Distribution and sources of fatty acids in surface sediments of mangrove ecosystems in the Northern Kerala Coast, India

Abstract

Fatty acids and bulk geochemical proxies were employed to understand the sources and transformation of sedimentary organic matter from surface sediments of major five mangrove systems in the northern Kerala coast. Texture, tidal rhythm and the proximity to the south eastern Arabian Sea were the main factors influencing distribution and accumulation of the organic matter in these systems. A total of 118 fatty acids were quantified and grouped into short-chain (SCFA), long-chain (LCFA), monounsaturated (MUFA), polyunsaturated (PUFA) and branched-chain (BrFA) fatty acids, hydroxy fatty acids, cyclic fatty acids, and dicarboxylic acids. The distribution of fatty acid groups was in the order SCFA > BrFA > MUFA > LCFA > PUFA. Total fatty acids (TFA) concentration exhibited profound seasonal variations and ranged from 6.25 to 580.49 μg/g (pre-monsoon > post-monsoon > monsoon except in Kadalundi which follows the reverse order). The sedimentary fatty acids in the study region reveal a wide spectrum of inputs from terrestrial, planktonic (preponderance of diatom followed by dinoflagellates along with brown algae, cyanobacteria, red algae) and bacterial sources (e.g., Desulfobulbus-type bacteria, sulfur-reducing bacteria, Sulfur-oxidizing bacteria). Significant concentrations of bacterial fatty acids suggest the functioning of an effective microbial loop and various biogeochemical pathways operating in these sediments (sulfate reduction, iron and manganese oxide reduction, etc.).

Keywords:

• Source characterisation
• fatty acid biomarker
• biogeochemical process
• mangrove

Acknowledgments

We also express our sincere gratitude to Professor, Anindya Sarkar, IIT Kharagpur, for stable carbon isotope analysis. We would like to thank Dean and Director, School of Marine Sciences, Cochin University of Science and Technology for providing the facilities. We also acknowledge the laboratory and instrumental facilities provided by the Head, Department of Chemical Oceanography and the Hon. Director, Inter-University Centre for Development of Marine Biotechnology, School of Marine Sciences, CUSAT.

Additional information

Funding

The study was funded by the Ministry of Earth Sciences (Grant No:MoES/11-MRDF/1/37/P/08), India; Department of Science and Technology (Grant No:SR/S4/ES-290/2007), India and Kerala State Council for Science and Technology (Grant No:404/2011/KSCSTE).