Sources and major biogeochemical pathways of organic matter in the mangrove system of Rufiji estuary

ABSTRACT

Fatty acids were extracted from the surface sediments (10 cm) of three sampling sites of Rufiji estuary to infer their sources and biogeochemical pathways. The fatty acids ranging from C₈ to C₂₄ were distinguished from this study, and were broadly classified into saturated (SFAs), monounsaturated (MUFAs) and polyunsaturated fatty acids (PUFAs). SFAs were found to be the major fraction at station 1 and 3 where as at station 2, MUFAs dominated. A total of 19 fatty acids with a total concentration of 64.91 μg/g dry weight were characterised at station 1. C_16:0 was the most abundant fatty acid contributing 21.94% of total fatty acids (TFAs). C_22:2 was the second most abundant, which accounted for 9.46% of TFAs. Fatty acids ranging from C₁₂ to C₂₄ were identified at station 2. C₂₀ fatty acid was the most abundant fatty acid contributing 21.94%, followed by C_16:0. At station 3, fatty acids ranging from C₈ to C₂₄ were obtained. The PUFA C_20:5n-3 was the most abundant fatty acid contributing 21.65%, followed by C_24:0 (15.00% of TFAs). The ratio of lower molecular weight (LMW) to higher molecular weight (HMW) biomarkers was used as an indicators to distinguish higher plants organic matter from algae-derived fatty acids.

KEYWORDS:

• Biomarkers
• fatty acids
• biogeochemical pathways
• organic matter
• mangrove system
• Rufiji estuary

Acknowledgments

The following persons are kindly thanked for their help in this investigation: Mr. Richard Masinde and Amos Lugata for sampling and initial processing of samples, Mr. Wang Fuqiang for valuable practical assistance in the lab.

Disclosure statement

No potential conflict of interest was reported by the author.

Notes on contributor

Daniel Abel Shilla is the Senior Lecturer at the University of Dar es Salaam, Department of Aquatic Sciences and Fisheries Technology with strong bias in aquatic pollution, Organic geochemistry in marine environments, production and transport of organic matter in marine environments, and cycling of nutrients and organic matter in aquatic ecosystems.