Geochemical and isotope data of karstic aquifer systems
in the
Mulankavil area in northwest Sri Lanka were investigated to constrain
recharging and discharging mechanisms, and possible seawater intrusions.
The electrical conductivity (EC) of groundwater was measured in the
dry (n = 139) and rainy (n = 78)
seasons to assess possible saltwater intrusions, from which 25 wells
were selected for detailed geochemical analyses. Water isotope analyses
(expressed as δ2HH2O, δ18OH2O) were measured in 32 wells for
five months. The mean EC of groundwater during both seasons was 2,435
μS/cm, and higher values from the coastal stretch indicated
seawater intrusion. Increasing EC values in the dry period indicated
a temporary inland saltwater wedge. High hydraulic gradients with
rapidly discharging groundwater partially removed seawater intrusions
during the monsoon season. Water isotopes in the region defined an
individual evaporation line with δ2HH2O= 6.69*δ18OH2O −0.77
(r
2 = 0.989), indicating a long enough
residence time to allow evaporation before infiltration. Groundwater
near sinkhole systems was found to be predominantly of the Ca–Mg–HCO3 type and changes to the Na–Cl type toward the coast.
The results of this study revealed conduit systems in the karst subsurface
as essential pathways for controlling seawater intrusion.
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