Abstract
Purpose
Salinization of groundwater by seawater intrusion is a major concern for the coastal aquifers worldwide. Seawater intrusion occurs mainly due to overpumping of freshwater and sea-level rise which causes lateral and vertical movements of seawater into the coastal aquifers.
Methods
There are several methods to identify and assess the extent of seawater ingress towards land. In the present study, a hydrochemical approach is adopted to understand the status of intrusion. The ions such as Na+, K+, Ca2+, Mg2+, Cl−, SO4 2−, HCO 2−3 , and in-situ parameters namely TDS, pH, and EC were determined for 174 water samples collected both in pre- and post-monsoon in Puducherry region, India.
Results
Ionic ratios such as HCO3 2−/Cl−, Na+/Cl−, Ca2+/Cl−, Ca2+/Na+, Mg2+/Cl−, K+/Cl−, SO4 2−/Cl−, and Cl−/Br− were calculated and correlated with total dissolved solids (TDS) to evaluate seawater intrusion. The ionic ratios such as HCO3 2−/Cl−, Ca2+/Cl−, Mg2+/Cl−, K+/Cl−, and SO4 2−/Cl− vs. TDS shows negative correlation indicating salinization of groundwater. Cl−/Br− ratio is used to distinguish the causes of salinity in groundwater. The Hydrochemical Facies Evolution diagram (HFE-diagram) and heat maps generated out of it have been very well used to understand evolution of seawater intrusion and freshening process in the coastal aquifer to time. The majority of samples in pre-monsoon fall under the facies Na–HCO3/SO4, followed by Na–mixHCO3/mix SO4, Mix Na–HCO3/Mix SO4, and MixNa–MixHCO3/mix SO4 facies indicating direct cations exchange process, whereas, in post-monsoon, Na–Cl, Mix Na–Cl, and Mix Ca–Cl facies are dominant indicating reverse ion exchange process. In the study area, five locations, viz. Ariyankuppam, Kariambattur, Kalapet, Mutialpet, and Parikalpet, fall under Na–Cl and Ca–Cl facies in pre- and post-monsoon which indicates consistent seawater intrusion. The hydrochemical changes that take place during seawater freshwater interaction along coastal aquifer are determined by ionic exchange.
Conclusion
About 24.2% of samples in pre-monsoon and 13.5% of samples in post-monsoon show mixing of seawater. The highly negative ionic exchange values of sodium during pre-monsoon indicate increased amount of seawater fraction in groundwater.
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Acknowledgements
The current work has been supported financially by University Grants Commission, New Delhi [F.No. 41-1035/2012 (SR); Date: 23.07.2012] through major research project. We extend our sincere thanks to Department of Earth Sciences, Department of Ecology and Environmental Sciences and Central Instrumentation Facility of Pondicherry University for providing facilities for analysis. We also extend our thanks to the editor and anonymous reviewer for their valuable suggestions for bringing this research paper to the present level.
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Sridharan, M., Senthil Nathan, D. Hydrochemical Facies and Ionic Exchange in Coastal Aquifers of Puducherry Region, India: Implications for Seawater Intrusion. Earth Syst Environ 1, 5 (2017). https://doi.org/10.1007/s41748-017-0006-x
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DOI: https://doi.org/10.1007/s41748-017-0006-x