Biomarkers as indicators of sedimentary organic matter sources and early diagenetic transformation of pentacyclic triterpenoids in a tropical mangrove ecosystem

13 páginas.- 7 figuras.- 3 tablas.- referencias.- Supplementary data related to this article can be found at https://doi.org/10.1016/j.ecss.2019.106403.Mangrove vegetation covers extensive areas along Brazilian tropical coasts and accumulates large amounts of organic carbon in the intertidal sediments. We have investigated the molecular biomarker composition of mangrove sediments from the Potengi estuary North-East Brazil. To characterise sources and fate of sedimentary organic matter (OM), a direct analytical pyrolysis approach was used. The sediment pyrolysates yielded homologous series of aliphatic compounds (n-alkane/n-alkene doublets, n-alkanoic acid and n-alkan-2-ones), triterpenoids and lignin-derived methoxphenols, indicating that most of the sedimentary OM input originates from terrestrial vascular plants. High abundance of long-chain n-alk-1-ene series with an even carbon number predominance peaking at C28:1 ―most likely originated from local mangrove vegetation― is found co-eluted with the saturated odd carbon n-alkane series. The occurrence of lignin and n-alkan-2-one biomarkers in the sediments has provided parallel information about the input from vascular plants dominating the intertidal zone. This was further corroborated by the presence of the triterpenols (β-amyrin, and germanicol), that provided chemotaxonomic information on mangrove derived leaf wax in sedimentary OM. The unsaturated triterpenoid including teraxerol acetate, olean-12-ene, olean-18-ene, oleana-11, 13(18)-diene, a-neoursa-3(5), 12-diene and aneooleana-3(5), 12-diene, were also observed in sediment pyrolysates. The presence of these unsaturated pentacyclic triterpenoids revealed an early diagenetic alteration of terrestrial OM in the sediments. This study has demonstrated that routine application of analytical pyrolysis may provide important insight into the sources of sedimentary OM and its diagenetic fate in mangrove intertidal sediments.Mukesh Kumar acknowledges funding by an EU Erasmus Mundus Joint Doctorate fellowship administered by FUECA, University of Cadiz, Spain. Research was supported by EU contract numbers FP7-ENV-2011 Grant agreement no: 282845 and FP7-ENV-2012 Grant agreement no: 308392 and MINECO project INTERCARBON (CGL2016-78937-R). Ms. Alba Carmona Navarro and Ms. Desire Monis Carrere are thanked for their technical assistance. Graphical abstract is shaped by the image symbols created by the Integration Application Network (IAN), University of Maryland Center for Environmental Science, Cambridge, Maryland, USA (http://ian.umces.edu/).Peer reviewe