Characterization of tidally influenced seasonal nutrient flux to the Bay of Bengal and its implications on the coastal ecosystem

Abstract

Submarine groundwater discharge (SGD) introduces solute and nutrients to the global oceans, resulting in considerable nutrient cycling and dynamics in the coastal areas. We have conducted high-resolution, spatio-temporal, lunar tidal cycle patterns and variability of discharged solute/nutrient assessment to get an overview of seasonal nutrient flux to the Bay of Bengal in eastern parts of the Indian subcontinent. Whereas the premonsoon season SGD was found to be dominant in the marine influence (M-SGD), the postmonsoon season was found to be predominated by the terrestrial component of SGD (T-SGD), extending from coast to near offshore. The solute fluxes and redox transformation were found to be extensively influenced by tidal and diurnal cycles, overlapping on seasonal patterns. We have assessed the possible role of SGD-associated solute/nutrient fluxes and their discharge mechanisms, and their associated temporal distributions have severe implications on the biological productivity of the Bay of Bengal. The estimated annual solute fluxes, using the average end-member concentration of the SGD-associated nutrients, were found to be 240 and 224 mM·m -2 ·day -1 for NO 3 - and Fe tot , respectively. Together with huge freshwater flux from the Himalayan and Peninsular Indian rivers, the SGD has considerable influence on the bay water circulation, stratification, and solute cycling. Thus, the observation from this study implies that SGD-associated nutrient flux to the Bay of Bengal may function as a nutrient sink, which might influence the long-term solute/nutrient flux along the eastern coast of India.