Hydrochemical Facies and Ionic Exchange in Coastal Aquifers of Puducherry Region, India: Implications for Seawater Intrusion

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. -/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-HCO 3 / SO 4 , followed by Na-mixHCO 3 /mix SO 4 , Mix Na-HCO 3 / Mix SO 4 , and MixNa-MixHCO 3 /mix SO 4 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.

Hydrochemical Characteristics and Irrigation Suitability Evaluation of Groundwater with Different Degrees of Seawater Intrusion

“…The proportion of SO 4 2− is not strongly correlated with the degree of seawater intrusion, and the SO 4 2− of groundwater varies within the range of 10 to 30% at each degree of seawater intrusion. In seawater, Cl − usually occupies the highest proportion, while in fresh groundwater, HCO 3 − usually occupies the highest proportion [38]. As the Cl − concentration in seawater is much higher than that of HCO 3 − in fresh groundwater, with the deepening of seawater intrusion, the proportion of Cl − in groundwater will gradually increase while that of HCO 3 − will gradually decrease [39].…”

Hydrogeochemical and salinity appraisal of surficial lens of freshwater aquifer along Lagos coastal belt, South West, Nigeria

“…Marine impact evaluation. Ionic ratios are widely employed worldwide to understand the seawater ingress along the coastal aquifer domain (Batayneh et al, 2014;Sridharan and Nathan, 2017;Masindi and Abiye, 2018). It is well known that no single variable definitively identifies seawater intrusion; however, by considering various analyses, we can ascertain when fresh groundwater mixes with seawater (Werner and Gallagher, 2012).…”

Geochemical variations due to salinization in groundwater along the southeast coast of India

“…In this scenario, the groundwater-seawater interface varies frequently and the salinity is observed to increase toward inland in the recent years. Studies have tried to demarcate the seawater intrusion through modeling techniques [46,47]. Hydrogeochemical parameters to determine the seawater intrusion [46], and delineation of the areal extent of seawater intrusion by preparing a vulnerability map by [47] were also attempted by the earlier researchers.…”

“…Studies have tried to demarcate the seawater intrusion through modeling techniques [46,47]. Hydrogeochemical parameters to determine the seawater intrusion [46], and delineation of the areal extent of seawater intrusion by preparing a vulnerability map by [47] were also attempted by the earlier researchers. The studies on geochemical processes for limited area and limited samples were attempted [48,49] and inferred that the geochemical weathering and ion exchange are the predominant factors.…”