Sedimentary organic matter characteristics in the core sediments of Cochin Estuarine–Coastal Lagoon, South India

The Vypin, an estuarine-coastal lagoon, is a habitat with organic matter (OM) inputs from terrestrial and marine origin. Organic matter profiling in these lagoon sediments is crucial for understanding biogeochemical processes, ecosystem health, and restoration strategies. This is the first research endeavour to understand the changes in the organic matter content in the depth sediments and trophic status of the Vypin lagoon, part of the second-largest Ramsar site in India. The analysis of the core sediment samples revealed the average trends in biochemical contents recorded as Carbohydrate (CHO) > Protein (PRT) > Lipid (LPD). Moreover, the PRT/CHO ratio (< 1) unveiled the presence of aged organic matter in the Vypin third (V3) core. LPD/CHO confirmed a higher nutritional quality in the second core (V2) sediments. The biopolymeric carbon (BPC), CHO, and PRT-based trophic state classifications described a meso-oligo trophic benthic status in the study area. TOC/TN and the C/N ratio indicate the marine input of OM in the first Vypin sample -V1 and V2, and mixed terrestrial and marine origins in the V3 core. A significant correlation between the phytopigments and the labile organic components indicates that settling material is closely associated with the phytodetritus. Principal component analysis also suggests a high influence of planktonic communities and terrestrial depositions in the particular area. The results highlight the importance of regular monitoring and sustainable management in the lagoon ecosystem.