Assessment of Hydrogeochemical Characteristics and Seawater Intrusion in Coastal Parts of Mangaluru City, Karnataka, India

Seawater intrusion is a global phenomenon that affects the groundwater quality in coastal aquifers due to extensive urban developments associated with over-exploitation of groundwater resources for the activities such as drinking, industrial, and agricultural. Seawater intrusion poses a challenging environment for the freshwater management in coastal areas. Hence, present study is carried out in the coastal region of Mangaluru city, Karnataka, India, to investigate the possibility of the seawater intrusion. The study area is divided into six zones from the coast to inland and 35 groundwater samples were collected during each season of post-monsoon (Dec 2018–Jan 2019) and pre-monsoon (Mar 2020). Groundwater samples were analyzed for both in situ and laboratory water quality parameters. The seawater intrusion is assessed using the hydrochemical methods such as ionic ratio, index method, and graphical method. As per the results of Gibbs plot, hydrogeochemistry of the samples is influenced by rock-water interaction. The modified Piper identifies dominance of freshwater (Ca-HCO3 water type) in the inland areas (zones 3 to 6) and identifies slight intrusion (Na-Cl water type) in the near to the coastal line (zones 1 and 2). Further, the results of ionic ratio (Na/Cl; Ca/Mg; Ca/(HCO3 + SO4); and Cl/(HCO3 + CO3)), index method (BEX index), and graphical methods (EC v/s Cl plot, hydrochemical facies evaluation diagram) identify the influence of salinization due to seawater intrusion up to 2 km (zone 2) from coastal line. The findings of study help to establish a supportive base for the decision-makers for the improved coastal groundwater management.