Depicting the seasonal and spatial sensitivity of anthropogenic nutrient enrichment on phytoplankton in the Bay of Bengal, India

Abstract

High nutrient loading discharge into the oceans is an evolving threat to the marine biota at large, including the Bay of Bengal (BoB) which receives one of the highest inflows of nutrient fluxes from rivers like the Ganga and the Brahmaputra. Further, the complex riverine and deltaic formations are difficult to be quantified, hence satellite-based observation of chlorophyll and phytoplankton species can add more insight in the nutrient aggregation process. We evaluated the spatial sensitive zones in the BoB in terms of anthropogenic nutrients. Our study shows that coccolithophore population and chlorophyll a concentration can be an active indicator of flood mediated nutrient inflow into the oceans. SST illustrated weaker correlation with phytoplankton species during the monsoon owing to prevalence of cyclonic conditions and high nutrient concentration, however, the relationship is relatively stronger during the pre-monsoon when more stable oligotrophic conditions exist. Higher concentration of diatoms, cyanobacteria and chlorophytes in BOB compared to the Pacific Ocean indicates the ecological sensitivity and the resilience of the Bay of Bengal in terms of nutrient cycling.

Keywords: Bay of Bengal; Chlorophyll; Eutrophication; Nutrient; Phytoplankton.