An investigation of Submarine Groundwater Discharge and related fluxes in parts of the southeast coast of India: combined Radon and Nutrients mass balance approach

•Lower radon in groundwater due to freshwater mixing and seawater fractions.•Negative radon mass balance due to varying lithotypes.•Groundwater nitrate and phosphate sources are mainly from fertilizer, manure, and wastewater.•Higher groundwater silicate due to weathering of silicate-rich sediments.•Varying nutrients in groundwater due to oxic, nitrification, and denitrification process in aquifers.