Groundwater and pore water inputs to the Bay of Bengal supported by geochemical tracers: Example from Tamil Nadu and Pondicherry, East Coast of India

Abstract

Submarine groundwater discharge (SGD) and Saline water intrusion (SWI) are the two major processes that influence coastal aquifers resulting in severe water stress. It is essential to characterize groundwater dynamics and discriminate geochemical characterization to understand both approaches. The present study investigates the zones influenced by SGD and SWI along the coastal aquifers of Tamil Nadu and Pondicherry. Pore water (PW) and groundwater (GW) samples were collected during the monsoon season at low tide and analyzed for major ions adopting standard procedures. Hydrogeochemical characterization of water samples revealed by the piper, ionic ratio, ionic delta (Δmi), and seawater fraction (fSea) plots suggest that the PW samples, irrespective of location and GW samples in specific areas, were attributed to SWI, while the remaining samples suggested SGD. The average chloride-attributed SGD flux calculated for PW was 23.45 × 10−7 L cm−2 S−1 and for GW, 0.58 × 10−7 L cm−S−1. Higher fluxes observed in PW suggest seawater recirculation as the primary mechanism, and GW samples were found to be influenced by fresh, recirculated, and saline intrusions. Overall, the northern parts of the study region were influenced by freshwater discharge. However, the central and southern parts of the study regions were influenced by mixed RSGD and SWI water types. The present work suggests locations influenced by fresh, recirculated, and saline water zones that can benefit the stakeholders in planning strategies to identify proper aquifer recharge and suggest ideal pumping scenarios to sustain groundwater resources.