ABSTRACT
A twenty-four month long observational study conducted in an Asia's largest brackish water ecosystem, Chilika Lagoon, India, aimed to unravel dissolved organic matter (DOM) dynamics in this tropical brackish water ecosystem. The study assessed the interplay between allochthonous and autochthonous DOM sources during lean and active flow periods based on regional rainfall. Dissolved organic carbon (DOC), nitrogen (DON), and phosphorus (DOP) fluxes were analyzed, considering catchment runoff, phytoplankton production, benthic-pelagic interactions, and sea-lagoon exchanges as contributors. Contrary to conventional thinking, the study found autochthonous processes to be more significant than conservative mixing in shaping DOM dynamics. It introduced a novel conceptual model illustrating the multifaceted origins of DOM, encompassing catchment runoff, phytoplankton, benthic-pelagic interactions, bacterial activity, and sea-lagoon exchanges. These findings underscore the importance of holistic management strategies for Chilika Lagoon to preserve its ecological health, given its vital role in global carbon cycling, fisheries, and aquaculture.