. (2016): Controls of evaporative irrigation return flows in comparison to seawater
intrusion in coastal karstic aquifers in northern Sri Lanka: evidence from solutes and stable
isotopes. - Science of the Total Environment, in press, [doi:10.1016/j.scitotenv.2016.01.050]. |
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