The rare earth elements (REEs) in the sediments of the Pichavaram mangrove of the Coleroon-Vellar estuarine complex in India were measured by inductively coupled plasma mass spectrometry. The light rare earth elements (LREEs) were more enriched than the heavy rare earth elements (HREEs) and the Eu anomaly was relatively weak. No obvious differences were found among the different zones of the mangrove except for a few metals and very few REEs. Intense weathering of the surface crustal areas controls their distribution. The shale-normalized values indicate a similar pattern except for a few fluctuations in their distribution patterns. The variation in the enrichment of HREEs was controlled by the salinity gradient and inputs from estuarine zones. Correlation and factor analysis also explain the contribution from the continental weathering followed by other processes like salinity control, input from anthropogenic sources, etc. The enrichment factor substantiates that most of the REEs have weathering sources and are altered in the complex biogeochemical processes operating here. Few metals were derived from anthropogenic activities but were generally below the contamination levels. The Ce, Gd, and Eu ratios confirm the natural and anthropogenic source. In general, the interior channels and high-salinity zones were more enriched with HREEs than LREEs (i.e., HREEs seemed to be trapped more here). The mangroves contribute around 70%–80% of the LREEs (including middle rare earth elements) and 20%–30% of HREEs to the adjacent sea.
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Vol. 24 • No. sp1