Submarine groundwater discharge and associated nutrient flux from southwest coast of India

Abstract

The nutrient discharge associated with submarine groundwater discharge (SGD) into the Arabian Sea has been investigated for the first time using the Radon isotope (²²²Rn) mass balance model at three sites along the southwest coast of India. The SGD flux varied in the range of 49.48×10⁴ - 335.84×10⁴ m³/day, with high (low) discharge during the low (high) tide. SGD delivers a considerable amount of the nutrient into the Arabian Sea with 2.10×10⁴ to 11.66×10⁴ mol/day dissolved inorganic nitrogen (DIN), 1.23×10² to 56.31×10² mol/day dissolved inorganic phosphate (DIP), and 7.28×10⁴ to 24.44×10⁴ mol/day dissolved silicate (DSi). This significant nutrient input to the coastal waters through SGD is mainly attributed to the land-use practices like agricultural activities, improper waste disposal, and thickly populated coastal settlement zones. The increase in the nutrient discharge may lead to phytoplankton bloom in the nearshore environment and can accelerate seasonal coastal hypoxia over the western Indian shelf. This evidence of considerably high nutrient flux through SGD advocates the importance of understanding SGD associated flux along the southwest coast of India to maintain a sustainable ecological balance.

Keywords: Coastal aquifers; Nutrient flux; Radon; Southwest coast of India; Submarine groundwater discharge.