Evaluation of triterpenols and sterols as organic matter biomarkers in a mangrove ecosystem in Northern Brazil

bkoch [ at ] awi-bremerhaven.de


Mangrove leaves, sediment, and excrement from the land crab Ucides cordatus (swamp ghost crab) from the coastal mangrove areas of Bragança peninsula in North Brazil were analysed to determine suitable biomarkers for mangrove-derived organic matter. Leaves of Rhizophora mangle (red mangrove), the dominant species in the area, were characterised by high amounts of b-amyrin, germanicol, taraxerol, and lupeol. Avicennia germinans (black mangrove) mainly contained betulin, lupeol, and b-sitosterol, whereas significant quantities of b-sitosterol and lupeol were typical of Laguncularia racemosa (white mangrove), the locally least abundant species. Except for betulin, the excrement of U. cordatus contained all of the above substances, but most strongly reflected the triterpenol signature of R. mangle leaves, the predominant diet of this crab. Surface sediments from various mangrove locations had relatively uniform compositions that possibly reflect tidal mixing. Sediment extracts were dominated by taraxerol and contained smaller amounts of b-amyrin, germanicol, and lupeol. Only sediments in a marsh area, dominated by Sporobolus virginicus (seashore dropseed) and Eleocharis sp. (spikerush), revealed a different biomarker distribution. Core samples of subrecent sediment (up to 4000 14C yr BP), for which previous pollen analysis indicated vegetation dominated by mangroves, had compositions similar to that of surface sediment. Taraxerol was the main component in the examined mangrove sediments and may be a marker for mangrove matter in this region, although analysis of plant material did not unequivocally support this. Germanicol is suggested to be a biomarker for organic matter from R. mangle in North Brazil. It was detected in older sediments and apparently not significantly affected by ingestion by land crabs.

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Koch, B. , Rullkötter, J. and Lara, R. (2003): Evaluation of triterpenols and sterols as organic matter biomarkers in a mangrove ecosystem in Northern Brazil , Wetlands, 11 , pp. 257-263 .

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