Distribution and characterization of organic matter using lipid biomarkers: A case study in a pristine tropical bay in NE Brazil

Lipid biomarkers (sterols, alcohols and taraxerol) were quantified in 30 surface sediments from the Camamu Bay (CB), NE Brazil, with the aim of evaluating the sources and distribution of organic matter (OM) in a tropical, well-preserved coastal system. The total organic carbon varied in a wide range (0.8–38.3 mg g−1), reflecting distinct patterns of sediment grain size and hydrodynamics at CB. A mean C/N molar ratio of 22.2 ± 5.2 suggests an important allochthonous source of OM. This is confirmed by the distribution of the total quantified lipids (3.15 ± 2.58 μg g−1) and statistical (PCA) analysis. Taraxerol and long-chain n-alcohols indicated the major contribution of continental materials associated with the west and south catchments. The PCA also allowed for the distinction of the n-alcohols sources, suggesting that the C24 and C26 compounds are derived from mangroves and the C30 and C32, from the Atlantic rain forest vegetation. The taraxerol to total quantified lipid ratio indicated the influence of mangrove vegetation even in OM-depleted and deeper portions of the bay. Low coprostanol concentrations suggest the absent of human sewage influence and confirm previous results that suggest CB is a pristine tropical bay that could be used as a reference area.