Environmental Research 250 (2024) 118406 Available online 20 February 2024 0013-9351/© 2024 Elsevier Inc. All rights reserved. Fresh and recirculated submarine groundwater discharge zones along the central west coast of India Prakash R a, * , Loveson V.J b , Pratima M. Kessarkar b , Ashwini Kumar b , Chris Pesso c , Concy Gomes b a Chemical Oceanography Division, CSIR-National Institute of Oceanography, Dona Paula, Goa, 403 004, India b Geological Oceanography Division, CSIR-National Institute of Oceanography, Dona Paula, Goa, 403 004, India c University of Reading, Reading, UK A R T I C L E INFO Keywords: Fresh SGD Recirculated SGD Groundwater level Sea surface temperature Hydrochemistry ABSTRACT The study area receives an average of 2840.0 mm of rainfall within four months every year. A portion of the rainwater is flown to the sea as surface water, and the other part is percolated into the bottom as groundwater. In coastal aquifers, the groundwater is transported to the sea due to a hydraulic gradient, and it contains a sig- nificant quantity of dissolved materials and nutrients. SGD processes impact the ocean productivity, mangrove and coral growth, local acidification and many. To isolate the SGD on the central west coast of India, different data was referred. The GWL concerning MSL contributed significantly to demarcating the SGD zones by considering the positive (>0 m) and negative (<0 m) values of GWL concerning above MSL. Thermal images for SST of pre-monsoon and post-monsoon periods of 2020 exhibit cooler surrounded by warmer, which might be the SGD buffering zones in the off-central west coast of India. By considering the results from GWL and SST, 8 SGD beach sites were identified for the further particularized study. The water samples were collected in March 2022, and analyzed using standard procedures and instruments. Fresh and mixing (recirculated) zones have been isolated by piper, hydrochemical facies evolution, and Ca 2+ +Mg 2+ /K + +Na + Vs log Cl  ionic ratio plots. The aquifer water chemical elements are converting possibly due to ionic exchange processes. The decrease in salinity and conductivity observed in the pore water just below the seawater might be due to the influence of freshwater inputs, helping to isolate the fresh SGD and recirculated SGD zones in the study area. Among 8 sites, 3 were found to be fresh SGD sites and 5 were noticed to be mixing/recirculated SGD sites. Most of these Beaches are bounded by hills, which helps to lead the SGD along the central west coast of India. 1. Introduction Submarine groundwater discharge (SGD) is defined as the flow of all water from land to the sea, it includes fresh groundwater discharge (FSGD) and recirculated sea/groundwater discharge (RSGD) from the coastal aquifer and sediment (Taniguchi et al., 2002, 2019; Burnett et al., 2006). SGD is the most common hydrologic process and occurs in most coastal aquifers present as seepage or submarine springs (depending on the depth of the aquifer and velocity of the groundwater flow), with a length of a few centimeters to a kilometer (Moore, 2010). It is controlled and guided by a few factors like hydraulic gradient, li- thology, precipitation, groundwater drafting, groundwater flow veloc- ity, tide, porosity, and permeability of the aquifer (Michael et al., 2005). SGD is quite important due to its role in both quantity and quality; it discharges more than 60% of freshwater than riverine flux; it also transports polluted ions, nutrients, trace elements, Rare Earth Elements (REEs), dissolved ions, organic substances, biochemical particles, and discharges them into the sea (Lee and Kim, 2007; Peterson et al., 2010). It is a main source and primary pathway to the sea; it links the land and ocean (Jeong et al., 2012; Trezzi et al., 2017; Srinivasamoorthy et al., 2019). Submarine groundwater discharge is an essential component in the biogeochemical budget by contributing the above-said dissolved materials to the sea. More than 60% of the dissolved nutrients and 30% of the dissolved carbon are transported from land to the sea through SGD than riverine inputs (Liu et al., 2012; Wang et al., 2015; Chen et al., 2018). Nutrients up to 93% are contributed by SGD, leading to high * Corresponding author. E-mail addresses: rprakash@nio.org (P. R), vjloveson@gmail.com (L. V.J), pratimak@nio.org (P.M. Kessarkar), ashwinik@nio.org (A. Kumar), chrispesso@gmail. com (C. Pesso), concygomes23@gmail.com (C. Gomes). Contents lists available at ScienceDirect Environmental Research journal homepage: www.elsevier.com/locate/envres https://doi.org/10.1016/j.envres.2024.118406 Received 7 September 2023; Received in revised form 12 January 2024; Accepted 1 February 2024