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Abstract:
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Mangroves are diverse group of trees, palms, shrubs, and ferns that share a
common ability to live in waterlogged saline soils exposed to regular flooding, and are
highly specialised plants which have developed unusual adaptations to the unique
environmental conditions. They are sites of accumulation and preservation of both
allochthonous and autochthonous organic matter owing to their strategic loction at
the interface between land and sea and prevailing reducing environment. They are
among the most productive ecosystems and are efficient carbon sinks with most of the
carbon stored in sediments.Mangrove ecosystems play a significant role in global
carbon cycle and hence the knowledge on the processes controlling the delivery of
organic matter to coastal sediments, and how these signatures are preserved in the
sediment is a prerequisite for the understanding of biogeochemical cycles.
The evaluation of nature and sources of organic matter can be accomplished by
the determination of biochemical constituents like carbohydrates, proteins and lipids.
When characterised at molecular level, lipids provide valuable information about the
sources of organic matter, even though they account only small fraction of organic
matter. They are useful for the paleo-environmental reconstruction because of their low
reactivity, high preservation potential and high source specificity relative to other
organic class of compounds. The application of recent analytical techniques has
produced a wealth of useful information but has also indicated the gaps in our
knowledge on cycling of organic matter in the coastal ecosystems. The quantity and
quality of organic matter preserved in sediments vary depending up on the nature of
material delivered to the sediment and on the depositional environment. The input from
both autochthonous and allochthonous sources sharpens the complexity of
biogeochemistry of mangrove ecosystem and hence bulk sedimentary parameters are not completely successful in evaluating the sources of organic matter in mangrove
sediments. An effective tool for the source characterisation of organic matter in coastal
ecosystems is biomarker approach. Biomarkers are chemical "signatures" present in
environmental samples whose structural information can be linked to its biological
precursor. The usefulness of molecular biomarkers depends on high taxonomic
specificity, potential for preservation, recalcitrant against geochemical changes, easily
analysable in environmental samples and should have a limited number of well-defined
sources. |