Sterols in the Ria Formosa lagoon, Portugal

Fifty nine surface sediment samples from the Ria Formosa lagoon were analysed for lipid biomarkers and 26 sterols were identified and quantified using a GC-MS technique. The total concentrations ranged from 0.1 to 27.8 μg g−1 DW although this accounted for much less than 1% of the total organic carbon content. The principal sterols were cholesterol and β-sitosterol indicating marine fauna and terrestrial plants, respectively. Sewage markers (coprostanol and epi-coprostanol) were present around the known sewage discharge points at Faro, Tavira and Olhão; the former two sites had untreated effluent whereas the latter site has partially treated discharges which was reflected in an increase in the epi-coprostanol/coprostanol ratio. Phytoplankton biomarkers (e.g. brassicasterol) were concentrated in the region near Armona, the major inlet to the lagoon from the Atlantic Ocean. Sterols indicative of other types of organic matter were also present but were restricted to selected regions. Multivariate statistical techniques (PCA, PLS) were able to produce readily explainable diagrams which highlighted the contribution that each of the major sources, marine fauna, sewage, phytoplankton and terrestrial organic matter made to the sites of the lagoon.