Geochemical Characterization of the Sources and Distribution of Fatty Acids in Recent Sediment Cores from Cross River System, South-South, Nigeria

Background and Objective: Fatty acids have been utilized to trace organic matter source, fate and fluxes transmitted between estuaries, rivers, tributaries and their drainage basins worldwide. However, such correspondence is scarce in Sub-Saharan African region, particularly in sediment cores of Cross River system. A comparative evaluation of recent sediment cores (50 cm long) from the upper and lower Cross River system, was undertaken to characterize the sources, distributions and fate of fatty acids. Materials and Methods: These were achieved by solvent extraction, purification, identification/quantification using gas chromatography-mass spectrometry and principal component analysis-multiple linear regression statistics. Dispersion of fatty acid classes followed the trends short-chain>long-chain>branched-chain>monounsaturated fatty acids for the upper system and short-chain>branched-chain>long-chain>monounsaturated for the lower. Results: Principal component analysis-multiple linear regression apportioned 53.14% to a mixed source of phytoplankton (dinoflagellate), heterotrophic bacteria and terrestrial plant (Rhizophora avicennia) and 48.86% to a mixed source of phytoplankton (diatom) and photosynthetic bacteria in the case of the upper system. For the lower, a mixed source of phytoplankton (dinoflagellate), heterotrophic bacteria and terrestrial plant Nypa fruticans made the larger contribution of 93.32%, while photosynthetic bacteria and terrestrial plant metabolites contributed 6.68% to the total fatty acids flux. The irregular fatty acids distribution patterns observed down cores were attributed to differences in the water depth, sediment texture, biodegradation and depositional environmental conditions. Conclusion: Detection of considerable levels of bacterial fatty acids suggested the involvement of an essential aerobic/anaerobic microbial activity and operation of varying biogeochemical processes at these sites.