Source characterisation of Sedimentary organic matter in mangrove ecosystems of northern Kerala, India: Inferences from bulk characterisation and hydrocarbon biomarkers
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Date
2016Author
Resmi, P.
Manju, M.N.
Gireeshkumar, T.R.
RatheeshKumar, C.S.
Chandramohanakumar, N.
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Surface sediment samples from five mangrove ecosystems along the Kerala coast, north of Kochi were analysed for elemental ratios, stable isotopes of carbon and hydrocarbon biomarkers (n-alkanes, n-alkenes and hopanes) to assess the sources and early diagenesis of sedimentary organic matter. The elemental and isotopic ratios along with sedimentary chlorophyll a content, suggested substantial contribution of planktonic organic matter apart from mangrove/terrestrial derived organic matter. The sources of organic matter showed variability in relation with the geographical setting of mangrove systems as well as with seasons. The n-alkanes in mangrove sediments consist of organic matter derived from varying contributions of planktonic, bacterial and terrestrial sources. The distributional features of n-alkanes with low molecular weight (<C<sub>20</sub>) indicated the preponderance of algal derived organic matter, whereas the unresolved complex mixtures for low molecular n-alkanes indicated active microbial reworking. The n-alkane derived molecular indices enable the effective source appropriation of different end members in the study region, while diagenetic alteration products of lipids such as n-alkenes, branched alkanes and n-alkylcyclohexanes along with hopanes are indicative of organic matter diagenetic pathway in sediments. The n-alkenes in the study area probably derived from decarboxylation reactions of unsaturated fatty acids and other terrestrial inputs. The higher input of mangrove/terrestrial derived organic matter is evident by the average chain length data. Information obtained using biomarkers will allow to discriminate organic carbon sources in these mangrove ecosystems
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